| Climate change is mainly characterized by atmospheric CO2 concentration elevation and temperature increase, which strongly affects crop growth and yield. Wheat (Triticum aestivum) and rice (Oryza sativa) are the two most important food crops. Therefore, to assess food security on the long run, it is necessary to analyse the responses of wheat and rice to elevated CO2 and increased temperature. FACE (free air CO2 enrichment)experiments under field conditions including increased air temperature is the effective way to explore the crop responses to elevated CO2 and increased temperature. We designed four experimental treatments, that is, one with target atmospheric CO2 up to 500 μmol mol-1(C+T), one with warming of canopy temperature by 1.5-2.0 ℃ above ambient (CT+), and one with combined CO2 enrichment and warming (C+T+), and taking an untreated plot with ambient condition as control (CT) , to analyse the responses of winter wheat and rice to elevated CO2 and increased temperature in T-FACE system established in Kangbo village(31°30’N, 120°33’E), Guli Township, Changshu Municipality, Jiangsu, China during 2012-2014. We also explored any differences between winter wheat and rice in growth duration, above-ground nitrogen uptake, canopy leaf-nitrogen content, leaf area index,photosynthesis, radiation-use efficiency,above-ground biomass,yield and yield components response to elevated CO2 and temperature during two gowing seasons for both crops. The main research results were as follows:1. The combination of elevated CO2 and increased temperature advanced heading of winter wheat and rice by 12-14 d and 4-5 d, respectively. Advanced heading of winter wheat under the combination of elevated CO2 and increased temperature indirectly resulted in a decrease in dialy mean canopy air temperature after heading by 2.0-2.2 ℃. However,the combination of elevated CO2 and increased temperature increased dialy mean canopy air temperature after heading by 1.3-2.0 ℃.2. The enhancement ratio of light-saturated gross photosynthetic rate and initial quantum efficiency of photosynthesis in winter wheat and rice leaves and radiation-use efficiency in winter wheat by elevated CO2 increased with an increase in temperature. Elevated CO2 may be more effective for radiation-use efficiency in winter wheat than in rice.3. Elevated CO2 and increased temperature did not affect the functional relationship between leaf area index and canopy leaf-nitrogen content for winter wheat and rice. The increase of in CO2 in our experiment was unable to compensate for the negative impact of the increase in temperature on above-ground biomass of winter wheat and rice. The combination of elevated CO2 and increased temperature decreased above-ground biomass of winter wheat and rice by 9.5% and 8.7-19.6%, respectively.4. For winter wheat, the combination of elevated CO2 and increased temperature decreased leaf partitioning index, but increased stem partitioning index and ear partitioning index However, for rice, the combination of elevated CO2 and increased temperature increased leaf partitioning index,but decreased panicle partitioning. Meanwhile, the response of stem partitioning index of rice to the combination of elevated CO2 and increased temperature varied with seasons. The increase in CO2 in our experiment was unable to compensate for the negative impact of the increase in temperature on yield of winter wheat and rice. The combination of elevated CO2 and increased temperature decreased yield of winter wheat and rice by 9.8-11.5% and 16.6-34.6%, respectively. The number of filled grains per unit area was the most important yield component accounting for the effects of elevated CO2 and increased temperature in winter wheat and rice.Meanwhile, the number of filled grains per unit area increased with the increase in nitrogen uptake before heading in winter wheat and rice under elevated CO2 and increased temperature. Therefore, nitrogen uptake before heading was crucial in minimizing yield loss due to climate change in both crops. However, increased temperature significantly decreased harvest index of rice, but hardly affected harvest index of winter wheat. For rice,a breeding strategy to increase grain number per m-2 and spikelet fertility at high temperature is also required to prevent yield reduction under conditions of global change.This study provided sufficient data to assess the effect of climate change on yield of winter wheat and rice and facilitated decision supports to develop adapation and mitigation strategies for winter wheat and rice to prevent winter wheat and rice yield reduction under conditions of global change. |
