Responses to nonaeration and/or salinity stress in hydroponically cultured Populus nigra and Populus alba cuttings

Growth, photosynthesis, and Na+, K+, Ca2+, and Mg2+ distributions were examined in two-year-old hydroponically cultured Populus nigra and Populus alba cuttings exposed to salt stress (0, 50, or 100 mM NaCl) for four or six weeks and to nonaeration stress for one or three weeks, followed by a three-week aeration period in 2/5 Hoagland solution. Salt stress with 100 mM NaCl totally inhibited height increase in P. nigra cuttings. Combined salinity and nonaeration inhibited height increase to a greater degree than either stress alone in both species. Simple salt stress did not affect diameter increase in P. alba, whereas combined high salinity (100 mM NaCl) and nonaeration inhibited diameter increase. Growth and biomass accumulation were more sensitive to salt stress in P. nigra cuttings than in P. alba, although P. alba showed a more rapid decrease in photosynthesis in response to nonaeration stress. Ion distributions in the leaves and roots differed between species. P. alba was superior to P. nigra in terms of Na+ exclusion capacity, such that most of the absorbed Na+ was confined to the root system, with little reaching the leaves. The distributions of K+, Ca2+, and Mg2+ in the leaves and roots of each species under the two stressors were also analyzed. The lower Na+/K+ ratio in leaves indicated that P. alba was more tolerant to salt stress than P. nigra.