Response of Ecosystem Productivity to High Vapor Pressure Deficit and Low Soil Moisture: Lessons Learned From the Global Eddy‐Covariance Observations

Abstract

Although there is mounting concern about how high vapor pressure deficit (VPD) and low soil moisture (SM) affect ecosystem productivity, their relative importance is still under debate. Here, we comprehensively quantified the relative impacts of these two factors on ecosystem gross primary production (GPP) using observations from a global network of eddy‐covariance towers and two approaches (sensitivity analysis and linear regression model). Both approaches agree that a higher percentage of sites experience GPP reduction from high VPD than from low SM over the growing season. However, the constraint of high VPD and low SM on GPP reduction is tightly linked with climates and plant functional types. Humid and mesic ecosystems including forests and grasslands are dominated by VPD, while the semi‐arid and arid ecosystems including shrublands and savannas are dominated by SM. The varying dominant role of these two factors on GPP is closely related to plant stomatal behavior, as predicted by a stomatal conductance model. Additionally, we highlight the non‐linear impact of SM on GPP during droughts and the possible underestimation of the SM effects for deep‐rooted plants when only using surface‐layer SM. Our results shed light on a better understanding of the impacts of VPD and SM on vegetation productivity, with important implications for modeling the response and feedback of ecosystem dynamics to current and future climates.

The Respective Effects of Vapor Pressure Deficit and Soil Moisture on Ecosystem Productivity in Southwest China

“…SM and VPD are strongly coupled, and the experiment requires a reduction in the coupling of the two elements to better investigate the influence of each on regional ecosystem production [10]. This experiment employs a data-binning approach [35,36] to reduce the strong coupling correlation between SM and VPD, which is performed as follows. The data binning process is outlined as follows: For each pixel, we established the 10th, 20th, and up to the 100th percentile thresholds for both SM and VPD.…”

Developing a Multivariate Agro‐Meteorological Index to Improve Capturing Onset and Persistence of Droughts Utilizing Vapor Pressure Deficit and Soil Moisture

“…It is worth stating that VPDSDI aims to detect both agricultural and meteorological droughts, considering the impacts on soil, and atmosphere. While reductions in gross primary production (GPP) are more attributable to high VPD rather than low SM according to Xu et al (2023), our index incorporates both VPD and SM to capture the combined effects on agricultural systems (measured by SM). Besides, VPD plays a significant role in controlling topsoil moisture, while precipitation predominantly affects deeper soil layers.…”