Influence Of Elevated CO₂ And Changing Precipitation On Biomass Allocation And Carbon-nitrogen Characteristics In Plant-soil Of Reaumuria Soongarica

Atmospheric CO₂ concentrations are expected to reach 700?mol·mol^–1 by the end of 21st century and have an indirect influence on rainfall patterns.Elevated CO₂concentrations and changing precipitation will have profound effects on structure and function of the plant-soil ecosystems,especially the interactions on the biomass,carbon and nitrogen allocations of the desert ecosystem have attracted little attention to date.R.soongarica is a typical species of the arid regions of Northwest China.Therefore,the understanding of carbon and nitrogen circulation and biomass allocation of R.soongarica in the plant-soil ecosystem,within increasing atmospheric CO₂concentration context and changing precipitation,will be important to evaluate the trend of carbon and nitrogen allocations and biomass in terrestrial ecosystem.In this paper,R.soongarica seedling and its soil were used as a case study species to study biomass,organic carbon,total nitrogen,C/N and calculated organic carbon and total nitrogen accumulation in its roots,stem and leaf.The main plot included three CO₂concentrations(350,550 and 700?mol·mol^–1)and five precipitation conditions?natural precipitations control[W0],precipitation minus 30%[-W2],precipitation minus 15%[-W1],precipitations plus 15%[+W1],precipitation plus 30%[+W2]?.The results showed that:1?Elevated CO₂ concentration and precipitation increasing significantly increased the biomass content in roots,stem and leaf of R.soongarica,especially under[-W2]precipitation and 700?mol·mol^–1 CO₂ concentration,the biomass contents are significantly higher than 350?mol·mol^–1 CO₂ concentration in roots,stem and leaf of R.soongarica.But the effect of 550 and 700?mol·mol^–1CO₂ concentration is reduced in roots,stem and leaf of R.soongarica with treatment two year.This show that elevated CO₂ concentration have a great impact on remit the drought influence of biomass in roots,stem and leaf of R.soongarica.However,these affect will be decreased in the next year.With the precipitation increased or decreased significantly promote or restain the biomass content of root,stem and leaf,but it promote roots of R.soongarica with the treatment two year.Under the interaction of elevated CO₂ concentration and changing precipitation,the biomass allocation of R.soongarica it that leaf>stem>root.2?Elevated CO₂ increased organic carbon,C/N and decreased total nitrogen in roots,stem and leaf of R.soongarica.When[-W2]and 700?mol·mol^–1 CO₂concentration,the organic carbon contents are significantly is higher than 350?mol·mol^–1 CO₂ concentration in roots,stem and leaf of R.soongarica.This show that even precipitation decreasing and elevated CO₂ concentration have a positive effect on the ability of turn the inorganic matter into the organic matter.But photosynthetic capacity of R.soongorica decreased under elevated CO₂ and photosynthetic acclimation occurred with treatment two year and the organic carbon content were decreased in the root and stem of R.soongarica.In some extent,it can alleviate the dilution of carbon accumulation to total nitrogen,and increase the total nitrogen content of the root,stem and leaf of R.soongorica with treatment two year.Under the interaction of elevated CO₂concentration and precipitation with treatment two year,the total nitrogen content of roots,stem and leaf were 3,2.8,2.4 times as much as before,but organic carbon contents are decreased.Until treating in the next year,the organic carbon allocation of roots,stem and leaf of R.soongarica had chang from root>stem>leaf to leaf>stem>root.Elevated CO₂ concentration has a significant effect on the organic carbon and total nitrogen accumulation in the root,stem and leaf of R.soongarica with the increasing precipitation increased.3?Elevated CO₂ concentration,changing precipitation and the interaction have difference effect on the organic carbon,total nitrogen and C/N in the R.soongarica between treatment one or two year.The effects of CO₂ concentration and precipitation have not apparent changing rule on the organic carbon,total nitrogen and C/N of soil in the R.soongarica with treatment one year.However,organic carbon and total nitrogen accumulation in soil of R.soongarica with treatment two year was increased with the elevated CO₂ concentration,while organic carbon C/N increased and total nitrogen decrease in soil of R.soongarica with treatment two year.It was indicated that the pattern of carbon and nitrogen in soil have changed under the long CO₂ concentration.