Resilience of the microbial communities of semiarid agricultural soils during natural climatic variability events

The microbial community carries out important processes that support plant growth and maintain soil health. However, extreme climatic variability such as higher temperatures and prolonged drought may cause fluctuations in the microbial community abundance, composition, and activity, thus affecting essential functions they govern including nutrient cycling and soil organic matter (SOM) dynamics. This study evaluated five agricultural lands under continuous cotton (Gossypium hirsutum L.) production from the Texas High Plains semi-arid region during the growing season and post-harvest from 2014 to 2018. Although sites differed in irrigation practices and soil textural class (e.g. from sandy loam to clay), all responded similarly to a decrease in precipitation, and increase in temperatures from 2015 to 2016. Microbial abundance via ester linked-fatty acid methyl ester (EL-FAME) analysis during the growing season of 2016 decreased by 82% in the sandiest soil, and by 38% in the soil with highest clay, when compared to 2015, a year of record precipitation for this region (e.g., 693 vs. 465 mm). Similarly, enzyme activities were reduced by as much as 87% (depending on the site) in the 2016 growing season when compared to 2015. The significant decreases in the soil microbial component could be explained by extremely low soil moisture (e.g., gravimetric water content averaged 2% in drylands, and 6% in irrigated sites) associated to low precipitation and high soil temperatures during the 2016 growing season (6.7 degrees C warmer than 2015). Furthermore, these conditions resulted in shifts in microbial community composition, especially significant decrease (p < 0.05) of saprophytic fungal markers by 59% (e.g., from an average of 26.8 to 10.9 nmol g(-1) soil). However, after 2016 all biological parameters showed increasing trends, thus demonstrating a remarkable recovery and higher resilience than expected for semiarid soils, which experience extremes in temperature, frequent droughts and have low SOM (< 1%).