Soil microbial biomass and functional diversity in shrub-encroached grasslands along a precipitation gradient

- Soil carbon and microbial properties in shrub-encroached and open grasslands were compared.
- In semi-arid regions soil organic carbon was high in encroached grasslands.
- In humid region soil organic carbon was high in open grasslands.
- Soil microbial biomass and respiration was higher in shrub-encroached grasslands.
- Microbial functional diversity differed between encroached and open grasslands.

The use of soil microbial and biochemical parameters could play an important role in monitoring effects of shrub encroachment in grasslands due to their rapid reaction to environmental fluctuations. We compared total organic carbon (Corg), soil total nitrogen (TON), microbial biomass, basal respiration, soil microbial quotient (Cmic/Corg) species and functional diversity between pairs of neighbouring, leguminous shrub-encroached and open grassland plots along a rainfall gradient (300 mm to 1500 mm mean annual precipitation (MAP)) in South Africa. "In semi-arid regions, soil Corg was higher in shrub-encroached grasslands than in open grasslands while the reverse was true in humid regions (1500 mm MAP)". Soil total nitrogen was generally higher in the shrub-encroached grasslands compared to open grasslands. Soil microbial biomass and basal respiration was higher in shrub-encroached grassland across the precipitation gradient. There was also a difference in microbial functional diversity between the encroached and adjacent open grasslands, which was most evident in the semi-arid regions. Our results suggest that land-cover change might influence microbial properties along the rainfall gradient.