Responses Of Gas Exchange Characteristics Of Plants With Different Life Forms To Drought Stress

Stomata is the“gateway”of plant gas exchange.Under drought stress,plants close their stomata and reduce transpiration,which is the key way to prevent drought.Therefore,there have been a lot of research reports on stomatal closure of plants in response to drought.However,it remains to be revealed whether there are differences in stomatal responses of different life-forms plants（trees,shrubs and herbs）to drought,and whether the water use strategies based on the differences in drought responses are the same.In this paper,five species of trees,shrubs and herbs from different families,genera and genetic backgrounds were selected to carry out drought stress,to reveal the response differences of gas exchange among trees,shrubs and herbs along with the decrease of soil relative water content and plant leaf water potential,and to understand their differentiation laws;On this basis,combined with the existing literature Meta,meta-analysis was carried out to further confirm the drought adaptation strategies of different life-forms plants.The following conclusions are obtained:1、Under high water condition（80%soil relative water content,SRWC）,the maximum stomatal conductance(g_s-max-s)of trees,shrubs and herbs were 0.29,0.40 and0.40 mol m^-2 s^-1,respectively,and the maximum net photosynthetic rate(A_max-s)were12.9,17.2 and 18.2μmol m^-2 s^-1,respectively.With the decrease of soil relative water content,the stomatal conductance sensitivity of trees,shrubs and herbs was 40.7%,33.1%and 43.4%,respectively,and the net photosynthetic rate sensitivity(soil relative water content corresponding to 50%decrease in photosynthesis,A S₅₀)was 32.9%,28.6%and42.0%,respectively.With the decrease of soil water content,stomata were more sensitive than photosynthesis,water use efficiency(WUE_i=A_max-s/g_s-max-s)of three life-forms plants increased continuously,stomata and photosynthesis of herbaceous plants were more sensitive than trees and shrubs,and WUE_i began to increase earlier than trees and shrubs.2、Under high water condition（-0.4 MPa leaf water potential）,the g_s-max of trees,shrubs and herbs were 0.25,0.37 and 0.39 mol m^-2 s^-1 respectively.the maximum net photosynthetic rate(A_max)were 11.2,15.9,and 17.6μmol m^-2 s^-1,respectively.With the decrease of leaf water potential,the sensitivity of stomatal conductance of trees,shrubs and herbs(leaf water potential corresponding to a 50%decrease in stomatal conductance,g_sP₅₀)was-1.07,1.16 and-0.74 MPa,respectively,and the sensitivity of net photosynthetic rate(leaf water potential corresponding to a 50%decrease in photosynthesis,A P₅₀)was-1.33,1.56 and-0.87 MPa,respectively.With the decrease of leaf water potential,stomatal conductance was more sensitive than photosynthesis,and stomata and photosynthesis of herbaceous plants were more sensitive than trees and shrubs.3、Based on soil water content,g_s-max-s and g_sS₅₀ of 66 species and A_max-s and A S₅₀ of 94 species were extracted from the literature.Based on leaf water potential,g_s-max and g_sP₅₀ of 143 species and A_max and A P₅₀ of 98 species were extracted for meta-analysis.The results were found to be consistent with experimental results,confirming that stomata and photosynthesis of herbaceous plants are more sensitive and universal than those of trees and shrubs.4、Based on the mapping of stomatal maximum and sensitivity,photosynthetic maximum and its sensitivity,it was found that there was a trade-off between A_maxand photosynthetic sensitivity,g_s-max and stomatal sensitivity based on soil water content or leaf water potential.Herbaceous plants have high photosynthesis and stomatal conductance,are sensitive to drought and tend to have drought avoidance strategies.Trees and shrubs have relatively low photosynthesis and stomatal conductance,slow response to drought and tend to have drought tolerance strategies.In short,the study shows that trees,shrubs and herbs respond to drought stress through different photosynthetic and stomatal behaviors,and form different drought adaptation strategies.The results enrich the drought adaptation mechanism of plants and provide theoretical support for drought adaptation of plants.