Halophyte and glycophyte salt tolerance at germination and the establishment of halophyte shrubs in saline environments

摘要

Saline sites suffer variations in surface salinity, available soil water, temperature, soil crust strength and other factors which can influence germination and establishment. For establishment to occur the germinating seed must capitalise on a window of opportunity. This window can be widened by placing seeds in a low-salt niche, covering the seeds with a mulch (such as vermiculite), spraying the seed and mulch placement with a coating which may stabilise the favourable situation and raise soil temperature. In this paper it is shown that using seeds collected from plants of Atriplex amnicola which produce many volunteer seedlings in their vicinity can assist establishment from direct seeding. These seeds had the ability to germinate under saltier and cooler conditions than seeds from A. amnicola bushes which did not produce volunteers. Seeds of a halophyte (Atriplex lentiformis) and a non-halophyte (Medicago sativa) are able to imbibe water from a saline substrate in a similar manner. The water enables the seeds of both species to mobilise stored growth materials and produce and elongate radicles. When the seedlings try to erect a hypocotyl and spread their cotyledons, the non-halophyte, in a saline medium, becomes flaccid, distorted and dies. The halophyte seedling shows evidence of high salt tolerance in the form of succulence of cotyledons and trichomes on true leaves even before they are visible and goes on to successfully develop a functioning plant. Nevertheless, germination of halophyte seeds is inhibited or severely reduced at salinity levels above 250 mM NaCl and slowed and reduced progressively up to those levels.