Incorporating plant hydraulics improves modeled ecosystem response to environmental stress

Abstract:

Plant response to environmental stress has direct impacts on ecosystem carbon and water cycling. A central challenge to modeling plant response to water limitation and atmospheric drought is accurately capturing stomatal regulation of carbon uptake and water use. Recent modeling advancements aimed at improving accuracy have incorporated mechanistic representations of plant hydraulic functioning using measurable plant trait information. We evaluate these advancements by implementing several model formulations of stomatal functioning and plant hydraulics into a multilayer canopy model. Specifically, we compare model response to soil moisture limitations and atmospheric drought conditions against observational estimates of carbon uptake and evapotranspiration from a long running AmeriFlux site that experiences seasonally dry conditions. This site is well instrumented with supporting measurements of sap flow, soil moisture, and leaf temperature which make it a valuable testbed for thorough model evaluation. Sapflow measurements indicate that high mid-day atmospheric vapor pressure deficits constrain transpiration. We found that this response is well captured by stomatal optimization modeling approaches, particularly when soil moisture is limiting. Additionally, we found that implementing hydraulic constraints on modeled stomatal conductance alter the simulated water use efficiency, which impacts the evolution of soil water limitations throughout the dry season. We conclude that model formulations generally perform similarly but start to diverge under extreme environmental conditions which has repercussions on simulated ecosystem resilience. Collectively, these results indicate that accurately capturing plant hydraulics in ecosystem models may alter carbon and water exchanges and feedbacks on climate variability and change.