Soil microbial extracellular enzyme activites from a Northern temperate forest with experimental temperature and moisture manipulations

Background/Question/Methods

Climate change scientists predict large and lasting alterations of both temperature and precipitation in temperate regions, yet the responses of the soil microbial community to changes in temperature and moisture remain poorly understood. Microorganisms are important drivers of soil carbon cycling due to the activity of the enzymes that microbes produce to break down polymers in the soil.  Increases in temperature and moisture availability may alleviate limitations to potential enzyme activity, at least in the short term, with acclimation possible in the long term.  The goal of this study was to evaluate the impact of climate change on the potential enzyme activity of soil microorganisms.  Soils were collected from a climate change manipulation in Northern Michigan with both temperature (+4-5 °C) and moisture (+30% over ambient precipitation) treatments in a fully factorial blocked design.  Three replicate samples were collected monthly from March to October 2012 from each of the 12 plots.  Hydrolytic extracellular enzyme activities measured included cellobiodisase, β-glucosidase, N-acetylglucosaminidase and acid phosphatase.  Assays for two oxidative enzymes, phenol oxidase and peroxidase, were performed.  Field samples were incubated at 15 °C and 20 °C in the laboratory to measure the temperature sensitivity of potential enzyme activity. 

Results/Conclusions

Preliminary results indicate that enzyme activity increases from the early spring into the summer months.  This finding was significant for all enzyme activities tested, at an alpha of 0.05, with the exception of phosphatase and phenol oxidase activities.  Although a pattern of increasing peroxidase activity through time was noted, the trend was not significant.  Extracellular enzyme activities of cellobiodisase, β-glucosidase, N-acetylglucosaminidase were significantly impacted by treatment. Cellobiodisase activity was higher in all treatments versus the control and was highest in the heat only treatment.  β-glucosidase activity was significantly higher in the heat only treatment versus all other treatments. N-acetylglucosaminidase activity showed a similar pattern to cellobiodisase activity, with all treatments demonstrating higher activity levels than the control and the heat only treatment having the highest activity rates.  Acid phosphatase activity shows a similar trend to cellobiodisase and N-acetylglucosaminidase activity, with the highest activity levels occurring in the heated treatment; however this trend was not significant.  Phenol oxidase and peroxidase activities both tended to be highest in treatments receiving heat versus control or water only treatments.  This suggests that the oxidative enzymes may be more sensitive to changes in temperature than previously thought, although further study is needed.