Asymmetry in the sensitivity of gross primary productivity to soil moisture and vapor pressure deficit
Abstract
Soil and atmospheric `drought' characterized by different levels of soil water content (SWC) deficit and vapor pressure deficit (VPD) profoundly affect gross primary productivity (GPP) and water use. However, their sensitivities and contributions to GPP variability are largely unclear. We used in situ observations, Earth system models and non-linear machine learning techniques to show that the sensitivity to SWC is strongly depend on the SWC-VPD interactions while the sensitivity to VPD is partly independent on SWC. Even when soil is extremely wet, exposure to high VPD still causes a large negative sensitivity of GPP, e.g. during flash atmospheric drought that do not trigger SWC feedbacks but impacts stomatal closure. Contrary to the response patterns of GPP, surface conductance has a larger negative sensitivity to increasing VPD even at intermediate VPD values, leading to increasing intrinsic water use efficiency during drought. We found that VPD contributes more than SWC to GPP variation under high VPD and for wet soils, but SWC deficit dominates over VPD when soils get dry. Earth system models overestimate the sensitivity of GPP to low SWC and underestimate the sensitivity to extremely high VPD. As both soil and atmospheric dryness will increase dramatically with climate change, our study highlights the importance of correctly evaluating the ecosystem-scale response to changes in aridity and dryness and their threats for the capability and rate of continents to absorb atmospheric carbon dioxide.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMB045...07F
- Keywords:
-
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0495 Water/energy interactions;
- BIOGEOSCIENCES