Differential effects of extreme drought on production and respiration: synthesis and modeling analysis

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

Biotic and climatic controls on interannual variability in carbon fluxes across terrestrial ecosystems

“…Climatic stresses affected photosynthesis and respiration differentially (Shi et al, 2014). In general, GPP was more sensitive to drought than RE (Schwalm et al, 2010).…”

“…while heterotrophic respiration was a C pool-controlled process at the situation of long-term drought (Shi et al, 2014). In addition, although the thermal acclimation of photosynthesis and respiration was found widely at both species and ecosystem scales, the different responses of these two processes to low temperature have not been well studied (Atkin and Tjoelker, 2003;Way and Yamori, 2014;Niu et al, 2012).…”

Rain events decrease boreal peatland net CO2 uptake through reduced light availability

“…These authors showed in a climate chamber experiment that rewetting by rain may be too brief for peatmoss to offset the autotrophic respiration cost associated with restarting their photosynthetic machinery. From other ecosystems, it is known that rain frequency, intensity and duration may have a larger impact on key carbon cycling processes than the total rain amount, indicating that rain characteristics are important controls on the carbon balance (Knapp et al, 2002;Shi et al, 2014;Xu et al, 2013). Small rain events may, for example, trigger short-term bursts of heterotrophic respiration in semi-arid ecosystems due to increased water and substrate availability, whereas larger rain events may also stimulate photosynthesis (Lee et al, 2004;Schwinning & Sala, 2004;Unger et al, 2010).…”

Model–data fusion approach to quantify evapotranspiration and net ecosystem exchange across the sagebrush ecosystem at different temporal resolutions

“…Different sensitivity of GPP and R e to those 2 months reflects the complex relationship between carbon exchange and varying intensity of precipitation ( Figure 11; Ciais et al, 2005;Resco et al, 2009;Jentsch et al, 2011;Shi et al, 2014). As the balance between GPP…”