Ecosystem response of pasture soil communities to fumigation-induced microbial diversity reductions: an examination of the biodiversity-ecosystem function relationship

A technique based on progressive fumigation was used to reduce soil microbi al biodiversity, and the effects of such reductions upon the stability of k ey soil processes were measured. Mineral soil samples from a grassland were fumigated with chloroform for up to 24 h and then incubated for 5 months t o allow recolonisation by surviving organisms. The diversity of cultivable and non-cultivable bacteria, protozoa and nematodes was progressively reduc ed by increasing fumigation times, as was the number of trophic groups, phy la within trophic groups, and taxa within phyla. Total microbial biomass wa s similar within fumigated soils, but lower than for unfumigated soil. Ther e was no direct relationship between biodiversity and function. Some broad- scale functional parameters increased as biodiversity decreased, e.g. thymi dine incorporation, growth on added nutrients, and the decomposition rate o f plant residues. Other more specific parameters decreased as biodiversity decreased, e.g. nitrification, denitrification and methane oxidation. Thus specific Functional parameters may be a more sensitive indicator of environ mental change than general parameters. Although fumigation reduced soil mic robial biodiversity, there was evidence to suggest that it selected for org anisms with particular physiological characteristics. The consequences of t his for interpreting biodiversity - function relationships are discussed. T he stability of the resulting communities to perturbation was further exami ned by imposing a transient (brief healing to 40 degrees C) or a persistent (addition of CuSO4) stress. Decomposition of grass residues was determined on three occasions after such perturbations. The soils clearly demonstrate d resilience to the transient stress; decomposition rates were initially de pressed by the stress and recovered over time. Resilience was reduced in th e soils with decreasing biodiversity. Soils were not resilient to the persi stent stress, there was no recovery in decomposition rate over time, but th e soils with the highest biodiversity were more resistant to the stress tha n soils with impaired biodiversity. The study of functional stability under applied perturbation is a powerful means of examining the effects of biodi versity.