Biogeosciences Discuss., 10, 16043-16074, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG.
Differential effects of extreme drought on production and respiration: synthesis and modeling analysis
Z. Shi1, M. L. Thomey2, W. Mowll3, M. Litvak2, N. A. Brunsell4, S. L. Collins2, W. T. Pockman2, M. D. Smith3, A. K. Knapp3, and Y. Luo1
1Department of Microbiology and Plant Biology, University of Oklahoma, OK, USA
2Department of Biology, MSC03-2020, University of New Mexico, Albuquerque, NM 87131, USA
3Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA
4Department of Geography, University of Kansas, Lawrence, KS 66045, USA

Abstract. Extremes in climate may severely impact ecosystem structure and function, with both the magnitude and rate of response differing among ecosystem types and processes. We conducted a modeling analysis of the effects of extreme drought on two key ecosystem processes, production and respiration, and to provide broader context we complemented this with a synthesis of published results across multiple ecosystems. The synthesis indicated that across a broad range of biomes gross primary production (GPP) generally was more sensitive to extreme drought (defined as proportional reduction relative to average rainfall periods) than was ecosystem respiration (ER). Furthermore, this differential sensitivity between production and respiration increased as drought severity increased. The modeling analysis was designed to better understand the mechanisms underlying this pattern and focused on four grassland sites arrayed across the Great Plains, USA. Model results consistently showed that net primary productivity (NPP) was reduced more than heterotrophic respiration (Rh) by extreme drought (i.e., 67% reduction in annual ambient rainfall) at all four study sites. The sensitivity of NPP to drought was directly attributable to rainfall amount, whereas sensitivity of Rh to drought was driven by both soil drying and a drought-induced reduction in soil carbon (C) content, a much slower process. However, differences in reductions in NPP and Rh diminished as extreme drought continued due to a gradual decline in the soil C pool leading to further reductions in Rh. We also varied the way in which drought was imposed in the modeling analysis, either as reductions in rainfall event size (ESR) or by reducing rainfall event number (REN). Modeled NPP and Rh decreased more by ESR than REN at the two relatively mesic sites but less so at the two xeric sites. Our findings suggest that responses of production and respiration differ in magnitude, occur on different timescales and are affected by different mechanisms under extreme, prolonged drought.

Citation: Shi, Z., Thomey, M. L., Mowll, W., Litvak, M., Brunsell, N. A., Collins, S. L., Pockman, W. T., Smith, M. D., Knapp, A. K., and Luo, Y.: Differential effects of extreme drought on production and respiration: synthesis and modeling analysis, Biogeosciences Discuss., 10, 16043-16074, doi:10.5194/bgd-10-16043-2013, 2013.
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