Study of the photosynthesis characteristics and physical signs of four plants at the desert-oasis ecotone The Developmental and Physiological Responses of Amorpha fruticosa to Different Soil Moisture Contents under Lead Stress during Initial Growth Stage Photosynthetic and physiological characteristics of introduced plants at the desert-oasis ecotone Effects of salicylic acid on growth and photosynthetic characteristics of Melilotoides ruthenica in branching stage under different water stress