H042-04
Plant Hydraulic Transport Controls Transpiration Sensitivity to Soil Water Stress

Tuesday, 8 December 2020: 07:12
Virtual
Xue Feng, University of Minnesota Twin Cities, Civil, Environmental, Geo-Engineering, Minneapolis, MN, United States, Brandon Sloan, University of Minnesota Twin Cities, Civil, Environmental, and Geo-Engineering, Minneapolis, MN, United States and Sally E Thompson, University of Western Australia, Crawley, Australia
Recorded Presentation
Abstract:
Understanding plant water use, or transpiration, in response to soil water stress is crucial for accurately predicting the global energy, water, and carbon cycles. In ecohydrology, the downregulation of transpiration in response to soil water stress has been characterized through a monotonically decreasing function of soil water availability, based on Feddes’s work from 1978. Since then, this empirically derived function has been widely adopted in hydrological and land surface models, although it has been more recently shown to perform poorly under extreme drought conditions. Therefore, there is a need for understanding the theoretical basis for this empirical downregulation function to potentially overcome its limitations while preserving its parsimonious representation of soil water stress.

Here, we adopt a supply versus demand framework that explicitly accounts for the role of plant hydraulic transport to characterize plant water use response to soil water stress. We demonstrate that transpiration under soil water stress lies on a spectrum of plant hydraulic transport limitation, and that the Feddes’s model (in which the effects of soil water stress on transpiration is represented by a single function) is an end-member scenario in which the soil-plant system is infinitely conductive. Furthermore, in a system with finite plant hydraulic conductance, the functional form of Feddes’s model is sensitive to dynamic changes in a theoretical well-watered maximum transpiration (ETww). This ETww differs from classical conceptualizations of aerodynamic or energy derived potential evapotranspiration, and accounts for the roles of atmospheric water demand as well as, importantly, plant hydraulic regulation. These results highlight the limitations of the Feddes’s model under dynamic soil and atmospheric conditions and the importance of utilizing alternate representation of soil water stress in cases where plants can exert strong influences on hydraulic transport.

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