Print PageUnder predictive climate change models, species’ ranges are expected to move poleward in latitude and upward in elevation with warming. Understanding the implications of this movement for biogeochemical cycles will be necessary to accurately predict global change impacts on forested ecosystems. Given the possibility that biogeographic patterns in microbial communities may translate to dissimilarity in microbial community function, novel litters may be perceived differently to what would be expected based on their chemical and physical composition. Therefore, as tree species migrate, leaf litter inputs to the soil microbial community may cycle differently than in their current environments. We asked if movement upslope of “higher quality” litter species impact nutrient cycling in a manner expected based on the litter’s chemical composition. We used a reciprocal transplant litter bag design with single and mixed-species bags. Litter bags were deployed at three sites along an elevation gradient (795m to 1634m). The four tree species selected are expected to migrate under both conservative (PCM Low) and extreme (Hadley High) global climate change scenarios, and represent the dominant tree species at each elevation plus a ubiquitously-dispersed control: Liriodendron tulipifera, Betula alleghaniensis, Picea rubens, and Acer rubrum. Bags were collected at 4, 7, and 11 months.
Results/Conclusions
At each sampling event, 160 litter bags plus soil samples were collected from 4 blocks at each of the 3 sites. As expected, there was a clear effect of litter quality among the single-species litter bags. For example, L. tulipifera lost 55% AFDM across 11 months at the low elevation site while P. rubens lost 36% AFDM. Despite differences in temperature across sites, higher temperatures only seemed to explain faster rates of decomposition for the two more recalcitrant litters (e.g. B. alleghaniensis lost 69%, 49%, 39% AFDM moving upslope). Interestingly, the litter of highest chemical quality, L. tulipifera, degraded fastest at the highest elevation (59% AFDM lost), the site with the least favorable climate for decomposition. This pattern instead supports the idea of functional breadth. The data also indicate a potential interaction between site and abundance in mixed-species bags. For example, B. alleghaniensis at its “home” site and low abundance (20%), and at the “away site” and larger abundances (50%, 80%), had a positive, non-additive decomposition rate. Collectively, we find evidence that litter decomposition rates are not simply a product of litter chemical quality and climate, but familiarity of the soil microbial community to litter, both single species and mixtures.
