Soil Bacterial and Fungal Community Responses Across a Conservation Reserve Program Chronosequence in Texas High Plains Region.

We investigated changes in soil bacterial and fungal communities with increasing restoration time across a Conservation Reserve Program chronosequence (CRP) on fine sandy loam soils in the Texas high plains region. Soil samples (0-10cm) were collected in 2012 and 2014 from seven dryland croplands (0 years), eight ‘young’ CRP fields (6-15 years), eight ‘old’ CRP fields (20-26 years), and three rangelands (never plowed or cropped in >50 years). Soil genomic DNA was isolated and 16S rRNA and ITS genes were amplified to determine the bacterial and fungal community composition, respectively. Compared to croplands, soil bacterial and fungal richness and diversity were higher in young and old CRP fields and rangelands, indicating that less disturbed grassland ecosystems promote higher microbial diversity and richness compared to disturbed agroecosystems. Bacterial and fungal community composition responded differently with restoration time. Bacterial composition differed only between croplands and grasslands (both CRP groups and rangelands). Croplands were dominated by taxa that respond to nutrient fluxes following harvest and turnover of crop residues (e.g. Bacteriodetes, Proteobacteria). CRP and rangelands were dominated by taxa that have high affinity to C and are sensitive to disturbances (e.g. Acidobacteria, Verrucomicrobia, Rubrobacteria, Planctomycetes, and Firmicutes). In contrast, differences in soil fungal communities persisted between young and old CRP. Croplands supported a higher abundance of Telleromycetes (containing numerous plant pathogens). Young CRP and rangelands were characterized by greater abundance of Leotiomycetes and Glomeromycetes (stress tolerant) whereas old CRP had a greater abundance of Eurotiomycetes (decomposers and phosphate solubilizers). Our results suggest that CRP restoration had a more immediate effect on bacterial composition with similar populations throughout the entire chronosequence including rangelands (never cropped), whereas fungal communities diverged with increasing restoration time.