An experimental and modeling synthesis to determine seasonality of hydraulic redistribution in semi-arid region with multispecies

Hydraulic Redistribution

Lee, Esther ; Kumar ; Praveen

关键词: Hydraulic Redistribution;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/93058/LEE-THESIS-2016.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

A key challenge in critical zone science is to understand and predict the interactionbetween aboveground and belowground eco-hydrologic processes. Roots play an important rolein linking aboveground plant ecophysiological processes, such as carbon, water and energyexchange with the atmosphere, and the belowground processes associated with soil moisture andcarbon, and microbial and nutrient dynamics. In this study, I have analyzed aboveground andbelowground interaction through hydraulic redistribution (HR), a phenomenon that roots serve aspreferential pathways for water movement from wet to dry soil layers. HR process is simulatedby multi-layer canopy model (MLCan) and compared with relative measurements from the fieldto study effect of HR on different plant species where Posopis velutina Woot. (velvet mesquite)and understory co-exist and share resources. The study site is one of Ameriflux sites: Santa RitaMesquite savanna, AZ, with a distinct dry season that indicates occurrence of HR. The model ismodified to better represent Santa Rita Mesquite site where fractions of plants and soil coveragechange from season to season.I analyzed how two plants share and utilize the limited amount of water by HR in bothdry and wet seasons. During dry season, water moves from deep layer to shallow layer throughroots and hydraulic lift (HL) occurs. During wet season, water moves from shallow layer to deeplayer through roots and hydraulic descent (HD) occurs. Mesquites deposit water to deeper soilthrough their roots right after rain to prevent water loss due to surface evaporation. About 40%of precipitation is transferred to deep soil layer with HD and 15% of that is transported back toshallow soil layer with HL in dry season. Assuming water supplied through HL supportsevapotranspiration of plants, HL supports 10% of evapotranspiration. The ratio of mesquite andunderstory root conductivities is an important factor that determines how two plant speciesinteract and share resources in water-limited environment. The sensitivity analysis of rootconductivities suggests that high understory root conductivity facilitates water transported by HR and increases mesquite transpiration and photosynthesis. Understory transpiration andphotosynthesis show increase with HR only in dry season when water is supplied to shallowlayer through HL. With low understory root conductivity, understory looses the competition forwater against mesquite and show decrease in transpiration and photosynthetic fluxes when HR isallowed.