Co-application of liquid cattle manure and straw promotes labile organic carbon accumulation and microbial community response in Mollisols

Under straw incorporation systems, the effects of co-applying anaerobically fermented liquid cattle manure (LCM) with straw on the partitioning of straw-derived carbon among labile organic carbon (LOC) fractions and on microbial communities remain unclear. In this study, a 180-day laboratory incubation using ¹³C-labeled maize straw and LCM was conducted to examine their co-application effects on LOC fractions, transformation of straw-derived carbon, and soil microbial community structure. The results showed that co-application of LCM and straw significantly increased soil organic carbon, microbial biomass carbon, and particulate organic carbon, and significantly enhanced the incorporation of straw-derived carbon into LOC fractions. This treatment increased soil pH and significantly stimulated α- and β-glucosidase activities. Moreover, high-throughput sequencing and network analyses indicated that under the LCM-straw co-application treatment, microbial network complexity was greater and lignocellulose-degrading keystone taxa, including Sphingomonas , Asticcacaulis , and Arthrobacter , were enriched. According to partial least squares path modeling, the LCM–straw co-application treatment could have increased AG and BG activities and enriched lignocellulose-degrading keystone taxa to influence the accumulation of straw-derived carbon. Overall, co-application of LCM and straw shows potential to enhance LOC accumulation and the incorporation of straw-derived carbon, providing important evidence to inform organic resource management in Mollisols.