The increasing importance of atmospheric demand in regulating ecosystem functioning

Authors: NOVICK, K.A. - Indiana University; FICKLIN, D. - Indiana University; STOY, P.C. - Montana State University; WILLIAMS, C.A. - Clark University; BOHRER, G. - The Ohio State University; OISHI, A.C. - Us Forest Service (FS); PAPUGA, S.A. - University Of Arizona; BLANKEN, P.D. - University Of Colorado; NOORMETS, A. - North Carolina State University; SULMAN, B. - Princeton University; Scott, Russell - Russ; WANG, L. - Indiana University; PHILLIPS, R.P. - Indiana University

Submitted to: Nature Climate Change
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2016
Publication Date: 9/5/2016
Citation: Novick, K., Ficklin, D., Stoy, P., Williams, C., Bohrer, G., Oishi, A., Papuga, S., Blanken, P., Noormets, A., Sulman, B., Scott, R.L., Wang, L., Phillips, R. 2016. The increasing importance of atmospheric demand in regulating ecosystem functioning. Nature Climate Change. 6:1023-1027. https://doi.org/10.1038/NCLIMATE3114.
DOI: https://doi.org/10.1038/NCLIMATE3114

Interpretive Summary: Plants experience drought stress via two different mechanisms. There is a supply limitation at their roots due to drying soils and an increasing demand for moisture at their leaves due to drier air. The impact of these two drivers of drought stress has historically been difficult to disentangle. Using data collected throughout the U.S. over a broad variety of different ecosystems, we show that, in many ecosystems, atmospheric aridity often independently limits both plant photosynthesis and water use more than soil moisture. This is especially true in forests that are currently the largest sink for atmospheric carbon dioxide. Furthermore, we analyzed future projections from climate models to show that climate change will likely result in nearly universal increases in atmospheric aridity but with more widely varying and inconsistent changes in soil moisture. Consequently, increasing aridity will become increasingly important with climate change. These results suggest that plant responses to future drought stress could diverge from our present conceptual understanding, and management approaches like increasing irrigation amounts during drought may become increasingly ineffective at mitigating plant stress.

Technical Abstract: The profound effects of hydrologic stress on ecosystem productivity, water use, and mortality are driven by two variables – soil moisture supply and atmospheric demand for water. The impact of these two drivers on ecosystem processes has historically been difficult to disentangle, and often the role of atmospheric demand is not adequately represented. Here we show that, in many biomes, atmospheric demand independently limits both surface conductance – a key variable linked to carbon and water cycling – and evapotranspiration as much or more than soil moisture. This is especially true in temperate forests that drive the continental land carbon sink. Furthermore, we leverage projections from 10 general circulation models to show that climate change will drive nearly universal increases in atmospheric demand but more widely varying and inconsistent changes in soil moisture. Consequently, atmospheric constraints will become increasingly important with climate change, accounting for >70% of growing season limitation to surface conductance in forests, for example. These results suggest that ecosystem responses to future hydrologic stress could diverge from our present conceptual understanding, and management approaches that improve soil moisture balance may become increasingly ineffective at mitigating drought stress.