Microbial community succession of assimilating and utilizing straw-derived carbon based on DNA stable-isotope probing technique

Objectives This study explored the microbial ecological succession of assimilating straw-derived carbon, identified the microbial taxa involved in the process of straw decomposition to provide a scientific basis for the efficient use of straw resources.

Methods ¹³C straw was prepared firstly. A microcosm incubation experiment was performed using calcareous fluvo-aquic soil as the test soil. The three treatments were without straw addition, addition of ¹²C-straw, and addition of ¹³C straw in soil, and the incubation period lasted 30 days. Then isotopic tracing and high-throughput sequencing methods were used to investigate the priming effect of straw addition on soil organic carbon, and analysis the bacterial and fungal microbial communities that assimilating straw-derived carbon, and the soil extracellular enzymes activities.

Results 1) Straw addition significantly increased soil CO₂ flux. The priming effect on soil native organic carbon reached peaks at the first day of incubation, and both the soil and straw-derived CO₂ emission proportion reached peaks at day 3. 2) During the 30-day incubation period, a total of 238 bacterial OTUs and 24 fungal OTUs were identified using straw-derived carbon. The bacteria OTUs were primarily existed in the bacterial phyla of Proteobacteria, Actinobacteria, Bacteroidetes and Chloroflexi, and the fungal OTUs were belong to class of Sordariomycetes within Ascomycota. 3) The microbial communities varied significantly over the straw decomposition process. Seven bacterial genera, especially Thermomonas and Lysobacter, respond rapidly to straw addition, and 6 bacterial genera, represented by Pseudoxanthomonas and Terrimonas, were identified as delayed responder. Similarly, fungi Cladorrhinum and Stachybotrys respond rapidly to straw addition, Neocosmospora and unclassified_f_ Halosphaeriaceae were identified as delayed responder. 4) Mantel analysis showed that bacterial Thermomonas, Lysobacter, Chloroflexi and fungal Schizothecium were positively correlated with the activities of soil extracellular enzymes related to C and N transformation (P<0.05).

Conclusions Exogenous straw has obvious priming effect on soil organic carbon, and could increase soil CO₂ emission significantly. The microbes that assimilate straw carbon show obvious community succession along the decomposition process, in which bacteria Thermomonas, Lysobacter, Chloroflexi, along with fungi Schizothecium play important roles in the maize straw decomposition.