The interaction between earthworms, liming and soil microbial community diversity and function in upland grassland
Soil microbial effects of adding lime and earthworms to acidic upland grassland were investigated. Experiments were conducted in-situ, in an outdoor macrocosm and in laboratory microcosms. This was one of 16 team projects designed to assess biological diversity and ecosystem function in an upland grassland ecosystem as part of the UK NERC's Thematic Programme on Biological Diversity and Ecosystem Function in Soil. Liming had a much greater effect than earthworm additions. The majority of treatment effects were limited to the surface L, F and H horizons. Liming reduced microbial biomass (ATP analysis) and activity (dehydrogenase analysis) in the field studies, but did not affect microbial activity in the microcosm soil. Earthworms had no effect on microbial biomass or activity in the macrocosm or limed microcosm soil, but reduced both the microbial biomass and activity of the un-limed microcosm soil. Principal component analysis of phospholipid fatty acid (PLFA) profiles separated the microbial community structure of the limed from the un-limed soil. Effects of liming common to all experiments included increases of the fatty acid 16:lco5 (indicative of arbuscular mycorrhizal fungi), monounsaturated straight chain fatty acids and an increased fungi :bacterial fatty acid ratio. The fatty acid 18:2co6 (indicative of ectomycorrhizal fungi) only increased in the Sweethope experiment. Both bacterial PLFAs and the trans:cis ratio of 16: Ico7 (indicating bacterial stress) were reduced. Substrate amendment increased CO 2 generation of the limed microcosm soil. Application of Grime's ecological strategy theory suggests that liming shifted the soil microbial community from a stress tolerator to a ruderal community. Earthworm effects on microbial fatty acid composition were limited. These affects were apparent in the un-limed but not the limed microcosm soil. Conversely, earthworms affected the limed rather than un-limed soil in the Sweethope experiment, but effects were only evident 17-months after earthworm additions. The biomass of A. chlorotica was correlated negatively to bacterial PLFA and positively to 16: Ico5. Earthworm faeces could be distinguished from surrounding soil by reduced Shannon diversity and evenness scores and shifts in PLFA profiles. The effect of earthworms on CO 2 generation of microcosm soil was minor in comparison to the effect of liming.