Effects Of Elevated Atmospheric CO₂ Concentration And Increased Temperature On Carbon And Nitrogen Metabolism And Yield In Soybean

The elevated atmospheric CO₂ concentration and increased air temperature are the two most important features of global climate change.Soybean is one of the most important food,oil and feed crops in the world.The elevated atmospheric CO₂ concentration and increased air temperature will inevitably affect the production of soybeans due to climate change in the future.The experiment was carried out in the closed gas chamber of Shanxi Agricultural University.Soybean variety ‘Zhonghuang35’ was used as the test materialin 2018 and 2019.The experiment was conducted to study the effect of different CO₂ concentration(normal CO₂ concentration of 400 μmol·mol^–1;elevated atmospheric CO₂ concentration of 600 μmol·mol^–1)and different temperature treatment（normal air temperature,normal air temperature +2 ℃）on yield components,carbon and nitrogen metabolism.It is proposed to provide a theoretical basis for the soybean production under the background of future climate change.The results are as follows:1.In 2018,the Pn and WUE of soybean leaves was increased significantly with the elevated CO₂ concentration,while Pn of soybean leaves was decreased significantly with the increased air temperature.Compared with increased air temperature alone,WUE was increased significantly with the combination of elevated CO₂ concentration and increased air temperature.In 2019,at the seed filling stage,the Pn of soybean leaves was decreased significantly with the increased air temperature,the Pn was not significantly changed under elevated CO₂ concentration alone,whileit was increased under the combination of elevated CO₂ concentration and increased air temperature.The A_max and P_nmax were significantly decreased under elevated CO₂ concentration or increased air temperature.2.In 2018,at the flowering stage and seed filling stage,the soluble sugar content were significantly decreased with elevated CO₂ concentration or increased air temperature,but it was not significantly changed at flowering stage.The starch content was significantly increased at flowering stage.The sucrose content,starch content and sucrose metabolizing enzyme activity in soybean leaves were significantly decreased with the increased temperature.The soluble sugar content of soybean leaves was not significantly changed with the combination of elevated CO₂ concentration and increased air temperature a at the flowering stage and seed filling stage,but sucrose content was significantly decreased.3.In 2018,at the flowering stage,the activity of enzymesrelated to nitrogen metabolism of soybean leaves was not significantly changed with elevated CO₂ concentration,while it was increased with the increase of air temperature.The soluble protein content of soybean leaves was not significantly changed with increased air temperature alone,but it was significantly decreased with the combination of elevated CO₂ concentration and increased air temperature.At seed filling stage,the activity of enzymes related to nitrogen metabolism and soluble protein content of soybean leaves were significantly decreased with elevated CO₂ concentration.The activity of enzymes related to nitrogen metabolismwas significantly increased with the increased air temperature,but the soluble protein content was significantly decreasedat the flowering stage and seed filling stage.The NR activity（nitrate reductase activity）was significantly increased with the combination of elevated CO₂ concentration and increased air temperature,but soluble protein content of leaves was not significantly changed.All treatments significantly increased the accumulation of nitrogen in the above ground part of soybean after harvest,but not significantly changed of the total nitrogen content.4.In 2018,the plant height,pod number per plant and grain weight per plant of soybean were significantly increased with elevated CO₂ concentration,thus biomass and yield of upper ground were significantly increased.The 100 grain weight of soybean was significantly decreased with increased air temperature.In 2019,the above ground part and yield of soybean were not significantly changed with elevated CO₂ concentration.The number of pods per plant,aboveground biomass and yield of soybean were significantly decreased with the increased air temperature,however,the decreased extent byelevated CO₂ concentration and increased air temperature was less than that of elevated air temperature alone.In conclusion,elevated CO₂ concentration could inhibit the nitrogen metabolism pathway in soybean leaves,but had no significant effect on the nitrogen content in shoots and grains,and promoted the carbohydrate accumulation in leaves at flowering stage.Increased temperature could promote the activity of nitrogen metabolism related enzymes in leaves and nitrogen accumulation in shoots,but it would reduced the nitrogen content in grains,and was not conducive to the carbon accumulation of soybean leaves.However,the combination of elevated CO₂ concentration and increased air temperature could maintain the normal level of carbohydrate in soybean leaves.In the northern China,in normal years without high temperature（e.g.2018）,elevated CO₂ concentration and increased temperature by 2 ℃ could promote the growth and yield of soybean,but in high temperature stress years（e.g.2019）,the fertilizer effect of elevated CO₂ concentration disappeared,while warming would have a greater negative effect.In the future,the risk of soybean production suffering from extreme high temperature will be increased under the climate warming environment.