Effects of Agricultural Organic Waste Incorporation on the Metabolic Capacity of Microbial Carbon Sources of Dissolved Organic Matter in Paddy Soil

Abstract

A long-term fertilization experiment with a system of rice-wheat rotation was conducted in Chengdu Plain. Three fertilization treatments including conventional fertilization (T1), pig manure substituting for 50% nitrogen fertilizer (T2), and T2 plus straw (T3) were set up to study the characteristics of microbial carbon source utilization of soil and dissolved organic matter (DOM). The results showed that T3 improved the soil microbial carbon source metabolism in comparison with those of the T1 and T2 treatments; the average color change rate (AWCD) increased by 16% and 48%, respectively. Meanwhile, T3 improved the soil DOM microbial carbon source metabolism, and the AWCD value was 0.43. The highest Shannon, Simpson, and McIntosh indexes of soil and DOM were all found in the T3 treatment, and the Shannon, Simpson, and McIntosh indexes of DOM were 2.73, 0.91, and 3.75, respectively. The results of principal component analysis and enrichment analysis showed that the main carbon sources used by microorganisms of soil and DOM were different under different fertilization treatments. For DOM, the main carbon source used by microorganisms in the T1 and T2 treatments was sugar, whereas T3 increased the utilization of amino acids, carboxylic acids, polymers, and amines. The changes in soil pH and texture were the main factors that caused the difference in soil DOM microbial carbon source metabolism. In conclusion, the application of organic fertilizer (pig manure plus straw) significantly increased the microbial community diversity and carbon source metabolic capacity of soil and DOM and promoted the diversification of microbial carbon source preference.