Does the aboveground herbivore assemblage influence soil bacterial community composition and richness in subalpine grasslands?

Abstract

Grassland ecosystems support large communities of aboveground herbivores that can alter ecosystem processes. Thus, grazing by herbivores can directly and indirectly affect belowground properties such as the microbial community structure and diversity. Even though multiple species of functionally different herbivores coexist in grassland ecosystems, most studies have only considered the impact of a single group, i.e. large ungulates (mostly domestic livestock) on microbial communities. Thus, we investigated how the exclusion of four groups of functionally different herbivores affects bacterial community structure, diversity and abundance in two vegetation types with different grazing histories. We progressively excluded large, medium and small mammals as well as invertebrate herbivores using exclosures at 18 subalpine grassland sites (nine per vegetation type). We assessed the bacterial community composition using terminal restriction fragment length polyphormism (T-RFLP) on each site and exclosure type in three consecutive years (2009-2011) for rhizosphere and mineral soil separately. In addition, we determined microbial biomass carbon, root biomass, plant carbon:nitrogen ratio, soil temperature and moisture. Even though several of these variables were affected by herbivore exclusion and vegetation type, this did, against our expectations, not affect bacterial community structure, diversity or abundance, as we found no treatment or vegetation effects. In contrast, the bacterial communities strongly differed between the three growing seasons. Our study indicates that the inter-annual variability in soil micro-climate has much stronger effects on the soil bacterial communities than the alterations in these variables caused by changes in grazing regime or by different vegetation types in our high-elevation ecosystems.

Citation

Hodel, Melanie; Schütz, Martin; Vandegehuchte, Martijn L.; Frey, Beat; Albrecht, Matthias; Busse, Matt D.; Risch, Anita C. 2014. Does the aboveground herbivore assemblage influence soil bacterial community composition and richness in subalpine grasslands? Microbial Ecology. 68(3): 584-595.