Germination of three threatened halophytes in Castilla-La Mancha under salt-stress conditions

Abstract

The influence of incubation temperature, light, and salinity on seed germination of Arthrocnemum macrostachyum, Senecio auricula, and Lepidium cardamine was studied. Seeds were incubated at constant temperature of 5ºC and fluctuating temperatures of 15-4, 20-7, 25-10, 28-14 y 32-18ºC, both at 12 h-photoperiod and darkness. In fluctuatingtemperature treatments, the highest temperature was programmed to coincide with the light phase. Salt concentration ranged from 0 to 3% NaCl. Seed treatments lasted 30 days. Final germination percentages showed highly significant variations among species. Main effects of temperature, light, and salinity, and interactions of the three factors were highly significant on that parameter as well. Final germination percentage exceeded 68% in all species when seeds were incubated at 20-7ºC, 25-10ºC, 28-14ºC, and 32-18ºC with photoperiod and distilled water. Both percentage and velocity of germination decreased with salt concentration at all temperatures. At 2% NaCl concentration, only A. macrostachyum showed relevant germination percentage (57% at 20-7ºC). Negative correlation between salinity and germination were first manifested at higher temperatures (28-14ºC and 32-18ºC). For most temperatures, A. macrostachyum and L. cardamine seeds reached higher final germination when incubated with photoperiod than in darkness. In S. auricula, however, it was only true for 5ºC. In A. macrostachyum and S. auricula, germination velocity increased when seeds where transferred from hipper-saline solution (4% NaCl) during 6 months to distilled water. That change in salinity conditions also increased final germination of A. macrostachyum seeds when incubated at 15-4ºC. The existence of salt concentrations over 2% NaCl in the natural habitat of the three species studied, may transitorily prevent germination until rainfall reduces salinity in the soil.