Effects of addition of nitrogen-enriched biochar on bacteria and fungi community structure and C, N, P, and Fe stoichiometry in subtropical paddy soils

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Biochar can be a soil amendment that increases nutrient retention and carbon (C) sequestration in rice paddy systems. However, biochar can lose nutrient during its production processes so modifications such as coating with the nitrogen (N) that can slowly release nutrients to soil following application are necessary. Dynamic changes in paddy soil microbial communities affect the biogeochemical cycling of soil nutrients; however, the effects of addition of N-enriched biochar on paddy soil microorganisms and nutrient stoichiometry are unclear. Here, we investigated the effects of N-enriched biochar on soil bacteria and fungi community structure and on carbon (C), N, phosphorous (P), and iron (Fe) stoichiometry in subtropical paddy soils. The soil concentrations of TC, TN and TP increased by 0.27–18.55%, 1.31–18.15% and 10.35–54.24% respectively under the nitrogen rich biochar treatment. Under N-enriched biochar application, ratios of N/P and C/P decreased, while P-fixation capacity increased; the decrease in N/P ratio indicated that rice productivity was N-limited. The quantity of soil fungi increased by 42.07% and 10.89% in early and late rice, respectively in the treatment group applying 4t ha−1 of N-enriched biochar. Relative abundance of the bacteria Bacillus, Geobacter, and Sideroxydans decreased with N-enriched biochar, whereas that of Thiobacillus and Thermomonas increased; relative abundance of the fungi Spicellomyces and Crustoderma increased with biochar. Relative abundance of the bacteria Bacteroides was negatively correlated with TC and Fe3+ (P < 0.05) and Sideroxydans and Geoyhrx was negatively correlated with soil TP (P < 0.05). Relative abundance of the fungi genera Westerdykella, Synchytrium, Russula, and Orbilia was positively correlated with soil TC (P < 0.05), Trapelia, Leptosphaerulina, and Tremella was positively correlated with soil TN (P < 0.05), and relative abundance of Leucanium, Monoblepharis was positively correlated with soil TP (P < 0.05). Overall, application of N-enriched biochar to paddy soils affected the microbial community composition through changes in soil physicochemical properties that led to shifts in microbial community function and associated improvements in soil nutrient enrichment.