Effects of increasing NaCl concentration on stem elongation, dry mass production, and macro- and micro-nutrient accumulation in Poncirus trifoliata

Abstract

The effects of salinization with 0, 30, 60, 90, and 120 mМ sodium chloride (NaCl) on Poncirus trifoliata (L.) Raf. cv. Pomeroy were studied by means of stem elongation patterns, whole plant and tissue mass production, and mineral nutrient accumulation. The elements analyzed in leaf, stem, structural root and fine root tissues included Na, Cl, P, K, Ca, Mg, Mn, Fe, Cu, Al, and Zn. At the end of the 12-week experimental period, shoot length was reduced 30–80% in the 30 to 120 mМ NaCl treatments. The linear relationship found between stem elongation and salt concentration, and different tissues and salt concentration suggests that a 40–60 mМ NaCl concentration is optimal to test P. trifoliata or its progeny for salt stress. Root production was found to be continuous and plants apparently used this process as an avoidance mechanism to remove excess ions and delay onset of ion accumulation in this tissue. This phenomenon, designated ‘Fine Root Turnover’, is unique to P. trifoliata and may be used as a genetic resource to improve Citrus for salinity tolerance through intergeneric hybridization. Plants were able to delay accumulation of Na ions in leaves but not Cl ions, resulting in high Cl accumulation in leaves and accumulation of both ions in fine roots. The data suggested that, while Cl ions were more toxic in leaf tissues, Na ions were at least as toxic in fine root tissues. Among other nutrients, K was affected the most in response to salinity, decreasing within root tissues and increasing in leaf tissues with increased salin-ization. A similar phenomenon was observed for P levels in salinized tissues. Changes in tissue and whole plant accumulation patterns of the other tested elements as well as possible mechanisms for how excess Na and Cl ions are removed from and/or transported to less vulnerable tissues in Poncirus trifoliata during salinization are discussed.