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Lanzhou University (2013)

Hydraulic Redistribution of Roots and It’s Ecohydrologic Effects for Desert Riparian Plants on the Lower Heihe River

鱼腾飞;Yu Teng Fei

Titre : Hydraulic Redistribution of Roots and It’s Ecohydrologic Effects for Desert Riparian Plants on the Lower Heihe River

Auteur : 鱼腾飞;Yu Teng Fei

Grade : Doctoral Dissertation 2013

Université : Lanzhou University

Résumé partiel
In desert ecosystems, the mainly mechanisms of plants delay dehydration to resist droughts is to increase water income via roots and reduce it expenditure via stoma of leaf. To tolerate drought during dry season, desert also riparian plants undergo hydraulic redistribution (HR), the passive movement of water between different soil parts via plant root systems, driven by water potential gradients in the soil-plant interface. Patterns of HR include hydraulic lift (HL), hydraulic descent (HD), lateral redistribution (LR), foliar uptake (FU) and tissue dehydration (TD). Now, HR has been described in approximately120species that involves a wide variety of ecosystems and a wide range of life forms. Apart from its magnitude, the potential ecohydrologic consequences of HR have attracted recent attention. However, the study status in China is started late, single means and the content focus on HL and the rarely reported refer to ecohydrologic consequences of HR. The objectives of this study were (1) to search for the evidence, quantify the magitude and discuss the ecohydrologic consequences of that the roots of two desert riparian plants, Populus euphratica Oliv. and Tamarix ramosissima Ledeb., carry out HR. To demonstrate HR, we present data on patterns of sap flow in the stems or branches and lateral roots of those two desert riparian species and soil volumetric moisture content where these species grow, and the datas of plant water physiology with different scales also been provided.(1) Patterns of hydraulic redistributionWe not only confirm the previous knowledge on HL of P. euphratica, but also the water can transport from moist topsoil to dry subsoil after rain, i.e. HD. In addition, water also moved from lateral moist soil layer to opposite dry soil layer, i.e. LR. Interestingly, we observed bidirectional flow in the lateral roots of P. euphratica during the time of lateral redistribution, and it may be mediated by stem tissues and, by inference, the radial sectoring in the xylem that the stem base seems in connection with the root xylem. The water absorbing from the wet side adjacent to river was transported to the stem ; the circumferential movement of sap flow around the heartwood becomes available to the downstream flow. Although no direct evidence indicated reverse sap flow of lateral roots and associated HR in T. ramosissima, several factors indicate that HR is occurring :(1) diel fluctuations of volumetric moisture content in the upper soil layer and (ii) the identification of primary water sources as groundwater and vadose zone water through stable isotope studies. The reason of HR not occurred in lateral roots of T. ramosissima was potential nocturnal transpiration suppression. Thus, we inferred that HR occurs in T. ramosissima via adventitious roots rather than via lateral roots.(2) Magitudes and controlling factors of hydraulic redistribution For P. euphratica. the magnitude of HR based on nagitive sap flow in lateral roots was ranged from0.16mm d-1to0.26mm d-1with an average of0.21mm d-1. For T. ramosissima, the magnitude of HR based on diurnal fluctuations of soil volumetric moisture content at20cm to60cm depths was ranged ranged from0.14mm d-1to1.02mm d-1with an average of0.48mm d-1during the growing season, which was far less than that in2011. The correlation and stepwise regression analysis demonstrated that apart from the transpiration tension, the climate and soil moisture availability can accounted for the variation of HR. Specifically, HR was significantly positive correlation with vapor pressure deficit, soil temperature and soil moisture content, instead negative correlation with relative humidity.(3) Hydrological effects of hydraulic redistributionThe effect of HR on soil moisture balance is positive. For example, in T. ramosissima stand, approximately71.00%of the water removed daily (7.59mm) from the upper80cm of soil was replaced by nocturnal hydraulic redistribution (5.42mm) during dry season (14to23July). If hydraulic redistribution had not occurred, the soil water content observed at the end of the10-day monitoring period would have been attained about4days sooner. Because of the increase of soil moisture, the transpiration was also increased that indirectly induced by HR. For P. euphratica. hydraulic redistribution increased transpiration ranged from14.60%to113.04%with an average of38.75%during the growing season.

Mots clés : hydraulic redistribution; desert riparian plants; heat ratio method; soil moisture content; the lower Heihe River;

Présentation (CNKI)

Page publiée le 1er avril 2014, mise à jour le 30 septembre 2017