Soil microbial community restoration in Conservation Reserve Program semi-arid grasslands

The Conservation Reserve Program (CRP) in the Southern High Plains (SHP) is known to play a crucial role in maintaining ecosystem health by reducing soil erosion. However, the restoration of soil biological health (biological community and its function) over time under CRP have not been clearly elucidated. The objective of this study was to describe the changes in the soil microbial community composition using a CRP chronosequence. Soil samples (0-10 cm and 10-30 cm) were collected in 2012 and 2014 from 26 fields across seven counties within the SHP and included seven croplands (representing 0 y in CRP), 16 CRP fields of varying ages (8-28 y as of 2014), plus three rangelands (representing no disturbance for > 30 y). Multiple regression analysis was conducted to evaluate the impacts of CRP restoration on soil microbial biomass. Shifts in soil microbial community composition, according to fatty acid methyl ester (FAME) profiles, with increasing CRP restoration years were explored using multivariate ordination. Total microbial biomass (using total FAME content as a proxy) increased with CRP years at 10-30 cm in 2012 and both depths in 2014. Although different environmental conditions were present during the two sampling years (2012 followed a record extreme drought in 2011 with conditions improving in 2014), the physiological stress of microbial community indicated by ratios of saturated to monounsaturated FAME biomarkers consistently decreased with CRP restoration years in both sampling years and both depths. A shift in microbial community composition was measured during CRP restoration at 0-10 cm in both sampling years (and at 10-30 cm in 2012) with an increase in relative fungal abundance through the initial 15 y of CRP and then a decline after 15 y. The overall increase in soil microbial biomass and decrease in microbial physiological stress indicators with increasing years under CRP illustrates how this is a valuable restoration program for building soil health in fragile, sandy SHP soils. The mechanisms underlying the decline in fungal abundance in years 15-28 are unclear and the associated reduction in the fungal to bacterial ratio does not necessarily reflect reduced soil health. Overall, the CRP program is an effective restoration practice in the SHP that can restore overall soil biological attributes including microbial biomass, re-establish the soil microbial community with decreased microbial physiological stress, and improve soil microbial functions related to C sequestration.