Using Multilevel Omics to Gain Insights in to the Response of Microbial C Cycling to Rainfall.

We collected soil in early and late summer from before, during, and after rainfall events in both Ambient and Altered precipitation interval (more “droughty”) experimental treatments at a tallgrass prairie in Kansas. At each sampling we collected soil immediately prior to a 1” rainfall event and at one and five days following the rainfall. Results of soil activity measurements lead to hypotheses regarding microbial physiological adaptation to drought stress in prairie soils. Molecular data (454 sequencing and QPCR of bacterial 16S rRNA and fungal ribosomal genes and transcripts, full transcriptomes, and proteomes) were collected to test these hypotheses. We found little change in microbial community composition but transcriptome libraries reflected a dynamic pool of genes expressed in the context of soil wetting and drying via both seasonal drought and individual rainfall events, although there was no clear relationship between the taxonomic or functional gene expression in soils subject to long-term alteration of precipitation timing. Analysis of transcripts related to catabolic vs. anabolic processes were found to correspond with measurements of microbial carbon use efficiency. Expression of trehalose or compatible solute production genes was not correlated with soil water content; however, the sum of transcripts categorized as “cellular responses to stress-tolerance” (including oxidative stress, osmotic stress and general stress response, KO annotated) declined with soil water content. A related link between soil water variability, soil organic matter (SOM) decomposition and microbial C utilization was apparent, however, in the concurrent increase in b-glucosidase potential activity and cellobiose transport following the June rainfall event, both indicating an increase in cellobiose availability for microbial utilization. In summary, transcripts provided mechanistic insights into soil microbial carbon dynamics under changing soil water conditions in this field experiment.