Straw Input Altered the Composition of Aggregate‐Associated Organic Carbon in Soils With Different Initial Carbon Status

ABSTRACT

Initial soil carbon (C) status affects microbial utilization for plant residue and changes the retention of plant‐ and microbial‐derived C in soils. Soil aggregates stabilize organic C components through physical protection and mineral adsorption. Nevertheless, the information about how crop straw incorporation affects aggregates‐associated organic C sources and composition is limited, especially in soils with different initial C status. Here, the initial low (LC) and high C (HC) Mollisols were incubated with or without the addition of maize straw (followed as 12 t ha ⁻¹ ) for 360 days in Northeast China. The SOC content in the topsoil (0–20 cm) of LC and HC was 15.5 and 25.2 g kg ⁻¹ , respectively. The effect of inherent soil C on the accumulation of lignin phenol and microbial necromass and the chemical composition of organic C within soil aggregates (macroaggregates, > 0.25 mm; and microaggregates, < 0.25 mm) was investigated after adding maize straw. Maize straw addition increased the concentration of total lignin phenol within macroaggregates by 39% in LC soil but decreased that concentration within both macroaggregates and microaggregates by 18% and 41% in HC soil, respectively. These results indicated that straw addition had a positive significance in enhancing the contribution of plant lignin components to macroaggregates‐associated organic C in initial low C soil. Moreover, maize straw addition increased the contribution of amino sugar to organic C within macroaggregates and increased the relative proportion of O‐alkyl C in organic C within microaggregates in both LC and HC soils, indicating that independent of initial soil C status, microbial necromass and labile organic C components played differential roles in mediating aggregate‐associated organic C in soils following maize straw addition. Overall, changes in aggregate‐associated organic C in both initial low and high C soils following straw amendment were depicted by organic C molecular composition alteration.