Impact of Hydraulic Redistribution on Multispecies Vegetation Water Use in a Semiarid Savanna Ecosystem: An Experimental and Modeling Synthesis

Abstract

A major challenge in critical zone science is to understand and predict the interaction between above‐ground and below‐ground ecohydrologic processes. One process that facilitates this connection is hydraulic redistribution, a phenomenon by which roots serve as preferential pathways for water movement from wet to dry soil layers. We use a multilayer canopy model in conjunction with experimental data to quantify the influence of hydraulic redistribution on ecohydrologic processes in order to characterize the competitive and facilitative interaction between mesquite trees and bunchgrasses in a semiarid savanna. Both measured and simulated results show that hydraulic descent dominates during the wet monsoon season, whereas hydraulic lift occurs between precipitation events. For 2015 year‐long simulation, we find about 17% of precipitation is absorbed as soil moisture, with the rest of the precipitation returning to the atmosphere as evapotranspiration. In the wet season, 13% of precipitation is transferred to deep soil (>1.5 m) through roots, and in the dry season, 9% of this redistributed water is then transported back to shallow soil depths (<0.5 m). Assuming water supplied through hydraulic redistribution is well‐mixed with moisture transported directly through the soil matrix and supports vegetation evapotranspiration, hydraulic redistribution supports 47% of mesquite transpiration and 9% of understory transpiration. Through modeling and experimental synthesis, this study demonstrates that in semiarid savanna ecosystems, mesquite exhibits a competitive advantage over understory bunchgrass through hydraulic redistribution. This analysis evaluates the relationship between two coexisting vegetation types that could be expanded to multiple vegetation species sharing resources in an ecosystem.

Discerning the thermodynamic feasibility of the spontaneous coexistence of multiple functional vegetation groups

“…MLCan has been previously validated for each of the sites considered 30 , 40 . Since entropy cannot be directly measured, we provide a comparison of the model outputted latent heat fluxes with the observed fluxes at each site in Fig.…”

“…SRM has a hot semi-arid climate and consists of woody savannas with mesquite trees ( Prosopis velutina Woot.) and C4 grasses and subshrubs 40 , 41 .…”

Water acquisition, sharing and redistribution by roots: applications to agroforestry systems

“…Hydraulic lift has other side benefits such as higher fine root survival (Bauerle et al 2008), a limited root embolism during the day by refilling xylem conduits at night (Domec et al 2004(Domec et al , 2006Prieto and Ryel 2014) or improved soil nutrient recycling that could benefit both the woody species and associated crops (Aanderud and Richards 2009;Armas et al 2012;Cardon and Gage 2006;Cardon et al 2013;Prieto et al 2012a). For neighboring plants, water that is redistributed to shallow soil layers can also be taken up by plants living in close association to plants engaged in HL enhancing their transpiration and ultimately increasing their survival and biomass production (Bogie et al 2018;Izumi et al 2018;Lee et al 2018;Prieto et al 2011). Nevertheless, the net effects that species engaged in HR have on their neighbors is still unclear (Prieto et al 2012b).…”

Evaluation of seasonal patterns of hydraulic redistribution in a humid subtropical area, East China

“…Vertical changes of Δ θ followed a unimodal distribution, which first increases then reaches a peak and subsequently decreases with increasing soil depth (Figure b). Vertical distribution of HR is considered to be mainly regulated by water potential gradients between shallow and deep soil layers, and between roots and the soil matrix (Domec et al, ; Horton & Hart, ; Lee et al, ; Priyadarshini et al, ). Thus, the bimodal distribution is partly caused by the shallow soil–fractured rock profile (fractured rocks underlying shallow soil) in the study area (Sun et al, 2019a, 2019b), another reason could be due to interactions between plant (root distribution, physiological properties) and soil moisture status.…”

“…Soil water status is regulated by many factors, such as precipitation, evapotranspiration, and soil properties (Huang et al, ; Nishat, Guo, & Baetz, ; Ojha, Morbidelli, Saltalippi, Flammini, & Govindaraju, ; Xu et al, ). However, despite those factors, plant roots can release water to the soil profile, and this phenomenon has been observed in different species across multiple systems (Lee et al, ; Neumann & Cardon, ). Hydraulic redistribution (HR) is used to describe this process by which water is distributed (typically at night) from moist soil to drier soil via plant roots (Bazihizina, Veneklaas, Barrett‐Lennard, & Colmer, ; Brooks, Meinzer, Coulombe, & Gregg, ; Dawson, ; Richards & Caldwell, ).…”