Contrasting nitrate leaching from an abandoned Moso bamboo forest and a Japanese cedar plantation: role of vegetation in mitigating nitrate leaching

Nitrate (NO3−) leaching from forest ecosystems can differ depending on the plant species because of differences in nitrogen (N) retention capacities. Moso bamboo, a fast-growth species, expands into adjacent forests worldwide, potentially leading to increased N retention and subsequently reduced NO3− leaching. Accordingly, this study aims to compare NO3− leaching and potential factors between Moso bamboo and neighboring forest. We measured NO3− concentrations in soil solutions at a Moso bamboo site (BF) and an adjacent Japanese cedar plantation (CF). We also evaluated soil nitrification and plant N uptake by the in situ depletion method. The NO3− concentration in the soil solution below the root zone (50 cm) was lower in BF (48 ± 8 µmol L−1) than in CF (305 ± 16 µmol L−1). The NO3− concentration in the soil solution was significantly higher for surface soil (0–5 cm) (111 ± 11 µmol L−1) than for soil below the root zone in BF, but not significantly different between these two layers in CF (357 ± 25 µmol L−1), indicating high N retention in BF. The net nitrification rates and root NO3− uptake rates were higher in BF than in CF, indicating that plant N uptake could be the main contributors to the low NO3− leaching. Bamboo invasion has the potential to mitigate forest NO3− leaching due to its high N uptake. Our findings highlight the importance of vegetation with higher N uptake in enhancing N retention under elevated atmospheric N deposition.


Introduction
In recent decades, human activities including agriculture and fuel combustion have resulted in increased atmospheric nitrogen (N) deposition in forest ecosystems (Vitousek et al. 1997).Forests in high N deposition areas are prone to accumulating excess mineral N in soils, leading to conversion from N-limited to Vol:. ( 1234567890) N-saturated forests with high rates of nitrate (NO 3 − ) leaching (Aber et al. 1998).It has been reported that NO 3 − leaching, a major pathway of N loss from soil, is one of the main causes of deteriorating stream water quality and eutrophication around the world (Fang et al. 2009;Aber et al. 2003;Chiwa et al. 2019).Therefore, it is important to understand the variations in NO 3 − leaching and the factors controlling this process in forest ecosystems.
Various environmental factors, such as precipitation (Schwenke and Haigh 2016) and topography (Watanabe et al. 2018), affect NO 3 − leaching in forest ecosystems.Additionally, different tree species have different N retention capacities (Crowley and Lovett 2017), so the species is an important factor affecting NO 3 − leaching.Different tree species may result in marked differences in the level of NO 3 − leaching, even between neighboring forest stands growing under similar environmental conditions.For example, Chiwa et al. (2015) reported that Japanese cedar (Cryptomeria japonica) plantations leach more NO 3 − into stream water in Japan than other forest stands due to their low capacity for N retention (Yang and Chiwa 2021).Conversely, fast-growing species with rapid rates of N acquisition have the potential to retain the nutrients in their plant-soil systems (de Vries and Bardgett 2012).For example, Fukuzawa et al. (2006) reported that the cutting of the dwarf bamboo (Sasa senanensis) caused marked NO 3 − leaching from a forested watershed in northern Japan, indirectly indicating the role of dwarf bamboo on N retention.Wang et al. (2010) also found that the fast-growing exotic eucalypt (Eucalyptus urophylla) and Acacia (Acacia crassicarpa) plantations had the lowest N leaching compared to the other native plantations in southern China.Although NO 3 − leaching may vary among different forest stands, the mechanisms responsible for these differences have not been understood sufficiently.
Moso bamboo (Phyllostachys pubescens), an important commercial species native to China, was imported into Japan in the 1700s (Isagi and Torii 1997).This species had been planted in western and central Japan, and was used as a building material, for handcrafts, and as a food.However, bamboo forests are being abandoned because of the decreased demand for bamboo products and workforce shortages.If bamboo plantations are not controlled, the plants spread rapidly owing to the extensive root rhizome system, so they readily expand into adjacent coniferous forests and broadleaved forests.
Previous studies have focused primarily on the negative effects of bamboo expansion on the community structure and function of forest ecosystems, such as the loss of plant diversity (Ouyang et al. 2016) and decreased plant biomass (Song et al. 2016(Song et al. , 2017)).Some studies have also investigated the biogeochemical effects of bamboo expansion, such changes in the size of the soil labile N pool after Moso bamboo invasion into a broadleaved mixed forest (Song et al. 2016).Li et al. (2017) detected significantly lower NO 3 − concentrations in soil solution in a Moso bamboo forest than in a broad-leaved forest.Song et al. (2016) assumed that bamboo expansion into broadleaved forest degraded litter quality and decreased soil nitrification, resulting in decreased generation of NO 3 − .Zhou et al. (2020) compared NO 3 − leaching between different vegetation types in eastern China, and found that NO 3 − leaching was significantly lower in a managed Moso bamboo forest than in an adjacent tea plantation.Because abandoned and uncontrolled Moso bamboo is expanding rapidly into forests, investigations on NO 3 − leaching in abandoned Moso bamboo forests and their neighboring woody forests can shed light on the role of vegetation with a high N retention capacity in reducing N leaching from forested ecosystems.
Soil nitrification is an important soil N transformation process driven by soil microbes that produce NO 3 − .Elevated nitrification rates can potentially contribute to NO 3 − leaching in forest ecosystems (Gundersen and Rasmussen 1990).Past studies showed inconsistent impacts of bamboo invasion on soil nitrification in the invaded forest ecosystems, including decreased (Yan et al. 2008;Song et al. 2016) and increased net nitrification rates (Chen et al. 2021).These variations indicate that soil nitrification and its effects on NO 3 − leaching can vary under different environmental conditions.
It is typically thought that lower N leaching is associated with higher N uptake (Brooks et al. 2011;Campbell et al. 2014;Yang and Chiwa 2021).Templer et al. (2005) reported that N uptake rates can directly affect N losses in mature forests.Compared with trees, Moso bamboo exhibits much higher growth rates and a larger root biomass (Kobayashi et al. 2015), so it has the potential to absorb a large amount of N. Therefore, plant N uptake may play an important role in controlling NO 3 − leaching in Moso bamboo forests.Furthermore, Ueda et al. (2009) reported that roots of Moso bamboo have high nitrate reductase activity (NRA), which has been used as an indicator of nitrate assimilation (Thomas and Hilker 2000).Because of its extremely fast growth rate, Moso bamboo probably assimilates large amounts of nitrate from soil, leading to low rates of NO 3 − leaching.The objectives of this study were as follows: (1) to evaluate stand-scale N leaching in an abandoned Moso bamboo forest and an adjacent Japanese cedar plantation; and (2) to explore the factors that affect N leaching, including plant N uptake and soil nitrification.

Site description
This study was carried out in an abandoned Moso bamboo forest (BF) and an adjacent Japanese cedar plantation (CF), both located in the Kasuya Research Forest (33° 37′N, 130° 32′E) of Kyushu University, situated 15 km west of the Fukuoka urban area (the fourth largest metropolitan area in Japan) (Fig. 1).There have been high levels of atmospheric N deposition from 2009 to 2018 in the Kasuya Research Forest (Chiwa 2021).The mean annual temperature and precipitation were 17.4 °C and 1880 mm, respectively, over the last 2 years (Japan Meteorological Agency).The BF and CF were located on a steep slope at 180-280 m a.s.l.The BF was a pure abandoned Moso bamboo forest without human disturbance.The CF was approximately 70 years old and dominated by the evergreen coniferous tree C. japonica, the main plantation species in Japan.A more detailed description of the study site has been provided in a previous study (Shimono et al. 2021) (Table S1).

Soil solution collection
We collected soil solution samples at basically 1-month intervals from April 2021 to October 2022, using a tension lysimeter with a porous cup and a pressure syringe.Nine points were selected along the slope between 180 to 280 m a.s.l. to install the lysimeters in both BF and CF (Fig. 1).At each point, a lysimeter was inserted at a depth of 50 cm, which Fig. 1 Topographic map and location of the study site, Kasuya Research Forest (KRF).Circles show sample collection points for N leaching and soil nitrification measurements in Japanese cedar plantation (CF) and Moso bamboo forest (BF).Squares in the topographic map represent sample collection sites for plant root N uptake measurements.The dotted black lines represent boundary lines between BF and CF.The area between these two lines represents the transition area (mixed bamboocedar forest, referred as transitional forest area moderately invaded by Moso bamboo).The elevation data was provided by the Geospatial Information Authority of Japan was below the rooting zone of the plants, to collect soil leachate samples.We used the nutrient chemistry of the leachates as an indirect representation of potential leaching.Lysimeters were also installed in the shallow forest soil layer (0-5 cm) to collect surface soil solutions, which were used to measure the nutrient conditions of the surface soil.In each month, all lysimeters were set up for 24 h, and then the soil solutions in the syringes were collected.After collection, the samples were transported to the laboratory within 2 h and immediately filtered through syringe filters (0.45-μm, Ekicrodisc, Acro LC3CR, Nihon Pall Ltd., Tokyo, Japan).Ion chromatography was conducted to determine the concentrations of NO 3 -(Dionex Aquion, Thermo Fisher Scientific, Waltham, MA, USA) and NH 4 + (Dionex ICS-1000, Thermo Fisher Scientific).

Soil nitrification rate
The soil net nitrification rate and N mineralization rate were determined by laboratory incubation (Tateno and Takeda 2003;Urakawa et al. 2016) at constant temperature of 25 °C as described below.In October 2022, we collected mineral soils from 0-5 cm depth within a frame (25 cm × 25 cm) near the points where soil solutions were collected (Fig. 1).The soil samples were placed in plastic bags, transported to the laboratory in a cool box, and then sieved (5 mm) to remove roots, stones, and coarse gravel.A 5 g sample of fresh soil was extracted with 50 mL KCl (2 M) for 1 h.After initial extraction, another 5 g fresh soil was placed in a plastic bag and incubated for 28 days at 25 °C.The concentrations of NO 3 -and NH 4 + in the extract solution were determined using an auto analyzer (AACS-4, BL-TEC Inc., Osaka, Japan).The net N mineralization and nitrification rates were calculated as the differences in NO 3 -and NH 4 + concentrations in soils between before and after the incubation period.

Plant N uptake
The uptake rates of NO 3 -and NH 4 + by plants per unit fine root mass (μmol g −1 h −1 ) were measured using the in situ depletion method (Lucash et al. 2008;Socci and Templer 2011;Campbell et al. 2014;Ito et al. 2022).Uptake experiments were conducted basically once a month on sunny days from October 2021 to August 2022 (n = 5 per species per month).At each sampling time, we randomly selected five individuals per species in a plot (Fig. 1) and excavated fine roots (< 2 mm diameter) from the soil surface within 3 m of the base of the target tree.We used fine roots because they are the most active in nutrient acquisition (Eissenstat 1992).To ensure that the measurements were comparable, experiments were conducted in BF and CF at the same altitude (Fig. 1) and during the same time (from 10:00 AM to 2:00 PM).The fine roots of Moso bamboo and Japanese cedar were identified on the basis of their morphological traits, such as color, diameter, and mycorrhizal type (Liu et al. 2017;Yahara et al. 2019).We excavated fine roots at the soil surface and ensured that they were connected to the trees.After excavation, the fine roots were rinsed with de-ionized water and gently dabbed with paper towels to remove soil particles.Each root sample was placed in a 15-mL tube containing 12 mL nutrient solution (200 μmol L −1 NH 4 + and 200 μmol L −1 NO 3 − ) and incubated for 4 h from 10:00 AM to 2:00 PM.We determined the concentration of the nutrient solution according to Japanese forest soil datasets (Urakawa et al. 2015;Ito et al. 2022).Each tube was sealed with parafilm and covered with aluminum during incubation to minimize evaporation and contamination.At the end of the incubation period, the volume of the nutrient solution was measured, then it was filtered through a syringe filter (0.45-μm, Ekicrodisc).The incubated fine roots were cut, oven-dried at 70 °C for 72 h, and weighed (mean dry root mass = 0.38 mg).We measured the NO 3 − and NH 4 + concentrations in the solutions by ion chromatography as described above.The uptake rates of NO 3 − and NH 4 + by the fine roots were calculated as follows: where N uptake is the uptake rate of NO 3 − or NH 4 + by fine roots (μmol g −1 h −1 ); N initial is the concentration (μmol L −1 ) of NO 3 -or NH 4 + before the incubation; N final is the concentration (μmol L −1 ) of NO 3 − or NH 4 + at the end of the incubation; Mass root is dry root mass (g); V solution is the volume (L) of the nutrient solution; and T is the incubation time (hr).

Statistical analyses
Comparisons of NO 3 -concentrations in soil solutions between BF and CF and between the different depths (soil leachate and surface soil solution) were performed using t-test (P < 0.05).Differences in the NO 3 -or NH 4 + uptake rates, net nitrification rates, net mineralization rates, and soil inorganic N concentrations between BF and CF were also determined by t-test (P < 0.05).Linear regression models were plotted to determine the effects of slope position on the NO 3 − concentration in soil solutions between BF and CF and between the different depths.The explanatory variable was the slope position, and the objective variable was the NO 3 − concentration.Statistical analyses were conducted in R version 4.4.2software (R Core Team 2022).

Inorganic N concentration in the soil solution
The concentration of NO 3 -in soil leachate (50 cm depth) was significantly lower in BF (47.5 ± 7.8 μmol L −1 ) than in CF (305.1 ± 16.2 μmol L −1 ) (Table 1).The NO 3 -concentration in the surface soil solution was also significantly lower in BF (110.5 ± 11.4 μmol L -1 ) than in CF (356.6 ± 24.9 μmol L -1 ) (Table 1).These differences between BF and CF were consistent during the observation period from April 2021 to August 2022 (Figs. 2 and 3).Additionally, in BF, the concentration of NO 3 -was significantly lower in the soil leachate (50 cm depth) than in the surface soil solution (Table 1).In contrast, in CF, there was no significant difference in NO 3 -concentrations between the soil leachate (50 cm depth) and the surface soil solution (Table 1).Among all soil solutions, only the NO 3 -concentration in soil leachate in BF showed a significant correlation with slope position (Table S2).However, the coefficient of determination was low (0.11).
The NH 4 + concentrations in soil were markedly lower than the NO 3 -concentrations in soil in both BF (from 6 to 27 μmol L −1 ) and CF (from 2 to 7 μmol L −1 ) (Table 1).In addition, the NH 4 + concentration in the surface soil solution was significantly higher in BF than in CF (Table 1).
The soil-extracted NH 4 + content was higher in BF (10.7 mg N kg −1 ) than in CF (6.96 mg N kg −1 ), but the soil-extracted NO 3 − content was lower in BF (1.86 mg N kg −1 ) than in CF (3.70 mg N kg −1 ) (Table S3).

Stand-scale N leaching in Moso bamboo and Japanese cedar forests
The soil leachate NO 3 -concentrations were lower in BF than in CF during the whole observation period (Table 1, Fig. 2), indicating that NO 3 -leaching loss may be lower in BF compared to CF.The low NO 3 -leaching and low NO 3 -concentration in soil Table 2 Mean values of net nitrification, mineralization rates (mg kg −1 day −1 ), and percentage nitrification (fraction of mineralized N converted to nitrate; %) in the surface soil (0-5 cm depth) in Moso bamboo (BF) and Japanese cedar plantation (CF) Data are average ± standard error (SE).Asterisks indicate significant differences between BF and CF at P = 0.05 (t-test)

Moso bamboo
Japanese cedar P value Nitrification (mg kg −1 d −1 ) 0.69 ± 0.13 0.39 ± 0.01 * Mineralization (mg kg −1 d −1 ) 0.71 ± 0.10 0.40 ± 0.01 * Percent nitrification (%) 94% 98% ns leachate detected in BF in this study are consistent with the results reported by Zhou et al. (2020), who found lower soil leachate NO 3 -concentrations in a managed bamboo forest than in an adjacent tea plantation on hillslopes in eastern China.In contrast, the high NO 3 -concentration in soil leachate in CF indicates high levels of NO 3 -leaching.Previous studies have also reported high N leaching from Japanese cedar plantations.For example, Yang and Chiwa (2021) detected high NO 3 -concentrations (607 ± 59 μmol L -1 ) in soil solutions in Japanese cedar plantations in western Japan.Oyanagi et al. (2002) also detected high NO 3 -concentrations (approximately 240 μmol L −1 ) in soil solutions from deeper soil (50-cm and 80-cm depths) in a Japanese cedar plantation in eastern Japan with high levels of atmospheric N deposition (10.5 kg N ha -1 yr -1 ).
Nitrate is a mobile ion that is easily transported with soil water flow and readily moves from the plant root zone via the movement of water (Jobbágy and Jackson 2001).In BF, the NO 3 -concentration was significantly lower in the soil leachate than in the surface soil solution (Table 1).These results suggest that NO 3 -could be retained by soil N transformation processes and/or plants uptake that occurred between the surface soil and deeper soil below the rooting zone in BF.In contrast, in CF, the NO 3 -concentrations were not significantly different between the surface soil solution and the soil leachate (Table 1), suggesting that NO 3 -was not depleted and remained at a high level in the soil solution.
The NO 3 -concentration in the surface soil solution was significantly lower in BF than in CF (Fig. 3).The lower NO 3 -in surface soil solution in BF was also reflected by the initial content of NO 3 − in the soil-extracted solution (Table S3).Nutrients in the throughfall contribute considerably to the nutrient chemistry of the forest floor (De Schrijver et al. 2007), which may affect the nutrient chemistry of surface soil solution.Previous studies have shown that inorganic N uptake by the canopy is comparable in Moso bamboo and conifer forests (Sievering et al. 2000).Additionally, Chiwa et al. ( 2010) demonstrated higher inorganic N fluxes from throughfall in a Moso bamboo forest than that in a forest site of western Japan.The results of those studies suggest that the lower NO 3 -concentrations in the surface soil solution in BF than in CF cannot be attributed to N inputs from throughfall.
The NO 3 -concentration in soil leachate differed between BF and CF, but this was probably not due to differences in the amount of soil water percolation below the rooting zone (50 cm depth) (Fig. 2).Soil water percolation can directly influence the nutrient concentration in the soil solution, because dissolved substances are commonly diluted by water.Here, we roughly evaluated the amount of soil water percolation by subtracting the canopy transpiration (E) and rainfall interception (I) from precipitation (P) (Komatsu et al. 2008).In the Kasuya Research Forest, E accounts for 20% of P in bamboo stands, compared with 10% in neighboring Japanese cedar plantations (Ichihashi et al. 2015).However, a summary of earlier studies on I in bamboo and coniferous forests across Japan by Komatsu et al. (2010) indicated that the I/P was significantly lower for bamboo forests (11%) than for coniferous forests (20%).This suggests that the higher E in bamboo stands was compensated by the lower I, and the amount of soil water percolation in BF is likely similar to that in CF.
Factors that may contribute to differences in NO 3 leaching rates between BF and CF A higher soil nitrification rate is one possible reason for increased NO 3 -leaching (Gundersen et al. 1998).In this study, the high proportions of net nitrification rates to net mineralization rates in both BF and CF (Table 2) indicate that soil nitrification in both BF and CF was high enough to lead to NO 3 -leaching.Our laboratory incubation measurements indicated that net nitrification rates were higher in BF than in CF (Table 2).This result differs from those of Shimono et al. (2021), who found no significant differences in soil nitrification rates between BF and CF using the in situ buried bag method (Eno 1960).Although our results also differ from those of Song et al. (2016) and Yan et al. (2008), who reported lower soil nitrification in Moso bamboo forest than in woody forest, it could be argued that the relatively high nitrification rate in BF in this study could not explain the low NO 3 − leaching from BF. Plant N uptake is another primary factor that controls N retention and subsequent NO 3 -leaching (Templer et al. 2005;Chiwa et al. 2015).Plants generally acquire nutrients via their roots, among which fine roots (< 2 mm diameter) are the most active (Eissenstat 1992).A previous study reported that root damage caused by soil freezing reduced N uptake by plants and led to NO 3 -leaching (Campbell et al. 2014), suggesting that N uptake rates of fine roots directly affect NO 3 -leaching.The in situ depletion method (Lucash et al. 2008) can directly evaluate the inorganic N uptake rates of fine roots and provide an accurate assessment of the effects of plant N uptake in different inorganic N forms on stand-scale NO 3 -leaching.The values of uptake rates measured in this study are comparable to those reported by Ito et al. (2022).They determined the NO 3 -and NH 4 + uptake rates of four coniferous species (Larix kaempferi, Pinus densiflora, Chamaecyparis obtusa, Cryptomeria japonica) in central Japan to be within the ranges of − 1.59 to 2.09 μmol g −1 h −1 and from 2.37 to 14.6 μmol g −1 h −1 , respectively.
In the present study, the NO 3 -uptake rates of fine roots were significantly higher in BF than in CF (Fig. 4a), indicating that Moso bamboo exhibits a higher NO 3 -uptake capacity than that of Japanese cedar.Higher NO 3 -uptake rates of Moso bamboo (Fig. 4a) are likely attributed to the high NRA in roots (Ueda et al. 2009).Roots with high NRA usually exhibit high NO 3 -uptake rates when exposed to a high concentration of NO 3 - (Min et al. 1998).Because the fine roots of Moso bamboo in this study were incubated in a solution with a higher concentration of NO 3 -(200 μmol L −1 ) than that in the soil solution, the potentially high NRA of bamboo roots may be one reason for the high NO 3 -uptake rates.Although the NH 4 + uptake rates were lower in BF than in CF (Fig. 4b), a previous study conducted at the same study sites as this study found that the fine root biomass in BF (15.1 ± 4.8 Mg ha −1 ) was approximately 17 times higher than that in CF (0.89 ± 0.21 Mg ha −1 ) (Shimono et al. 2021).Thus, we roughly estimated the annual NH 4 + uptake of fine roots by multiplying the NH 4 + uptake rates by the fine root biomass, which was nine times higher in BF than in CF in this study.Therefore, high NO 3 -uptake rates and a large fine root biomass may lead to elevated N retention in BF.
The higher N uptake in BF in this study was also consistent with the results of Shimono et al. (2021), who estimated higher N uptake in BF (117 ± 12 kg N ha −1 yr −1 ) than in CF (37.1 ± 3.9 kg N ha −1 yr −1 ) by multiplying the N content of each plant organ by net primary production.A previous study conducted in China also revealed that the expansion of Moso bamboo into broad-leaved forests increased the N pool in plants by 40% but reduced the size of the soil inorganic N pool by 30% (Song et al. 2017), providing further evidence that N is retained by Moso bamboo.
Vol.: (0123456789) The lower NO 3 -uptake rates (Fig. 4a, Table 3) and lower fine root biomass (Shimono et al. 2021) in CF than in BF suggest that Japanese cedar has lower N uptake than that of Moso bamboo.Consistent with this result, Yang and Chiwa (2021) found that N uptake was lower in Japanese cedar plantations than in Japanese oak plantations (Quercus crispula).According to Min et al. (1998), coniferous species exhibit relatively low NRA and NO 3 -uptake rates, potentially leading to low NO 3 -uptake.In addition, it was revealed that N-saturated Japanese cedar plantations are large non-point N sources in Japan, probably because of the low N retention by these trees (Chiwa et al. 2015(Chiwa et al. , 2019)).
In this study, net efflux of NO 3 -by fine roots occurred in both BF and CF.Past studies also detected the efflux of NH 4 + and NO 3 -using the in situ depletion method (Lucash et al. 2008;Campbell et al. 2014;Ito et al. 2022).Several reasons were proposed to explain this efflux, such as the high energic cost of NO 3 -uptake (Lambers and Oliveira 2019), changes in the osmotic potential of roots when incubated in solutions with high concentrations of NO 3 -and NH 4 + (Rygiewicz and Bledsoe 1986), and physical disturbance to roots during excavation (Lucash et al. 2008).Interestingly, we detected a lower proportion of net efflux of NO 3 -out of total data (i.e., total NO 3 -uptake rates measured by the in situ depletion method) in BF (46%) than in CF (66%) (data not shown).This finding, together with the higher NO 3 -uptake rates of Moso bamboo than Japanese cedar (Fig. 4a, Table 3), further explains the high NO 3 -uptake capacity of Moso bamboo.

Conclusion
The results of this study show that NO 3 -leaching is much lower in abandoned Moso bamboo forest than in Japanese cedar forest.Soil nitrification could not explain the lower NO 3 -leaching in BF than in CF.Analyses of NO 3 -and NH 4 + uptake by the in situ depletion method demonstrated greater uptake by Moso bamboo fine roots than by Japanese cedar fine roots, indicating that expansion of Moso bamboo into coniferous forests may increase plant N uptake, leading to lower NO 3 -leaching.Moso bamboo generally invades Japanese cedar plantations, the main plantation species accounting for approximately 20% of the total forest area in Japan.Until now, most past studies have reported potentially negative impacts of Moso bamboo invasion into Japanese cedar plantations such as reduced plant diversity (Ouyang et al. 2016), increased transpiration rates (Laplace et al. 2017), and increased N 2 O emission (Fang et al. 2021).However, this study demonstrates the positive effect of Moso bamboo invasion on the mitigation of NO 3 -leaching.Our findings further highlight the importance of fastgrowing plant species with higher N uptake in mitigating N leaching from forest ecosystems under elevated atmospheric N deposition.

Fig. 3
Fig. 3 NO 3 − concentrations in the surface soil solutions at each sampling time.Error bards indicate standard errors (n = 9).Closed circles refer to Japanese cedar plantation (CF); open circles refer to Moso bamboo forest (BF).Significant differences between BF and CF were detected by t test (P < 0.01)

Fig. 4
Fig. 4 Net uptake rates of a) NO 3 − and b) NH 4 + by fine roots during the study period from October 2021 to September 2022.Error bars indicate standard error (n = 5).Closed circles refer to Japanese cedar (CF); open circles refer to Moso bamboo (BF)

Table 1
Mean values of NO 3 -and NH 4 + concentrations (μmol L −1 ) in surface soil solution (0-5 cm depth) and soil leachate (50 cm depth) in Moso bamboo (BF) and Japanese cedar plantation (CF) Data are average ± standard error (SE).Lowercase letters in the same column indicate significant differences between soil solutions of 0-5 cm and 50 cm at P = 0.05 (t-test) Vol:. (1234567890)