The increasing frequency of dry periods in many regions of the world and the problems associated with salinity in irrigated areas frequently result in the consecutive occurrence of drought and salinity on cultivated land. Currently, 50% of all irrigation schemes are affected by salinity. Nutrient disturbances under both drought and salinity reduce plant growth by affecting the availability, transport, and partitioning of nutrients. However, drought and salinity can differentially affect the mineral nutrition of plants. Salinity may cause nutrient deficiencies or imbalances, due to the competition of Na+ and Cl– with nutrients such as K+, Ca2+, and NO$ _3^- $. Drought, on the other hand, can affect nutrient uptake and impair acropetal translocation of some nutrients. Despite contradictory reports on the effects of nutrient supply on plant growth under saline or drought conditions, it is generally accepted that an increased nutrient supply will not improve plant growth when the nutrient is already present in sufficient amounts in the soil and when the drought or salt stress is severe. A better understanding of the role of mineral nutrients in plant resistance to drought and salinity will contribute to an improved fertilizer management in arid and semi‐arid areas and in regions suffering from temporary drought. This paper reviews the current state of knowledge on plant nutrition under drought and salinity conditions. Specific topics include: (1) the effects of drought and salt stress on nutrient availability, uptake, transport, and accumulation in plants, (2) the interactions between nutrient supply and drought‐ or salt‐stress response, and (3) means to increase nutrient availability under drought and salinity by breeding and molecular approaches.

, H. 1998. Physiological responses of plants to salinity: A review. Can. J. Plant Sci. 78: 19-27. Root-zone salinization presents a challenge to plant productivity that is effectively countered by salt-tolerant halophytic plants, but unfortunately, much less successfully by major crop plants. The way in which salt affects plant metabolism is reviewed. Cellular events triggered by salinity, namely salt compartmentation, osmotic adjustment and cell wall hardening are connected to the whole plant responses, namely leaf necrosis, altered phenology and ultimately plant death. The roles of ion exclusion and K/Na discrimination in mediating crop response to salt appear to be central to the tolerance response, but they are by no means essential. The processes involved in regulating ion uptake at the membrane level are considered. Recent work elucidating the interaction between calcium and salinity tolerance is reviewed.Key words: Cell growth, cell turgor, ion regulation, K + /Na + discrimination, osmotic adjustment, salt tolerance Volkmar, K. M., Hu, Y. et Steppuhn, H. 1998. Réponse physiologique des plantes à la salinité: Mise au point bibliographique. Can. J. Plant Sci. 78: 19-27. La salinisation de la rhizosphère est un obstacle à la productivité végétale, qui est exploité avec succès par les plantes halophytes (tolérantes au sel), mais qui est beaucoup plus difficile à surmonter pour les principales espèces cultivées. Les auteurs présentent une mise au point bibliographique des effets des sels sur le métabolisme végétal. Les phénomèmes cellulaires déclenchés par la salinité, notamment la compartimentation des sels, les adaptations osmotiques, le durcissement des parois cellulaires sont reliés aux réactions de la plante, nécrose foliaire, perturbation phénologique et finalement la mort. L'exclusion et la discrimination K/Na dans la médiation des réponses de la plante semblent être au centre des réactions de tolérance, encore qu'elles ne soient en aucun point essentielles. Les auteurs analysent les mécanismes impliqués dans la régulation de l'absorption ionique au niveau membranaire. Ils passent également en revue les travaux récents éclairant l'interaction entre le calcium et la tolérance à la salinité. Mots clés:Croissance cellulaire, turgesgence de la cellule, régulation ionique, discrimination K + /Na + , adaptation osmotique, tolérance au sel A generalized model of plant response to salt stress will be described, relating the whole-plant manifestations of root-zone salinity to initial responses to soil salinity at the cellular level. PRINCIPLESThere is a continuous spectrum of plant tolerance to saline rooting media, ranging from very sensitive glycophytes showing the effects of salt at concentrations of less than 1/10 sea water (50 mol m -3 ), to halophytes, that complete their life cycles at 500 mol m -3 (Flowers et al. 1986; Ungar 1991). The halophyte, Suaeda maritima, for example, exhibits a growth optimum of around 200 mol m -3 and is able to tolerate root zone salinity levels up to 1000 mol m -3 (Clipson et...

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Arbuscular mycorrhizal fungi alleviate drought stress in their host plants via the direct uptake and transfer of water and nutrients through the fungal hyphae to the host plants. To quantify the contribution of the hyphae to plant water uptake, a new split-root hyphae system was designed and employed on barley grown in loamy soil inoculated with Glomus intraradices under well-watered and drought conditions in a growth chamber with a 14-h light period and a constant temperature (15 degrees C; day/night). Drought conditions were initiated 21 days after sowing, with a total of eight 7-day drying cycles applied. Leaf water relations, net photosynthesis rates, and stomatal conductance were measured at the end of each drying cycle. Plants were harvested 90 days after sowing. Compared to the control treatment, the leaf elongation rate and the dry weight of the shoots and roots were reduced in all plants under drought conditions. However, drought resistance was comparatively increased in the mycorrhizal host plants, which suffered smaller decreases in leaf elongation, net photosynthetic rate, stomatal conductance, and turgor pressure compared to the non-mycorrhizal plants. Quantification of the contribution of the arbuscular mycorrhizal hyphae to root water uptake showed that, compared to the non-mycorrhizal treatment, 4 % of water in the hyphal compartment was transferred to the root compartment through the arbuscular mycorrhizal hyphae under drought conditions. This indicates that there is indeed transport of water by the arbuscular mycorrhizal hyphae under drought conditions. Although only a small amount of water transport from the hyphal compartment was detected, the much higher hyphal density found in the root compartment than in the hyphal compartment suggests that a larger amount of water uptake by the arbuscular mycorrhizal hyphae may occur in the root compartment.

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Although the mechanisms of salt tolerance in plants have received much attention for many years, genotypic differences influencing salt tolerance still remain uncertain. To investigate the key physiological factors associated with genotypic differences in salt tolerance of wheat and their relationship to salt stress, 13 wheat genotypes from Egypt, Australia, India, and Germany, that differ in their salt tolerances, were grown in a greenhouse in soils of 4 different salinity levels (control, 50, 100, and 150 mm NaCl). Relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), photosynthesis, chlorophyll content (SPAD value), and leaf water relations were measured at Days 45 and 60 after sowing. Mineral nutrient content in leaves and stems was determined at Day 45 and final harvest. Salinity reduced RGR, NAR, photosynthetic rate, stomatal conductance, water and osmotic potentials, and K+ and Ca2+ content in stems and leaves at all times, whereas it increased leaf respiration, and Na+ and Cl– content in leaves and stems. LAR was not affected by salinity and the effect of salinity on SPAD value was genotype-dependent. Growth of salt-tolerant genotypes (Sakha 8, Sakha 93, and Kharchia) was affected by salinity primarily due to a decline in photosynthetic capacity rather than a reduction in leaf area, whereas NAR was the more important factor in determining RGR of moderately tolerant and salt-sensitive genotypes. We conclude that Na+ and Cl– exclusion did not always reflect the salt tolerance, whereas K+ in the leaves and Ca2+ in the leaves and stems were closely associated with genotypic differences in salt tolerance among the 13 genotypes even at Day 45. Calcium content showed a greater difference in salt tolerance among the genotypes than did K+ content. The genotypic variation in salt tolerance was also observed for the parameters involved in photosynthesis, and water and osmotic potentials, but not for turgor pressure.

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