Effects of combined elevated temperature and drought stress on anti-oxidative enzyme activities and reactive oxygen species metabolism of Broussonetia papyrifera seedlings
In recent years, under the global climate change scenario, the occurrence of seasonal high temperature and temporal drought phenomena has increased in some subtropical regions. Consequently, the survival and growth of plants are restrained under the combined stress of elevated temperature and drought. In the present study,a pot experiment was performed at the Xiashu Forest Station of Nanjing Forestry University in 2013. One-year-old Broussonetia papyrifera seedlings were grown in 27-cm pots with brown loam soil, using a completely randomized design with four replicates. Seedlings were initially grown in the field environment and then transferred to a controlled greenhouse with three elevated-temperature and soil-moisture treatments, and the effects of combined elevated temperature and drought stress on anti-oxidative enzyme activities and reactive oxygen species (ROS) metabolism were measured in B. papyrifera seedling leaves. The results indicated that under either elevated temperature or drought stress,the superoxide dismutase (SOD),peroxidase (POD), and catalase (CAT) activities of seedlings increased with the increase of stress level. Under the combined elevated temperature and drought stress,the activities of SOD and POD were higher than those under single temperature or drought stress,and increased over stress exposure time. Significant variation was observed in SOD activity of the seedlings between combined stress treatments, revealing the synergistic effects of combined stress on SOD activities. Under the combined elevated temperature and drought stress,ROS, including O_2~- production rates and hydrogen peroxide (H202) and malondialdehyde (MDA) contents,were significantly higher than those under the single temperature or drought stress treatment,which suggests the limited role of antioxidant enzyme activities in alleviating the damage of the cell membrane of seedlings due to differences in ROS metabolite accumulation.