Physiological responses of yellow-horn seedlings to high temperatures under drought condition

Drought and hot stresses are the primary limiting factors for the growth and seed production of yellow-horn (Xanthoceras sorbifolia Bunge), especially in Xinjiang Province of China. A better understanding of its physiological and biochemical characteristics under drought-hot stress is requisite for its efficient cultivation in the arid and semi-arid areas. In this study, the physiological and biochemical responses of 3-month-old yellow-horn seedlings were evaluated after 7 days of treatments of five temperatures (25 degrees C/20 degrees C, 30 degrees C/25 degrees C, 35 degrees C/25 degrees C, 40 degrees C/25 degrees C and 45 degrees C/25 degrees C) under two watering conditions [adequate water supply (HW): 80 +/- 5% FC (field capacity); low water supply (LW): 40 +/- 5% FC] by a pot experiment. The increased temperature (above to 35 degrees C) markedly aggravated the damage on biomass accumulation and membrane integrity of yellow-horn seedlings under the LW. The accumulation of soluble sugars and proteins exhibited a growing trend as the temperature increased from 25 to 40 degrees C, which declined when the temperature was higher than 40 degrees C except for the soluble protein accumulation under HW. In addition, captured responsive characteristics of the gas-exchange parameters and chlorophyll fluorescence have indicated that the combinations of high temperature (above to 35 degrees C) and LW induced significant decrease in photosynthetic activities of yellow-horn seedlings. All these results showed that the hot stress significantly aggravated the drought damage on yellow-horn plant growth, especially when the temperature increased above 35 degrees C under drought stress.