Do seasonal changes in temperature and precipitation alter soil microbial community response to ecosystem level acidification as determined by 454 pyro-sequencing?

Background/Question/Methods

Chronic acid deposition can reduce soil pH and P availability and affects many temperate hardwood forests of the Northeastern United States. In previous work, we demonstrated that microbial communities in soil and roots respond to pH increases during summer and autumn when plant growth is greatest. Seasonal variability in temperature and precipitation can also affect microbial communities, and could potentially affect microbial community response to alterations in soil chemistry. However, how seasonal variation interacts with acidification to affect microbial communities is poorly understood. In this study, we hypothesized that 1) increases in pH and P availability would affect both bacterial and fungal communities during summer when temperatures and microbial activity are highest, and, thus, soil chemistry may more strongly limit microbial activity and 2) fungal communities would also respond to chemical changes during winter, when pH and P could limit their activity during a time of high decomposition. We examined these hypotheses in an ecosystem-level pH and P manipulation experiment which increased pH by more than 1.5 units and/or increased P availability in 72 experimental plots. Tag-encoded 454 pyro-sequencing of rDNA was used to examine microbial community structure at five time points over the course of one year.

Results/Conclusions

Using non-metric multidimensional scaling and PERMANOVA procedures, we found significant effects of treatment, time and region (glaciated versus unglaciated regions of Ohio) on fungal communities in soil, as well as significant region by treatment interactions. Fungal communities in the glaciated region of Ohio responded significantly to increases in soil pH and time, whereas communities in the unglaciated region of Ohio responded to changes in soil pH, P, and time. Bacterial communities also revealed significant effects of treatment, region, and time as well as a significant treatment by region interaction. For the glaciated region of Ohio, bacterial communities responded to changes in pH and P availability, and strongly responded to time, whereas in unglaciated sites, bacterial communities responded significantly to time and pH increases, but not changes in P availability. For both bacterial and fungal communities, no significant interactions between time and treatment were found, suggesting that the effects of treatment on community changes did not differ throughout the year. Our results suggest that ecosystem acidification and changes to pH and P availability have large effects on soil microbial communities that are unaffected by seasonality but microbial communities response to acidification may reflect regional differences in soil chemistry and resource availability.