Climate history shapes contemporary leaf litter decomposition

Litter decomposition is mediated by multiple variables, of which climate is expected to be a dominant factor at global scales. However, like other organisms, traits of decomposers and their communities are shaped not just by the contemporary climate but also their climate history. Whether or not this affects decomposition rates is underexplored. Here we source decomposer communities from three forest sites contrasting in climate (tropical, temperate, boreal), and, using experimental microcosms, quantify decomposition of a common litter under a factorial combination of four temperature (15, 20, 25, and 30 °C) and five moisture regimes (35, 55, 70, 85, and 100 % water holding capacity). We find that the climate history of the decomposer community is an important determinant of litter decomposition, explaining the same amount of variance in decomposition as both temperature and moisture. Further, climate history also shapes the effect of contemporary climate (i.e. experimental) on decomposition, both in terms of the magnitude of decomposition under optimal conditions and the range of abiotic conditions at which high decomposition rates are maintained. For example, at optimal conditions (i.e. 25 °C/70 % WHC) the tropical site has a greater decomposition rate than the other two sites. However, the temperate and boreal sites have greater ‘niche breadth’, where decomposition rates are more sustained (i.e. decrease less) as temperature and moisture deviate further from the optimum. Our data suggest that climate history shapes the functional response of the soil decomposer community, as it does for animals and plants. Yet how this shaping affects decomposition rates across regional and global climate gradients, and how such relationships are applied to temporal predictions, remain unanswered questions.