Biogeographically distinct controls on C₃ and C₄ grass distributions: merging community and physiological ecology Public Deposited

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  • AIM: C₄ photosynthesis is an adaptation that maintains efficient carbon assimilation in warm and low-CO₂ conditions. Due to the importance of C₄ grasses for carbon and surface energy fluxes numerous models have been proposed to describe their spatial distribution and forecast responses to climate change. These models often rely on broad climate predictors (e.g., temperature and precipitation) but fail to integrate other ecologically relevant factors, such as disturbance and competition, which may modify realized C₃/C₄ grass distributions. We evaluate the contribution of ecological factors, in addition to climate predictors, to C₃/C₄ grass distributions across multiple biogeographic regions of North America in a multi-source database of >40,000 vegetation plots. LOCATION: Conterminous United States of America (USA). METHODS: We identified a comprehensive pool of physiological-climatic models in the literature and used information theoretic criteria to select a primary physiological predictor of C₃ and C₄ grasses. Subsequently, the climate model was combined with ecological predictors using a multiple regression framework and tested within eight regions within the USA. RESULTS: Surprisingly, grass-dominated communities across the USA exist largely in a C₃ or C₄ dominated state. Transitions between C₃/C₄ dominance were best explained by models that integrated temperature and precipitation with ecological factors that varied according to region. For some regions, such as Eastern Temperate Forests, local, ecological factors were comparable in strength to broad climate predictors of C₃/C₄ abundance. MAIN CONCLUSION: Local, ecological factors modify C₃/C₄ grass responses to broad-scale climatic drivers in ways that manifest at regional scales. In Eastern Temperate Forests, for example, C₄ grass abundances are maintained below climatic expectations where tree cover creates light limitation, but above expectations where frequent fires reduce tree cover. Thus, local ecological factors contribute to major among-region differences in the climate responses of C₃/C₄ grasses.
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  • Griffith, D. M., Anderson, T. M., Osborne, C. P., Strömberg, C. A. E., Forrestel, E. J., & Still, C. J. (2015). Biogeographically distinct controls on C₃ and C₄ grass distributions: merging community and physiological ecology. Global Ecology and Biogeography, 24(3), 304–313. doi:10.1111/geb.12265
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  • 24
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  • 3
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  • DG was supported by National Science Foundation Graduate Research Fellowship under Grant No. 0907738 and National Evolutionary Synthesis Center (NESCent), NSF #EF-0905606.
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