New Zealand Journal of Botany abstracts

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Salt-tolerance of the coastal plant, Tetragonia trigyna Banks et Sol. ex Hook, (climbing New Zealand spinach)

C. B. WATKINS*
J. M. A. BROWN
F. I. DROMGOOLE

Department of Botany
University of Auckland
Private Bag, Auckland
New Zealand

Present Address:Division of Horticulture and Processing, DS1R, Private Bag, Auckland, New Zealand. Abstract A field and laboratory study of the salt tolerance of Tetragonia trigyna has been carried out. The mineral element composition of the soil in native sand dune and cliff habitats of the plant showed that the concentrations of extractable sodium, chloride, potassium, magnesium, calcium, phosphorus, and total nitrogen varied, probably reflecting differences in exposure, leaching, and ageing processes. Sodium and chloride ion concentrations were lower than those found in fully saline soils and never exceeded those of the predominant cation, calcium. However, T. trigyna accumulated sodium and chloride ions, particularly in its leaves, in high amounts relative to those of potassium, calcium, magnesium, and total phosphorus. Such accumulations of sodium and chloride are a noted halophytic attribute but it is suggested that these may also aid survival in low soil moisture conditions. Total nitrogen concentrations were often comparable with those found in cultivated pasture plants despite low concentrations in some soils. The growth response of T. trigyna to NaCl in water culture was similar to that of a salt-tolerant nonhalophyte or marginal halophyte; plant fresh weights were not stimulated by any NaCl concentration and were only severely inhibited above 150 mM whereas dry weights declined rapidly above 20 mM. However, T. trigyna showed several adaptations which could aid survival under saline conditions. The water content of leaves and stems increased, the growth of leaves and roots was less sensitive to salt stress than that of stems, and leaf areas were relatively less depressed than were leaf numbers. Also, the plant responded to increasing NaCl concentrations by accumulating sodium and chloride ions in its leaves to levels typical of those of halophytes. It is suggested that T. trigyna is a marginal halophyte rather than a salt-tolerant glycophyte.

Keywords ecophysiology; sand dune; cliff; sodium chloride; growth; semihalophyte; Tetragonia trigyna

Received 30 September 1986; accepted 23 December 1986
New Zealand Journal of Botany, 1988, Vol. 26: 153-162
0028-825X/88/2601-153$2.50/0 © Crown Copyright 1988

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