Using DNA stable-isotope probing method tracing the microbial communities assimilating the maize straw-derived carbon

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 was 30 days. Using ¹³C-labeled maize straw and high-throughput sequencing, we aimed to investigate The priming effect of straw addition on soil organic carbon, and the bacterial and fungal microbial communities assimilating straw-derived carbon were analyzed by combining utilization of ¹³C-tracing and high throughput methods, and the soil extracellular enzymes activity were analyzed at the same time.

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 234 bacterial OTUs and 24 fungal OTUs, which utilized straw-derived carbon, were identified. The bacteria OTUs were primarily distributed 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 along 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 soil extracellular enzyme activity 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 the carbon source of straw showed obvious community succession along the decomposition process, in which bacteria of Thermomonas, Lysobacter, Chloroflexi, and along with fungi of Schizothecium played an important role in the maize straw decomposition.