Effects And Mechanisms Of Elevated Atmospheric CO₂ And Temperature On Water And Nutrient Use In Wheat

The atmospheric CO2 concentration is rising steadily, and is expected to increase from 354 umol mol-1 in 1990 to 530 umol mol-1 in 2050, and could exceed 700 umol mol-1 by the end of 21st century. The effects and mechanisms of atmospheric CO2 enrichment and temperature rise on water and nutrient use in wheat were studied in this thesis using the chamber pot experiment and open top experiment. In the chamber pot experiment, spring wheat (Triticum aestivum L. cv. Dingxi No. 8654) was treated with two atmospheric CO2 concentrations (350 and 700 uinol mol-1), two levels of soil moisture (wet and drought) and five rates of nitrogen fertilizer (0, 50, 100, 150, 200 mg kg-1 soil). In the open top experiment, winter wheat (Triticum aestivum L. cv. Xinong 8727) was treated with 350 and 700 urnol mol-1 of atmospheric CO2 concentrations, two levels of nitrogen fertilizer (45, 90 kg hm-2, NI and N2). In addition, spring wheat {Triticum aestivum L. cv. Dingxi No. 8654) was treated with two kinds of temperature (22 and 28) and four fertilizer treatments (NiP,Ki, NiP2K2, N2P,Ki, N2P2K2).1. The results of pot experiment show under different N level and soil water, elevated atmospheric CO2 concentration increases more photosynthetic rate with nitrogen fertilizer applied, but limited increment in photosynthetic rate without nitrogen added. High CO2 concentration decreases more stomatal conductance and evapotranspiration in drought treatment than in wet treatment, in no N added treatment more than in N added treatment. Doubled CO2 enhances more canopy water use efficiency (WUE) in N added treatment than in no N added treatment. Irrespective of CO2 concentration, canopy WUE increases with the increase of nitrogen fertilizer, but canopy WUE is the lowest without nitrogen added. The results indicate that crop WUE increases significantly with theincrease of N application in certain range of nitrogen fertilizer application rates. In order to exert the stimulatory effect of elevated CO2 on photosynthesis fully, spring wheat planted on Huang Mian soil (loess soil) should be applied enough nitrogen fertilizer under high atmospheric CO2 concentration in the future. In addition, Canopy WUE is inversely related to root/ shoot ratio. The greater the root/shoot ratio is, the lower the WUE is.2. The results of pot experiment show under different N level and soil water, CO2 concentration enrichment does not increase tillers of spring wheat, on the other hand, in low N treatment, high CO2 concentration reduce tillers significantly. The results indicate that tillering of spring wheat needs enough N nutrition under atmospheric CO2 concentration enrichment. At 55 days after sowing, elevated CO2 increases leaf width and leaf area ffidex (LAI) with N added treatment but does not show any increase without N added treatment. Adequate N and water can hasten leaf growth and increase tiller, thus increase leaf area. The effects of CO2 concentration enrichment on shoot dry mass depend on soil nitrogen level. In medium N and high N treatment, shoot dry mass increases significantly; while in low N treatment, shoot dry mass does not increase significantly. CO2 concentration enrichment does not increase more shoot dry mass in drought treatment than in wet treatment. Thus, elevated CO2 does not ameliorate the depressive effects of drought and nitrogen stress ori the growth and dry matter accumulation of spring wheat. In addition, elevated CO2 concentration does not enhance root dry mass and root/shoot ratio, on the other hand, high CO2 concentration reduces root dry mass slightly and root/shoot ratio significantly in no N added treatment under wet condition.3. The results of pot experiment show elevated CO2 decreases shoot N content significantly and root N content slightly. Shoot and root N concentration is significantly lower in the well-watered treatments compared to the drought treatments, and rises dramatically with increasing N applied irrespective of the CO2 concentration. Enriched CO2 concentration reduces shoot P and K content and increa...