Deciphering the microbial players driving straw decomposition and accumulation in soil components of particulate and mineral-associated organic matter

Abstract

Soil organic carbon (SOC) in terrestrial ecosystems is reliant mainly on plant-derived carbon (C) inputs. Although the contribution of plant straw to soil C accrual within particulate organic matter (POM) and mineral-associated organic matter (MAOM) has been widely investigated, the microbial groups responsible for driving straw decomposition and the allocation of C into POM and MAOM pools remains elusive. The main challenge is the ability to separate the soil fractions without severely disrupting the microbial community. By using ultrasonic energy (kept 80 J mL^-1) and size fractionation, this study effectively isolated POM and MAOM with negligible impact on microbial community in two paddy soils (i.e., the Mollisol and Ultisol). The isolated POM and MAOM were subsequently mixed with C4 maize straw and incubated for 87 days to investigate straw decomposition and accumulation using natural ¹³C abundance and the underlying microbial community difference. This study revealed that: (i) mineralization of straw-derived C was significantly higher in the POM fraction compared to the MAOM fraction, whereas straw-C retention was concomitantly greater in MAOM; (ii) compared to bacteria, fungi contributed more significantly to straw mineralization in POM, likely due to their lower metabolic nutrient requirements and extensive hyphal interactions. In contrast, the interaction between Fe-OC, Ca-OC, and bacteria played a crucial role in facilitating straw-derived C stabilization in MAOM. This study reveals the microbial drivers involved in straw-C transformation within POM and MAOM by a proper separating approach and highlights the microbial mechanisms underpinning the fate of straw C in these two soil components.