The development of selenium-rich millet via soil fertilization and the interactions among microbial community, plants and rhizosphere soil

doi:10.21203/rs.3.rs-2332175/v1

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The development of selenium-rich millet via soil fertilization and the interactions among microbial community, plants and rhizosphere soil

https://doi.org/10.21203/rs.3.rs-2332175/v1

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Selenium is an important microelement for both plants and human health. The deficiency of selenium would result in various diseases and has attracted much attention. In modern agriculture, different strategies have been adopted for selenium biofortification. In this study, selenium soil fertilization was applied at different levels to develop selenium-rich millet. External supplementation of selenium showed positive effects on plant growth and nutrient transport. The activities of key enzymes of plant and soil were observed to enhance after selenium fertilization, such as glutathione peroxidase (GSH-Px), sucrose, and urease. The major objective of obtaining selenium-rich millet grain successfully achieved as the final selenium content in grain increased by 5–10 folds. Middle level of selenium showed the best performance among all the treatments. The analysis of microbial community in rhizosphere soil suggested the good adaptation of both bacteria and fungi toward environmental conditions modified by fertilization.

Biological sciences/Plant sciences/Plant ecology

Biological sciences/Microbiology/Communities

enzyme activities

microbial community

millet

selenium

soil fertilization

Selenium is an important microelement for not only the growth of plants but also human health. Previous studies have shown that low-level selenium can promote the growth of plant and also uptake of other nutritional elements ^1–3. The antioxidant capacity of selenium can also protect the plants from damage of cell membrane and enhance plants’ resistance toward adverse conditions such as drought and toxic metals ⁴. In addition, selenium plays a vital role in the normal function of immune system, endocrine system and reproductive system of human ^5,6. Long-term selenium deficiency would pose negative effects on cardiovascular system and lead to myocardial infarction. The low level of selenium has also been related to Keshan disease and Kashin-Beck disease, which are mostly found on children and women of child-bearing age ⁷. In most countries, agricultural crops are the primary source of selenium followed by meat and seafood. However, the selenium content in plants is affected by growth conditions, especially the effectiveness of selenium in soil. That would result in the regional disparity on selenium intake and external investment of selenium is necessary for areas with selenium-deficient soil ⁸.

In modern agriculture, different agronomic measures have been applied for biofortification of selenium such as soil fertilization and foliar fertilization ^9,10. The crops can intake the inorganic selenium in fertilizer (mainly in the form of SeO₄²⁻ and SeO₃²⁻) and convert into organic selenium which is more biologically available ¹¹. Intensive studies have reported the interaction between fertilization and microbial community in rhizosphere. The alteration of nutritional level in soil by fertilization could modify the structure and diversity of rhizospheric microbial community, which consequently affect the plant growth and yield of grain ^12,13. For example, applying nitrogen fertilizer affected microbial species involved nitrogen cycle, increasing the relative abundance of Actinobacteria, Bacteroidetes, Firmicutes, and Armatimonadetes while decreasing the relative abundance of Acidobacteria and Chloroflexi ¹⁴. The microorganisms would in turn affect the uptake of both macro- and microelements therefore the performance of fertilization ¹⁵. Considering that, it is meaningful to investigate interactive effects between selenium fertilization and rhizospheric microbial community of crop and explore the most efficient fertilization mode.

Millet is a kind of drought-enduring crops commonly grown in the northern area of China. It also has a strong tolerance to barren soil and negative environmental conditions. Its grain has a high nutritional value, rich in carbohydrates, protein, healthy fats, vitamins and carotenoids. In the major selenium-deficient regions of China, millet is an important crop and food source. The development of selenium-rich millet is an effective strategy to improve the intake level of selenium and optimize the daily dietary pattern. Based on current research, most efforts are put into rice, wheat and corn ^16,17, and limited research has been conducted on application of selenium fertilizer and the subsequent influences on soil microbial community of millet. In this study, the effectiveness of soil selenium fertilization was investigated and different levels of selenium were compared. The properties of mille plants, yield and quality of grains were evaluated under different selenium levels. The features of soil including selenium content, enzymatic activities and microbial community were also measured. The correlations between microbial characteristics in rhizosphere soil and physiochemical properties of aboveground parts of crops were analyzed accordingly. The results would provide the optimized parameters for the production of selenium-rich millet, and also lay the foundation for the further research on millet crop-rhizospheric microorganisms-soil interactions

2.1 Materials

There are two varieties of millets for study, coming from Institute of millet crops, Hebei Academy of Agriculture and Forestry Sciences. Jigu 38 is a superior variety with sethoxydim resistance and grain selenium content of 0.03 mg/kg. Jigu 19 has Ai88 as male parent and Qingfeng millet as female parent. Its grain selenium content was 0.02 mg/kg. The experimental research and field studies on millet crops complies with relevant institutional, national, and international guidelines and legislation.

2.2 Experimental design

The experimental position was located in a village of Shunping County, Baoding City, Hebei Province (38º56′N, 114º56′ E, altitude = 270 m). Jigu 19 and Jigu 38 were tested respectively using Na₂SeO₃ as selenium fertilizer. Different concentration levels were applied and compared. Specifically, the low level (Se1) was 15 g/ha, the medium level (Se2) was 30 g/ha and the high level (Se3) was 45 g/ha. Each treatment was performed in triplicates on individual plot with the size of 5 m*6 m. Totally 24 experimental plots were set. The base fertilizer was N-P₂O₅-K₂O (20-16-12) compound fertilizer with the dosage of 450 kg/ hm². Na₂SeO₃ was first dissolved in tap water and then sprayed on the surface of soil and mix in each plot. The sowing date was Jul. 1 and the harvest date was Oct. 10. The experiments were repeated from 2019–2020, and the results were expressed as year-to-year average.

2.3 Analysis of physiochemical properties of crops

For analysis of glutathione peroxidase (GSH-Px) activity, 0.2 g fresh sample was grinded with pre-cold phosphate buffer (pH = 7.0, 0.05 M) on ice. The mixture was centrifuged at 4 ℃, 12,000 rpm for 10–15 min. The supernatant was taken to catalyze the reaction between GSH and 5,5'-Dithiobis-(2-nitrobenzoic acid). The absorbance of final solution at 422 nm was measured.

The root, stem and leaves, and panicles were dried and smashed individually for determination of nitrogen, phosphorus and selenium contents. The samples were digested with sulfuric acid and hydrogen peroxide, and then distilled under alkaline conditions. The vapor was adsorbed with boracic acid and titrated with standard sulfuric acid to determine the total nitrogen content. The total phosphorus content of aboveground parts was determined by Molybdenum-antimony-ascorbic acid colorimetry. The selenium content was determined using atomic fluorescence spectrometry after microwave-cyanide co-digestion ¹⁸.

Upon the maturation of millet, a sample unit of 1 m² was selected in each plot and 10 plants were taken to measure the panicle length and thousand-grain weight. The averages were regarded as the representative values of corresponding plot. The yield was determined after the harvest of all crops. To determine the content of dietary fiber in grain, ground samples were digested under thermophilic conditions (above 60 ℃) using thermal-stable α-amylase, protease and glucosidase to remove carbohydrates and proteins. The digestate were then precipitated with ethanol and the precipitates were washed with ethanol and acetone prior to weighing. The content of total dietary fiber was calculated as the weight of precipitate divided by the weight of initial sample ¹⁹. The content of vitamin B1 was determined by acid hydrolysis and derivatization with alkaline potassium ferricyanide ²⁰.

2.4 Analysis of physiochemical properties of rhizosphere soil

For physiochemical properties analysis, the rhizosphere soil was air dried, grounded and sieved with 1mm mesh. The selenium content was measured by atomic fluorescence spectrometry following the national standard of China (NY-T 1104–2006) ²¹.

The enzymatic activities were determined using spectrophotometry colorimetry. For urease, 5 g processed soil sample was first mixed with 1 mL methylbenzene. After 15 min, 10 mL urea solution (10%) and 20 mL citrate buffer (pH = 6.7) were added and the mixture was incubated at 37 ℃ for 24 h. After incubation, the mixture was filtered and 1 mL filtrate was taken to react with 4 mL sodium phenate solution and 3 mL sodium hypochlorite solution. The absorbance was measured at 578 nm. For sucrase, 5 g sample was mixed with 15 mL sucrose solution (8%), 5 mL phosphate buffer (pH = 5.5) and 5 drops of methylbenzene. The reaction was performed at 37 ℃ for 24 h. After incubation, the mixture was filtered immediately and the concentration of generated glucose was determined by reaction with 3,5-dinitrosalicylic acid. The absorbance was determined at 508 nm. For acid phosphatase, 1.0 g sample was mixed with 9 mL acetate buffer (pH = 6.0), 0.25 mL methylbenzene and 1 mL p-NPP. The reaction system was mixed evenly and incubated at 30 ℃ for 60 min, and 1 mL NaOH was used to terminate the reaction. After filtration, the absorbance of filtrate was determined at 405 nm.

2.5 Analysis of microbial community of rhizosphere soil

The genomic DNA of microbial community residing in rhizospheresoi was extracted by and sequenced by Illumina Miseq technique on Miseq PE300 platform. Trimmomatic was used for data quality control and FLASH was used for assembly. The assembled sequences were clustered into OTUs with UPARSE (version 7.1 http://drive5.com/uparse/) based on 97% similarity. The taxonomic annotation was performed against Silva database (SSU128) with threshold value of 70% using RDP classifier (http://rdp.cme.msu.edu/).

2.6 Data analysis

The data analysis was performed with SPSS Statistics 25.0 at significance level of 0.05.

3.1 The effects of selenium on physiochemical properties of crops

In this study, fertilization of selenium affected diverse physiochemical properties of millet plants and those effects differed between two varieties (Table 1). Applying selenium improved the plant height especially during shooting stage, and higher concentration exhibited higher improvement. For Jigu 19, 6% of improvement was observed compared to 5% of 38%. The chlorophyll concentration was obviously elevated during seedling stage, shooting stage, and grain-filling stage. Medium level (Se2) showed the best performance. In maturation stage, no significant effects on chlorophyll concentration were observed. The GSH-Px activity in leaves was significantly improved during seedling stage, grain-filling stage and maturation stage, with Se2 as the optimal fertilization level. Selenium fertilization also facilitated the absorption of macro-elements such as nitrogen and phosphorus (Table 2). During shooting stage, the nitrogen content of aboveground part was increased. Jigu 38 exhibited a higher phosphorous content with Se2 during filling stage and maturation stage. However, too much selenium was adverse to uptake of nitrogen and phosphorus and the contents in aboveground parts decreased accordingly under Se3.

Table 1

Plant height, chlorophyll and GSH-Px activities of millet under different selenium fertilizer levels
Stage	Treatments	plant height(cm)		chlorophyll(SPAD)		GSH-Px (U/L)
Stage	Treatments	Jigu 38	Jigu 19	Jigu 38	Jigu 19	Jigu 38	Jigu 19
seedling stage	CK	31.93 ± 2.08a	33.13 ± 0.93a	31.77 ± 1.08b	30.69 ± 0.41b	54.39 ± 8.39b	78.75 ± 3.39b
	Se1	32.39 ± 4.40a	31.48 ± 3.10a	33.99 ± 1.19ab	37.40 ± 2.68a	72.71 ± 8.28ab	92.98 ± 5.18ab
	Se2	32.06 ± 3.62a	32.05 ± 2.34a	36.70 ± 1.77a	35.22 ± 0.64a	85.19 ± 9.98a	101.17 ± 8.11a
	Se3	29.93 ± 2.88a	29.57 ± 2.82a	34.25 ± 1.21ab	37.02 ± 1.21a	82.26 ± 9.00a	88.50 ± 5.43ab
Shooting stage	CK	110.21 ± 1.52b	111.20 ± 1.44b	44.13 ± 0.74b	43.39 ± 0.89b	127.93 ± 6.79a	143.63 ± 7.94a
	Se1	112.46 ± 1.45ab	114.88 ± 1.08ab	44.79 ± 1.15b	45.76 ± 0.63ab	138.99 ± 11.73a	149.03 ± 4.40a
	Se2	114.54 ± 1.36a	115.21 ± 1.27ab	48.67 ± 1.56a	47.39 ± 0.91a	142.08 ± 9.01a	152.12 ± 10.50a
	Se3	115.78 ± 1.02a	118.00 ± 1.68a	45.45 ± 0.56b	46.86 ± 0.82a	117.89 ± 8.32a	141.83 ± 6.80a
Filling stage	CK	114.20 ± 5.08a	120.97 ± 1.86a	48.47 ± 0.77b	47.24 ± 0.84b	111.54 ± 8.15b	135.35 ± 8.95b
	Se1	120.52 ± 2.85a	122.03 ± 2.56a	51.93 ± 1.63ab	51.37 ± 1.08a	118.62 ± 3.33b	138.82 ± 8.00b
	Se2	121.69 ± 3.48a	123.12 ± 3.14a	52.20 ± 1.27a	53.44 ± 1.61a	147.33 ± 8.54a	165.95 ± 4.19a
	Se3	120.25 ± 2.62a	122.88 ± 3.03a	51.81 ± 0.61ab	50.49 ± 1.09ab	121.93 ± 9.44b	162.19 ± 2.22a
Maturation stage	CK	129.41 ± 1.83a	130.82 ± 2.39a	37.84 ± 3.09a	37.74 ± 2.97a	166.91 ± 3.83b	162.62 ± 3.93b
	Se1	129.37 ± 1.07a	127.82 ± 3.09a	40.59 ± 4.72a	39.60 ± 2.81a	171.66 ± 0.55ab	168.03 ± 1.39ab
	Se2	131.10 ± 0.87a	134.46 ± 1.37a	43.43 ± 2.19a	45.59 ± 3.65a	178.71 ± 0.41a	170.52 ± 1.18a
	Se3	131.02 ± 1.56a	133.33 ± 2.41a	41.19 ± 3.42a	41.56 ± 4.69a	175.10 ± 2.44a	170.19 ± 1.22a
Note: different letters in the table represent statistical difference among different selenium application treatments (P ≤ 0.05).

Table 2

Nitrogen and phosphorus contents in aboveground parts millet under different selenium fertilizer levels
Stage	Treatments	N content(g/kg)		P content (g/kg)
Stage	Treatments	Jigu 38	Jigu 19	Jigu 38	Jigu 19
Seedling stage	CK	37.64 ± 0.68a	37.37 ± 2.18a	3.45 ± 0.19a	3.46 ± 0.21a
	Se1	39.81 ± 1.15a	38.05 ± 2.03a	3.56 ± 0.24a	3.64 ± 0.49a
	Se2	38.46 ± 1.52a	39.23 ± 1.60a	3.87 ± 0.36a	3.81 ± 0.43a
	Se3	38.26 ± 0.71a	42.18 ± 1.07a	3.98 ± 0.42a	3.83 ± 0.36a
Shooting stage	CK	25.17 ± 0.42b	22.27 ± 1.26b	2.07 ± 0.18a	2.03 ± 0.21a
	Se1	26.59 ± 0.48a	25.57 ± 1.63a	1.81 ± 0.19a	2.12 ± 0.23a
	Se2	26.28 ± 0.37ab	24.27 ± 1.64ab	2.09 ± 0.13a	2.26 ± 0.34a
	Se3	26.47 ± 0.17a	24.25 ± 0.82ab	2.44 ± 0.41a	2.14 ± 0.16a
Filling stage	CK	18.53 ± 0.67a	17.97 ± 0.33ab	1.87 ± 0.10b	2.28 ± 0.03a
	Se1	20.12 ± 0.85a	18.74 ± 0.22a	2.08 ± 0.01a	2.12 ± 0.18a
	Se2	19.07 ± 0.49a	18.22 ± 0.42ab	2.10 ± 0.01a	2.32 ± 0.13a
	Se3	19.20 ± 1.57a	17.51 ± 0.34b	1.86 ± 0.06b	1.62 ± 0.11b
Maturation stage	CK	11.89 ± 1.23a	11.71 ± 0.66a	0.86 ± 0.09ab	0.80 ± 0.09a
	Se1	13.48 ± 0.52a	12.00 ± 0.99a	0.63 ± 0.09b	1.10 ± 0.11a
	Se2	13.81 ± 0.50a	13.87 ± 1.13a	0.94 ± 0.09a	1.03 ± 0.20a
	Se3	12.29 ± 0.50a	13.03 ± 0.54a	0.69 ± 0.11ab	0.74 ± 0.12a
Note: different letters in the table represent statistical difference among different selenium application treatments (P ≤ 0.05).

For millet grain, the yield of Jigu 38 was improved by Se1 while the yield of Jigu 19 was decreased by Se3 (Table 3). Thousand-grain weight was barely affected and panicle length of Jigu 19 was improved by Se1 and Se2. In maturation stage, selenium fertilization remarkably enhanced the selenium contents of different aboveground parts (Table 4). Roots showed the highest selenium content followed by stem/leaves and panicles. Without selenium fertilization, the selenium content was ordered by steam/leaves, roots and panicles. The selenium content of grain was also effectively improved (Fig. 1). Se2 showed the best performance and under the same fertilizing level, Jigu 38 absorbed more selenium than Jigu 19. At the same time, selenium fertilization also increased the content of vitamin b1 in grain, while the dietary fiber content was limited affected.

Table 3

Panicle length, thousand-grain weight (TKW) and yield of foxtail millet under different selenium fertilizer levels
Treatments	Panicle length(cm)		TKW(g)		Yield(kg/hm²)
Treatments	Jigu 38	Jigu 19	Jigu 38	Jigu 19	Jigu 38	Jigu 19
CK	18.70 ± 0.43a	17.97 ± 0.69ab	2.60 ± 0.07a	2.63 ± 0.05a	4950 ± 48ab	5483 ± 217a
Se1	19.23 ± 1.00a	19.54 ± 0.61a	2.56 ± 0.08a	2.64 ± 0.07a	5157 ± 183a	5521 ± 219a
Se2	20.57 ± 0.90a	19.67 ± 0.63a	2.64 ± 0.08a	2.65 ± 0.03a	4850 ± 76ab	5587 ± 271a
Se3	18.37 ± 0.78a	17.30 ± 0.60b	2.56 ± 0.03a	2.62 ± 0.05a	4735 ± 30b	4720 ± 110b
Note: different letters in the table represent statistical difference among different selenium application treatments (P ≤ 0.05).

Table 4

Selenium contents in aboveground parts of millet under different selenium fertilizer levels
Treatments	Root (mg/kg)		Stem/leaf (mg/kg)		Panicle (mg/kg)
Treatments	Jigu 38	Jigu 19	Jigu 38	Jigu 19	Jigu 38	Jigu 19
CK	0.19 ± 0.01c	0.23 ± 0.02c	0.23 ± 0.02b	0.26 ± 0.02c	0.03 ± 0.00c	0.04 ± 0.00d
Se1	0.46 ± 0.06b	0.45 ± 0.06b	0.36 ± 0.02ab	0.36 ± 0.04b	0.13 ± 0.01b	0.15 ± 0.01c
Se2	0.69 ± 0.06a	0.63 ± 0.03a	0.48 ± 0.07a	0.45 ± 0.02a	0.25 ± 0.01a	0.26 ± 0.01a
Se3	0.64 ± 0.03a	0.57 ± 0.09ab	0.43 ± 0.05a	0.43 ± 0.02ab	0.23 ± 0.01a	0.23 ± 0.01b
Note: different letters in the table represent statistical difference among different selenium application treatments (P ≤ 0.05).

3.2 The effects of selenium on physiochemical properties of rhizosphere soil

For physiochemical properties of rhizosphere soil, selenium fertilization showed limited impact on pH, actual selenium content of rhizosphere soil as well as urease activity (Tables S1&S2). Se2 significantly increased acid phosphatase and sucrase activity in soil of Jigu 19. These results suggested that pH and urease activity may not be related to selenium absorption and transportation. The unaffected selenium content of rhizosphere soil indicated that external selenium fertilizer primarily functioned on millet plants therefore did not accumulate and remain in soil.

3.3 The effects of selenium on microbial community of rhizosphere soil

To explore the effects of selenium fertilization on the microbial community located in rhizosphere soil, different analysis methods were applied from different aspects. The Venn analysis shown in Figure S1 indicated that the number of bacterial OTU (sequences with similarity > 98% were regarded as the same OTU) enhanced with the increase of selenium fertilization level for both Jigu 38 and Jigu 19. The richness and diversity of bacterial community were shown by sobs index and Shannon index respectively. As shown in Table S3, selenium fertilization slightly improved both indices compared to CK. Se3 exhibited the highest level of bacterial richness and diversity.

Species with relative abundance > 1% were selected for further analysis of bacterial community composition (Fig. 2). At the phylum level, Actinobacteriota was observed as the dominant phylum, followed by Proteobacteria, Acidobacteriota, Chloroflexi, and Firmicutes. These dominant phyla accounted for more than 80% of relative abundance. Compared to CK, selenium fertilization decreased the relative abundance of Actinobacteriota and Proteobacteria. However, no significant differences were observed among groups with different fertilization levels. At the genus level, various undefined genera appeared for both Jigu 38 and Jigu 19. Bacillus, Blastococcus, Rubrobacter, Microvirga, and Sphingomonas were observed as the dominant genera. In addition, norank_f__JG30-KF-CM45, norank_f__Vicinamibacteraceae, and norank_f__norank_o__Vicinamibacterales also had high relative abundance. The relative abundance of those dominant genera was lower in Se2 compared to Se1 and Se3.

For fungi, the OTU number increased with the elevation of selenium level for Jigu 38, while increased first and then decreased for Jigu 19 (Figs. 2c&2d). Se2 and Se3 also improved the richness and diversity of fungal community for both Jigu 38 and Jigu 19, while the differences were not statistically significant.

At the phylum level, Ascomycota, Basidiomycota and Mortierellomycota were observed as the dominant phyla, constituting more than 90% of relative abundance (Fig. 3). For Jigu 38, selenium fertilization decreased the relative abundance of Ascomycota while increased the relative abundance of Mortierellomycota. However for Jigu 19, such trends were the opposite. The relative abundance of Basidiomycota was improved for both Jigu 38 and Jigu 19. At the genus level, Jigu 38 and Jigu 19 showed similar fungal composition, with Cladosporium, Mortierella, Gibberella, Chaetomium, Solicoccozyma, Cephaliophora, and Acremonium as the dominant genera. Se3 decreased the relative abundance of Cephaliophora while increased the relative abundance of Cladosporium.

3.4 The correlations between microbial community and physiochemical properties of crops and rhizosphere soil

The correlations between microbial community and physiochemical properties of soil were studied with RDA analysis (Fig. 4). The results showed different correlations for different crops. For Jigu 38, the environmental factors contributed to microbial community to different extents, and the order of environmental factors was similar for bacteria and fungi. Sucrase activity and pH were significantly correlated with the change of both microbial communities. For Jigu 19, environmental factors posed different effects on bacterial and fungal community variation. Only urease activity had significant correlations with fungal community variation.

In this study, the selenium fertilization showed obvious improvement on the selenium content of different plant parts (especially the grain) and the objective of obtaining selenium-rich millet has been achieved. The chlorophyll concentration was effectively improved especially during seedling and grain-filling stage. As the important active component of GSH-Px ²², selenium fertilization also enhanced the GSH-Px activity. The uptake of nitrogen and phosphorus was also facilitated due the presence of abundant selenium. The synergy between nitrogen and selenium was because that nitrogen stimulated the sulfur metabolism key regulator, O-acetyl-L-serine, during cysteine synthesis ²³. The selenium metabolism was therefore improved due to its similar metabolic pathway with sulfur. In addition, both selenium and phosphorus existed in soil as anions. They shared similar ionic radius and physiochemical properties and can be adsorbed by plants. The middle level of selenium showed the best performance and the enzyme activities (sucrase and urase) of rhizosphere soil were also improved. However, high level of selenium fertilization showed inhibitive effects and grain yield decreased significantly. The possible reason was that excessive selenium may disturb the sulfur metabolism and therefore altered the functions of important proteins. The selenium fertilization posed limited effects on other physiochemical properties of rhizosphere soil such as pH and remaining selenium content in soil.

The microbial community of rhizosphere soil with or without selenium fertilization was similar to each other in terms of diversity, composition and dominant species. That suggested that the indigenous microorganisms achieved good adaptation toward the modified soil environment resulting from selenium fertilization ²⁴. The relative abundance of dominant species was slightly decreased in selenium fertilized plots and the species contributing to selenium uptake and transport may be promoted. For example, considering the structural similarity between selenium and sulfur ²⁵, microbes responsible for sulfur cycle may also help the uptake of selenium such as Bacillus ²⁶. Selenium cycle may also overlap with phosphorus cycle and genes involved in phosphorus transport have also been observed to be upregulated with selenium fertilization (e.g. Ospt2) ^27,28. The abundant norank_f__JG30-KF-CM45 was also commonly observed in municipal active sludge and rhizosphere soil. It was assumed to own the function of carbohydrate degradation, nitrosification and macroelement assimilation ^29,30. Other than bacteria, fungi residing in rhizosphere soil also played an important role in the element transport and assimilation. Mycorrhizal fungi have been widely studied to favor the growth and nutrients accumulation of plants ³¹. Mycorrhizal fungi account for about 10% of identified fungal species. Substantial fractions of the Ascomycota and Basidiomycota belong to Mycorrhizal fungi ³². As the dominant phyla observed in this study, Ascomycota and Basidiomycota may have important function during selenium fertilization.

In this study, selenium fertilization was adopted to millet aiming to obtain selenium-rich grain products. Positive effects were observed on plant height, nutrient transport (nitrogen and phosphorus) as well as selenium content of mille grains. Activities of enzymes such as GSH-Px, sucrase and urase were also enhanced which facilitated the growth and nutritional improvement of millets. Middle level of selenium showed the best performance among all the treatments. The analysis of microbial community in rhizosphere soil suggested the good adaptation of both bacteria and fungi toward environmental conditions modified by fertilization.

Funding sources

This study was supported by Special Project of Agricultural Park (Base), Hebei, China (20536402D) and Key Research and Development Program, Hebei, China (20325001D).

Author contribution

Study conception and design were performed by H. G. and A. Z.. Material preparation, data collection and analysis were performed by D. W., H. G., and A. Z.. The first draft of the manuscript was written by D. W. and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Conflict of interest

None

Data availability

Data available on request from the authors.

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No competing interests reported.

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The development of selenium-rich millet via soil fertilization and the interactions among microbial community, plants and rhizosphere soil

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Abstract

Figures

1. Introduction

2. Materials & Methods

2.1 Materials

2.2 Experimental design

2.3 Analysis of physiochemical properties of crops

2.4 Analysis of physiochemical properties of rhizosphere soil

2.5 Analysis of microbial community of rhizosphere soil

2.6 Data analysis

3. Results

3.1 The effects of selenium on physiochemical properties of crops

3.2 The effects of selenium on physiochemical properties of rhizosphere soil

3.3 The effects of selenium on microbial community of rhizosphere soil

3.4 The correlations between microbial community and physiochemical properties of crops and rhizosphere soil

4. Discussion

5. Conclusions

Declarations

References

Additional Declarations

Supplementary Files

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