Interactive effects of salinity and water stress on growth, leaf water relations, and gas exchange in amaranth(Amaranthusspp.)

Abstract

New Zealand Journal of Crop and Horticultural Science, 2006, Vol. 34: 33^4 0014- Abstract Amaranth (Amaranthus spp.) is a promising vegetable species often grown under semiarid conditions prone to both drought and salinity. This study was initiated to evaluate the effects of water and salinity stresses, both individually and in combination, on plant growth/leaf water relations and gas exchange of two amaranth genotypesAmaranthus tricolor and A. cruentus. Plants were grown in a greenhouse in plastic pots filled with a sand/vermiculite mixture and exposed to 8 days of drought and/or salinity stress, a recovery period of 8 days, followed by a final 2 weeks of stress. The treatments consisted of: (1) unstressed control; (2) 100 mM Nad (salt stress); (3) PEG (polyethylene glycol M w 6000) iso-osmotic to 100 mMNaCl (water stress); and (4) 50 mM NaQ + PEG iso-osmotic to 50 mM NaCl (salt + water stress). Plant growth (leaf, stem, root dry mass, root: shoot ratio, leaf area) were reduced by stress treatments. The reduction in shoot growth was greater in plants subjected to PEG-induced water stress (41% in A. tricolor and 44% in A. cruentus) than in salinised plants (37% in A. tricolor and 27% in A. cruentus). Leaf water and osmotic potentials were reduced by stress treatments whereas turgor potential was largely maintained. Photosynthetic rate, stomatal conductance, and water loss were reduced by all stress treatments. Photosynthetic water-use efficiency was increased by stress and was greater in salinised than in waterstressed plants. Salinised plants and those subjected to salt + water stress had a greater degree of osmotic adjustment, so that plants were able to continue growth for a longer period before drying, compared to water-stressed plants. Most parameters recovered when the stress treatments were discontinued. However, photosynthesis in salt-stressed plants did not recover indicating a toxic effect of salt on the photosynthetic apparatus. The combined effect of salt + water stress is less detrimental to plant growth than the sum of individual stresses.

Response of Wheat Seedlings to Combined Effect of Drought and Salinity

“…Hence, contrary to initial expectations that stress factors had additive nature on plants' performance, the productivity of amaranth was higher at double water-salt stress (Omami and Hammes 2006) that, according to the authors, was associated with reduction of water loss through transpiration and withering of old leaves. Richards (1992) also reported on beneficial effects of salinity on the plants grown in dry soil.…”

“…Reduction of photosynthetic activity at high salt concentrations (0.2 and 0.3 M) can be due to both the decrease of RWC L , and ions toxicity. According to other researchers, among three types of stresses the salinity had really minimal damage to photosynthetic plants' apparatus (Omami and Hammes 2006). This might be due to high water potential of the leaves and turgor maintenance during salinity as compared with the plants at water stresses (Xu et al 1994).…”

“…At succulents (Slama et al 2008), mangrove plants (Atreya et al 2009) and Ipomoea (Sucre and Suárez 2011) similar effect of double stress was on the growth rate of the leaves and their total area. At amaranth in salt stress and in combined water-salt stress, biomass accumulation was higher as compared to the plants at only water stress (Omami and Hammes 2006). Pérez-Alfocea et al (1993) found that several genotypes of tomatoes had similar response to salinity and drought.…”

“…Salinization, water stress, and their combined effect induce strong reduction in photosynthesis (Ouerghi et al 2000;Yousfi et al 2009Yousfi et al , 2010Omami and Hammes 2006). Usually the first symptom of salt and water stress is a reduction of stomatal conductivity that leads to a reduce of transpiration rate and intercellular CO 2 concentration (Tezara et al 2003;Meloni et al 2003;Flexas et al 2004;Rodríguez et al 2005;Ramani et al 2006;Chaves et al 2009; Cha-um and Kirdmanee 2009).…”

“…A decrease in stomatal conductivity is considered to be the main cause of reduction in leaf transpiration at all kinds of stresses (Omami and Hammes 2006;Sucre and Suárez 2011). A decrease of transpiration in salt and water stress in different plant species was observed (Ashraf 2001;Liu and Stützel 2002).…”