| We are currently facing one of the most important challenges, the global warming, caused by increasing global atmospheric CO2 concentration. The rising CO2 has a strong impact on the ecological environment and the global carbon balance by changing material cycle and energy flow process driven by photosynthesis process. In agricultural ecosystem, the elevated CO2 concentration could result in the changes of carbon(C) and nitrogen(N) allocation in soil-plant systems, thus causing a significant influence on the conversion process and the recovery of fertilizer N used by plant and soil, which is closely associated with fertilizer management and the reduction of area-source pollution. Therefore, the allocation and sequestration of plant photosynthetic C and fertilizer N and the environment effect have become an important issue in C and N cycling. Solving this problem will have profound significance in dealing with the environmental problems caused by elevated atmospheric CO2 and excessive fertilizer application.In order to study the allocation of photosynthetic C and fertilizer N in plant-soil system as well as the ecological environment effect, our study are conducted based on wheat pot culture experiment by supplying 13C-CO2 and 15N-(NH4)2SO4 at different concentration, respectively. By differentiating isotope-labeled C and N from native portion, we quantified the enrichment of photosynthetic C(new carbon) and fertilizer N(new nitrogen) in wheat as well as the dynamic of C assimilate and fertilizer derived N in soil at different growth stages of the wheat(jointing stage, heading stage and maturity). By particle size fractionation, we also study the allocation and dynamic change of photosynthetic C and fertilizer N in different-size particles(sand, silt and clay) to probe into the stabilization of C and N controlled by C and N coupling effect. We can draw the following conclusions:1) Higher nitrogen application(at middle and high-N rates) is conducive to the accumulation of biomass under the elevated CO2 concentration. At jointing stage, the biomass increase of stem, leaf and root is the most significant in middle-N treatments. Because of dilution effect caused by the rising biomass, the content of total N in all of the organs reduces with the elevated CO2 concentration, and there are differences at different stages and organs. The N content in root at the jointing and that in the stem and leaf at heading stage have a biggest reduction in the high-N treatment(respectively 18.75% and 15.03%), and the biggest N decline in the wheatear and grain occur at the maturity stage under low-N treatment(respectively 33.33% and 10.13%).2) Along with the growth of wheat, 13CO2 was constantly assimilated as photosynthetic products. The increasing CO2 concentration obviously improves the enrichment of photosynthetic C(new carbon) in all of organs, with the value in grain boosted in higher nitrogen application(middle and high-N treatments). The significantly larger amount of photosynthetic C in grain occurs at the maturity. The elevated CO2 concentration resulted in the decline of the total N in all of organs, but enhances the enrichment of new nitrogen(δ15N). The new nitrogen in root was transferred significantly to grain, so there has the largest amount of photosynthetic C in the grain of wheat, which shows that elevated CO2 concentration increase the biomass of wheat and promotes the accumulation of photosynthetic C and improve the crop yields.3) With the input of photosynthetic C(13C), the elevated CO2 concentration constantly improves the 13 C enrichment in the soil, but do not influence the C content, suggesting that elevated CO2 enhanced the turnover of soil organic C. The incorporation of photosynthetic C is the largest at heading stage, which increase with the increase of nitrogen level, but in middle-N treatments, the highest enrichment occurs at maturity, suggesting the manipulation role of N level. With the growth of wheat, the enrichment of 15 N gradually reduces under the rising CO2 concentration, which improves the utilization rate of fertilizer nitrogen in the plant, and reduces the residues of the fertilizer nitrogen in the soil. But under the condition of high CO2 concentration and high fertilizer application the recovery rate of the fertilizer nitrogen in the plant-soil system is low, which possibly causes N pollution of the environment.4) The elevated CO2 accelerates photosynthetic C transformation to soil, and the photosynthetic C in sand fraction significantly increases under the middle-N treatments. It is well known that the sequestration of soil organic carbon in sand fraction is unstable, the increasing CO2 concentration therefore may not benefit for the stabilization of photosynthetic C in long time. The degree of allocation of fertilizer N(15N) in particle size fractions increases with the increased nitrogen application rate. Under the same fertilizer nitrogen levels, the elevated CO2 promotes the transformation of fertilizer N(15N) to clay fraction, which is conducive to the immobilization of fertilizer N in soil... |
PDF Full Text Request