Effects Of Elevated CO₂ And Increased Temperature On Nitrogen Uptake And Partitioning In Winter Wheat And Rice

Nitrogen uptake and partitioning can directly affect crop growth,yield and product quality.Climate change is characterized mainly by atmospheric CO₂ elevation and temperature increase,which not only directly impacts on the crop growth and development,but also indirectly influence on crop by affecting crop nitrogen uptake and partitioning.In order to better understand and quantify the effects of the combination of atmospheric CO₂ enrichment and increased temperature on crop nitrogen uptake and partitioning,field experiments were conducted with winter wheat?Triticum aestivum L.?cultivar Yangmai 14 and rice?Oryza sativa L.?cultivar Changyou 5 from November 2013 to October 2014 under climate change conditions in the middle of twenty-first Century,simulated by the platform of free air CO₂ enrichment and elevated temperature?TFACE?.Four treatments with three replications for each treatment were designed in the experiments:one with target free air CO₂ concentration up to 500ppm,one with canopy temperature increased by 1.5-2?,and one with combined of free air CO₂ enrichment and increased temperature,one untreated plot with ambient condition as control.Based on experiment research data,we made a quantitative analysis of responses of nitrogen uptake and partitioning to combinations of elevated CO₂ and temperature in winter wheat and rice.The main study results are as follows:?1?Elevated CO₂was unable to compensate for the negative impact of the increase in temperature on aboveground nitrogen accumulation of winter wheat and rice.Aboveground nitrogen accumulation in maturity stage of winter wheat and rice were decreased by 5.4%and 12.0%,respectively,under the combination of elevated CO₂ and increased temperature.As for winter wheat,compared with the ambient,elevated CO₂ increased nitrogen accumulation in each developmental stages and nitrogen accumulation in maturity stage was increased by 2.6%under elevated CO₂.The increase in nitrogen accumulation was associated with an increase in number of culms under elevated CO₂.Increased temperature decreased nitrogen accumulation in each developmental stages and nitrogen accumulation in maturity stage was decreased by 14.2%under increased temperature.The decrease in nitrogen accumulation was associated with a decrease in number of culms under increased temperature.The combination of elevated CO₂ and increased temperature decreased nitrogen accumulation in each developmental stages and nitrogen accumulation in maturity stage was decreased by 5.4%under the combination of elevated CO₂ and increased temperature.The decrease in nitrogen accumulation was associated with a decrease in number of culms under the combination of elevated CO₂ and increased temperature.As for rice,compared with the ambient,elevated CO₂ increased nitrogen accumulation in each developmental stages and nitrogen accumulation in maturity stage was increased by 0.9%under elevated CO₂.The increase in nitrogen accumulation was associated with an increase in number of culms under elevated CO₂.Increased temperature increased nitrogen accumulation before heading but decreased nitrogen accumulation after heading and nitrogen accumulation in maturity stage was decreased by 20.1%under increased temperature.The effects of increased temperature on aboveground nitrogen accumulation mainly relied in the effects of increased temperature on nitrogen accumulation per culm.The combination of elevated CO₂ and increased temperature increased nitrogen accumulation before heading but decreased nitrogen accumulation after heading and nitrogen accumulation in maturity stage was decreased by 12.0%under the combination of elevated CO₂ and increased temperature.The increase in aboveground nitrogen accumulation before heading was associated with an increase in number of culms and an increase of nitrogen accumulation per culm under the combination of elevated CO₂ and increased temperature.And the decrease in nitrogen accumulation was associated with the decrease in nitrogen accumulation per culm after heading under the combination of elevated CO₂ and increased temperature.?2?The combination of elevated CO₂ and increased temperature significantly increased nitrogen use efficiency of heading stage of winter wheat and had no significant effect on nitrogen use efficiency of maturity stage of winter wheat;the combination of elevated CO₂ and increased temperature significantly decreased nitrogen use efficiency of heading stage of rice,but significantly increased nitrogen use efficiency of maturity stage of rice.As for winter wheat,compared with ambient,nitrogen use efficiency was higher under elevated CO₂ by 3.6%and 6.4%at heading and maturity stage,respectively.Nitrogen use efficiency was decreased by 1.2%and 5.4%at heading and maturity stage,respectively,under increased temperature.Nitrogen use efficiency was increased by 5.4%at heading stage and was decreased by 3.4%at maturity stage under the combination of elevated CO₂ and increased temperature.As for rice,nitrogen use efficiency was higher under elevated CO₂ by 5.4%and 7.6%at heading and maturity stage,respectively.Nitrogen use efficiency was decreased by 2.2%at heading stage and was increased by 3.7%at maturity stage under increased temperature.Nitrogen use efficiency was decreased by 5.0%at heading stage and was increased by 3.7%at maturity stage under the combination of elevated CO₂ and increased temperature.?3?The combination of elevated CO₂ and increased temperature decreased leaf nitrogen partitioning index and increased panicle nitrogen partitioning index of winter wheat and rice,and stem nitrogen partitioning index in each developmental stage of winter wheat after heading and in each developmental stage of rice was decreased under the combination of elevated CO₂ and increased temperature.As for winter wheat,leaf nitrogen partitioning index and ear nitrogen partitioning index was decreased but stem nitrogen partitioning index was increased under elevated CO₂.Leaf nitrogen partitioning index was decreased and ear nitrogen partitioning index was increased under increased temperature.Stem nitrogen partitioning index was increased before heading but was decreased after heading under increased temperature.Leaf nitrogen partitioning index was decreased and ear nitrogen partitioning index was increased under the combination of elevated CO₂ and increased temperature.Stem nitrogen partitioning index was increased before heading but was decreased after heading under the combination of elevated CO₂ and increased temperature.As for rice,Leaf nitrogen partitioning index was decreased and panicle nitrogen partitioning index was increased under elevated CO₂.Stem nitrogen partitioning index was increased before heading but was decreased after heading under elevated CO₂.Leaf nitrogen partitioning index was decreased and panicle nitrogen partitioning index was increased under increased temperature.Stem nitrogen partitioning index was increased before heading but was decreased after heading under increased temperature.Leaf nitrogen partitioning index and stem nitrogen partitioning index was decreased but panicle nitrogen partitioning index was increased under the combination of elevated CO₂ and increased temperature.?4?The combination of elevated CO₂ and increased temperature had no significant effect on nitrogen translocation amount,nitrogen translocation rate and contribution rate of nitrogen translocation to grain nitrogen accumulation in leaf and stem of winter wheat,but significantly increased nitrogen translocation rate and contribution rate of nitrogen translocation to grain nitrogen accumulation in leaf and stem of rice.As for winter wheat,elevated CO₂,increased temperature and the combination of elevated CO₂ and increased temperature had no significant effect on nitrogen translocation amount,nitrogen translocation rate and contribution rate of nitrogen translocation to grain nitrogen accumulation of leaf and stem.As for rice,elevated CO₂ significantly increased nitrogen translocation rate of leaf and had no significant effect on nitrogen translocation amount and contribution rate of nitrogen translocation to grain nitrogen accumulation of leaf.However,elevated CO₂ significantly increased nitrogen translocation amount,nitrogen translocation rate and contribution rate of nitrogen translocation to grain nitrogen accumulation of stem.Increased temperature significantly increased nitrogen translocation rate of leaf and had no significant effect on nitrogen translocation amount and contribution rate of nitrogen translocation to grain nitrogen accumulation of leaf.However,increased temperature significantly increased nitrogen translocation amount,nitrogen translocation rate and contribution rate of nitrogen translocation to grain nitrogen accumulation of stem.The combination of elevated CO₂ and increased temperature significantly increased nitrogen translocation rate and contribution rate of nitrogen translocation to grain nitrogen accumulation of leaf and stem and nitrogen translocation amount of stem,but had no significant effect on nitrogen translocation amount of leaf.Our study showed that enriched CO₂ up to 500 ppm could not compensate the negative effect of increased canopy temperature by 1.5-2.0 ? on aboveground nitrogen accumulation of winter wheat and rice,which resulted in the reduction of aboveground nitrogen accumulation of winter wheat and rice by 5.4%and 12.0%,respectively,under the combination of elevated CO₂ and increased temperature.Our studies results can provide experimental basis and data support for further quantitatively study of the effects of climate change on wheat and rice production.Meanwhile,this study also provided a certain theoretical basis for the adjustment of cultivation measures and the application of nitrogen fertilizer in the background of climate change in the future.