microbial diversity of straw

Plant residues are one of the important sources of organic carbon (C) in agricultural soil. However, it is still unclear how nitrogen (N) status in farmland soil affects the organic C groups and its microbial mechanisms during plant residue decomposition. This study selected maize- (M) and potato-monoculture (P) soils with two N status (N0, unfertilized, and N2, 250 and 125 kg N ha-1 for M and P, respectively) as decomposition environments to conduct a 6-month decomposition of maize- (MS) and potato straw (PS). The results showed that soil N status had no significant effect decomposition rate of both straws, but changed the organic C groups for both straws. Alkyl C and aliphaticity increased for MS while decreased for PS at N2 relative to N0. The interaction between fungi-bacteria, and the abundance of recalcitrant C degradation genes (exoglucanase and chitinase) and enzyme activity (chitinase and sucrose) increased for MS, but decreased for PS at N2 as compared with N0. The structural equation model indicated that the increase of soil inorganic N reduced straw C/N, changed the microbial community structure and keystone in straw, enhanced enzyme activity, and thus altered the recalcitrant C content and the stability of organic C in decomposed straw. The results of this study emphasize the differential impact of soil N status on the chemical structure of different types of straw, as well as the coupling relationship between microbial communities and organic C chemical structure during the plant residue decomposition in farmland soil.

植物残体是农田土壤有机碳（Organic C）的重要来源之一。然而目前尚不清楚农田土壤的氮（Nitrogen, N）状况如何调控植物残体腐解过程中的有机碳组分及其微生物学机制。本研究选取两种氮素水平下的玉米连作（Maize-monoculture, M）与马铃薯连作（Potato-monoculture, P）土壤作为腐解环境，开展为期6个月的玉米秸秆（Maize Straw, MS）与马铃薯秸秆（Potato Straw, PS）腐解试验；其中N0为不施肥处理，N2处理下玉米连作土壤施氮量为250 kg N ha⁻¹、马铃薯连作土壤施氮量为125 kg N ha⁻¹。研究结果表明，土壤氮素状况对两种秸秆的腐解速率无显著影响，但会改变两种秸秆的有机碳组分构成。相较于N0处理，N2处理下玉米秸秆（MS）的烷基碳（Alkyl C）含量与脂族性均有所提升，而马铃薯秸秆（PS）则呈下降趋势。与N0处理相比，N2处理下玉米秸秆（MS）的真菌-细菌互作强度、难降解有机碳（Recalcitrant C）降解基因（外切葡聚糖酶exoglucanase与几丁质酶chitinase）的丰度以及酶活性（几丁质酶chitinase与蔗糖酶）均有所提升，而马铃薯秸秆（PS）则出现下降。结构方程模型（Structural Equation Model, SEM）分析结果显示，土壤无机氮含量的升高降低了秸秆的碳氮比（C/N），改变了秸秆中的微生物群落结构与关键类群，提升了酶活性，进而改变了腐解后秸秆中难降解有机碳的含量与有机碳稳定性。本研究结果揭示了土壤氮素状况对不同类型秸秆化学结构的差异化影响，同时阐明了农田土壤植物残体腐解过程中微生物群落与有机碳化学结构之间的耦合关系。