Effects of daily soil temperature range on microbial community dynamics in a dryland cotton production system in West Texas
Vargas-Gutierrez, Diana Lucia
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Global mean temperature has increased in the last decade from 0.10 to 0.16 ºC, leading to a decrease in the daily temperature range (DTR= Tmax-Tmin) where the night time minimum temperature (Tmin) is increasing at a faster rate. Changes in daily Tmin and Tmax can have a positive or negative consequence to agriculture production depending upon crop type and location, but little is known about the possible effects of DTRsoil on microbial community dynamics. The main goal of this study was to evaluate the impacts of daily temperature range (DTRsoil) on the microbial community size, structure and functional diversity in a dryland cotton production system on the South High Plains. Six plots were established during the 2013 growing season using wood-fiber erosion control blankets to reduce DTRsoil. Six control plots were established adjacent to the reduced DTRsoil plots. Soil samples were collected before planting and over the growing season, from planting beds and from the furrows between the beds, from each set of plots and analyzed to evaluate microbial biomass carbon, microbial community composition, enzymatic activities, and carbon usage by bacteria and fungi. DTRsoil was reduced by 11ºC at the soil surface and by 4°C at 15 cm under the erosion blankets in comparison with the controls plots across the growing season. The reduction in DTRsoil led to an increase in microbial biomass C as the crop developed as compared to control plots, as well as an increase in of Gram (-) bacteria, arbuscular mycorrhizal fungi, saprophytic fungi and protozoan FAME markers. Levels of extractable NO3--N, NH4+-N and P were higher under control plots in comparison with reduced DTRsoil plots indicating the reduction in DTRsoil regulated nutrient dynamics and increased nutrient uptake into microbial biomass. Microbial functional capabilities as evaluated by-glucosidase, -glucosaminidase, arylsulfatase, alkaline phosphatase and phosphodiesterase and BIOLOG functional diversity were higher within the reduced DTRsoil plots as the crop developed as compared to control plots. Fungal functional diversity, substrate activity and substrate richness did not show a response to either a reduction in soil DTR or if samples were taken from planting beds or furrows. Cotton stand development was poor in the control plots and was significantly higher in the reduced DTRsoil plots. The cotton in the reduced DTRsoil plots went on to produce a yield comparable to dryland cultivation under a good year. The reduction in DTRsoil positively affected the dynamics of microbial communities and relationship with plants, which can lead to good crop development.