Study On The Effect Of Elevated CO₂ Concentration On Soybean To Drought Stress

The global atmospheric CO₂ concentration continues to increase which leads to global temperature rise and the change in the pattern of precipitation,therefore the frequency and intensity of extreme weather such as drought will be increased.Soybean is an important oil crop.At present,it is unclear how climate change affects the growth and development of soybeans.Here,we grew two different drought-resistant soybean cultivars（Zhong huang 35: low drought-resistant soybeans,Xingxian small yellow soybean:drought-resistant soybeans）under different [CO₂]（400 ppm and 600 ppm）and water stress（leaf relative water content of normal and drought is 81%-92% and 64-77%）conditions.Photosynthetic pigment content,photosynthetic capacity,signal transduction enzymes,osmotic adjustment,hormones and protein content,and the related key genes were measured at flowering stage.The results showed:Drought stress significantly reduced the chlorophyll b content both in two soybean cultivars under higher CO₂ concentration conditions.Drought stress significantly reduced the net photosynthetic rate,stomatal conductance and water use efficiency of two soybean cultivars.Elevate [CO₂] significantly enhanced water use efficiency of Zhong huang 35 under drought stress.Drought stress significantly increased the content of MDA in two soybean cultivars.Elevate [CO₂]decreased the content of MDA both in two soybean cultivars under drought stress,especially on Xingxian small yellow soybean.Drought stress significantly declined the activity of glutathione s-transferase in two soybean cultivars under normal CO₂ concentration conditions.Elevate [CO₂] significantly promoted the activity of superoxide dismutase and glutathione s-transferase of Xingxian small yellow soybean,and significantly promoted the activity of glutathione transferase and peroxide of Zhong huang 35 under drought stress.Elevate [CO₂] had no impact on the content of soluble sugar both in two soybean cultivars.Elevate [CO₂] did not change the content of proline both in two soybean cultivars under normal water condition,while significantly reduced them under drought stress.Drought stress significantly increased the content of mitogen-activated protein kinase（MAPK）both in two soybean cultivars.Elevate [CO₂] significantly enhanced the content of calcium-dependent protein kinase activity,whereas significantly reduced the content of heat shock protein 70（HSP-70）both in two soybean cultivars under drought stress.The content of abscisic acid（ABA）in two soybean cultivars were significantly increased by elevate [CO₂].Elevate [CO₂] significantly up-regulated the gene expression of calcium-dependent protein kinase and glutathione transferase both in two soybean cultivars.Elevate [CO₂]significantly down-regulated the gene expression of HSP-70 in Xingxian small yellow soybean and the gene expression of MAPK in Zhong huang 35.On the summary,elevated [CO₂] did not alleviate the negative impacts of drought stress on photosynthesis in soybean.Elevate [CO₂] reduced the content of MDA both in two soybean cultivars under drought stress.This mitigation effects of elevated [CO₂] were attribute to increasing the content of ABA and CDPK in soybean leaves to regulate and transmit stimulus signals,leading to producing some resistant substances and improving soybean resistance to drought stress.