Background/Question/Methods
Soil biogeochemical functions and ecosystem processes are closely tied to the soil microbial community composition and function; however, the majority of soil microorganisms are difficult if not impossible to grow in culture. New methods adapted from molecular biology have begun to shed light on the diversity and function of many of these previously uncultureable microbes. In this study, new molecular techniques, such as functional genomic microarrays and terminal restriction fragment length polymorphisms, were utilized in conjunction with measures of soil biogeochemical pools to examine how the soil microbial community links with biogeochemical processes.

We used the conversion of native grasslands to exotic Eucalyptus plantations (i.e. afforestation) to study how changes in plant inputs to soil alter the function of soil microbes and their associated biogeochemical functions. Afforestation provides a good opportunity to examine how the soil microbial community responds to altered quality and quantity of plant matter inputs. We tested the functional genomic and community structure response of soil microbes using DNA microarrays that simultaneously quantify >27,000 genes with ecological functions and tRFLPs. Responses to afforestation in soil pools of carbon and nitrogen were also measured.

Results/Conclusions
We found that changes in plant input change soil microbial community structure and function, as well as pools of different forms of soil carbon and nitrogen. The change from grass to plantation altered soil bacterial community structure. The change in plant structure also lowered the quantity of carbon degradation, nitrification, N mineralization, and urease genes. The alteration of carbon and nitrogen cycling genes shifted the distribution of pools of soil carbon and nitrogen. We conclude that afforestation’s combined effect on grassland soil microbes was to alter functional genomic capacity and decrease the soil microbial biomass, which decreased the microbial community’s cycling of carbon and nitrogen.