Ecosystem and Atmosphere Water and Carbon Exchanges at the Extremes
Abstract
The climate is getting drier and hotter throughout many of Earth's dryland regions. With these changes, dryland ecosystems are experiencing more extreme climate conditions that are expected to alter their exchanges of water and carbon with the atmosphere. Under normal conditions, these exchanges are closely linked and conform to stomatal optimality, but evidence from plant-level and limited ecosystem-level studies suggest that they may become decoupled during extremes of temperature and/or atmospheric dryness. In this presentation, we use data from unique, long-term, riparian woodland and grassland eddy covariance sites that access groundwater but are subject to the hot and dry conditions of their semiarid climate. At these sites, transpiration is not constrained by soil water, but may be limited by plant hydraulics. We address the coupling between water and carbon exchanges by examining the behavior of canopy-scale stomatal conductance and water use efficiency under normal versus hot and/or dry extremes and compare this coupling between the c4-photosynthesis of the grassland and the c3-photosynthesis of the woodland. Given that stomatal conductance responds to leaf water status which tends to decrease with an increase in water loss from leaves (high VPD) or a decrease in water supply (low soil moisture), we also contrast these results with the functioning of nearby upland sites where the plant water use is closely tied to ephemeral, near-surface soil moisture. Does perpetual access to water at the riparian site allow stomata to remain more open during conditions of high atmospheric dryness than stomata in similar non-riparian systems even when soil moisture is not limiting? Observed differences in water use efficiency between these sites and species contribute to a mechanistic understanding of how drylands may respond to hotter conditions, independent of changing precipitation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMB053...06S
- Keywords:
-
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0495 Water/energy interactions;
- BIOGEOSCIENCES