Differentiation Of Intraspecific Functional Traits In Different Tree Ages In Hainan Island

Old trees are"witnesses"of history and culture,with high scientific research value.The adaptation of plants may be different in different environments and different life cycle stages.Based on the investigation of the old tree resources in Hainan Island,different sizes of Bombax malabaricum,Ficus altissima,Ficus microphylla,Litchi chinensis and Dimocarpus longan are used to represent different ages of trees,to explore the changes and correlations of tree traits of different ages,geographical environment and kinship,and to reveal the differentiation rules of functional traits of different sizes of trees,so as to provide basis for the protection of old trees.The main results are as follows:1)According to the investigation of old tree resources in Hainan Island,it is found that there are 17944 old trees,belonging to 67 families,179 genera and 313 species.The number of Ficus microphylla trees is the largest,3727,accounting for 20.60%of the total,followed by Tamarindus indica,2096,accounting for 11.59%of the total.There are 159old trees over 500 years old,919 old trees over 300-499 years old and 16866 old trees over100-299 years old.There are 14914 normal old trees,accounting for 83.11%of the whole province;2785 weak old trees,accounting for 15.52%of the total;246 endangered old trees,accounting for 1.37%of the total.2)In Hainan Island,there wre a significant relationship between the functional traits of Bombax malabaricum in different ages,among which the leaf thickness(LTh)was significantly related to the sponge tissue thickness(PT),palisade tissue thickness(ST),lower epidermis thickness(LE),upper epidermis thickness(UE),guard cell length(GCL)and stomatal area index(SAI);the lower epidermis thickness(LE)and leaf thickness(LTh)of old trees ware significantly related.There was a significant trade-off between leaf thickness(LTh)and leaf epidermis thickness(LE)in different diameter classes of Bombax malabaricum.It showd that we should give priority to protecting the old trees.The relationship of LE-LTh allometric growth in different distribution of kapok also showed that hydraulic physiology played an important role in the old tree.It was suggested that measures should be taken to protect old trees,such as artificial transplanting,improving soil moisture and water absorption capacity.3)The hydraulic traits in old trees of Litchi chinensis,such as water potential,water capacity,transpiration rate,potential water use efficiency and hydraulic conductivity,were significantly higher than those of small trees.The chlorophyll b old trees content in the leaves was significantly higher than that of small trees,while Rubisco activity was significantly lower than that of small trees.The plasticity indexes of transpiration rate,potential water use efficiency,osmotic potential of swelling pressure loss point,standardized water capacity and hydraulic conductivity of ancient trees were significantly lower than those of small trees,and there was no significant difference between other plasticity indexes and small trees.In the photosynthetic correlation of litchi,the plasticity index of chlorophyll b of ancient leaves was significantly lower than that of small trees.The transpiration rate,net photosynthetic rate and stomatal conductance(T_r-P_n,T_r-G_s)of litchi ancient trees showed significant different growth rate,while the transpiration rate,net photosynthetic rate and stomatal conductance(T_r-P_n,T_r-G_s)of litchi small trees showed significant different growth rate.The functional traits of Litchi chinensis ware affected by the environmental conditions and the age of its own trees.Therefore,when we protect the ancient trees,we needed to take appropriate measures,such as real-time irrigating in the dry season,improving the soil water and water absorption capacity and other measures to ensure that the old trees have sufficient water.The results also showed that different age plants have different adaptability to the environment,and further expand the research about old trees and Litchi chinensis.4)Ficus altissima and Ficus microphylla belong to the same genus,but the variation of functional characters is different with the increase of tree age.Litchi chinensis and Dimocarpus longan are sapless subfamilies,but the variation of functional traits is not consistent with the increase of tree age.The results showed that there were no difference in PT,UE,chlorophyll b and Rubisco between F altissima,F microphylla,L chinensis,D longan;Tr,WUE,Pn and Gn had difference between F altissima,F microphylla,L chinensis,D longan.There are different correlation strategies between water photosynthetic traits of F altissima and F microphylla.The former has a large investment in photosynthesis and hydraulic traits,while the latter has a different investment in water and light at large and small scale.The water photosynthetic investment of litchi and longan is the investment of hydraulic and photosynthesis.To sum up,the correlation between the close relatives of F altissima and F microphylla is not the same,while that between the distant relatives of L chinensis and D longan is the same.