Journal
AGRICULTURAL AND FOREST METEOROLOGY
Volume 287, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.agrformet.2020.107930
Keywords
Agroecosystem; Agricultural drought; Ecosystem stomatal conductance; Vapor pressure deficit; Soil water content
Categories
Funding
- NASA New Investigator Award
- NASA Carbon Monitoring System Award [NNX16AI56G, 80NSSC18K0170]
- Illinois Water Resources Center (IWRC)
- USDA National Institute of Food and Agriculture (NIFA) [2017-67013-26253]
- DOE Early Career grant
- NASA [NNX16AI56G, 903006] Funding Source: Federal RePORTER
- NIFA [2017-67013-26253, 914657] Funding Source: Federal RePORTER
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The U.S. Corn Belt, the worlds biggest production region for corn and soybean combined, is prone to droughts. Currently 92% of the U.S. Corn Belt croplands are rainfed, and thus are sensitive to interannual climate variability and future climate change. Most prior studies identify the lack of soil moisture as the primary cause of agricultural drought impacts, although water-related stresses are also induced by high atmospheric water demands (i.e., vapor pressure deficit, VPD). Here we empirically attributed the variability of canopy-level stomatal conductance (Gs) and gross primary productivity (GPP) to VPD and soil water supply (i.e. volumetric soil water content, SWC), using eddy-covariance data from seven AmeriFlux eddy covariance sites in maize and soybean fields across the U.S. Corn Belt, which are well represented for the current rainfed part of the Corn Belt croplands. We used three independent approaches, including two statistical models (i.e. a multiple-linear regression model and a semi-empirical, non-linear model) and information theory, to quantify the relationship of Gs (or GPP) with VPD and SWC. The attribution result from the two models shows that VPD explains most of Gs variability (91% and 89%, respectively), and mutual information also attributed 91% of GPP variability to VPD. This finding was robust over the gradients of rainfall and temperature, crop types (maize vs. soybean), and management practices (whether irrigated or not). We reconciled our finding with the previously emphasized importance of precipitation and SWC, by conducting a path analysis, which revealed the causal relationships between precipitation, air temperature (Ta), relative humidity (RH), VPD, SWC, and Gs. We find that precipitation impacts on Gs through reduced RH and Ta to VPD (rather than directly through SWC). With increased VPD robustly projected under climate change, we expect increased crop water stress in the future for the U.S. Corn Belt.
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