Abstract. Free amino acids (FAAs) in soil play an important role in the soil nitrogen cycle and plant nutrition. However, the attributing factors and migration characteristics of free amino acid pools in paddy soils after green manure application during the entire growth period of rice have not been elucidated. In this study, a single application of chemical fertilizer (CK) was used as a control under equal nitrogen, phosphorus and potassium conditions, and different application rates of milk vetch (15 000 kghm⁻²(CL), 30 000 kghm⁻²(CM) and 45 000 kg hm⁻²(CH)) were selected to investigate the dynamic of FAAs concentration and composition in paddy soil. Soil FAAs concentration at different growth stages under the same fertilization treatments was highest at the seedling stage and lowest at the tillering stage. The concentration of threonine, alanine, valine, isoleucine, leucine, phenylalanine was most abundant under different fertilization treatments during the growth period, accounting for 59.42 %–76.46 % of the respective FAAs pool. The application of milk vetch was shown to increase the soil FAAs concentration, especially glutamic acid, which increased by 368.17 %–680.78 %, but excessive application had an inhibitory effect. Soil pH, organic matter, protease, bacterial biomass and community were critical factors affecting the concentration of soil FAAs. Bacteroidetes, Firmicutes and Nitrospirae significantly affected the dynamics of FAAs in bacterial communities, and their total contribution rate was 56.89 %. FAAs displayed significant vertical profile characteristics, and the mobility of serine, glycine and proline was high. Conclusively, the application of milk vetch was able to significantly change the concentration and composition of soil FAAs, which may affect the capture of N by plants.

中文翻译：

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施用紫云英后水稻全生育期土壤游离氨基酸动态及迁移特征

摘要。土壤中的游离氨基酸 (FAA) 在土壤氮循环和植物营养中起着重要作用。然而，水稻整个生育期施用绿肥后水稻土游离氨基酸库的成因及迁移特征尚未阐明。本研究以单次施化肥（CK）作为对照，在等氮磷钾条件下，不同施用量的紫云英（15 000 kghm ^-2 (CL)、30 000 kghm ^-2 ( CM) 和 45 000 kg hm ^-2(CH)) 被用来研究稻田中 FAA 浓度和组成的动态。相同施肥处理下不同生育阶段土壤FAAs浓度以苗期最高，分蘖期最低。生长期不同施肥处理下苏氨酸、丙氨酸、缬氨酸、异亮氨酸、亮氨酸、苯丙氨酸的浓度最高，占各自FAAs库的59.42%~76.46%。紫云英的施用增加了土壤FAAs浓度，尤其是谷氨酸，增加了368.17%~680.78%，但过量施用有抑制作用。土壤 pH 值、有机质、蛋白酶、细菌生物量和群落是影响土壤 FAA 浓度的关键因素。拟杆菌，Firmicutes 和 Nitrospirae 显着影响细菌群落中 FAA 的动态，它们的总贡献率为 56.89 %。FAA 显示出显着的垂直剖面特征，丝氨酸、甘氨酸和脯氨酸的迁移率很高。总之，紫云英的应用能够显着改变土壤 FAA 的浓度和组成，这可能会影响植物对 N 的捕获。