| Due to the aggravating human intervention, the global mean temperature in 20st century has increased 0.74℃and is projected to rise about 1.8℃-4.0℃by 2100. In our country, relevant forecast reports that the mean temperature will increase 2.3℃-3.3℃. Until now, the studies on the responses of terrestrial ecosystem to elevated temperature mainly focused on the natural ecosystem with few on agroecosystem. There exist researches showing that the global climate change will greatly threat the sustainability of food production increase in our country. However, these researches were mostly the model analysis based on historical data. Moreover, only a few experiments were not conducted in field and rarely studied the effects of asymmetric warming. At the same time, the academic and political societies think the researches about the global change in China must emphasize on the scientific problems relating the economy of our country and the people’s life, significant district traits and international impacts. Therefore, to study the responses of wheat production to the asymmetric warming accords with our country agricultural science and technology development and food security, and has great significance. Wheat is the major grain crops in our country. The global climate warming is more severe in spring and winter, which impacts the winter-wheat even greater. The sustainability of winter-wheat yield increase and the corresponding environmental problems are concerned by international society. Therefore, according to the field warming experiment in other countries, we set up the first Free Air Temperature Increase (FATI) system in winter wheat yield in Nanjing, Jiangsu, China during 2007 to 2009. Under different warming treatments in day and night in our experiment, we studied the winter wheat responses in biological characters, photosynthesis rate, respiration rate, grain filling rate, key enzymes in grain filling, dry matter accumulation, yield and its components, dry matter production efficiency. The main results were as follows:The FATI system could significantly increase the temperature within 4 m2 area and did not affect the trend of field temperature development. The asymmetric warming decreased soil moisture content but the effect was insignificant. In the three different warming treatments, the days from sowing to the beginning of the earing and from sowing to maturity shortened significantly. Therefore, our FATI system could accord with climate warming trend, and meet the experiment demands of the wheat responses to the asymmetric warming in typical agroecosystem.Asymmetric warming increased the effective tillers and decreased the ineffective tillers of winter wheat. The ineffective tillers in the control were 1.6,0.7 and 2.5 times higher than in all-day warming (AW), day warming (DW) and night warming (NW) treatments, respectively. But the effective tillers in the control decreased 13.7%,3.2% and 0.5% than in AW, DW and NW, respectively. The plant height in AW, DW and NW increased 5.6%,4.5% and 1.3%. The AW, DW and NW treatments significantly enhanced the flag leaf area by 45.7%,39.4% and 26.1%, and the total green leaves area at blooming stage by 25.1%,29.8% and 17.3%. Meanwhile, the green leaves biomass ratio significantly increased 37.7%,43.3% and 38.7%, respectively, in the AW, DW and NW treatments. Averaged across two years, AW, DW and NW shortened the period from sowing to heading by 14,9.5, and 11.5 days, and prolonged the period of maturity by 3,3 and 2.5 days. Warming increased the grain number per panicle by 4.1%,5.7%and 1.7%, respectively, in AW, DW and NW, and the filled grain number per panicle by 2.2%,5.3% and 2.6% averaged during the two years. However, the grain-leaf ratio averagely decreased 15.3%, 8.5% and 11.3% in AW, DW and NW, respectively, during two years. These results showed that the effects of the three warming treatments on the winter wheat benefit its yield formation. So, the anticipated warming may further improve wheat yield in Jianghuai region.Averaged across two years in AW, DW and NW treatments, the dry matter accumulations were 6.3%,7.9% and 7.2% higher than the control, and the yields were 8.5%, 16.6% and 21.3% higher, and the effective panicles were 7.5%,3.8% and 6.9% higher, and the grains per spike were 2.3%,6.5% and 3.3% higher, and the 1000 grain weights were 7.8%,9.2%and 18.1% higher(P<0.05). Starch components, protein content and components in grains changed obviously, also. Three warming treatments impacted the total starch content insignificant but significantly increased the ratio of amylose to amylopectin. The content of total protein in the grain protein was significantly decreased by warming with the order as CK> DW> NW> AW. In DW, the albumin content and the ratio of glutelin to gliadin were the lowest, and the globulin content was the highest. Therefore, climate warming benefits the winter wheat production in Jianghuai region. In future climate warming, based on the adaptive ability of winter wheat to the climate warming, we can take effective measures on application of fertilizer and water to improve winter wheat high-yield and high-quality cultivation.The asymmetric warming could increase the N content in the leaf and stem but decreased the N content in the panicle. Averaged across two years at wheat maturity, the N contents in the leaf were 8.4%,15.9% and 28.3% higher in the AW, DW and NW treatments than in the control, and the N contents in the stem were 29.6%,21.0% and 45.1% higher, and the N contents in the panicle were 11.7%,5.2% and 8.3% higher. The asymmetric warming also increased the spike rate, dry matter transport rate, harvesting index, N use efficiency and N production efficiency. The AW, DW and NW treatments increased the spike rate by 55.2%,29.4% and 71.2%, dry matter transport rate by 32.3%, 12.6% and 23.9%, harvesting index by 10.2%,15.2% and 14.8% and nitrogen fertilizer production efficiencyby 13.0%,19.3% and 24.0%. Therefore, the climate warming will improve the wheat material production efficiency in Jianghuai region.Warming can significantly change the content and composition of the leaf. The chlorophyll a of flag leaf at jointing stage increased 18.8% in DW and decreased 21.8% in NW. The chlorophyll b significantly increased 21.4%-48.9% at jointing stage and 20 days post-anthesis (DPA). The net photosynthesis rate of flag leaf has a decreasing trend under warming with insignificant difference. But the photosynthesis product of flag leaf has a significantly increased 15.5%-37.0% from jointing stage to 20 days post-anthesis (DPA) under warming. The respiration rate in night was significantly decreased 18.4-119.8% under warming. The responses of stomatal conductance, intercellular CO2 concentration and transpiration rate to warming were the same. They were lower at jointing stage and 20 DPA but higher at 10 DPA. The responses of winter-wheat flag leaf to warming indicate that the climate warming may positively impact the winter-wheat production in Jianghuai region.The activities of sucrose synthase (SS), ADP-giucose pyrophosphorylase (AGPase), and starch branching enzyme (SBE) were higher in superior grains than in inferior grains, and also higher in the daytime than at night. In the control during the grain filling stage, the average activities of SS, AGPase, and SBE were 72.9%,111.4% and 7.8% higher in superior grains than in inferior grains. In superior grains, the SS activities in all-day warming, daytime warming and nighttime warming treaments were 8.4%-31.2% higher than those in the ambient control in the daytime, and 11.1%-20.3%higher than those in the control at night. In inferior grains, the increased percentages were 9.7%-20.3%in the daytime and 6.1%-32.0%at night. In inferior grains, the AGPase activities were elevated significantly compared to the control with 54.2%-124.4%in the daytime and 20.7%-99.3% at night. The SBE activities were also higher in the warming treatments than in the control with the increase of 3.9%-12.1%in the daytime and 1.0%-7.6%at night. Besides, the correlations existed between the activities of AGPase and SBE and the 1000-grain weight were positive and significant, therefore, this result indicated that elevation of AGPase and SBE activities play an important role in the enhancement of 1000-grain weight. |
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