Soil organisms and global climate change

Climate changes will influence soil organisms both directly (warming) and indirectly (warming and elevated CO 2 ) via changes in quantity and quality of plant‐mediated soil C inputs. Elevated atmospheric CO 2 commonly stimulates flow of organic C into the soil system, increases root production and exudation, but decreases litter quality. There is little evidence that atmospheric CO 2 enrichment will increase total soil organic matter content because greater C flow into soil stimulates the soil food web, often leading to equivalent increases in soil CO 2 efflux. Effects of warming on C allocation belowground, on the other hand, will depend largely on the temperature optima of different plant species. Warming is likely to increase the rate of soil organic matter decomposition by stimulating soil heterotrophic respiration, although some degree of acclimatization to warming is likely. Mycorrhizal and N 2 ‐fixing relationships are generally enhanced by CO 2 enrichment, but effects of warming are highly variable. Data suggest that energy flow through fungal pathways may be enhanced relative to bacterial pathways by both warming and atmospheric CO 2 enrichment. Whether the shift toward fungal domination of soils will increase soilborne fungal disease occurrence in the future is still an open question. Plant heat and drought tolerance, along with resistance to pathogens in warmer and wetter soils, may be achieved, to some unknown extent, by exploitation and management of beneficial soil organisms. Further study is needed to develop a more holistic understanding of the effects of climate change on belowground processes.