| Since the 21 st century,with the acceleration of industrialization and urbanization,the concentration of O3 in the surface layer has increased caused by the combustion of fossil fuels,and global climate change has led to frequent drought,which has become a major environmental problem.Plants were subjected to both O3 and drought stress in the growing season,which affected the growth and development of plants.Non-structural carbohydrate?total nonstructural carbohydrates,TNC?is the main product of photosynthesis in plants,which has the functions of transport,energy metabolism and osmotic regulation.Provides substrates for the synthesis of defensive compounds or for exchange with symbionts involved in nutrient acquisition or defense.It can be used as energy carrier and cornerstone of primary and secondary metabolism,and plays an important role in the growth of plants.However,drought and high concentration of O3 seriously affect the storage of TNC in plants by affecting the photosynthetic rate and the amount of carbon needed for growth.In order to investigate the effects of elevated O3 concentration and drought stress on plant physiology,biochemistry and TNC accumulation and distribution,a sensitive poplar variety '546'?Populus deltoids cv.55 /56 × P.deltoides cv.‘Imperial'?The effects of O3,drought and their interaction on the physiology and biochemistry of poplar leaves were studied by means of open-top chamber(open top chambers,OTCs and poplar pot experiment.The effects of O3,drought and their interactions on the accumulation and distribution of TNC in leaves and fine roots were studied,including the effects of saturated photosynthetic rate,stomatal conductance,antioxidant enzyme activity and soluble protein content,It includes: the changes of soluble sugar components and starch content and the ratio of root to leaf.The results are as follows:?1?The increase of O3 concentration significantly decreased the saturated photosynthetic rate?Asat?,of poplar leaves,but drought treatment had no significant effect on Asat.but the effect of drought treatment on Asat was not significant,and there was a significant interaction between O3 and drought.The activities of Catalase?CAT?activity increased significantly under drought conditions and superoxide dismutase?SOD?enzyme activity decreased significantly,and the activities of CAT and SOD decreased significantly with the prolongation of treatment time.The activity of ascorbate peroxidase?APX?also decreased significantly with the prolongation of treatment time,while the content of soluble protein increased significantly with the prolongation of treatment time.Peroxidase?POD?was not significantly affected by O3,drought and the interaction between O3 and drought.?2?With the increase of O3 concentration,the content of total soluble sugar in leaves increased significantly,the content of glucose and fructose also increased,while the content of starch decreased significantly.Under drought conditions,the contents of glucose and sucrose increased significantly,but the content of starch decreased.With the prolongation of treatment time,the content of sucrose in poplar leaves increased obviously.the change of starch content was the same as sucrose,but the contents of glucose and fructose in leaves decreased.Time treatment significantly increased the content of sucrose and starch in leaves,and significantly decreased the content of glucose and fructose.O3 and time had significant interaction on poplar leaves,drought and treatment time had interaction,O3 and drought had interaction on leaves.?3?The content of fructose and starch in fine roots of poplar was significantly increased with the increase of O3 concentration.Drought significantly increased sucrose content,but significantly decreased fructose,polysaccharide and total sugar content.The treatment time significantly increased the starch content of poplar fine roots,but significantly decreased the content of polysaccharide and total sugar.Treatment time and drought had significant interaction on poplar fine roots,O3 and drought had significant interaction on poplar fine roots.Under compound stress,the accumulation of starch in poplar leaves and fine roots caused by drought is to better resist the absorption of O3,so it is a kind of toxic effect on the growth of poplar.?4?With the extension of time,the content of TNC in poplar leaves increased obviously.The content of TNC in fine roots of poplar decreased significantly under drought,and there was a significant interaction between O3 and drought on TNC of fine roots.TNC is the sum of soluble sugar and starch,which changes with the change of soluble sugar components and starch content.Under the combined action,the content of TNC decreased because drought could reduce the absorption of O3 by poplar.?5?The ratio of root to leaf of poplar was studied by O3 and drought stress,which was an important parameter to reflect the distribution of TNC in poplar.The results showed that the root-leaf ratio of starch was significantly increased by the increase of O3 concentration and drought.However,the root-leaf ratio of total sugar to TNC was significantly decreased by time treatment.Time and O3 had significant interaction on rootleaf ratio of poplar starch,time and drought had significant interaction on total sugar rootleaf ratio,O3 and drought had significant interaction on starch and total sugar root-leaf ratio.The ratio of root to leaf reflected the distribution of TNC in poplar.under compound stress,poplar distributed more starch to fine roots and soluble sugar to leaves to deal with O3 and drought stress,so the ratio of starch root to leaf increased and the ratio of total sugar to root and leaf decreased.This study is to simulate the global change of O3 concentration and drought degree in the future environment.this result may provide a basis for plants to respond to the stress environment.This paper has important theoretical and practical significance for evaluating the response characteristics of poplar stress under the condition of O3 and drought combined pollution in the surface layer of China. |
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