关键词: 高温敏感期, 高温胁迫, 气候变化, 小麦产量, 中国

Abstract: Yield losses caused by heat stress are particularly severe when high temperatures occur concomitantly with the reproductive period of wheat. The stages most sensitive to, and adversely affected by, high temperature stress for wheat yield, so called the thermal sensitivity period, are the ones prior to flowering and during flowering. Temperatures that exceed thresholds throughout the thermal sensitivity period are calculated as the value of heat stress intensity. In addition, we will experience greater climate variability characterized by increased frequency of short periods of extreme climate events, including temperature stress. In this report, PRECIS regional climate modeling system is used to project the future climate in 2001-2090. Based on CERES-Wheat model, experiments on the sensitivity of wheat yield to maximum temperature in thermal sensitivity periods are conducted at six representative stations in China. High temperature stress intensity index is calculated and spatial distribution of heat stress on China's wheat in the future is estimated. The results show that pre-flowering, flowering, and post-flowering stages are sensitive to heat stress, however, with varying degrees of sensitivity. Pre-flowering and anthesis stages are relatively more sensitive to high temperature, compared to post-flowering stage. But it is difficult to design an experiment to simulate extremely high temperatures at varying degrees for a long time period. Short periods of high temperature (single-day high temperature greater than 32℃) in pre-flowering and flowering stages would seriously reduce the wheat yield. The closer the period in which high temperatures occur is to anthesis, the greater the yield losses are. High temperature stress during flowering reduces the ability of pollen to germinate as well as the rate of pollen tube growth. These negative effects disrupt fertilization and reduce grain numbers. However, yield losses during post-flowering stages were mainly due to decreases in grain weight. Early grain filling periods are relatively more sensitive to high temperature stress compared to later periods. CERES-Wheat model shows a limitation in simulating the responses of wheat yields to high temperature during grain filling period. In a thermal sensitivity experiment with the temperature threshold roughly set at 32℃, wheat yields at the six stations decrease to varying degrees. Different wheat cultivars respond to heat stress differentially. The heat stress that will potentially cause substantial losses in the yields of the sensitive cultivars, commonly grown in northwestern China, is expected to increase during the mid-to-late period of this century. The areas susceptible to severe heat stress in China are primarily middle-high altitude areas, namely, Xinjiang, Hetao Region and Northeast China. The wheat cultivars in northern China, especially spring wheat cultivars, are more vulnerable to heat stress. The situation is further aggravated by climate warming, which increases both intensity and extent of heat stress. These adverse effects may be attributed to the factors such as increased frequency of extreme temperature events, climate change enhancing the probability of overlapping temperature peaks, and the timing of flowering. These effects will worsen more strongly in continental regions, such as northern China, than in southern regions, as in the former regions, stronger warming will occur in the future. Temperature increases accelerate wheat development as earlier anthesis and maturity take place. Climate warming will inevitably increase the intensity of heat stress and hence higher risk of wheat yield reduction.

Key words: China, climate change, heat stress, thermal sensitivity period, wheat yield