Anthropogenic acid deposition in the form of acid rain has created a legacy of low soil pH in many areas of the United States, including northeast Ohio. Acidic soil limits the availability of phosphorus (P) to plants, ultimately affecting litter chemistry. These ecosystem shifts may also alter soil microbial communities, subsequently influencing the rate of litter decomposition. We examined the potential effects of acid-rain induced shifts in soil microbes and litter chemistry to drive rates of decomposition using a lab-based mesocosm study. We incubated soil and litter (Acer saccharum leaves) collected from a field experiment that has manipulated soil pH and P in northeast Ohio for the past 7 years including: (1) 9 unamended and (2) 9 elevated pH and P plots. We combined litter with field soil in a fully factorial design: 1) soil and litter from the same plot, 2) soil and litter from the same treatment, but different plots, 3) soil and litter from different treatments. Soil CO2 evolution was measured on days 1, 2, 3, 5, 8, 15, 30, 60, 90, and 119. A replicate soil sample was removed for enzyme analyses on days 3, 15, and 119.
Results/Conclusions
Soil microbial communities from the amended plots (elevated pH and P) marginally elevated rates of decomposition over the 119 day duration of the experiment (F=3.297, p=0.0755). There was no impact of litter origin on cumulative decomposition (F=2.160, p=0.148). We found that the influence of soil origin on decomposition was more apparent initially, with slower rates of decomposition on soil microbial communities from pH and P-addition plots, while litter from pH and P-addition plots decomposed more quickly late in the study. Both litter and soil microbe origin had significant effects on phosphatase and b glucosidase activity early in the experiment, but treatment differences were no longer present later on. Leucine amino peptidase and phenol oxidase were not influenced by treatment. These results suggest that both aboveground (plant litter quality) and belowground (soil microbial community composition) changes associated with acid rain deposition are influencing rates of decomposition, and ultimately carbon storage capacity, in northern deciduous forests.