Photosynthetic Physiology And Growth Adaptation Strategies Of Plants With Different Photosynthetic Types To Drought-Rewatering

Under the background of global climate change,drought has become a global environmental problem.Drought could affect plant growth either directly by limiting the physiological metabolism,such as photosynthesis and respiration,it also restricts nutrient uptake and indirectly changes plant morphological characteristics.As an important physiological process of plants,plants can be divided into C₃ plants and C₄plants according to the different photosynthetic pathways.At present,the understanding of the relationship between photosynthetic physiological responses of different photosynthetic types of plants and their morphological characteristics in the process of drought-rewatering is still relatively poor,and most of the studies involve fewer species and do not represent functional groups.In this study,we conducted a pot experiment using seven widespread annual C₃ and C₄ plants,and their photosynthetic physiological responses and morphological responses under the influence of different intensities of drought-rewatering were measured to answer the following scientific questions:(1)Are there any function group differences of photosynthetic physiological response and limiting factors(stomatal limitation and metabolic limitation)between C₃ and C₄ plants almong drought gradient;(2)If the recovery of photosynthetic rate after rewatering depends on the intensity of drought treatment,and are there any functional group differences between C₃ and C₄ plants;(3)What are similarities and differences of the growth adaptation strategies for precipitation variation between C₃ and C₄ plants.The main results of this study are as following:(1)Over all,both net photosynthetic rate(A)and stomatal conductance(g_s)of all experimental species was significantly decreased under drought stress,whereas water use efficiency(WUE)was significantly increased.Although C₃ plants had greater g_s,its A and WUE was lower than C₄ plants.The photosynthetic drought sensivity of C₃plants were greater than C₄ plants.Such as,under severe drought treatment,the A of C₃ and C₄ plants decrease by 21.6%and 49.5%,respectively.In moderate and severe drought treatment,the photosynthesis of C₃ plants was controlled by relative stomatal limitation(RSL),but C₄ plants was controlled by relative metabolic limitation(RML).(2)The drought sensitivity of C₃ plant biomass was higher than that of C₄ plants.Under moderate and severe drought treatment,the biomass of C₃ plants decreased by19.6%and 40.3%,and that of C₄ plants decreased by 7.5%and 21%.Drought significantly increased the root-shoot ratio(R/S ratio),leaf dry mass per area(LMA)and leaf nitrogen content per unit area(N_area).The R/S ratio of C₃ plant increased by7.3%in moderate drought treatment,which was lower than 16%of C₄ plant.The R/S ratio of C₃ plant increased by 55.1%in severe drought treatment,which was higher than 37.7%of C₄ plant.In addition,the response rate of LMA and N_area of C₃ plants to drought was higher in both moderate and severe drought treatment.(3)The A of C₄ plants recovered more slowly than that of C₃ plants.After rewatering,the net photosynthetic rate of C₃plants,except for Triticosecale wittmack and Avena sativa,recovered for one week,while C₄ need two weeks.After rewatering treatment,the recovery of biomass of C₄ plants was higher than that of C₃ plants.The biomass of C₃ and C₄ plants recovered by 90.3%and 107.7%after rewatering in moderate drought treatment,and by 72.6%and 93%after rewatering in severe drought treatment,respectively.The recovery of R/S ratio of C₃ plants was lower than that of C₄ plants,but the recovery of LMA was higher than that of C₄ plants.Nearly all physiological processes and the growth and development of plants could be affected by drought.With the increase of drought intensity,the A of C₄ plants is gradually affected more than that of C₃ plants,and the photosynthesis of C₄ plants is mainly affected by RML,which lead to the slower recovery of net photosynthetic rate of C₄ plants after rewatering.In order to reduce the negative effects of drought on plant growth,plants need to adjust their morphological characteristics and growth adaptation strategies to cope with drought.C₃ plant have a stronger ability to retain water by increasing LMA,and to increase N_area of to maintain photosynthesis and carbon fixation.The recovery in biomass of C₄ plant was higher,and during the whole drought-rewatering process,C₄ plants maintained their growth advantage due to their higher A and higher resource use efficiency.The results of this study improve the understanding of the photosynthetic response and growth adaptation strategies of plants with different photosynthetic types to drought-rewatering,and provide experimental evidence to predict the changes of vegetation and ecosystem functions under future climatic change.