Tolerance and recovery responses of playa halophytes to light, salinity and temperature stresses during seed germination

Halogeton glomeratus (M. Bieb.) C.A. Mey., Lepidium tantalum Linn. and Peganum harmala Linn. are distributed in temperate salt playa habitats of Upper Hunza, Pakistan. Seeds were germinated under various salinity (0-500 mM NaCl), light (12 h-light: 12 h-dark and 24 h-dark) and temperature (5/15, 10/20, 15/25, 20/30, and 25/35 degrees C, dark/light) regimes for 20 days to determine the optimal conditions for germination and recovery of seeds from these factors when exposed to less than optimal conditions. Seeds that failed to germinate in dark were transferred successively to 12 h-photoperiod, salinity to distilled water and from various temperature regimes to 20/30 degrees C. to determine the effect of these stresses and the ability of these seeds to recover respectively. Highest seed germination (H. glomeratus and L latifolium: 100%; P. harmala: 80%) was obtained in non-saline control at 20/30 degrees C in 12 h-photoperiod, however, increase in salinity progressively inhibited seed germination. Seed germination of H. glomeratus and P. harmala was substantially inhibited and that of L. latifolium was prevented in dark. Salinity and dark treatments have a synergistic effect in inhibiting seed germination of all species. No seed of any species germinated at 5/15 degrees C; germination was substantially inhibited at 25/35 degrees C both for H. glomeratus and P. harmala while L latifolium failed to germinate at 25/35 degrees C. Rate of germination also decreased with an increase in salinity at all temperature regimes but this effect was minimal at optimal temperature regime of 20/30 degrees C. After successive elimination of light, salinity and temperature stresses, final seed germination was identical to respective controls. The results indicate that seeds of these temperate halophytes could endure environmental stresses without losing viability and germinate readily when these stresses are removed. Under the extremely variable conditions of the playa habitat these species are highly opportunistic exploiting the windows of opportunity available during spring or early summer. (C) 2010 Elsevier GmbH. All rights reserved.