Effect Of Air Pollution On Physiological Indexes And Photosynthetic Performance Of Lagerstroemia And Evaluation Of Resistance

Lagerstroemia indica L.is a summer-flowering deciduous shrub or small tree of the genus Lagerstroemia in the family Chiropterae,with rich flower colors and a flowering period of up to 100 days,which has both high ornamental value and the ability to absorb and purify harmful gases and has a strong resistance to pollution,and has been widely used in landscaping in China.Compared with other resistant plants,there is relatively little information on the resistance ability of plants of the genus Lagerstroemia,especially the physiological and biochemical response of Violet to environmental pollution gases and its evaluation system are not clear.The study was divided into two parts: indoor formaldehyde and benzene pollution stress and outdoor traffic exhaust pollution stress.’Susheng Yanhong’ Lagerstroemia,’Danhong Ziye’ Lagerstroemia,’Honghuoqiu’Lagerstroemia,’Tianerong’ Lagerstroemia and ’Bairizi’ Lagerstroemia were used as subjects in the indoor part,and Fujian Lagerstroemia,’Aishengfen’ Lagerstroemia,’Aishengzi’Lagerstroemia,’Honghuojian’ Lagerstroemia,’Caixia Mantian’ Lagerstroemia and Pink Lagerstroemia were used as subjects in the outdoor part.We measured the cell membrane permeable substances,antioxidant enzymes,osmoregulatory substances,photosynthetic characteristics and other indicators,analyzed their epidermal morphological characteristics,and used multivariate statistical analysis to comprehensively evaluate the anti-pollution ability of plants of the genus Lagerstroemia in two environments,indoor and outdoor,respectively,and the species that are resistant to indoor and outdoor pollutant gases are selected to explore the basic theory of the resistance of Lagerstroemia to pollution,to provide a basis for subsequent research,and to provide a reference for subsequent indoor and outdoor planting of Lagerstroemia.The relevant results of this study are as follows:1.Under formaldehyde and benzene pollution stress,the total chlorophyll content of all five Lagerstroemia species decreased to different degrees,malondialdehyde(MDA)content,ascorbate lyase(APX)activity,soluble sugar content(SS),and free proline(Pro)content increased with increasing pollution stress concentration,and the remaining physiological indicators varied during the stress.The net photosynthetic rate(Pn)decreased with the increase of stress concentration.High concentrations of formaldehyde and benzene pollution were able to inhibit the activity of some photosystem Ⅱ(PSⅡ)reaction centers,reduce the overall photosynthetic activity of PS Ⅱ,and affect energy dissipation and electron transfer between PSⅠ and PSⅡ.When the concentration of formaldehyde single stress reached 4 mg/m3,the photosynthetic system of ’Danhong Ziye’ leaves was severely damaged and the photosynthetic capacity of ’Honghuoqiu’ was least affected;when the concentration of benzene stress reached 4 mg/m3,the photosynthetic system of ’Tianerong’ was severely damaged and the photosynthetic capacity of ’Honghuoqiu’ was least affected;when the concentration of combined formaldehyde and benzene stress reached 4mg/m3,the photosynthetic system of ’Susheng Yanhong’ was severely damaged and the photosynthetic capacity of ’Honghuoqiu’ was least affected.The upper epidermal cells of the leaves of the five varieties of Lagerstroemia were reticulate and without stomata,and the lower epidermal cells were corrugated in different depths,with stomata of different sizes,mostly long oval,and the stomata of the leaves of ’Honghuoqiu’ were more rounded.Under formaldehyde and benzene pollution stress,the stomatal density of the leaves of five species of Lagerstroemia showed a trend of increasing and then decreasing with the increase of treatment concentration,and the long and short axes of stomata both showed a trend of decreasing and then increasing.2.The results showed that,under formaldehyde stress,the following were found:’Honghuoqiu’,’Danhong Ziye’,’Susheng Yanhong’,’Tianerong’,’Bairizi’,in descending order;under benzene stress,the following were found: ’Susheng Yanhong’,’Danhong Ziye’,’Tianerong’,’Bairizi’,’Honghuoqiu’,in descending order;under formaldehyde and benzene stress,the following were found:’Honghuoqiu’,’Susheng Yanhong’,’Tianerong’,’Bairizi’,’Danhong Ziye’,in descending order.3.In the traffic exhaust pollution test,the MDA content,superoxide anion radical(O2-)content,soluble sugar content(SS),soluble protein(SP)content,and proline(Pro)content of the six Lagerstroemia species were higher in the polluted area than in the clean area,chlorophyll content decreased significantly in the polluted area,and antioxidant enzyme activities varied.The upper epidermal cells of the leaves of all six Lagerstroemia varieties were reticulate and without stomata,while the lower epidermal cells were corrugated in different depths and had stomata of different sizes,all of which were long-elliptical.The long-to-short axis ratio of stomata in the lower epidermis of ’Aishengzi’ leaves decreased the most in the polluted area,suggesting that this variety may resist traffic exhaust pollution by regulating the stomatal opening.4.The resistance of six Lagerstroemia species in the traffic exhaust pollution area was evaluated comprehensively by principal component analysis and affiliation function method,and the results showed that among the six Lagerstroemia species,Fujian Lagerstroemia was the most resistant,followed by Pink Lagerstroemia,’Caixia Mantian’ Lagerstroemia,’Honghuojian’ Lagerstroemia,and ’Aishengzi’ Lagerstroemia and ’Aishengfen’Lagerstroemia were the least resistant.