Divergent accumulation of microbe- and plant-derived carbon in different soil organic matter fractions in paddy soils under long-term organic amendments

Paddy soil is an important terrestrial carbon (C) pool. Understanding the impact of organic amendments on soil organic matter (SOM) stabilization pathways is critical for the accurate estimation of C storage potential and SOM stability in paddy soil. However, the impact of organic matter amendment on plant- and microbe-derived C distribution within different SOM fractions, i.e., particulate organic matter (POM) and mineral-associated organic matter (MAOM), remains poorly understood. To address the knowledge gap, five fertilization treatments were selected from a 40-year field experiment: no fertilizer (CK), inorganic NPK fertilizer (NPK), inorganic NPK combined with green manure (GM), inorganic NPK combined with green manure and pig manure (GM+PM), and inorganic NPK combined with green manure and rice straw (GM+RS). The application of organic amendments increased total SOC content through promotion of POM formation. Organic amendments increased both microbe- and plant-derived C contents in POM, and the GM+PM treatment had the greatest impact. In MAOM, organic amendments only altered the proportions of plant- and microbe-derived C, particularly increasing the proportions of bacterial-derived C. Organic amendments also led to the accumulation of less decomposed plant-derived C (C type lignin phenols) in POM, while more decomposed plant-derived C (V type lignin phenols) was stabilized within MAOM. The major factors driving microbe- and plant-derived C fraction distribution varied between the POM and MAOM fraction, i.e., C/N ratio of the exogenous organic materials was the dominant factor in POM, whereas DON and DOC were the primary factors in MAOM. The results of the present study enhance our understanding of the SOC stabilization pathways under organic amendments in paddy soil and offer insights into potential effective soil emissions and fertility management strategies.