Microorganisms, their residues, and soil carbon storage under a continuous maize cropping system with eight years of variable residue retention

Understanding the effects of agricultural management on microbial community dynamics and their relationships with soil carbon (C) properties is crucial to designing better management strategies (e.g., crop residue and tillage management) to enhance soil organic carbon (SOC) storage and other ecosystem services. In a no-till (NT) continuous maize production system in Northeast China, we combined living and dead microbial biomarker analyses, mid-infrared spectroscopy, and multivariate statistics to examine the effect of variable rates (0 %, 33 %, 67 % and 100 %) of maize stover retention for eight years on soil microbial community structure and the related change in soil C properties. We observed increases in the relative abundance of saprotrophic fungi (SF%) and the fungal to bacterial biomass ratio in the 33 % (NT33) and 67 % (NT67) retention treatments relative to complete stover removal (NT0). However, these increases were absent in the 100 % (NT100) stover return treatment suggesting a non-linear microbial community response to retention rate. Structural equation modeling revealed a negative relationship between dissolved organic carbon (DOC) concentration and the microbial stress indicator, as determined by ratios of cyclopropane phospholipid fatty acids to their precursors. Such negative relationship had a negative impact on SF%, subsequently influencing the fungal to bacterial necromass ratio and the aromaticity of soil C. A radar diagram area-based Soil Quality Index (SQI) approach showed that NT33 was associated with the highest SQI area, suggesting that low rates (33 %) of residue return had the greatest SOC sustainability through the enrichment of the labile DOC pool, efficient microbial growth and maintaining fungal necromass C persistence. This study adds to the mechanistic understanding of cellular trait-based microbial strategies with implications for soil C dynamics, and provides guidance for future management strategies in conservation agriculture.