Difference In Leaf Characters And Physiological Response To High Temperature Of Two Mangrove Seedlings From Different Provenances

Plant leaves have the ability to adjust phenotypic characteristics according to different environmental conditions.The adaptability of leaf traits to the environment directly affects the survival,distribution and migration of plants under the background of climate change.Mangrove forests are woody plant community growing in intertidal zone of tropical and subtropical regions,which are composed of evergreen shrubs or trees with mangrove as the main body.Affected by global warming,mangrove forests are expanding to high latitudes.However,there is still a lack of understanding about the adaptability of leaf traits of different mangrove populations to temperature variation.In addition,occasional high temperature event is an important cause of death of mangrove plants.Global warming makes high temperature events occur more frequently,and there is a lack of research on the photosynthetic response of mangrove species and populations to abnormal high temperature.In this study,two mangrove species Kandelia obovata and Bruguiera gymnorrhiza seedlings from different provenances were selected as the research materials to explore the adaptive inheritance of leaf structural and functional traits of mangrove plants from different provenances to temperature and the physiological response of photosynthesis to high temperature.(1)The relationship between leaf anatomical parameters and photosynthetic capacity of seedlings from different provenances was studied.The results showed that the palisade tissue,spongy tissue and leaf thickness of the two mangrove species were significantly positively correlated with photosynthetic rate.The stomata of K.obovata seedlings were larger and sparser,and the leaf structure showed higher stress resistance,specifically with thicker epidermis and cuticle compared to B.gymnorrhiza.The leaf thickness,palisade tissue thickness and epidermis thickness of six populations of B.gymnorrhiza seedlings were significantly negatively correlated with the temperature of provenance,while the leaf anatomical structure of different populations of K.obovata seedlings were not correlated with the temperature of the native sites.The leaf anatomical structure of the two mangrove seedlings is different,and the genetic adaptation to the temperature of the provenance is also different.The leaf structure of B.gymnorrhiza has high genetic difference,which can be adapted to the high latitude environment by increasing the leaf thickness and palisade tissue thickness.The leaf anatomical structure of K.obovata is genetically conservative to the temperature adaptation of the provenance stress resistance.(2)The effects of high temperature treatment on photosynthetic characteristics of leaves of two geographical populations from Guangxi(lower latitude)and Okinawa(higher latitude)in Japan were studied.The effects of two days high temperature treatment on photosynthetic system characteristics of leaves were analyzed.The contents of xanthophyll cycle and chlorophyll a and b were determined.The photosystem I(PSI)and the photosystem II(PSII)activity in leaves were measured using a Dual-PAM-100 system.The main results are as follows: high temperature significantly reduced the maximum photochemical efficiency(Fv/Fm)of PSII in both species.The Fv/Fm decreased less in populations from lower latitude than that from higher latitude,but with less decrease in B.gymnorrhiza than in K.obovata seedlings.The P700 oxidation-reduction state(Pm)decreased less in lower than higher latitude populations.The leaf non-photochemical quenching(NPQ)increased with a higher rate in lower than in higher latitude populations.The xanthophyll pool size(V+A+Z)and deepoxidation ratio(A+Z)/(V+A+Z)increased by the heat treatment.Larger increase was observed in lower compared to higher latitude populations.(A+Z)/(V+A+Z)was correlated negatively with Fv/Fm,but positively with NPQ.Compared to other hardy habitats such as savannas and Midetteranean woodlands,mangroves had the largest xanthophyll pool size.On the second day of recovery,Fv/Fm was still at 0.69 in the K.obovata seedlings from the higher latitude,indicating irreversible photoinhibition of PSII,while all seedlings still maintained the higher deepoxiation ratio and NPQ to protect the photosystems.In conclusion,the lower latitude populations showed higher adaptability to heat stress partly because of strong photprotection through xanthophyll cycle,and there appeared a trade off between chilling and heat-tolerance between species and populations.In conclusion,this study provides new insights on the adaptive inheritance of leaf traits to temperature and the physiological mechanism of heat tolerance of mangrove plants,and has important reference significance for their survival,distribution and migration under the background of climate change in the future.