Response Of Poplar Seedling Photosynthesis To Phenolic Acid Stress In Soil

Poplar is an important tree species commonly used in the construction of shelter forests,timber forests and landscaping in China.The multi-generation continuous cropping and short-rotation cultivation management model is widely used in many regions of China.Previous studies have shown that multiple generations of continuous cropping can have significant adverse effects on poplar forest productivity,root growth and development,and soil physical and chemical properties.The reason is closely related to the accumulation of phenolic allelopathic substances in the soil,and soil phenolic acids.The effects of these substances on the physiological processes of poplar growth and development,especially the photosynthetic physiological processes,need to be further studied.At the Forestry Experimental Station of Shandong Agricultural University,a 1-year-old potted seedling of Populus×euramericana‘Neva’was used as a test material,and the phenolic acid content X in the rhizosphere of the second-generation poplar plantation was used as a reference.Under 6 kinds of soil phenolic acid concentrations（0.5X,1.0X,1.5X,2.0X,2.5X,3.0X）and control（0X）treatments,photosynthetic photosynthetic light response parameters,chlorophyll fluorescence parameters,chlorophyll content,changes in antioxidant enzyme activity and plant biomass.Main purpose:To explore the response characteristics and mechanism of poplar photosynthesis to phenolic acid stress in the soil,in order to provide a reference for further understanding of the effects of continuous cropping on poplar photosynthesis efficiency and productivity.Main results:（1）Effect of soil phenolic acid stress on photosynthetic efficiency parameters of poplar As soil phenolic acid concentration increased,the degree of inhibition of photosynthesis in poplar leaves increased.When the phenolic acid concentration exceeds 2.0X,the inhibitory effect is significantly intensified,and the photosynthetic efficiency parameters such as leaf P_n、P_nmax、Φ、F_v/F_m、Ф_PSII、LUE and WUE are significantly reduced,and photosynthesis appears obvious photoinhibition under high light intensity.（2）The main reasons for the limitation of photosynthesis of poplar by soil phenolic acid stress.With the increase of soil phenolic acid concentration,the main reasons for limiting photosynthesis of poplar changed.The main reason for the limitation at low concentrations（not exceeding 1.5X）is the stomatal factor,that is,the reduction of the stomatal opening of the leaves causes the supply of CO₂ to the photosynthetic mechanism to be blocked,and the PSII reaction center is temporarily deactivated;the main reason at higher concentrations（over1.5X）Transformed into non-stomatal factors,the photosynthetic mechanism has been damaged,the light energy absorbed and transmitted by PSII is reduced,the electrons are blocked in transmission,and the photoreactivity is reduced.（3）Physiological strategies of poplar photosynthesis to adapt to soil phenolic acid stress.Poplar photosynthesis has a certain resistance and protection mechanism against phenolic acid stress in soil.When the concentration of phenolic acid increases,PSII can release excess light energy by increasing heat dissipation,avoiding or reducing the damage of strong light suffered by photosynthetic mechanisms;when the concentration of phenolic acid is low（not exceeding 1.5X）,the leaf antioxidant enzymes（POD and SOD）activity and active oxygen scavenging ability are enhanced to protect the photosynthetic mechanism to reduce the damage of active oxygen,and at high concentrations（over 1.5X）,the antioxidant activity of the leaves decreases or suffers damage.（4）Morphological adaptation strategies of poplar plant growth to soil phenolic acid stress.Poplar growth has certain morphological adaptability to phenolic acid stress in the soil.Increased phenolic acid concentration,total biomass and leaf biomass of seedlings decreased,and growth was significantly inhibited;but the plant root-shoot ratio（RSR）increased significantly,which is beneficial to maintaining the ability of roots to absorb and supply soil nutrients,and enhance the growth of poplar Resistance to soil phenolic stress.To summarize the above:The increase of soil phenolic acid concentration increased the degree of inhibition of photosynthesis of poplar trees.When the concentration exceeded 1.5X,the main reason for inhibition changed from stomatal factors to non-stomatal factors,and photochemical reactions and antioxidant enzyme activities decreased.Poplar has certain physiological and growth adaptation strategies to soil phenolic acid stress.As the phenolic acid concentration increases,poplar can protect the photosynthetic mechanism by increasing heat dissipation,which can increase the root-shoot ratio of plants and increase resistance to phenolic acid stress.