Climatic effects on soil organic nitrogen fractions and amino acid chirality in paddy soils

Abstract

Soil organic nitrogen (N) accounts for more than 90% of the total N (TN) in paddy soils. An inadequate understanding of the different organic N fractions in paddy soils and their corresponding bioavailability under different climatic conditions has constrained the development of appropriate nutrient management strategies in rice production. Here we apply a modified Bremner method coupled with High Performance Liquid Chromatography (HPLC) to characterize how Soil Organic Nitrogen (SON) fractions and amino acid chirality vary under different climatic conditions by sampling five typical rice production sites along a latitudinal gradient. According to the results, climate had no obvious influence on TN, N form, and individual amino acid concentrations. However, the proportions of various N forms in TN had linear relationships with annual mean temperature, with high correlation coefficients. Amino acid components also exhibited similar trends (with correlation coefficients as high as 0.85). Most notably, consistent linear relationships were observed between the D/L ratios of several amino acids and annual mean temperature in paddy soils (correlation coefficients = 0.18–0.92). The findings of the present study could provide insights on SON and amino acid dynamics in paddy soil systems under intensive production along climate gradients.