Background/Question/Methods
In light of the changing global climate, understanding the soil microbial community response to warming temperature is increasingly important. The microbial response to warming may be different depending on external factors (soil type, plant biomass) and changing microbial dynamics across the landscape (community composition and function). Combining research approaches and measurements in new ways may offer a better understanding of the relationship between soil temperature and microbial community dynamics. In this study we simultaneously studied several aspects of the microbial community (gene abundance, turnover, and activity) to elucidate the relationships between elevated temperature, plants, soil type, and microorganisms. Our treatments included elevated temperature (unheated or +5 °C using soil heating cables), two soil types (organic farm soil versus tallgrass prairie soil), and three planting treatments (soybean, sunflower, and an unplanted control). After two and three months of heating and plant growth, we examined aspects of microbial community dynamics including: activity (extra-cellular enzyme activity, gross N mineralization and nitrification, and respiration), abundance (gene abundance and chloroform fumigation-extraction) and turnover (gross N mineralization as well as from microbial biomass C and respiration).

Results/Conclusions

Our results suggest (after preliminary analysis) that microbial communities have distinct biogeography between soil types that could be related to nitrogen cycling and temperature response. For instance, the relative abundance of ammonium oxidizing archaea (AOA), and total archaea in general, were higher in farm soil, where AOA were also more correlated with nitrogen cycling rates than ammonium oxidizing bacteria (AOB)and extra-cellular enzyme activity. On the contrary in the prairie soil, AOB and total eubacteria appeared to correlate with nitrogen cycling parameters. In addition to shifting community dynamics, we found differences in warming effects between the two soil types. In the farm soil gross N mineralization and gross nitrification both decreased under warming and in planted treatments, AOA and AOB abundance however increased under warming without plants, but decreased under warming in planted treatments. In the prairie soil there was little effect of warming on gross N mineralization where gross nitrification decreased under both planting and warming treatments. AOA acted much the same under warming and planting in prairie soil as in farm soil, but the AOB in prairie soil instead of increasing under warming without plants, decreased under both warming and planting. These results suggest that changes in microbial community structure between soil types may be correlated with differences in nutrient cycling and response to soil warming.