Effects of tillage and crop rotation on soil microbial residues in a rainfed agroecosystem of northeast China

Agricultural management has significant impacts on soil microorganisms, which in turn influence soil relevant processes including soil organic matter (SOM) turnover. Amino sugars, as a microbial residue biomarker, are highly involved in microbial-mediated SOM cycling. However, the response of microbial-derived amino sugars to changes in soil management practices is poorly characterized in the arable soils (Typic Hapludoll, USDA Soil Taxonomy) in northeast China. The objective of this study was to assess the effects of soil tillage (conventional tillage CT vs. no tillage NT) and crop rotation (continuous corn (Zea mays L.) monoculture vs. corn–soybean [Glycine max (L.) Merr.] rotation) on the accumulation of amino sugars in this region. The following hypotheses were tested: (1) in an agroecosystem, tillage and crop rotation influence the accumulation of microbial residues in soils; (2) responses of fungal and bacterial cell wall residues to the practices are different, i.e., fungal-derived cell wall residues more benefited by no-tillage practices than bacterial. Implementation of no-tillage practices for 6 years significantly increased soil total amino sugars with an increase of 59% as compared with conventionally tilled plots (P < 0.05). This highlights the positive effects of NT that promotes the accumulation of microbial-derived organic matter. The ratios of glucosamine to muramic acid in the NT soils across three soil depths significantly exceeded those in the respective CT soils due to a higher enrichment of glucosamine. This confirms our hypothesis that the microbial community shifted towards fungal dominance under NT and the phenomenon was more pronounced within the 0–5 cm layers. When NT systems were evaluated, the type of crop rotation used had a significant influence on the soil amino sugar content. Significant enrichment of total amino sugars (1042–1317 mg kg−1 soil) occurred in the continuous corn monoculture system as compared with the corn–soybean rotation field (943–1112 mg kg−1 soil) in the soil layers from 0 to −20 cm. Data obtained suggest that NT practices combined with continuous high C inputs can be adopted as an effective strategy to improve the cropland SOM in northeast China. Our results also indicate that it is possible to use amino sugars as an indicator to assess the changes in microbial community within a given ecosystem.