Phylogenetic Underpinning of Groundwater Use by Trees

Abstract

Transpiration mediates the transfer of water and energy between the land surface and the atmosphere (Fan et al., 2017;Good et al., 2015), impacting the regulation of climate and distribution of vegetation over land (Beerling & Berner, 2005). Trees play a particularly relevant role in water and energy transfer because they exhibit a wide range of maximum rooting depths (RD MAX ). This suggests that trees may be able to access groundwater that is not immediately available for evaporation. Root water uptake (RWU) of local soil moisture and groundwater by trees thereby influences the partitioning of precipitation between surface runoff (immediate streamflow), water infiltrating into forest soils (i.e., catchment stored water) and transpiration. Establishing a possible environmental and physiological basis for RD MAX and RWU patterns is specifically important because current ecohydrological models at catchment and continental scales tend to oversimplify RWU strategies (Warren et al., 2015). These simplifications in turn limit model veracity and utility for predicting future global change (

Parameterizing Vegetation Traits With a Process‐Based Ecohydrological Model and Xylem Water Isotopic Observations

“…Both δ XYLEM datasets indicated that approximately 2/3 of hemlock‐transpired water was taken up by roots from the shallowest 30 cm of soils during the summer season. This finding is also in general agreement with observations of a reliance on shallow water uptake by conifers (Allen et al., 2019; Knighton et al., 2021). The lack of a significant correlation between K ROOT and DBH conflicts with empirical analysis of this data set (Li & Knighton, 2022).…”

“…Though recent progress supports possible identification of individual species in mixed‐species stands (Mäyrä et al., 2021; Onishi & Ise, 2021; Schiefer et al., 2020), widely available vegetation index products (e.g., Normalized Difference Vegetation Index (NDVI), Vegetation Optical Depth (VOD)) may accurately support trait estimation for distinct species in mixed stands (Didan, 2015; Moesinger et al., 2020). Phylogenetic models can potentially predict traits from the underlying genetic relationships among plants; however, these methods are largely unvalidated (L. D. L. Anderegg et al., 2022; Knighton et al., 2021). New methods of estimating plant hydraulic traits could remove a significant barrier to progress in the study and simulation of soil‐water‐plant interactions.…”

“…Isotopes ( 2 H, 18 O) in plant xylem water ( δ XYLEM ) are of particular importance in ecohydrological studies as they support developing reliable estimates of root water uptake (RWU) depth distributions (Beyer et al., 2018; Miguez‐Macho & Fan, 2021; Rothfuss & Javaux, 2017), water storage within vegetation (Knighton, Kuppel, et al., 2020; Knighton, Singh, & Evaristo, 2020), and the partitioning of evapotranspiration into plant transpiration and evaporation from bare soils (Good et al., 2015; Rothfuss et al., 2021). Xylem water isotopic data have strengthened our understanding of biome‐scale variations in vegetation water use (Allen et al., 2019; Barbeta & Peñuelas, 2017; Evaristo & McDonnell, 2017; Knighton et al., 2021; Tetzlaff et al., 2021) and subsurface resource partitioning in mixed‐species ecosystems (Brum et al., 2019; Gaines et al., 2016; Knighton, Conneely, & Walter, 2019; Knighton, Souter‐Kline, et al., 2019; Magh et al., 2020).…”

“…Observations of water isotopes in xylem represent the mixture of all water sources taken up by vegetation roots across some representative timescale (Knighton, Kuppel, et al., 2020; Knighton, Singh, & Evaristo, 2020; Seeger & Weiler, 2021). Observed δ XYLEM is highly variable because of both variations in rooting depths across species (Knighton et al., 2021), and within‐species variations which are dependent on local hydrologic conditions (Fan et al., 2017). Field measurement of δ XYLEM is a resource intensive practice (Freyberg et al., 2020), often limiting the temporal frequency and feasible number of trees that can be sampled.…”

“…Our capacity to simulate terrestrial water storage, vegetation water use, tree drought mortality risk, and the hydrologic consequences of forest species composition change is dependent on our understanding of soil‐water‐plant interactions, particularly plant traits influencing rooting strategies, stomatal conductance, and tree water storage (W. R. L. Anderegg, 2015; Feldman et al., 2021; Kannenberg et al., 2022; Konings et al., 2021). Process‐based representations of vegetation‐water interactions are rapidly improving such that complex plant responses to water stress can be reliably simulated where sufficient empirical data are available to constrain the model parameterizations of vegetation (Berzaghi et al., 2020; Cochard et al., 2021; Fisher et al., 2018; Maneta & Silverman, 2013; Matheny et al., 2017; Mirfenderesgi et al., 2016; Silva et al., 2022; Simeone et al., 2019; Stephens et al., 2021); however, hydrologic characterization of the critical zone (Beyer & Penna, 2021; Goldsmith et al., 2019), measurement of vegetation water contents (Novick et al., 2022), and identification of plant hydraulic traits (L. D. L. Anderegg et al., 2022; Knighton et al., 2021; Matheny et al., 2017) to support such modeling is challenging.…”