Climate, biogeochemistry and the thermal performance of decomposition in brown food webs

Background/Question/Methods

Decomposition rates in a given ecosystem (i.e., a given climatic regime and biogeochemistry) arise from the performance of decomposers. The Thermal Adaptation Hypothesis assumes that organisms adapt to their thermal regime, and that the physiological mechanisms promoting performance at a greater variety of temperatures are costly.  It predicts that environments with more variable temperatures will have lower temperature sensitivity in decomposition rates. The Diversity-Competence Hypothesis assumes that a wider variety of metals, enzymes, and species are required to generate robust performance across temperature. It predicts environments with diverse biogeochemistry and/or diverse decomposer assemblages will show decreased temperature dependence

Results/Conclusions

We evaluated both hypotheses across a range of temperatures from 10-40C,in mesocosms stocked with soils from four temperate ecosystems—alpine forest, temperate rainforest, and two hardwood forests. Consistent with the Thermal Adaptation Hypothesis, peak decomposition of cellulose filter paper occurred at 30C, except for the alpine site’s 25C. Moreover, the alpine ecosystem also showed the least temperature dependence. This greater robustness to temperature did not arise from higher diversity; species richness of microbes and invertebrates was lowest in the alpine soils. After 3 months, mesocosms showed significant increases in decomposition performance at low, but not high temperatures.