Below-ground microbial community development in a high temperature world

The response of above-ground plant and ecosystem processes to climate chang e are likely to be influenced by both direct and indirect effects of elevat ed temperature on soil biota and their activities. This study examined the effects of elevated atmospheric temperature on the development of the soil microbial community in a model terrestrial ecosystem facility. The model sy stem was characterized by a soil of low nutrient availability, a condition that simulates most native terrestrial plant communities. The experiment wa s run over three plant generations, broadly mimicking the early stages of a plant succession, and showed that microbial biomass, measured using phosph olipid fatty acid (PLFA) analysis, increased significantly in response to e levated temperature during the first generation only. This increase was unr elated to changes in plant productivity or soil C-availability, and was lar gely due to a direct effect of elevated temperature on fast-growing Gram-po sitive bacteria. Slow growing soil micoorganisms such as fungi and actinomy cetes were unaffected by elevated temperature throughout the experimental p eriod. Measures of microbial biomass, microbial respiration and N-mineraliz ation were also unaffected by elevated atmospheric temperature over the thr ee generations. The lack of effects on the soil microbial community is thou ght to be due to the fact that elevated temperature did not influence root biomass or soil C-availability. We suggest that the observed reductions in above-ground plant productivity, in response to elevated temperature, will become apparent in the longer term when litter decomposition pathways are m ore established. The temporal measures of PLFA and microbial biomass indica ted that over the experimental period rapid initial changes occurred in mos t soil biological characteristics, followed by periods of stabilization dur ing later plant succession. These changes were associated with increases in above ground plant productivity and amounts of available C in the soil. In contrast, total microbial biomass declined during the last plant generatio n. Reductions in the diversity of PLFAs in later plant generations appeared to be associated with an increase in the proportion of fatty acids associa ted with fungi, relative to those from bacteria. These changes are likely t o be related to increased competition for resources within the soil, and an associated reduction in N- and C-availability. These changes appear to be broadly consistent with those reported for other studies on the successiona l development of soil microbial and plant communities. Overall, our data su ggest that elevated atmospheric temperature has little effect on the develo pment of below-ground microbial communities and their activities in soils o f low nutrient status.