COS 269-6 - Soil microbiome response to drought under conservation management in semi-arid cotton production systems.

Abstract: Land managers in semi-arid regions such as the Texas Southern High Plains (SHP) face severe challenges related to water and nutrient scarcity while attempting to improve soil ecosystem functioning and productivity. Cotton production in the semi-arid Texas SHP has historically relied on continuous cropping, tillage, and irrigation to sustain productivity, yet declining water resources have prompted a greater focus on conservation management practices such as cover crops, crop rotations, and reduced tillage to improve soil properties and water storage. Despite previous studies showing improved soil characteristics and functioning under conservation management, we know little about the susceptibility of soil microbial communities and functioning to increased frequency and severity of disturbances such as drought experienced in these systems. We investigated soil and rhizosphere microbial community structure and function under three long-term ( > 7 years) established cotton production management strategies: 1) Continuous mono-crop cotton with conventional tillage, 2) no-till cotton with winter rye cover crop, and 3) no-till cotton with a wheat/fallow rotation located in Lamesa, TX with a sandy loam-textured soil. We assessed microbial nutrient-cycling activities via high throughput extracellular enzyme assays and microbial community size and structure via EL-FAME analysis and 16S rRNA/ITS sequencing in fresh soil samples, then subjected the soils to either well-watered or drought-stressed conditions in the laboratory to calculate the drought resistance index. We observed significantly lower overall enzyme activities (p < 0.05) and inconsistent drought response in conventional tillage, continuous cotton soils (CCCT) compared to in the conservation management systems, which provided little buffer against drought and further reduced the capacity of C-cycling enzymes (BG) to resist drought stress. Significantly greater microbial nutrient cycling activities (p < 0.05) were observed in conservation management treatments such as no-tillage and addition of cover crops (NTCR) or rotations (NTCW) compared to conventional practices. However, N-cycling enzymes in these systems were also relatively sensitive to drought stress and inhibited under drought conditions, while enzymes related to C and P cycling were better able to resist severe drought. Analyses of microbial community responses and enrichment or depletion of specific microbial groups in response to drought are ongoing. Our current results suggest that enhanced microbial activities that alter C, N, and P cycling under conservation management practices in these coarse-textured, semi-arid soils can also be more susceptible to drought disturbance, which further complicates potential plant and microbial availability of nutrients and nutrient losses from these systems.