Effects Of Soil Water Stress On Photosynthetic Characteristics Of H.syriacus’ Duede Brabaul’ Seedlings

Drought is an important factor limiting the normal development and growth of plants.Understanding the drought resistance characteristics of plants and further screening and evaluating plant varieties with strong drought tolerance are important means to deal with it.As an excellent shrub species for soil and water conservation,rose Hibiscus lacks research on its drought resistance from the level of photosynthetic physiology.Therefore,in this study,the potted 1-year-old H.syriacus’Duede Brabaul’seedlings were used as materials.Based on the principles and research methods of plant photosynthetic physiology and ecology,the changes of photosynthetic light response characteristics,chlorophyll fluorescence parameters and antioxidant enzyme activities of H.syriacus’Duede Brabaul’leaves under different water stress were measured,The effects of water stress on photosynthetic efficiency of H.syriacus’Duede Brabaul’seedlings were analyzed.The main results are as follows:（1）When water stress increased from T1 treatment to T2 treatment,the net light rate（P_n）of H.syriacus’Duede Brabaul’seedlings increased and maintained at a high level,while the water use efficiency（WUE）decreased,In T3 treatment,the Pn and WUE of H.syriacus’Duede Brabaul’seedlings reached the highest value,indicating that H.syriacus’Duede Brabaul’seedlings have high photosynthetic physiological activity under water stress;In T4 treatment,P_nand WUE of H.syriacus’Duede Brabaul’seedlings were low,H.syriacus’Duede Brabaul’seedlings were under strong stress and plant growth was threatened.From T2 to T4,P_n,stomatal conductance（G_s）and intercellular CO₂concentration（C_i）of rose Hibiscus showed a downward trend,while stomatal limit（L_s）increased significantly.Water stress continued to aggravate,P_n,G_sand L_sshowed a downward trend,while C_iincreased,vto non stomatal limit.（2）With the increase of soil moisture（T1 to T4）,Hibiscus seedlings F_m、Φ_PSⅡ、F_v/F_mand q P increased first and then decreased,while F_oand NPQ decreased first and then increased.The increase of the initial fluorescence value promoted the increase of the non photochemical quenching coefficient of Hibiscus seedlings and inhibited the non photochemical quenching coefficient;When serious water stress occurs in soil,the main limiting factor of photosynthesis of H.syriacus’Duede Brabaul’seedlings changes from stomatal limitation to non stomatal limitation,which shows that PSⅡis damaged,and the deepening of drought degree is conducive to the reduction of PSⅡheat dissipation and energy consumption of H.syriacus’Duede Brabaul’seedlings.（3）With the aggravation of soil moisture（T1 to T4）,superoxide dismutase（SOD）and peroxidase（POD）in leaves of Hibiscus seedlings increased first and then decreased,while malondialdehyde（MDA）and free proline（Pro）increased It shows that rose Hibiscus has a certain physiological and ecological adaptation strategy to soil water stress.Under water stress,it can protect photosynthetic institutions by increasing heat dissipation,and protect cells by increasing the activity of antioxidant enzymes and the content of Osmoregulation Substances.