Soil Microbial Community Structure and Functionality During Grassland Restoration In The Texas High Plains.

Soil microbial communities are an indispensable part of restoration programs due to their significant role in ecosystem functioning and sensitivity to disturbance. We evaluated soil microbial community structure using ester-linked fatty acid (EL-FAME) profiling and metabolic functioning, by measuring seven soil enzyme activities associated with C, N, P, and S cycling in a Conservation Reserve Program (CRP) chronosequence. Soil samples (0-10 and 10-30cm) were collected from Amarillo fine sandy loam in seven dryland crop fields (represented 0 years restored) and 16 CRP fields that ranged from 6 to 26 years under restoration. Absolute abundances for total FAMEs and biomarkers for Gram positive bacteria (GM+), Gram negative bacteria (GM-), saprophytic fungi, and arbuscular mycorrhizal fungi (AMF) were used as proxies for biomass. Although, there was a positive linear relationship between years of restoration and Total microbial biomass, GM+ and total bacterial biomass, the total FAMEs increased 236% from 0 years to 23 years restored but decreased 70% from 23 years to 26 years of restoration. Similarly, GM+ and total bacterial biomass increased 171 and 185%, respectively from 0 to 23 years restoration but decreased 62%from 23 to 26 years of restoration. A second order polynomial equation best described the relationship between time under restoration and GM- biomass and saprophytic fungal biomass. In general, values increased from 0 to approximately 15 years restored and then declined. AMF biomass exponentially increased to a maximum level around 15 years restored with no statistical difference beyond 15 years. The geometric mean of the seven enzymes increased linearly with years restored and the rate of increase was greater at 0-10cm (slope = 1.0) than at 10-30cm (slope = 0.29). Soil FAME biomarkers and enzyme activities were sensitive to time under restoration but declining levels beyond 23 years suggest factors other than time alone, influence restoration efforts.