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.
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