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Changes to dryland rainfall result in rapid moss mortality and altered soil fertility



Arid and semi-arid ecosystems cover 40% of Earth’s terrestrial surface1, but we know little about how climate change will affect these widespread landscapes. Like many drylands, the Colorado Plateau in southwestern United States is predicted to experience elevated temperatures and alterations to the timing and amount of annual precipitation2,3,4. We used a factorial warming and supplemental rainfall experiment on the Colorado Plateau to show that altered precipitation resulted in pronounced mortality of the widespread moss Syntrichia caninervis. Increased frequency of 1.2 mm summer rainfall events reduced moss cover from 25% of total surface cover to <2% after only one growing season, whereas increased temperature had no effect. Laboratory measurements identified a physiological mechanism behind the mortality: small precipitation events caused a negative moss carbon balance, whereas larger events maintained net carbon uptake. Multiple metrics of nitrogen cycling were notably different with moss mortality and had significant implications for soil fertility. Mosses are important members in many dryland ecosystems and the community changes observed here reveal how subtle modifications to climate can affect ecosystem structure and function on unexpectedly short timescales. Moreover, mortality resulted from increased precipitation through smaller, more frequent events, underscoring the importance of precipitation event size and timing, and highlighting our inadequate understanding of relationships between climate and ecosystem function in drylands.

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Figure 1: Water-induced moss mortality and associated N cycling consequences.
Figure 2: Relationships between rainfall amount and the C balance of the moss S. caninervis.

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This research was supported by the Office of Science (Office of Biological and Environmental Research) US Department of Energy Terrestrial Ecosystem Science programme and the US Geological Survey. We thank C. Cleveland and the University of Montana for access to biogeochemical facilities and office space. We are also indebted to the many field technicians that helped with the project, E. Grote for plot instrumentation and quality control, and D. Liptzin for help with statistical analyses. We are grateful to M. Bowker, M. Weintraub and T. Wertin for comments on a previous draft. Any use of trade names is only for descriptive purposes and does not imply endorsement by the US government.

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J.B. acquired financial support, established the field project and provided overall direction of the field operation. K.K.C. and J.P.S. designed and K.K.C. performed the laboratory research. D.C.H. and T.J.Z. collected moss community data in the field, and S.C.R. performed soil biogeochemical analyses and wrote the initial draft of the manuscript. All authors contributed to the synthesis of data and the finalizing of the manuscript.

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Correspondence to Sasha C. Reed.

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The authors declare no competing financial interests.

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Reed, S., Coe, K., Sparks, J. et al. Changes to dryland rainfall result in rapid moss mortality and altered soil fertility. Nature Clim Change 2, 752–755 (2012).

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