Publication Date:
2011-12-03
Description:
Decomposition of soil organic matter (SOM) is mediated by microbial extracellular hydrolytic enzymes (EHEs). Thus, given the large amount of carbon (C) stored as SOM, it is imperative to understand how microbial EHEs will respond to global change (and warming in particular) to better predict the links between SOM and the global C cycle. Here, we measured the Michaelis-Menten kinetics [maximal rate of velocity ( V max ) and half-saturation constant ( K m )] of five hydrolytic enzymes involved in SOM degradation (cellobiohydrolase, β-glucosidase, β-xylosidase, α-glucosidase, and N-acetyl-β- d -glucosaminidase) in five sites spanning a boreal forest to a tropical rainforest. We tested the specific hypothesis that enzymes from higher latitudes would show greater temperature sensitivities than those from lower latitudes. We then used our data to parameterize a mathematical model to test the relative roles of V max and K m temperature sensitivities in SOM decomposition. We found that both V max and K m were temperature sensitive, with Q 10 values ranging from 1.53 to 2.27 for V max and 0.90-1.57 for K m . The Q 10 values for the K m of the cellulose-degrading enzyme β-glucosidase showed a significant (P=0.004) negative relationship with mean annual temperature, indicating that enzymes from cooler climates can indeed be more sensitive to temperature. Our model showed that K m temperature sensitivity can offset SOM losses due to V max temperature sensitivity, but the offset depends on the size of the SOM pool and the magnitude of V max . Overall, our results suggest that there is local adaptation of microbial EHE kinetics to temperature and that this should be taken into account when making predictions about the responses of C cycling to global change.
Print ISSN:
1354-1013
Electronic ISSN:
1365-2486
Topics:
Biology
,
Energy, Environment Protection, Nuclear Power Engineering
,
Geography
