Linking enzymatic activities in soil and deadwood in a managed northeastern forest

Background/Question/Methods

Linkages between soil and deadwood microbiomes are poorly understood in temperate forest ecosystems yet may offer insight on how these communities drive important ecosystem functions such as decomposition and nutrient cycling. The microbial communities found within deadwood and the surrounding soil mediate these processes through the production of extracellular enzymes that alter the rate and capacity at which carbon and nitrogen are cycled throughout the ecosystem. While most research has focused on a single substrate, we investigate the impacts of forest management on enzymatic activities in both soil and deadwood in a temperate forest. Specifically, we hypothesized that (1) increased variation in temperature and moisture within management treatments that reduce canopy cover or create gaps, yield higher potential extracellular enzymatic activity (EEA) and that (2) deadwood is more sensitive to micro-climatic variation than soil. To test these hypotheses, we measured the activities of seven different enzymes related to carbon, nitrogen, and phosphorous cycling in deadwood and soil samples within the Adaptive Silviculture for Climate Change study (ASCC). The ASCC management treatments produced four distinct canopy conditions including an intact canopy (control), moderate canopy density (thinning), and 0.1 and 0.4-ha gaps, which influence the variation of understory micro-climates. Each treatment contains three deadwood logs in gap and non-gap areas, that are equipped with high-frequency temperature and moisture sensors. Within each of these logs and paired soil samples, we measured how EEA responded to the micro-climatic variation created by forestry management treatments.

Results/Conclusions

Surprisingly, EEA did not significantly differ between paired soils and deadwood. Although there were no significant differences in soil EEA, variability was high, suggesting a larger sample size may be necessary to find significant results. However, deadwood EEA was significantly different among treatments (p < 0.05). Deadwood EEA for six out of seven enzymes was highest within the 0.1-ha gap treatment. Variation in deadwood EEA was not well explained by the variation in temperature or moisture, therefore, there may be differences in substrate or other climatic variables influencing the microbial communities. Our results suggest that microbial communities within deadwood and the surrounding soil are similarly affected by the abiotic and biotic factors that are a result from forest canopy disturbance.