Drought alters soil microbial composition in grasslands, but less is known about the effects of drought in restored grasslands. Restorations may be particularly susceptible to drought in during establishment years because plants have yet to develop large root systems, and microbial communities remain bacteria-dominated from long-term agriculture. To understand the effect of drought on the recovery trajectory of soil microbial communities in restored prairie, we examined phospholipid fatty acid biomarkers in prairie restored under natural variation in precipitation. Phospholipid fatty acid profiles were quantified in two prairies restored for 2, 4, 5, and 9 years, but restorations were initiated in average, drought, and wet years. Soil microbial community structure was examined using Gram-positive bacteria, Gram-negative bacteria, non-specific bacteria, actinomycetes, arbuscular mycorrhizal fungi, and saprophytic fungi PLFA biomarkers and visualized using non-metric multidimensional scaling (NMDS). Effect of restoration age and initial climate conditions (annual precipitation, June/July precipitation) on community structure were analyzed with a repeated measures permutational multivariate analysis of variance (PERMANOVA). Microbial PLFA biomass and fungal:bacteria ratio were analyzed using mixed models to determine the effects of initial year climate and age of restoration.
Results/Conclusions
Soil microbial community composition changed with restoration age (PERMANOVA, P=0.001) and was affected by precipitation in June/July of the year samples were taken (P=0.020). Total biomass increased with age (P=0.007) due to increases in arbuscular mycorrhizal fungi (P=0.0236), saprophytic fungi (P=0.038), and non-specific bacteria (P=0.0013). Fungal:bacteria ratio also increased with age (P<0.001). Gram-negative bacteria were the only microbial group affected by climate in the establishment year, exhibiting decreased biomass when restored under June/July drought conditions (P=0.0236). Thus, initial climatic conditions have long-term effects on PLFA profiles as restorations develop and can alter microbial community recovery trajectories, but recovery of overall PLFA biomass is resilient to drought.