Decreases in organic C reserves in soils can reduce the catabolic diversity of soil microbial communities

An understanding of the main factors influencing microbial diversity in soi ls is necessary to predict the effects of current landuse trends on terrest rial diversity. We used microbial catabolic evenness as a measure of one co mponent of soil microbial diversity. Catabolic evenness was assessed by mea suring the short-term respiration responses of soil to a range of simple or ganic compounds. Differences in catabolic evenness between pasture and othe r land-uses on matched soils were related to differences in organic C pools (total organic C, microbial biomass C, and potentially mineralizable C). T his approach enabled comparison of land-use effects on organic C pools in r elation to catabolic evenness without the effects of soil type. In general, microbial catabolic evenness was greatest in soils under pasture and indig enous vegetation (range: 19.7-23.3), and least in soils under cereal/maize/ horticultural cropping (range: 16.4-19.6). Soils under mixed cropping land- uses had catabolic evenness that ranged between these extremes (range: 17.7 -20.5), but under pine forestry there was no characteristic level of evenne ss (range: 15.1-22.3). Catabolic evenness correlated poorly with the absolu te values of soil organic C pools (r(2) < 0.36). However, across a range of paired comparisons between pasture and other land-uses, greater difference s in microbial catabolic evenness corresponded with greater differences in organic C (r(2)=0.76) and, to a lesser degree, with differences in microbia l biomass C (r(2) < 0.45) or potentially mineralizable C (r(2) < 0.13). The refore, land-uses that deplete organic C stocks in soils may cause declines in the catabolic diversity of soil microbial communities. Although the imp lications of this for microbial processes are unknown, maintenance of soil organic C may be important for preservation of microbial diversity. (C) 200 0 Elsevier Science Ltd. All rights reserved.