The environmental adaptation strategy of seed germination, and roles of the seed pappus on dispersal and hypocotyl hairs on seedling anchorage inTamarix ramosissima

Seed dispersal, germination and seedling establishment are affected by various ecological factors in desert plant species. Tamarix ramosissima has evolved multiple strategies to facilitate its survival in harsh environments during the early stages of development. In this study, we investigated the effects of different ecological factors on seed germination and seedling growth, the function of the seed pappus in seed dispersal, as well as the function of the hypocotyl hairs in seedling establishment. We found that the seed germination of T. ramosissima was rapid and could occur under a wide range of temperatures (5-30 °C), after long periods of storage (at least 12 months on dispersal), under high concentrations of salts (700-900 mmol·L-1) and polyethylene glycol (PEG) 6000 (500 g·L-1) and under medium concentrations of alkalis (300-500 mmol·L-1). Lower concentrations of salts and PEG promoted seedling growth. The seed pappus had no effect on seed germination, but it might function as an accessory structure that provides a buoyancy force and promotes long-distance seed dispersal. The hypocotyl hairs located on the edge of the hypocotyl end might aid the upright positioning of the seedlings during early development, especially when seed germination occurs under floating or flooding conditions. In conclusion, the germination of T. ramosissima seeds and seedling development can occur under diverse types of abiotic stress, and the seed pappus and hypocotyl hairs played an important role in seed dispersal and seedling establishment.