Short-term disturbance events, such as dry-rewet cycles, can lead to rapid pulses of nitrous oxide (N2O). Since microbial processes are dominant for N2O production, how soil dry-rewet cycles affect microbial groups and microbially-driven processes of N2O emissions is still little known. Thus, our objective is to use multi-omics to evaluate active N2O-producers and pathways that correlate to N2O spikes during dry-rewet cycles in laboratory and field experiments. In an 8 year-old switchgrass field, we have designed 24 plots including three N rates. Soils collected at 0-5 and 5-15 cm at different seasons were subjective to Illumina MiSeq analysis of 16S and ITS amplicons. For laboratory experiment, twelve switchgrass soil column were set up with Picarro G2508 for continuous measurement of greenhouse gases and soil sampling for multi-omics analysis at 0-5 and 5-15 cm. Treatments included two N rates, control (0N) and 200 N ha-1 (200N), and two moisture cycles, 80% WFPS (FC) and drying-rewetting from 30% to 80% WFPS (DW). Soil was collected at multiple points of drying-rewetting phases to evaluate the dynamics of soil metagenome, metatranscriptomics, and metaproteomics related to N2O fluxes through high-throughput sequencing of soil DNA and RNA, and metaproteome using nano-2D-LC-MS/MS.
Results/Conclusions
Our preliminary field results showed that although sampling depth had effects on microbes, there was no pre-existing divergence of microbial community across plots. The N fertilization only showed slight effects at certain groups, such as Kineosporiaceae for bacteria and Archaeorhizomycetes for fungi. Initial soil metagenomic and metatranscriptomics analysis via MG-RAST showed diverse functional profile for switchgrass soils of two depths. Our laboratory results showed that N inputs increased soil N2O flux rates in 200N to 229 μml m-2 h-1. Although drying reduced N2O emissions to nearly zero for DW, rewetting instantly raised N2O fluxes to 44 μml m-2 h-1 in both DW-0N and -200N. Thereafter, N2O in DW-200N kept increasing to 93 μml m-2 h-1. Second round of dry-rewet cycle stimulated N2O emissions to 89 μml m-2 h-1 in DW-200N, significantly greater than DW-0N. Thus, cumulative N2O production in RW-200N was higher than others in 2st dry-rewet cycle. Ongoing work is evaluating the dynamics of soil metagenomes, metatranscriptomes, and metaproteomes related to N2O pulses and starting field monitoring of greenhouse gases. These efforts will provide detailed information about the most active microbes and microbially-driven processes responsible for the large N2O emissions driven by dry-rewet cycles.