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Accueil du site → Doctorat → Australie → 2012 → Responses of the halophyte Atriplex nummularia to non-uniform salinities in the root-zone

University of Western Australia (2011)

Responses of the halophyte Atriplex nummularia to non-uniform salinities in the root-zone

Bazihizina, Nadia

Titre : Responses of the halophyte Atriplex nummularia to non-uniform salinities in the root-zone

Auteur : Bazihizina, Nadia

Université de soutenance : University of Western Australia

Grade : Doctor of Philosophy (PhD) 2011

Résumé
Salinity of the soil solution in soils growing halophytes can reach extreme values, but salinity is often not uniform across sites. There is a surprising deficiency in knowledge of halophyte physiology under non-uniform salinity ; almost all experiments have applied uniform root-zone treatments. Atriplex nummularia was used in this thesis as a model halophytic plant to elucidate responses to non-uniform salinity in the root-zone. A split-root system with two pots was used to expose roots of plants for 21 days to either uniform or two different levels of salinity. The aims were to : (a) determine how growth, water and ion relations are affected in plants subject to laterally non-uniform moderate to extreme (up to 1500 mM NaCl) salinity ; (b) understand water uptake patterns, and in particular determine whether water uptake from the high-salt side is maintained ; (c) evaluate under non-uniform salinities whether various physiological parameters (shoot and root growth, stomatal conductance, water relations, and Na+, K+ and Cl- concentrations in leaves) are determined mostly by the low- or high-salt sides, or an average of the two salt concentrations in the root-zone. Overall, the research shows that A. nummularia was able to grow with up to 1500 mM NaCl in one root half, a level that when uniform in the root-zone completely inhibited shoot and root growth. Growth (shoot elongation and ethanol-insoluble dry mass), leaf gas exchange and leaf Na+ and Cl- concentrations responded to the ’root-weighted average’ salinity of the root-zone (i.e. mean NaCl concentration ’root-weighted’ for root ethanol-insoluble dry mass in the low and high-salt sides). As a consequence of A. nummularia having optimal growth in the 10–400 mM NaCl range, when the ’rootweighted average’ salinity in the root-zone was in the 120 to 340 mM NaCl range, shoot and root growth were both similar to that of control plants with 10 mM NaCl in both root halves.
Interestingly, as compensatory root growth in the 10 mM NaCl side (40% increase in ethanol-insoluble dry mass) was observed when the high-salt side contained 1500 mM NaCl, the root-weighted average salinity (316 mM) in the root-zone was still within the optimal zone, and therefore growth was similar to that of control plants (uniform 10 mM NaCl). This split-root treatment contrasted markedly to plants with uniform 1500 mM NaCl in the root-zone, for which there was no ethanol-insoluble dry mass increase and most leaves showed chlorosis by 21 days. One parameter that did not respond to the root-weighted average salinity of the rootzone was shoot water potential. Under non-uniform salinity plants took up water mostly from the low-salt side and, consequently, midday shoot water potentials under nonuniform conditions resembled those of plants grown under uniform conditions at the lower salinity level.... As A. nummularia, like most dicotyledonous halophytes, showed optimal growth in the 10- 400 mM NaCl range, if the root-weighted average salinities in the root-zone are within that range, plants can express optimal growth even with severe salinities in one root half. Given the intrinsic heterogeneity of saline landscapes, preferential root growth and water uptake in less saline areas could potentially explain the presence of halophytic vegetation on sites even with high to extreme areas of soil salinity. This study adds to the knowledge of halophyte physiology, which has previously been studied over a range of uniform salinities in the root-zone.

Mots clés : Salt-bush ; Water use ; Split-root system ; Atriplex ; Crops and water ; Salt-tolerant crops—Physiology ; Halophytes

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Page publiée le 7 novembre 2011, mise à jour le 30 mai 2017