Ecosystem response to climate change varies across a latitudinal gradient

Background/Question/Methods: Carbon sequestration in ecosystems is determined by the balance between net primary production and decomposition.  The impact of climate change on these processes may vary across geographic gradients, due to differences in environmental conditions and the functional traits of the species involved.  Based on the observation that lower latitude wetland plants have systematically tougher leaves than their conspecifics at higher latitudes, we hypothesized that the faster decomposition of leaf litter expected under climate warming scenarios would be limited by more recalcitrant litter produced by plants from lower latitudes.  To determine the influence of latitudinal origin and climate warming on litter decomposition, we collected four distinct genotypes of a widespread wetland plant, Phragmites australis, from each of three regions spanning a 2100 km latitudinal gradient.  Plants were grown in a common garden and fully senesced leaves were harvested and allowed to decompose in outdoor enclosures established in a Phragmites marsh.  Enclosures were designed to mimic either ambient temperature or a temperature rise of 4°C above ambient in line with climate warming scenarios. 

Results/Conclusions: We found that decomposition of low-latitude leaf litter was slowed compared to higher-latitude litter under both ambient and climate-warming conditions. In addition, low-latitude litter was less sensitive to warming than litter from plants grown at higher latitudes.  Genotypic variation among plants collected at a given latitude contributed to variability in decomposition rate.  However, differences in response to warming appeared to be related to systematically higher concentrations of recalcitrant carbon compounds in leaves from low latitude plants.  These results demonstrate that including geographic variation in plant functional traits can result in large differences in projections of litter decomposition rates under climate warming scenarios.