Resilience of soil microbial community function in an upland grassland soil
Soil microorganisms are critical to many processes in the environment such as decomposition and nutrient cycling; yet little is known about how functional processes performed by soil microbial communities respond to and recover from perturbation. The influences of microbial community structure, rhizosphere interactions and environmental factors on soil microbial community function were examined in a temperate upland grassland soil. Two contrasting methods were used to manipulate microbial community structure in soil microcosms. In a constructive approach, soil was g-irradiated and reinoculated with a progressively diluted soil suspension, producing 4 levels of microbial inoculum. In a deconstructive approach, soil was chloroform-fumigated for 0, 1/2, 2 or 24 h. Both sets of soils were then incubated for 8 months until a similar microbial biomass size was attained. Samples of each soil were either heat-stressed (40°C for 24h) or amended with Cu (1000 mg kg -1). Functional capability was assessed over 28 days following stress by monitoring the short-term decomposition of native plant residues. The progressively fumigated and g-irradiated and reinoculated soils were either amended to 200 mg kg-1 N or unfertilized, and planted with an indigenous grass, Agrostis capillaris L. cv. Highland for eight months. Temporal and rhizosphere effects were shown to influence the resilience of soil microbial function to perturbation. A field study of the grassland site and microbial toxicity assessment of soil pore water extracts using a lux-marked biosensor, E. coli HB101 (pUCD607), demonstrated that land management practices influenced functional resilience to Cu perturbation through changes in Cu bioavailability. Resilience of the decomposition process in the upland grassland soil was shown to be significantly affected by the type of perturbation applied, prevailing structure of the soil microbial community, temporal variation and land management practices.