Organic/Inorganic phosphorus forms and transformation in long-term paddy cultivation in the Pearl River Delta, China

doi:10.21203/rs.3.rs-2114717/v1

Download PDF

Research Article

Organic/Inorganic phosphorus forms and transformation in long-term paddy cultivation in the Pearl River Delta, China

https://doi.org/10.21203/rs.3.rs-2114717/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Soil P availability in subtropical regions is often limited due to depletion as well as immobilization by abundant Fe minerals. Identification and quantification of different soil phosphorus (P) fractions is important for improving agricultural productivity and developing sustainable management practices in these agricultural soils under long-term cultivation due to limited P efficiency. However, few studies have been conducted to investigate P composition and transformation in these soils. This study was conducted to characterize P fractions as affected by different paddy cultivation ages (200, 400 and 900 years) among soils of the Pearl River Delta Plain in China. A sequential chemical fractionation scheme was employed as well as enzyme assay and ³¹P nuclear magnetic resonance spectroscopy (³¹P NMR) to quantify various P fractions and species. Results showed Total P (TP) and available P (AP) increased with cultivation age, ranging from 0.60–2.12 g kg^− 1 and 3.67-224.17 mg kg^− 1, respectively. Easily-labile, moderately-labile and non-labile P had similar relationship in topsoils (Ap1, Ap2 horizon) with TP and AP, and inversed relationships in the subsoil (Br3, G horizons). Analysis with ³¹P NMR spectroscopy revealed that inorganic P including orthophosphate (Ortho-P) and pyrophosphate (Pyro-P) increased with cultivation age, while organic species monoester phosphate (Mono-P) and diester phosphate (Diester-P) decreased. Moreover, acid phosphatase (AcP) and neutral phosphatase (NeP) activities increased with cultivation age and positively correlated with P fractions (p < 0.05). NeP, AcP, exchangeable Ca and sand content are the main factors of affecting soil P composition, however, non-labile P (Dil.HCl-Pi) and Pyro-P made a significant contribution to P availability. Therefore, long-term paddy cultivation, influenced by these soil parameters including NeP, AcP, exchangeable Ca and sand, accelerated the transformation of soil organic to inorganic P.

P Speciation

P composition

31P NMR Spectroscopy

Sequential chemical fractionation

Cultivation age

Phosphorus (P) is one of the major nutrients limiting plant growth and agricultural production (Zhou et al. 2019; Zhang et al. 2021). Transformation between organic and inorganic forms during ecosystem development exerts a crucial influence on soil fertility and ecosystem properties (Gu et al. 2020; Sun et al. 2020). Processes involved in P cycling includes dissolution-precipitation reactions, sorption-desorption interactions between the solution and solid phases, and mineralization-immobilization reactions between organic and inorganic, soluble forms (Sims and Pierzynski 2005). Organic P constitutes 20-80% of the total P in surface soils and is not directly available to plants. This organic form can be converted to soil solution P forms, becoming plant-available via biotic processes such as mineralization (Wei et al. 2019; Yang et al. 2019). Most solution P transforms to insoluble and tightly bound inorganic phosphates forms and thus become unavailable for plant growth. These factors, as well as low native P in soils of south China, make this nutrient limiting for agricultural production.

In contrast, heavily fertilized paddy soils typically have P buildup to levels that far exceed the agronomic optimum required for satisfactory crop production (Huang et al. 2014). This excess P may lead to elevated P loss to water bodies and cause eutrophication of lakes, rivers and estuaries (Zhou et al. 2003). Thus, research on quantifying P fractions as well as the chemical reactions that govern P availability on these paddy soils with long cultivation history is essential to improve our understanding of P requirements for crop production, appropriate management practices, as well as pathways of P transformation and transport in the agroecosystem.

The effect of paddy cultivation on soil P composition has been widely studied among different agricultural soils (Huang et al. 2013; Huang et al. 2014). For example, short-term cultivation has been found to reduce the content of NaHCO₃-extractable inorganic P (NaHCO₃-Pi), NaOH-extractable inorganic P (NaOH-Pi), HCl-extractable inorganic P (HCl-Pi) and Residual-P in double-cropping rice system (Zhang et al. 2006). Huang et al. (2014) found that total P and various P fractions (such as calcium phosphates, organic phosphates, and non-occluded and occluded P) can accumulate to a maximum after 50-yr and 150-yr of cultivation that includes long-term P addition. In addition, soil phosphatase enzymes, including acid phosphatase and neutral phosphatase, play critical roles in organic and condensed P hydrolysis and P availability to crops. The activity of these enzymes can be affected by tillage (Wei et al. 2014). Land use and management practices (i.e. crop rotation, fertilization, residue input and farmyard manure application) can signiﬁcantly increase diﬀerent fractions of P and phosphatase activities (Zhang et al. 2006; Huang et al. 2014). However, most previous researches were based on short-term soil analysis, and little was known about how soil P fractions and speciation responds to crop cultivation over long-term agricultural land use timescales.

Sequential fractionation methodology is commonly used to determine soil forms of elemental constituents. For example, it has been used for determining existing pools of trace metals in contaminated soils (Burt et al. 2003). This approach has proven to be effective in understanding of soil P status in previous studies (Li et al. 2019; Zhang et al. 2021a) and the chemical sequential fractionation method is recognized as a systematic, comprehensive classification method by soil scholars (Wang et al. 2012). The power of this method for P is increased by additional use of solution ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy to quantify organic P species (Li et al. 2013; Liu et al. 2015). Use of both fractionation and this NMR analytical method should prove valuable in studying P transformation in soils that differ in cultivation age.

Climate of the Pearl River Delta (PRD) region in south China is humid and subtropical, with over 2000 years of cultivation (Zhao et al. 2011; Ye et al. 2021). Over the past three decades, the PRD has undergone rapid industrialization and urbanization, becoming a major manufacturing hub (Lu 1988; Xiao et al. 2017; Zhang et al. 2018). Due to the rapid economic development in this delta region, available land for agriculture is decreasing, increasing the need for a revised approach to farm management. Adjustments are needed accommodate multiple crops, with coexistence of rice, vegetables, fruit trees and other cash crops. These land use demands have increased the need for proper use of nutrients to maximize uptake and crop yields, while minimizing P fixation or nutrient loss to water bodies.

Maximizing soil P availability in the PRD by maintaining adequate amounts of soil P through application of inorganic and/or organic P sources is critical for the long-term sustainability of cropping systems (Vestergren et al. 2012; Hou et al. 2021). Previous studies have shown that cultivation can signiﬁcantly inﬂuence soil P composition, content and plant availability, and revealed some mechanisms of soil P transformation (Chen et al. 2015; Huang et al. 2017). Due to its long agricultural history and subsequent changes in land use, the PRD presents an important location to examine effects of long-term cultivation on agricultural soils and determine potential pathways of transformation between soil P forms.

This study was conducted to investigate the impact of time of cultivation in different soil P fractions and species, and whether it inﬂuences the abundance and composition of P-cycling-related phosphatase. We hypothesized that (i) time of paddy cultivation alters amount and distribution of P and its bioavailability; (ii) P composition diﬀers across soils and with depth in individual locations; and (iii) the abundance and species of P-cycling-related phosphatase enzymes is closely linked to P composition and other physicochemical factors.

Site description and cultivation age recognition

The Pearl River Delta (21°34′-23°45′ N, 112°07′-114°39′ E), an area within Guangdong Province of China, characterized as a subtropical monsoon climate zone with a mean annual temperature of 21–22°C and 1301–2700 mm annual precipitation. Soil samples were collected from paddy field (in different horizons) with cultivation age of 200 yrs (PF₂₀₀), 400 yrs (PF₄₀₀) and 900 yrs (PF₉₀₀) (Jia et al. 2017). According to the World Reference Base for Soil Resources (FAO 2015), the soils in the paddy field were classified as Stagnic Anthrosols derived from river alluvium. Historical records indicate that fertilizer application for rice production was in accord with local recommendations including 165 kg ha^− 1 of urea (46% N), 60 kg ha^− 1 superphosphate (12% P₂O₅), and 75 kg ha^− 1 potassium chloride (60% K₂O). Soil profiles were described and sampled by genetic horizons (Zhang et al. 2016). Mixed soil samples were collected in each genetic horizon across soil profiles. A total of 16 samples were collected from three representative soil profiles with different cultivation ages. Samples were divided into two parts; one sample air-dried for analysis of soil parameters and P fractionation, and another sample kept field moist and refrigerated at 4 C° for enzyme analysis.

Analysis of soil parameters and sequential P fractionation

Air-dried soils were sieved sieved to < 2-mm and < 0.15-mm prior to analysis, respectively. Characterization methods used are documented in Zhang et al. (2012b). Soil pH was determined using a pH electrode (PB-10, Beijing Selidos Scientific Instruments Co, LTD) in distilled water (1:2.5 soil:solution ratio). Particle size analysis determined sand (2 to 0.05 mm), silt (0.05 to 0.002 mm), and clay (< 0.002 mm) using the pipette method following hydrogen peroxide treatment. Soil organic carbon (SOC) was measured using a heated dichromate oxidation method. Cation exchange capacity (CEC) was determined with 1.0 M ammonium acetate (pH 7.0). Exchangeable Ca²⁺ (ECa) and Mg²⁺ (EMg) was measured using a boric acid-atomic absorption spectrometry method. Active iron (Fet) was determined with ammonium oxalate extraction and free iron (Fef) with dithionite-citrate-bicarbonate. Total-P was quantified by a digestion procedure using HNO₃-HF-HClO₄. Available P (AP) was determined by extracting soils with sodium bicarbonate at pH 8.5 (Table 1).

Table 1

Physiochemical characteristics of the studied soils from each soil profile.
Parameters	PF₂₀₀^†(Coefficient of Variation)	PF₄₀₀	PF₉₀₀
Soil pH	6.5-7.0^‡ (0.03)	6.7-7.0 (0.17)	6.2–6.9 (0.04)
Sand (%)	8.9–21.7 (0.34)	2.6–30.2 (1.10)	3.9–35.8 (0.68)
Silt (%)	49.5–52.6 (0.02)	41.9–57.9 (0.12)	36.3–50.2 (0.14)
Clay (%)	25.9–38.5 (0.15)	27.9–46.5 (0.17)	26.3–48.4 (0.22)
SOC (g kg^− 1)	10.0-22.4 (0.33)	8.0–18.0 (0.35)	4.1–13.7 (0.52)
CEC (cmol kg^− 1)	11.5–17.6 (0.16)	15.2–18.4 (0.07)	12.9–15.1 (0.06)
Exchangeable Ca (cmol kg^− 1)	18.4–45.1 (0.46)	13.6–44.7 (0.42)	11.8–33.0 (0.50)
Exchangeable Mg (cmol kg^− 1)	1.5–3.5 (0.27)	1.4–6.9 (0.51)	1.6–3.3 (0.32)
Active Fe (g kg^− 1)	6.9–29.7 (0.72)	1.6–33.8 (1.40)	1.1–9.2 (0.85)
Free Fe (g kg^− 1)	26.1–46.3 (0.23)	34.3–54.5 (0.18)	29.0-41.7 (0.13)
TP (g kg^− 1)	0.6–0.9 (0.21)	0.6-1.0 (0.18)	0.4-2.0 (0.69)
AP (mg kg^− 1)	4.8–13.3 (0.32)	3.9–24.6 (0.67)	3.7-227.2 (1.65)
†Footnote description of PF₂₀₀, PF₄₀₀ and PF₉₀₀ means paddy field with cultivation ages of 200, 400 years and 900 years, respectively. TP, total P by sequential P extraction; AP, plant available P as extracted by the Olsen reagent.
‡Footnote description of Data in table were the range for all horizons sampled between depths of 0-120, 0-118 cm and 0-113 cm of each cultivation age (PF₂₀₀, PF₄₀₀, and PF₉₀₀).

Sequential fractionation was determined on soil samples using the Hedley et al. (1982) method with the modifications of Tiessen et al. (1993) (Table S1). Samples were sequentially extracted using 0.5 M NaHCO₃, 0.1 M NaOH, 1.0 M HCl, and hot concentrated HCl, and a final digestion of the residue with HNO₃-HF-HClO₄ using colormetric method (Zhang et al. 2012b). In order to facilitate interpretations, P fractions were classified into three main groups (Tiessen et al. 1984): (i) easily-labile P, P that is considered readily available for plants, i.e, NaHCO₃-Pi and NaHCO3-Po; (ii) moderately-labile P, P that is strongly adsorbed by Al and Fe oxides, i.e. NaOH-Pi and NaOH-Po; (iii) non-labile, that P associated with calcium (Ca-P) and Residual-P, considered as non-available P to plants, i.e. HCl-P and Residual-P. In this study, the organic matter contents of soil samples were 0.7–3.9% (Table 1), thus we classified Residual-P as inorganic P due to the lower organic matter contents (Wei et al. 2019). Inorganic P (Pi) is the sum of P fractions with NaHCO₃-Pi, NaOH-Pi, Dil.HCl-Pi, Conc.HCl-Pi and Residual-P, while organic phosphorus (Po) is the sum of all fractions of NaHCO₃-Po, NaOH-Po and Conc.HCl-Po, respectively.

The accuracy of the TP by sequential P extraction was assessed by comparing with the sum of all the Pi and Po fractions (TP_sum), with an expected 1:1 relation between the two parameters for all soil horizons ((Fig. S1, n = 15). The null hypothesis of a linear relation could not be disproved (Fig. S1). The two measures were very strongly correlated (r² = 0.98). Thus, the efficiency of sequential extraction for the soils in this study was excellent.

³¹ P Nuclear Magnetic Resonance analyses

A modified procedure of Cade-Menun and Preston (1996) was used for solution ³¹P NMR spectroscopy to identify P species including Pi (orthophosphate, Ortho-P; pyrophosphate, Pyro-P) and Po (orthophosphate monoesters, Mono-P; diesters, Diester-P). Ground samples (3 g) were shaken with 60 mL of 0.25 M NaOH and 0.05 M Na₂EDTA in a 100-mL centrifuge tube at 20^◦C for 16 hr. The extract was centrifuged (10000 × g for 30 min at 16^◦C), and the supernatant filtered with a 0.45 µm membrane, and then 15 mL of the filtrate was freeze dried (lyophilized). The powder was dissolved in 1 mL of 0.25 M NaOH, and centrifuged at 8000 × g for 5 min at 4^◦C. Then, 0.6 mL of the supernatant was removed into a 5-mm NMR tube, followed by 0.05 mL of deuterium oxide (D₂O) for signal locking. Meanwhile, 5 mL of the filtrate was subjected to digestion (H₂SO₄-HClO₄) and measured to determine total P (TP_alkali).

Solution ³¹P NMR spectra were obtained using a Bruker AMX 600 spectrometer (Bruker, Germany) operating at 243 MHz with a 5-mm probe (Turner et al. 2003; Cade-Menun 2015). We used a 30° pulse width, a total acquisition time of 1.5 s (pulse delay 0.808 s, acquisition time 0.673 s) and broadband proton decoupling (additional spectra were acquired for some samples without proton decoupling). The delay time used here allows sufficient spinlattice relaxation between scans for P compounds in NaOH-EDTA, confirmed by a recent detailed study of relaxation times for P compounds in various soil extractants (Cade-Menun et al. 2002). Temperature was regulated at 24 °C. Between 80 and 400 scans were collected to obtain acceptable signals. Chemical shifts were measured relative to an external standard of 85% H₃PO₄ after Lorentzian convolution with a width of 10 Hz. We used the deconvolution process of the Bruker WinNMR program to determine chemical shift, line width, and area of individual signals. Spectra were plotted using a line broadening of 5 Hz. Spectra were collected immediately after preparation (usually within 1 h) and repeated at intervals during storage at room temperature to determine degradation, with the same number of scans collected each time. No degradation was observed unless specified (Turner et al. 2003; Cade-Menun 2005).

Phosphatase enzyme hydrolysis assay

Moist soil samples were extracted in duplicate with distilled water (1:4 soil-solution ratio) on a reciprocating shaker for 1 h (Shen 1987). The extract was centrifuged at 10000 × g for 10 min and filtered through 0.45-mm membrane filters. Two phosphatase enzyme activities involved in P cycles were determined. Acid (AcP) and neutral (NeP) phosphatase activities were assayed with p-nitrophenol phosphate as substrates with modified universal buffer pH values of 5 and 7, respectively. The activities of AcP and NeP were expressed as mg p-nitrophenol kg^− 1 soil (dry weight) h^− 1.

Statistical analysis

Phosphorus activation coefficient (PAC) is an important indicator of soil P availability and the transformation of P fractions (Wu et al. 2017). The higher PAC means more strongly activation ability of soil P, thus promotes the uptake of P by plants. Soil PAC is related to AP and TP as follows:

PAC (%) = Olsen-P (mg kg^− 1) × 100/[TP (g kg^− 1)×1000] (Eq. 1)

Microsoft Excel 2016 and Origin 2021b were used for data processing and cartography. Data were statistically analyzed using IBM SPSS Statistics 24.0 (SPSS Inc. Chicago, USA) software. Pearson correlation analyses were used to identify relationships between different P species and total P, available P contents and soil physicochemical properties. Principal Component Analysis (PCA) was used to evaluate the overall differences among P species and the soil properties in paddy soils.

Nuclear magnetic resonance data were processed using the Mnova 5.3.1 (Qingdao Tenglong Microwave Technology Co, LTD). Concentration of P species in soil samples identified in ³¹P NMR spectrum were calculated using the corresponding peak area (Schmieder et al. 2018) and ³¹P NMR spectra were plotted with Origin 2021b. Proportional soil concentration of specific P species identified in the ³¹PNMR spectra were calculated using the corresponding peak area and the recovery of P in NaOH-EDTA extracts relative to the corresponding soil P contents (Schmieder et al. 2018). By spectrum analysis, Ortho-P and Pyro-P were averaging at 6.0 ppm and 4.0 ppm chemical shift, respectively, and the chemical shifts of Mono-P and Diester-P were between 3.0–5.0 ppm and − 2.0–0.0 ppm (Table 2, Fig. 3).

Table 2

Relative percentages of P compounds in different chemical shifts as measured by ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy of NaOH-EDTA extractable total P (TP_alkali) at each soil layers in three soil profiles.
Soil	Horizon	Depth (cm)	TP_alkali (mg kg^− 1)	Phosphorus species distribution in different chemical shifts (ppm), % of total P in NaOH-EDTA extract
Soil	Horizon	Depth (cm)	TP_alkali (mg kg^− 1)	Inorganic ortho-phosphate, 5.0–7.0 ppm	Monoesters, 3.0–5.0 ppm	Diesters, -2.0 to 0.0 ppm	Inorganic pyro-phosphates, -5.0 to -3.0 ppm
PF₂₀₀	Ap1	0–14	300	84.5	14.0	1.5	nd^†
	Ap2	14–23	285	91.6	8.1	0.3	nd
	Br1	23–60	160	90.2	9.3	0.5	nd
	Br2	60–90	202	93.3	6.7	0.0	nd
	G	90–120	200	98.5	1.5	0.0	nd
PF₄₀₀	Ap1	0–13	239	84.1	15.0	0.5	0.4
	Ap2	13–28	225	91.7	8.1	0.2	nd
	Br1	28–45	138	95.3	4.7	nd	nd
	Br2	45–73	159	97.2	2.8	nd	nd
	Br3	73–92	193	98.0	2.0	nd	nd
	G	92–118	151	99.8	0.2	nd	nd
PF₉₀₀	Ap1	0–19	1543	95.7	3.7	nd	0.6
	Ap2	19–32	296	92.3	6.9	0.9	nd
	Br1	32–59	297	95.2	4.8	nd	nd
	Br2	59–82	193	96.8	2.6	nd	0.6
	G	82–113	112	93.4	6.6	nd	nd
†Footnote description of nd means not detected.

Relationship between selected soil properties and P compounds were evaluated with correlation, linear regression and path analyses using SPSS 24.0 (IBM, SPSS, New York, USA). Correlation heat map and PCA were used to reduce the number of variables and understand the relationships between selected soil properties and P compositions using Origin 2021b. Redundancy analysis (RDA) was used to visualize the relationships between response variables (i.e, P compositions) and explanatory factors (i.e, soil properties) using Canoco 5.0 (Canoco, NY, USA).

Total P and Soil P fractions by sequential chemical extraction

Total P ranged from 0.6 to 2.0 g kg^− 1 with an average of 0.79 g kg^− 1 (Table 1). It was highest in the 900-yr soil. Olsen-P ranged from 3.9 to 227.2 mg kg^− 1 and was also highest in the 900-yr soil (Table 1). The depth distribution of the P activation coefficient (PAC) was generally uniform throughout soil profiles for same cultivation age (Table S2). The PAC ranged from 0.7 to 3.0% with an average of 1.63%, and was greatest in the 900-yr soil (Table S2). Accumulation of Olsen-P in both the subsoils indicated that P addition by paddy cultivation not only resulted in surface P enrichment but also caused significant movement of P to lower horizons.

Soil P fraction in these alluvial soils was dominated by inorganic P (Pi) the fraction extracted by concentrated HCl (Conc. HCl-Pi) (10.9–49.7% of TP) while NaOH-Po accounts for 0.8–10.4% of TP (Fig. 1). The TP in surface horizons (Ap1) highest in the soil with 900 yrs of cultivation (Table S2, Fig. 1). In the subsoils (below the plow pan), TP decreased across cultivation age (Table S2), which can be mainly attributed to a decrease in the P fraction extracted by 1.0 M HCl (Dil.HCl-Pi) (regarded as Ca-bound P) despite a slight increase in the less readily extractable fractions (such as residue P) (Fig. 1). The distribution of soil P in subsoil was relatively unaltered in the first 400 yrs of cultivation but changed substantially in the older soil (900-yr) that accompanied formation of Fe- and clay-enriched horizons (Fig. 1). For example, TP was generally higher in the Br2 and G horizons of the 200-yr soil and the Br3 and G horizons of 400-yr soil than other subsoils (Fig. 1). The average topsoil Pi and Po concentrations were 0.73 and 0.07 g kg^− 1, respectively, comprising 90.8% and 9.2% of the TP_sum (the sum of Pi and Po), respectively. In addition, the labile Po and Pi (NaHCO₃-Pi and NaHCO₃-Po) constitutes a small fraction of the total composition, accounting for only 1.8 to 24.0% and 0.6 to 4.1% of the total extractable P reservoir, respectively (Fig. 1, Table S2).

Soil P pools were significantly affected by cultivation age due to the changes of P fractions. The Pi pools including moderately-labile Pi (NaOH-Pi) and non-labile Pi (Conc.HCl-Pi) at the 20–120 cm depth increased in the 400-yr soil compared to the 200-yr paddy soil (Fig. 2, Fig. S2). In contrast, Po pools including easily-labile Po (NaHCO₃-Po) and moderately-labile Po (NaOH-Po) between 20–120 cm showed a decrease in the 400-yr site, The Pi pools (including easily-labile Pi (NaHCO₃-Pi), moderately-labile Pi (NaOH-Pi) and non-labile Pi (Dil.HCl-Pi) within 0–60 cm for the 900-yr soil showed an increase compared with 400-yr soil. With the exception of NaHCO₃-Pi and NaHCO₃-Po, Pi and Po at 60–120 cm tended to decrease progressively with paddy soil development (Fig. 2, Fig. S2). Pi and Po pools of moderately-labile P (extracted by 0.1 M NaOH) and non-labile (extracted by 1.0 M HCl, concentrated HCl-Pi and Residual-P) changed in a similar pattern to that of Pi within 60–120 cm (Fig. 2, Fig. S2), and changes in these fractions accounted for more than 90% of the changes in TP (Fig. 1, Fig. S2). Our results (Figs. 1 & 2, Fig. S2) suggest that increasing years of cultivation caused redistribution of P forms within soil horizons.

Soil Pi speciations determined by ³¹P nuclear magnetic resonance (31P NMR) spectroscopy

Total P concentration extracted by NaOH-EDTA (TP_alkali) in paddy soils ranged from 112 to 1543 mg kg^− 1, equivalent to 30.8 to 75.5% of the total P (TP_acid) in soils (Table 2), respectively. Pi species determined by ³¹P NMR in our study mainly consisted of inorganic orthophosphate (Ortho-P) and pyrophosphate (Pyro-P) (Table 2, Fig. 3). In this study, Ortho-P accounted for 84.1%-99.7% of extractable TP_alkali and was the major constituent of Pi in all tested soils, while Pyro-P only existed in the Ap horizon of the 400-yr (0.4%) and 900-yr (0.6%) and Br2 horizon of the 900-yr soil. The proportion of Ortho-P increased with cultivation age, ranging from an average of 91.6–94.7% in the 200-yr and 900-yr soil profiles, respectively. Moreover, Ortho-P in 200-yr and 400-yr soil was found mostly in G horizon, while primarily existed in the Br horizon in 900-yr soil.

Soil Po speciations determined by ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy

Po detected by ³¹P NMR included orthophosphate monoesters (Mono-P) and diesters (Diester-P) (Fig. 3). Mono-P, 1.5%-15.0% of NaOH-EDTA extracted P, was higher in 200-yr and 400-yr soils than 900-yr soil (Table 2, Fig. 3). Diester-P were higher in 200-yr soil than in 400- and 900-yr soils, comprising 0.2%-1.5% of the NaOH-EDTA extracted P (Table 2). In our study, cultivation age had a large effect on Diester-P (Table 2). The 200-yr soil profile showed higher Diester-P than other soils. Moreover, Mono-P in 200-and 400-yr old soils decreased with soil depth, while Mono-P of 900-yr soil increased with depth (Table 2). With increasing of cultivation age, the proportion and composition of soil P compounds changed to some extent. As shown in Fig. 3, Mono-P and Diester-P contents in short-term (200-yr) cultivated soils decreased compared with long-term (900-yr) cultivated soils (Table 2; Fig. 3).

Soil phosphatase activities

Acid and neutral phosphatase (AcP and NeP) activities in paddy soils were affected by cultivation age and soil depth (Fig. 4). Overall, AcP activity was greater than that of NeP. The AcP and NeP activities in the Ap1 horizon were higher than that in other horizon, and both activities decreased with depth (Fig. 4). Soil AcP and NeP activities in the Ap1 horizon increased with increasing cultivation age. Paddy soils of 400 years and 900 years in Ap2, Br1 and Br2 horizons had lower AcP and NeP activities compared to that of 200 years, though similar AcP and NeP activities were found at Br2, Br3 and G horizons for the three soil ages. Thus, long-term cultivation in paddy soils increased AcP and NeP activities at topsoil and upper subsoil (Ap1, Ap2 and Br1) but remained stable in the lower subsoil (Fig. 4).

The relationships among P compositions, soil properties and phosphatase activities

The relative contribution of each P fraction to the change in TP during soil development can be determined between the change in that P faction relative to TP (Fig. S2). Soil available P (AP) was positively correlated with NaHCO₃-Pi, and negatively correlated with soil pH (P < 0.01) (Fig. 6). Path analysis showed that AP, Dil.HCl-Pi, Pyro-P and Conc.HCl-Po had a significantly positive effect on PAC, whereas NaOH-Po and Residual-P had significantly negative effect on this factor (Fig. 5).

Correlation analysis showed that Ortho-P was significantly and positively correlated with exchangeable bases, and negatively correlated with NaOH-Po, Conc.HCl-Po and SOC (P < 0.05) (Fig. 5, Fig. 6). Mono-P had a significant positive correlation with NaOH-Po, Conc.HCl-Po and SOC, and negative relationship with Ortho-P, whereas Pyro-P and Ortho-P were significantly and positively correlated (P < 0.05). Additionally, no relationship between soil phosphatase activities and Conc.HCl-Pi and Residual-P was found in this study (P > 0.05), however, soil AcP and NeP activities had a significant positive correlation with soil PAC, AP, NaHCO₃-Pi, NaHCO₃-Po, NaOH-Pi, NaOH-Po, Dil.HCl-Pi and Conc.HCl-Po (P < 0.05) (Fig. 5, Fig. 6). Positive relationships were found between AcP activity and SOC, sand and soil Mono-P (P < 0.05). Negative relationships were found between AcP activity with soil Ortho-P and clay (P < 0.05). Soil NeP activity had a significant positive correlation with sand and AcP, and was negatively correlated with pH, clay, silt and total Fe (P < 0.05). No relationship was found between soil phosphatases, Diester-P and Pyro-P (P > 0.05).

The PCA analysis of total P, available P, different P species and soil properties in soils with different cultivation ages is shown in Fig. 7. The two Principal Components axes explained 62.5% of the total variability. The different soils were mainly distributed along the first axis. Furthermore, it looks like there is a gradient between the three groups. The 200-yr site was about 20 degrees from vertical, the 400-yr site is about 45 degrees from vertical, and the 900-yr site is about 100 degrees from vertical (Fig. 7). Though the 900-yr site is in a different quadrant (Fig. 7). In order to confirm the degree of effect of soil properties on P fractions and species, the two-dimensional sequence diagram of redundancy analysis (RDA) was conducted (Fig. 8). The biplot space originated by the first two ordination axis of the RDA explained 93.7% of the total variance, with 75.7% rooting in the first ordination axis and 18.0% rooting in the second ordination axis. The contribution rates of NeP (56.2%), exchangeable Ca (11.9%), AcP (8.9%) and sand (7.2%) on P species were significantly higher than other soil properties, however NeP, exchangeable Ca, AcP and sand were the key factors to affect P species.

Effects of cultivation age on soil P composition by sequential chemical extraction and solution ³¹P NMR

We examined the effects of long-term cultivation on P composition and cycling in paddy soils with three different ages (200-, 400, and 900-yr). These subtropical soils from southern China had received typical P fertilizer applications for crop production. Results showed that long-term cultivation and management in paddy soils caused marked changes in P concentrations, especially for inorganic P which ranged from 30.8 to 75.5% of TP (Fig. 1). Total P, an indicator of long-term P sustainability especially for highly-weathered, subtropical cropland soils (Maharjan et al. 2018; Zhang et al. 2021b), was highly affected by cultivation age. Total-P accumulated in the topsoil and decreased with depth with increasing time of cultivation (Fig. 1). This increase in upper horizons results from receiving annual inputs of chemical fertilizers and/or manure. While these P sources increased production, they can also be important sources of P into surface waters due to leaching, runoff erosion (Perillo et al. 2021).

Mineral P, as Ca-bound P (determined by Dil.HCl-Pi), non-labile P (Conc.HCl-Pi), and highly resistant P (occluded P, Residual-P), were detected in all types of P fractions (Fig. 1). This degree of detection was due to the high concentration of non-labile P (Luo et al. 2021), which readily transforms between microbial biomass and non-labile P (Maharjan et al. 2018). Phosphorus immobilization by microorganisms sustains long-term P availability following microbial biomass turnover (Condron et al. 2005). Hence, soil P is mainly associated with Ca oxides and seasonal availability is sustained from P immobilization by microbes.

Higher concentrations of easily-labile Pi (NaHCO₃-Pi), moderately-labile Po (NaOH-Po) and non-labile Pi (Conc.HCl-Pi) are found in surface (Ap1 and Ap2) horizons (Figs. 1 and 2). In contract to the 200 years and 400 years old soils, the G horizon in the 900 years soil has a higher concentration of these three P pools. This fact can be explained by the continuous application of fertilizers with increasing time and sustained microbial activity, maintaining some P in mobile forms that are more easily translocated through the soil (Maharjan et al. 2018). Application of organic fertilizers provided readily available N to plants, which increases plant biomass. The crop residues that are generated by these applications are incorporated, resulting in accumulation of organic matter (C and N) (Maharjan et al. 2018). Meanwhile, flooding of these soils for rice production allows seasonal reduction and solubilization of soil Fe and Mn oxides. This flooding results in possible release of both adsorbed and precipitated P (Schrijver et al. 2012). These results show that long-term anthropogenic agricultural land use impacts forms of Pi and Po and their transformation. Also, results show translocation of P has occurred into the subsoil and demonstrate the conversion between Po and Pi forms and their respective conversion into soluble P due to soil microbial activity and fertilization.

The analysis with ³¹P NMR showed that P species were influenced by cultivation age and soil depth (Table 2, Fig. 3). Ortho-P was the major extractable Pi speciation in all paddy soils and increased with time of cultivation (Table 2, Fig. 3). Mono-P dominated organic P forms as they are stabilized in soils by association with amorphous metal oxides and can also be produced by alkaline degradation of RNA and phospholipids (Zhang et al. 2012a). The increasing inorganic P (including Pyro-P) with increasing cultivation age (Table 2, Fig. 3) could be attributed to the increased mineralization under long-term cultivation and tillage (Zhang et al. 2012a; Wei et al. 2014). Furthermore, ³¹P NMR showed that organic P mainly consisted of Mono-P and Diester-P, results that are in agreement with other studies (Bunemann et al. 2008). Diester-P is more readily degraded by microbes and enzymes than Mono-P (Mcdowell et al. 2007). This depletion of Pi results in a greater reliance on Po cycling via mineralization, i.e, depletion of the normally recalcitrant Mono-P pool (Mcdowell et al. 2007).

Likewise, the relatively large fraction of total organic P extracted with HCl, which is not available for plant uptake, is a very important P reserve (Maharjan et al. 2018). This will help buffer P availability via mineralization of organic P by phosphatases (Chen et al. 2002) once labile and solution P are insufficient for plant growth (Maharjan et al. 2017). In addition, under the condition of dry-wet cycling of paddy soils, solution P can readily form stable compounds with iron, while organic p can be translocated deeper into the soil (Dieter et al. 2010). Overall, long-term anthropogenic cultivation impacts soil P composition and chemistry, affecting P activation and transformation.

Effects of phosphatase activities and soil properties on P compositions

Soil enzymes are important indicators of biological property changes of soils because of their sensitivity to soil management practices (Wei et al. 2014). In this study, soil AcP and NeP activities were highest in the topsoil and decreased with soil depth. Both enzymes increased in topsoils over time from both addition of amendments and long-term agricultural cultivation (Fig. 4). This increase occurs as soil phosphatase activity is significantly influenced by soil microbial activity (Wei et al. 2014; Maharjan et al. 2018). Long-term agricultural cultivation and fertilizers can enhance soil microbial activities (Maharjan et al. 2017). Microbial activity would be increased with increasing C sources resulting from residue inputs (Wei et al. 2014). Enzyme activities increase with increasing residue inputs from long-term paddy cultivation (Fig. 4). Therefore, the increasing activity could be attributed to two factors: (1) increased substrates of soil phosphatases from crop residues and (2) increased microbial activities as soil phosphatases are believed to be derived primarily from microorganisms (Turner 2008; Wei et al. 2014).

The AcP activity was significantly and positively correlated with soil AP, SOC, TP and sand. These positive correlations demonstrate that AcP is a sensitive index for nutrients storage and could be used as an indicator of soil quality (Yang et al. 2016). In addition, the NeP activity was significantly and positively correlated with TP and AP, suggesting that NeP might play an important role in the hydrolysis and mobilization of soil-bound P in these soils (Yang et al. 2016). Also, AcP had a negative relationship with Ortho-P, but was positively correlated with Mono-P, suggesting that Ortho-P and Mono-P were influenced and regulated by AcP activity. Significant positive correlations were found among AcP, NeP and easily-labile P (NaHCO₃-Pi and NaHCO₃-Po), moderately-labile P (NaOH-Pi and NaOH-Po) and non-labile P (Conc.HCl-Po and Dil.HCl-Pi), indicating that AcP and NeP likely play an important role in transformation of soil P compositions in these soils (Yang et al. 2016).

Additionally, soil phosphatases catalyze the hydrolysis of organic compounds containing P, releasing inorganic P and thus increasing soil available P (Nash et al. 2014). In fact, different phosphatases have unique effects on individual P composition (Turner 2008). Briefly, monoesters can be hydrolyzed by AcP and NeP to release Ortho-P. High inorganic P concentrations may reduce phosphatase activities in long-term cultivated soils by inhibiting secretion of soil phosphatase by microorganisms and plants (Wei et al. 2017). Also, organic phosphate compounds are not readily degraded by soil microorganisms and phosphatases in acid soils due to the stronger adsorption capability of low pH soils (Zohar et al. 2014).

Correlation analysis showed that soil pH was significantly correlated with Pi, while SOC was significantly correlated with Po (Fig. 6). This correlation indicates that the availability of P is impacted by both pH and SOC concentration. Although parent material and soil pH have considerable influence on the distribution of inorganic phosphates between Ca (P_Ca) and metal oxide (Fe and Al) sorbents (P_Fe+Al) (Maharjan et al. 2018; Luo et al. 2021), our three soils were developed from similar alluvial parent materials. Thus, we quantitatively assessed the Pi fraction between these sorbents by assigning acid-extractable P (Dil.HCl-Pi) to Ca sorbents and base-extractable P (NaHCO₃-Pi + NaOH-Pi) to metal oxide sorbents and compared the P to Total-P proportion in each of these extracts. The soils at all three sites, with pH maintained between 6.2 and 7.0, released 1 to 4 times more P in the acid extraction than in the base extraction (Table 1, Fig. 2), consistent with a larger amount of P associated with inorganic Ca minerals than with Fe and Al oxides (Li et al. 2019).

Soil P available influenced by cultivation age and soil depth

Olsen-P in highly weathered soils is generally low and depends on organic phosphate mineralization (Maranguit et al. 2017). Po in the available pool (NaHCO₃-Po) is very important because it increases the apparent P availability (Johnson et al. 2003). Likewise, Po that occurs in the moderately-liable (NaOH-Po) pool is as important as NaHCO₃-Po because it contributes to P reserves (Maranguit et al. 2017). TP represents the long-term potential of the P supply, whereas easily-labile Pi represents the short-term bioavailability (Zhang et al. 2021a). Easily labile P, moderately liable P and non-available P increased in surface horizons (Ap1 and Ap2) with increasing cultivation age (Figs. 2). Phosphorus in these pools is contributing to the increase of total P in long-term paddy cultivation through fertilization (Fig. 1). Furthermore, easily liable P, moderately liable P and non-available P in the Br2 and G horizons declined with cultivation age between 400 and 900 years, whereas these soils had high P contents at Ap1 and Ap2 horizons. These trends indicate that P could accumulate at tropsoil due to paddy cultivation and P fertilizer (Liao et al. 2021).

In this study, soil Dil.HCl-Pi and Pyro-P increased with increasing cultivation age (Table 2, Fig. 1 and Fig. 3) indicating that long-term paddy cultivation increased the pool of soil inorganic P. This is probably due to microbial decomposition and mineralization of organic soil amendments from cultivation, with more secondary phosphate minerals formed resulting in more inorganic P in topsoils (Maranguit et al. 2017; Maharjan et al. 2018).

In many ecosystems, the pool of P is considered the regulator for soil C and N cycles (Lin et al. 2009). Therefore, characterization of the P pool is of great significance in order to understand biogeochemical cycling in ecosystems. Furthermore, P is an essential macronutrient, and its availability directly governs global crop production (Lidbury et al. 2020; Zhang et al. 2021a).

This study examined forms of P in soils with differing cultivation age that were developed on alluvial sediments with a long cultivation history. These soils presented an excellent opportunity for modeling pedogenic transformations of P during long-term agroecosystem development and to establish the influence of cultivation age on the trajectory of P evolution among forms. Results showed that distribution of soil P among different inorganic and organic P forms was strongly influenced by cultivation age. P stock was highest in the 900-yr soil and lowest in 200-yr soil. Soil concentrations of inorganic P were higher than organic P all three sites. Organic P was primarily composed of HCl-Po and NaOH-Po, with NaHCO₃-Po comprising a small fraction, indicating that availability of total organic P was low especially in subsoils. Moreover, acid phosphatase enzyme had higher activity than neutral phosphatase in these soils, but was significantly positive correlation with phosphate monoesters and negative correlation with orthophosphate. Long-term cultivation and addition of amendments appear to improve soil phosphatase activities, and increase concentrations of orthophosphate and decrease phosphate monoesters and diesters indirectly by its effects on phosphatases, further promote the conversion of phosphorus. Soil organic P mineralization to inorganic P in long-term agricultural cultivation plays a vital role to the increase of soil P availability. From these perspectives, understanding the factors driving P cycling and biological P availability is critical for maximizing agricultural productivity, proper use of applied nutrients, and minimizing pollution of surface and ground waters. Despite increasing knowledge of P use, microbal metabolic pathways related to P cycling are remain unclear and need further research.

PAC, P activation coefficient; Pi, inorganic P; Po, organic P; TPsum, sum of Pi and Po; AP, plant available P as extracted by the Olsen reagent; NaHCO3-Pi, NaHCO3-extractable Pi; NaOH-Pi, NaOH-extractable Pi; Dil.HCl-Pi, diluted HCl-extractable Pi; Conc.HCl-Pi, concentrated HCl-extractable Pi; NaHCO3-Po, NaHCO3-extractable Po; NaOH-Po, NaOH-extractable Po; Conc.HCl-Po, concentrated HCl-extractable Po; Ortho-P, orthophosphate; Mono-P, monoester phosphate; Diest-P, diester phosphate; Pyro-P, pyrophosphate; AcP, acid phosphatase activity; NeP, neutral phosphatase activity.

Ethics Approval This article is research in the direction of exhaust emission treatment and does not involve ethical codes.

Consent to Participate All authors agree with all participation conditions for publication in Environmental Science and Pollution Research.

Consent to Publish All authors agree with all publication consent conditions given for publication in Environmental Science and Pollution Research.

Competing Interests The authors declare no competing interests.

Availability of Data Not applicable.

Authors Contributions Xian Tang and Hongyi Liu designed the study, interpreted the results, and contributed to writing the manuscript. Chongjian Jia, Hailong Qin, Jianrong Zhao, Hong Wang and Bo Li contributed to modifying the manuscript. Ying Lu was responsible for proofreading and funding. All authors read and approved the final manuscript.

Funding This research was financially supported by the National Science Foundation of China (42277290) and the Special Project of National Science and Technology Basic Research (No. 2008FY110600).

Bunemann E K, Smernik R J, Marschner P, McNeill A M. 2008. Microbial synthesis of organic and condensed forms of phosphorus in acid and calcareous soils. Soil Biology and Biochemistry, 40, 932-946.
Burt R, Wilson M A, Keck T J, Dougherty B D, Strom D E, Lindahl J A. 2003. Trace element speciation in selected smelter-contaminated soils in Anaconda and Deer Lodge Valley, Montana, USA. Advances in Environmental Research, 8, 51-67.
Cade-Menun B J, Liu C W, Nunlist R, McColl J G. 2002. Soil and litter phosphorus-31 nuclear magnetic resonance spectroscopy: extractants, metals, and phosphorus relaxation times. Journal of Environmental Quality, 31, 457-465.
Cade-Menun B J, Preston C M. 1996. A comparison of soil extraction procedures for P NMR spectroscopy. Soil Science, 161, 770-785.
Cade-Menun B J. 2005. Characterizing phosphorus in environmental and agricultural samples by P nuclear magnetic resonance spectroscopy. Talanta, 66, 359-371.
Cade-Menun B J. 2015. Improved peak identification in ³¹P-NMR spectra of environmental samples with a standardized method and peak library. Geoderma, 257-258, 102-114.
Chen C R, Condron L M, Davis M R, Sherlock R R. 2002. Phosphorus dynamics in the rhizosphere of perennial ryegrass (Lolium perenne L.) and radiata pine (Pinus Radiata D. Don.). Soil Biology and Biochemistry, 34, 487-499.
Chen C R, Hou E Q, Condron L M, Bacon G, Esfandbod M, Olley J, Turner B L. 2015. Soil phosphorus fractionation and nutrient dynamics along the Cooloola coastal dune cultivation age, southern Queensland, Australia. Geoderma, 257-258, 4-13.
Condron L M, Turner B L, Cade-Menun B J. 2005. Chemistry and dynamics of soil organic phosphorus. Soil Science Society of America Press, America, 87-121.
Dieter D, Elsenbeer H, Turner B L. 2010. Phosphorus fractionation in low land tropical rainforest soils in central Panama. Catena, 82, 118-125.
FAO. 2015. World reference base for soil resources 2014. World Soil Resources Reports, Rome, Italy, 146-148.
Gu C H, Dam T, Hart S C, Turner B L, Chadwick O A, Berhe A A, Zhu M Q. 2020. Quantifying uncertainties in sequential chemical extraction of soil phosphorus using XANES spectroscopy. Environmental Science & Technology, 54, 2257-2267.
Hedley M J, Stewart J W B, Chauhan B S. 1982. Changes in inorganic and organic soil phosphorus fractions induced by cultivation practices and by laboratory incubations. Soil Science Society of America Journal, 46, 970-976.
Hou Q Y, Yang Z F, Ji J F, Yu T, Yuan J X. 2021. Effects of soil pH and mineral nutrients on Cadmium uptake by rice grain in the Pearl River Delta, China. Bulletin of Environmental Contamination and Toxicology, 106, 99-108.
Huang L M, Jia X X, Zhang G L, Shao M A. 2017. Soil organic phosphorus transformation during ecosystem development: A review. Plant and Soil, 417, 17-42.
Huang L M, Thompson A, Zhang G L. 2014. Long-term paddy cultivation significantly alters topsoil phosphorus transformation and degrades phosphorus sorption capacity. Soil and Tillage Research, 142, 32-41.
Huang L M, Zhang G L, Thompson A, Rossiter D G. 2013. Pedogenic transformation of phosphorus during paddy soil development on calcareous and acid parent materials. Soil Science Society of America Journal, 77, 2078-2088.
Jia C J, Lu Y, Xiong F, Cui Q C, Liu H Y, Qin H L, Gao Y J. 2017. Characteristics of iron oxide in soils different in cultivation age in the Pearl River Delta Plain (In Chinese). Acta Pedologica Sinica, 54, 894-904.
Johnson A H, Frizano J, Vann D R. 2003. Biogeochemical implications of labile phosphorus in forest soils determined by the Hedley fractionation procedure. Oecologia, 135, 487-499.
Li F Y, Liang X Q, Zhang H F, Tian G. M. 2019. The influence of no-till coupled with straw return on soil phosphorus speciation in a two-year rice-fallow practice. Soil & Tillage Research, 195, 104389.
Li M, Zhang J, Wang G Q, Yang H J, Wheland M J, Whited S M. 2013. Organic phosphorus fractionation in wetland soil proﬁles by chemical extraction and phosphorus-31 nuclear magnetic resonance spectroscopy. Applied Geochemistry, 33, 213-221.
Liao D, Zhang C C, Lambers H, Zhang F S. 2021. Changes in soil phosphorus fractions in response to long‐term phosphate fertilization under sole cropping and intercropping of maize and faba bean on a calcareous soil. Plant and Soil, 463, 589-600.
Lidbury I D E A, Borsetto C, Murphy A R J, Bottrill A, Jones A M E, Bending G D, Scanlan D J. 2020. Niche-adaptation in plant-associated Bacteroidetes favours specialisation in organic phosphorus mineralisation. The ISME Journal, 15, 1040-1055.
Lin J S, Shi X Z, Lu X X, Yu D S, Wang H J, Zhao Y C, Sun W X. 2009. Storage and spatial variation of phosphorus in paddy soils of China. Pedosphere, 19, 790-798.
Liu J, Hu Y, Yang J, Abdi D, Cade-Menun B J. 2015. Investigation of soil legacy phosphorus transformation in long-term agricultural fields using sequential fractionation, P K-edge XANES and solution P NMR spectroscopy. Environmental Science & Technology, 49, 168-176.
Lu F X. 1988. Soil in the pearl river delta. China Environmental Science Press, Beijing, China. (in Chinese)
Luo L, Ye H Y, Zhang D H, Gu J D, Deng O P. 2021. The dynamics of phosphorus fractions and the factors driving phosphorus cycle in Zoige Plateau peatland soil. Chemosphere, 278, 130501.
Maharjan M, Maranguit D, Kuzyakov Y. 2018. Phosphorus fractions in subtropical soils depending on land use. European Journal of Soil Biology, 87, 17-24.
Maranguit D, Guillaume T, Kuzyakov Y. 2017. Land-use change affects phosphorus fractions in highly weathered tropical soils. Catena, 149, 385-393.
Mcdowell R W, Cade‐Menun B, Stewart I. 2007. Organic phosphorus speciation and pedogenesis: analysis by solution ³¹P nuclear magnetic resonance spectroscopy. European Journal of Soil Science, 58, 1348-1357.
Nash D M, Haygarth P M, Turner B L, Condron L M, McDowell R W, Richardson A E, Heaven M W. 2014. Using organic phosphorus to sustain pasture productivity: A perspective. Geoderma, 221, 11-19.
Perillo V L, Cade-Menun B J, Ivancic M, Ross D S, Wemple B C. 2021. Land use and landscape position influence soil organic phosphorus speciation in a mixed land use watershed. Journal of Environmental Quality, 50, 967-978.
Schmieder F, Bergström L, Riddle M, Gustafsson J P, Klysubun W, Zehetner F, Kirchmanna H. 2018. Phosphorus speciation in a long-term manureamended soil profile-evidence from wet chemical extraction, ³¹P-NMR and P K-edge XANES spectroscopy. Geoderma, 322, 19-27.
Schrijver A D, Vesterdal L, Hansen K, Frenne P D, Augusto L, Achat D L, Verheyen K. 2012. Four decades of post-agricultural forest development have caused major redistributions of soil phosphorus fractions. Oecologia, 169, 221-234.
Shen G Q. 1987. Method for determination of phosphatase activity in soil. Journal of Soil Fertilizer, 23, 40-42. (in Chinese)
Sims J T, Pierzynski G M. 2005. Chemistry of phosphorus in soils. Soil Science Society of America Press, America, 151-192.
Sun B R, Gao Y Z, Wu X, Ma H M, Zheng C C, Wang X Y, Yang H J. 2020. The relative contributions of pH, organic anions, and phosphatase to rhizosphere soil phosphorus mobilization and crop phosphorus uptake in maize/alfalfa polyculture. Plant and Soil, 447, 117-133.
Tiessen H, Moir J O. 1993. Characterization of available P by sequential extraction, 2nd Ed. Canadian Society Soil Science Press, Canadian, 75-86.
Turner B L, Mahieu N, Condron L M. 2003. Phosphorus-31 nuclear magnetic resonance spectral assignments of phosphorus compounds in soil NaOH-EDTA extracts. Soil Science Society of America Journal, 67, 497-510.
Turner B L. 2008. Soil organic phosphorus in tropical forests: an assessment of the NaOH-EDTA extraction procedure for quantitative analysis by solution ³¹P NMR spectroscopy. European Journal of Soil Science, 59, 453-466.
Vestergren J, Vincent A G, Jansson M, Persson P, Ilstedt U, Gröbner G, Schleucher J. 2012. High-resolution characterization of organic phosphorus in soil extracts using 2D ¹H-³¹P NMR correlation spectroscopy. Environmental Science & Technology, 46, 3950-3956.
Wang G P, Bao K S, Yu X F, Zhao H M, Lin Q X, Lu X G. 2012. Forms and accumulation of soil P in a subalpine peatland of Mt. Changbai in northeast China. Catena, 92, 22-29.
Wei K, Bao H G, Huang S M, Chen L J. 2017. Effects of long-term fertilization on available P, P composition and phosphatase activities in soil from the Huang-Huai-Hai Plain of China. Agriculture, Ecosystems & Environment, 237, 134-142.
Wei K, Chen Z H, Zhu A N, Zhang J B, Chen L J. 2014. Application of ³¹P NMR spectroscopy in determining phosphatase activities and P composition in soil aggregates inﬂuenced by tillage and residue management practices. Soil & Tillage Research, 138, 35-43.
Wei X M, Hu Y J, Razavi B S, Zhou J, Shen J L, Nannipieri P, Ge T. 2019. Rare taxa of alkaline phosphomonoesterase-harboring microorganisms mediate soil phosphorus mineralization. Soil Biology and Biochemistry, 131, 62-70.
Wu Q H, Zhang S X, Zhu P, Huang S M, Wang B R, Zhao L P, Xu M G. 2017. Characterizing differences in the phosphorus activation coefficient of three typical cropland soils and the influencing factors under long-term fertilization. PloS One, 12, e0176437.
Xiao L, Guan D, Peart M, Chen Y, Li Q, Dai J. 2017. The influence of bioavailable heavy metals and microbial parameters of soil on the metal accumulation in rice grain. Chemosphere, 185, 868-878.
Yang X Y, Chen X W, Yang X T. 2019. Eﬀect of organic matter on phosphorus adsorption in a black soil from Northeast China. Soil & Tillage Research, 187, 85-91.
Yang X Z, Wei K, Chen Z H, Chen L J. 2016. Soil phosphorus composition and phosphatase activities along altitudes of alpine tundra in Changbai Mountains, China. Chinese Geographical Science, 26, 90-98.
Ye L, Zhong B Q, Huang M J, Chen W H, Wang X M. 2021. Pollution evaluation and children's multimedia exposure of atmospheric arsenic deposition in the Pearl River Delta, China. Science of the Total Environment, 787, 147629.
Zhang A M, Chen Z H, Zhang G N, Chen L J, Wu Z J. 2012a. Soil phosphorus composition determined by ³¹P NMR spectroscopy and relative phosphatase activities influenced by land use. European Journal of Soil Biology, 52, 73-77.
Zhang G L, Gong Z T. 2012b. Soil Survey Laboratory Methods. Science Press, Beijing, China. (in Chinese)
Zhang G L, Li D C. 2016. Manual of soil description and sampling. Science Press, Beijing, China. (in Chinese)
Zhang J R, Li H Z, Zhou Y Z, Dou L, Cai L M, Mo L P, You J. 2018. Bioavailability and soil-to-crop transfer of heavy metals in farmland soils: a case study in the Pearl River Delta, South China. Environmental Pollution, 235, 710-719.
Zhang L, Zhuang T, Bai J H, Ye X F, Wang D W, Wang W, Guan Y A. 2021a. Dynamics of phosphorus fractions and potential bioavailability along soil profiles from seasonal-flooding wetlands in a Chinese estuary. Environmental Science and Pollution Research, 28, 6549-6560.
Zhang L, Zhuang T, Bai J H, Ye X F, Wang D W, Wang W, Guan Y N. 2021. Dynamics of phosphorus fractions and potential bioavailability along soil profiles from seasonal-flooding wetlands in a Chinese estuary. Environmental Science and Pollution Research, 28, 6549-6560.
Zhang Q, Wang G H, Feng Y K, Sun Q Z, Witt C, Dobermann A. 2006. Changes in soil phosphorus fractions in a calcareous paddy soil under intensive rice cropping. Plant and Soil, 288, 141-154.
Zhang Y Q, Finn D, Bhattacharyya R, Dennis P G, Doolette A L, Smernik R J, Kopittke P M. 2021b. Long-term changes in land use influence phosphorus concentrations, speciation, and cycling within subtropical soils. Geoderma, 393, 115010.
Zhao S Q, Yang Z W. 2011. Development history of embankment water conservancy and agriculture in the Pearl River Delta. Guangdong: Guangdong People's Press, Guangzhou, China. (in Chinese)
Zhou J, Wu Y H, Turner B L, Sun H Y, Wang J P, Bing H J, Luo J, He X L, Zhu H, He Q Q. 2019. Transformation of soil organic phosphorus along the Hailuogou post-glacial chronosequence, southeastern edge of the Tibetan Plateau. Geoderma, 352, 414-421.
Zhou Q, Zhu Y. 2003. Potential pollution and recommended critical levels of phosphorus in paddy soils of the southern Lake Tai area, China. Geoderma, 115, 45-54.
Zohar I, Cade-Menun B, Paytan A, Shaviv A. 2014. Phosphorus transformations from reclaimed waste water to irrigated soil: A ³¹P NMR study. Soil Science Society of America Journal, 78, 1884-189.

Supplementalfiles.docx

Download PDF

Version 1

posted

You are reading this latest preprint version

Organic/Inorganic phosphorus forms and transformation in long-term paddy cultivation in the Pearl River Delta, China

Status:

Version 1

Abstract

Figures

Introduction

Materials And Methods

Site description and cultivation age recognition

Analysis of soil parameters and sequential P fractionation

Phosphatase enzyme hydrolysis assay

Statistical analysis

Results

Total P and Soil P fractions by sequential chemical extraction

Soil Pi speciations determined by ³¹P nuclear magnetic resonance (31P NMR) spectroscopy

Soil Po speciations determined by ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy

Soil phosphatase activities

The relationships among P compositions, soil properties and phosphatase activities

Discussion

Effects of phosphatase activities and soil properties on P compositions

Soil P available influenced by cultivation age and soil depth

Conclusions

Abbreviations

Declarations

References

Supplementary Files

Status:

Version 1

Organic/Inorganic phosphorus forms and transformation in long-term paddy cultivation in the Pearl River Delta, China

Status:

Version 1

Abstract

Figures

Introduction

Materials And Methods

Site description and cultivation age recognition

Analysis of soil parameters and sequential P fractionation

Phosphatase enzyme hydrolysis assay

Statistical analysis

Results

Total P and Soil P fractions by sequential chemical extraction

Soil Pi speciations determined by 31P nuclear magnetic resonance (31P NMR) spectroscopy

Soil Po speciations determined by 31P nuclear magnetic resonance (31P NMR) spectroscopy

Soil phosphatase activities

The relationships among P compositions, soil properties and phosphatase activities

Discussion

Effects of phosphatase activities and soil properties on P compositions

Soil P available influenced by cultivation age and soil depth

Conclusions

Abbreviations

Declarations

References

Supplementary Files

Status:

Version 1

Soil Pi speciations determined by ³¹P nuclear magnetic resonance (31P NMR) spectroscopy

Soil Po speciations determined by ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy