Effects Of CO₂ Concentration Elevation And Nitrogenapplication On Dry Matter Production And Nitrogen Utilization In Winter Wheat

The studies on the effect of CO2 concentration elevation on plants have been one of the hot issues. This research begun with1990s in China, and later than abroad. The research mostly focus on biological, physiological and yield characters of crops.There still need some experiments to proof the effects of all factors on crops because most of the study only took into account of CO2 concentration or combined it with nutrient and water, respectively. Our study used Open Top Chambers equipment to study the effect of elevated CO2 on photosynthetic fluorescence characteristics, growth, nutrient distribution and yield components of winter wheat (Triticum aestivum L.) which growing under three levles of nitrogen application (N0, N1 and N2, representing 0, 0.15 and 0.30 g nitrogen per kilogram soil, respectively). Major conclusions are as follow:1. The results showed that, compared with the background CO2 concentration, elevated CO2 had effect on chlorophyll content, fluorescence parameters and net photosynthetic rates of wheat leaf at different growth stages. Under no nitrogen application, CO2 concentration elevation significantly reduced chlorophyll concent at major growth stages, increased inordinately Fo , and decreased inordinately Fm, Fv, Fv / Fm, Fv / Fo and net photosynthetic rate,too.This indicated that under low nitrogen nutrition, elevated CO2 could increase light damage of PS II, inhibited the electron transfer, electron acceptor QA redox, photochemical efficiency and the potential reactivity of PS II and light energy conversion system and photosynthetic carbon fixation capacity. Meanwhile, different nitrogen levels also influcenced chlorophyll content, fluorescence and net photosynthetic rate of winter wheat leaf which at the different growth stages. Under elevated CO2 concentrations, chlorophyll content, Fm, Fv, Fv / Fm and Fv / Fo of two winter wheat varieties significantly higher in nitrogen application treatments(N1, N2) than these in no nitrogen applicationment treatment(N0), while there was no significant difference between two nitrogen application treatments2. CO2 concentration elevation affected leaf area, plant height, mature stem length, ear length of two wheat varieties. The influences were associated with nitrogen level. Under N0, Elevated CO2 did not change the growth of wheat, While under N1 trestment and N2 treatment, elevated CO2 increased all the growth indexs except leaf area. Similarly, the yield of wheat in CO2 concentration treatments was increased only under nitrogen application. The production change of Xiaoyan22 was much bigger than that of Xiaoyan6 for CO2 concentration elevation. The production increase was primarily due to the enhancement of spike number and grain number per spike. In addition, the change of wheat height and its composition after CO2 concentration increase were associated with the increaseing of stem frist node length and ear length. Both of them were controled by nitrogen application level. Meanwhile, it was good for the leaf maintaining a high photosynthetic area to receive more light through using more nitrogen.3. Elevated CO2 also influenced the nitrogen content of two wheat genotypes, and the infucenced degree depended on nitrogen application levels, organs and growth stages. It was not so conducive to nitrogen content in different organs of winter wheat, especially at late growth stage. The effect of elevated CO2 on the root was smaller than that on other parts. Elevated CO2 concentration would have negative effect on nitrogen accumulation at maturity stage because of nitrogen deficiency. The harvest index of nitrogen decreased significantly both in Xiaoyan6 and Xiaoyan22. After nitrogen application, Nitrogen accumulation increased significantly in elevated CO2 concentration and higher than that in the background concentration. Nitrogen harvest index increased along with the increase of nitrogen application level, especially in Xiaoyan 22 which was the high yield, high nitrogen efficiency variety4. In total, CO2 concentration elevation had inhibition or no significant effect on growth and metabolism of wheat under nitrogen deficiency, but it obviously stimulated crop growth under nitrogen application, which showed that a interaction between CO2 concentration elevation and nitrogen application was positive on winter wheat. Although the basic assumption that"CO2 concentration increased and nitrogen application on crop production and nitrogen utilization of material there is a positive interaction."was proved,"the level of N has something to do with effect on different varieties"lacked enough evidence. It would need further research on the impact mechanism of the CO2 concentration on wheat in the future.