Effect Of Different Concentrations Of Hydrogen Peroxide On Photosynthetic Properties Of 84K Poplar

Poplar,as an important tree species for soil and water conservation and timber forest in China,has been quite widely used in China,but the phenolic acid substances in the soil gradually accumulated on the continuous crop management mode and poplar yield decreased.To explore the response characteristics of photosynthetic efficiency parameters of poplar under different concentrations of H₂O₂ stress,to reveal the dynamic trends of chlorophyll fluorescence parameters of poplar under different concentrations of H₂O₂ stress,and to analyze the effects of different concentrations of H₂O₂ stress on This study was carried out in84K poplar plants with the aim of providing evidence and references for further understanding the effects of poplar crop barriers on the photosynthetic capacity and productivity of poplar.In this study,poplar was treated with different concentrations of H₂O₂as a positive control for oxidative stress,and the photosynthetic physiological status,chlorophyll fluorescence level and antioxidant enzyme activity of poplar in response to H₂O₂stress were investigated.The main results of the study are as follows.（1）Different concentrations of H₂O₂ significantly reduced the photosynthetic capacity of poplar.That is,the apparent quantum efficiency（Φ）,maximum net photosynthetic rate（Pnmax）,dark respiration rate（Rd）,and light saturation point（LSP）decreased and light compensation point（LCP）increased with increasing H₂O₂ concentration in poplar photo response.The CO₂ response parameters such as carboxylation efficiency（CE）,maximum net photosynthetic rate（Pnmax）,photorespiration rate（Rp）,and CO₂ saturation point（CSP）gradually decreased and the CO₂ compensation point（Г（CO₂））increased during the CO₂response.It shows that H₂O₂ decreases the ability of poplar to utilize both strong and weak light.At the same time,H₂O₂ also decreases the utilization efficiency of poplar for both high and low CO₂ concentrations.H₂O₂ causes the stomata of poplar to close gradually,and Tr and Gs of poplar gradually decrease as the H₂O₂ concentration increases,and Ci gradually decreases when the H₂O₂ concentration is 0-20 mM,while Ls increases,at which time the cause of the reduced photosynthetic efficiency of poplar is mainly stomatal limitation;when When the H₂O₂ concentration was increased from 20 mM to 25 mM,the Ci of poplar increased and Ls decreased,and Gs showed a negative correlation with Ci,indicating that the reason for the reduced photosynthetic efficiency of poplar at this time might be caused by the non-stomatal restriction caused by H₂O₂ destroying the photosynthetic mechanism of poplar leaves.（2）Different concentrations of H₂O₂ significantly reduced the chlorophyll fluorescence ability of poplar.As the concentration of H₂O₂ increased,the initial fluorescence（Fo）of poplar plants increased while the maximum fluorescence（Fm）decreased,and the actual photochemical efficiency(Φ_PSⅡ)and maximum photochemical efficiency（Fv/Fm）as well as photochemical burst（qP）also showed a decreasing trend,and the plants already exhibited photo in hibition.This indicates that H₂O₂ increases the degree of closure of the PSⅡ reaction center in poplar leaves,which decreases Fv/Fm andΦ_PSⅡ of the PSⅡ reaction center,and also inhibits the electron transfer activity.In addition,H₂O₂ increased the non-photochemical quenching（NPQ）in poplar,indicating that H₂O₂ increased the proportion of PSⅡ reaction centers used in the thermal dissipation pathway of antenna pigments and reduced the accumulation of excess light energy in PSⅡ reaction centers to protect the photosynthetic machinery from being damaged.In conclusion,H₂O₂ leads to a decrease in the capacity of photochemical reactions in plant leaves,the PSⅡ reaction centers of poplar plants are hindered in electron transfer,the content of primary quinone receptors（QA）in the oxidized state is reduced,the capacity of electron accumulation at the leaf plastid quinone（PQ）is enhanced but the efficiency of conversion into chemical energy is reduced;and poplar exhibits some self-protection mechanisms under the effect of H₂O₂.The leaf lutein cycle is used to increase the energy used for thermal dissipation and reduce the energy portion of photochemical reactions by light quanta to avoid damage to the photosynthetic mechanism of the leaves.（3）Poplar plants suffer from H₂O₂ stress,which will cause oxidative stress and osmotic stress in the plant will occur.The intracellular malonaldehyde（MDA）content increases,and the plant resists osmotic and oxidative stress by increasing the content of proline（Pro）and soluble sugars（SS）and the activity of various antioxidant enzymes.When poplar is subjected to oxidative stress caused by H₂O₂ stress,the levels of reactive oxygen species such as superoxide anion,hydrogen peroxide and hydroxyl radicals in the body are elevated causing damage to the normal physiology and biochemistry of the plant.To counteract the damage caused by reactive oxygen species,poplar activates its internal reactive oxygen species scavenging system when the reactive oxygen species level is elevated.At 0-20 mM,superoxide dismutase（SOD）,peroxidase（POD）,and catalase（CAT）contents in poplar increased with the increase of H₂O₂ concentration,and at the H₂O₂ concentration of 25 mM,SOD,POD,and CAT activities in poplar leaves decreased,indicating that the high concentration of H₂O₂ broke the balance of reactive oxygen scavenging system in plants and poplar’s The antioxidant system of poplar was damaged or destroyed.In addition,poplar responds to osmoregulation of the plant by increasing the content of Pro as well as SS osmotic substances as a way to better maintain the balance of osmotic pressure inside and outside the cells.