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Abstract. Global change is altering species distributions and thus interactions among organisms.Organisms live in concert with thousands of other species, some beneficial, some pathogenic, some which have little to no effect in complex communities. Since natural communities are composed of organisms with very different life history traits and dispersal ability it is unlikely they will all respond to climatic change in a similar way. Disjuncts in plant-pollinator and plant-herbivore interactions under global change have been relatively well described, but plant-soil microorganism and soil microbe-microbe relationships have received less attention. Since soil microorganisms regulate nutrient transformations, provide plants with nutrients, allow co-existence among neighbors, and control plant populations, changes in soil microorganism-plant interactions could have significant ramifications for plant community composition and ecosystem function. In this paper we explore how climatic change affects soil microbes and soil microbe-plant interactions directly and indirectly, discuss what we see as emerging and exciting questions and areas for future research, and discuss what ramifications changes in these interactions may have on the composition and function of ecosystems.

The dominant conceptual model of litter decomposition posits that the primary controls on the 55 rate of decomposition are climate, litter quality and decomposer organisms 1 . These controls are 56 hypothesized to operate hierarchically in space, with climate and litter quality co-dominant at 57 regional to global scales [2][3][4] , and decomposers operating only as an additional local control whose 58 effect is negligible at broader scales 5 . Consequently decomposers have been omitted as controls 59 4 from biogeochemical models, whereas a recent surge of interest in their inclusion has shown that 60 carbon-cycle projections depend strongly on whether and how microbial decomposers are 61 represented [6][7][8][9] . Yet evidence that microbial decomposers regulate decomposition rates at 62 regional-to global-scales, independent of climate variables such as temperature and moisture, is 63 generally lacking. One possibility for this lack of evidence is suggested by scaling theory, where 64 the influence of mechanisms that act locally can be obscured in emergent, broad-scale patterns 10 . 65Pattern and scale has been described as the central issue in ecology, where the inherent 66 challenge to prediction and understanding lies in the elucidation of mechanisms, which 67 commonly operate at different scales to those on which the patterns are observed 10 . This scale 68 mismatch appears true for at least some ecosystem processes, such as plant productivity 10,11 . 69Decomposition processes, also, are controlled by variables operating at finer scales than those at 70 which the variables are typically measured and evaluated 1 . For example, extensive empirical 71 support for the hierarchical model of litter decomposition has been provided through multi-site 72 climate gradient studies [12][13][14][15] . These multi-site studies have some common characteristics, which 73 include collecting few observations (typically 2 to 4 per site per litter species per collection) -74 from which a mean decomposition rate is determined -and also use of site-mean data to estimate 75 climatic controls1 . Yet the hierarchical model, and its representation in the structure of 76 biogeochemical models, is based on the assumption that controls act at the microsite level, by 77 regulating the activities of decomposer organisms 5,16 . That is, the hierarchical model is 78 conceptually grounded in local (i.e. microsite) dynamics, but has been developed and 79 substantiated with site-mean data that represents climate control of decomposition as an among-80 site relationship. 81 5 Understanding controls on litter decomposition across regional scales is then necessarily 82 intertwined with scaling theory. This body of theory 10 suggests that broad-scale patterns might 83 emerge from distinct, local-scale causative relationships, which contrasts with the assumption of 84 the hierarchical model that among-site patterns in decomposition approximate patterns operating 85 at the microsite (Fig. 1). We refer to this as the "assumption of scale invar...