Study On The Photosynthetic Characteristics And Environmental Response For Leaves Of Various Growth Periods Of Three Kinds Of Broadleaf Trees

The photosynthetic rates of poplar leaves of three different growth period and the pattern of daily changes of their photosynthetic parameters in summer and autumn and those of tulip tree and cyclocarya paliurus in autumn were measured, hoping to further master the pattern of poplar photosynthesis, offering scientific references for high-yield cultivation and management of these kinds of trees. Research results show that: 1、 The sequence of the value of the poplar leaf photosynthetic rate with different leaf growth periods in summer is as follows: mature leaves(4.94μmol CO2 m-2 s-1)>new leaves(4.91μmol CO2 m-2 s-1)>old leaves(4.40μmol CO2 m-2 s-1) while the sequence in autumn is mature leaves(6.96μmol CO2 m-2 s-1)>old leaves(6.75μmol CO2 m-2 s-1)>new leaves(5.53μmol CO2 m-2 s-1). The mature leaves have the most high-temperature and high-intensity resistance. Base on the photosynthetic model made of the relationship between ecological factors and three kinds leaves, we can know that the order of the required intensity for highest photosynthetic rate is old leaves(1533μmol m-2 s-1)>mature leaves(1333μmol m-2 s-1)>new leaves(1133μmol m-2 s-1), and the highest values go like mature leaves(15.22μmol CO2 m-2 s-1) > new leaves(13.69μmol CO2 m-2 s-1)>old leaves(12.18μmol CO2 m-2 s-1); The required temperatures of highest photosynthetic rate of three kinds leaves are similar, between 24℃~25℃. The main effected factors for poplar in summer are excessive temperature and intensity, while insufficient light in autumn. 2、 The sequence of the value of the tulip tree leaf photosynthetic rate with different leaf growth periods in autumn is as follows: mature leaves(7.00μmol CO2 m-2 s-1) > new leaves(6.29μmol CO2 m-2 s-1)>old leaves(2.97μmol CO2 m-2 s-1). Base on the photosynthetic model, we can know that the sequence of the required intensity for highest photosynthetic rate is new leaves(1064μmol m-2 s-1)>mature leaves(1056μmol m-2 s-1)>old leaves(894μmol m-2 s-1), and the highest values go like mature leaves(10.41μmol CO2 m-2 s-1) > new leaves(8.72μmol CO2 m-2 s-1)>old leaves(4.71μmol CO2 m-2 s-1); The required temperatures of highest photosynthetic rate of three kinds leaves are different, The values are 17℃(new leaves),20℃(mature leaves)and 18℃(old leaves) respectively. 3、 The sequence of the value of the cyclocarya paliurus leaf photosynthetic rate with different leaf growth periods in autumn is as follows: mature leaves(5.17μmol CO2 m-2 s-1)>old leaves(4.5μmol CO2 m-2 s-1)>new leaves(3.70μmol CO2 m-2 s-1). Base on the photosynthetic model, we can know that the sequence of the required intensity for highest photosynthetic rate is mature leaves(960μmol m-2 s-1)>old leaves(800μmol m-2 s-1)>new leaves(747μmol m-2 s-1), and the highest values go like mature leaves(6.69μmol CO2 m-2 s-1)>new leaves(5.43μmol CO2 m-2 s-1)>old leaves(5.28μmol CO2 m-2 s-1); The required temperatures for new leaves and mature leaves are both 23℃,that for old leaves is 21℃.4、 Through the research on the correlation analysis of three kinds leaves, we can conclude that stomatal conductance(Cond), concentration of intercellular CO2(Ci) and transpiration rate(Trmmol) are major physiological factors influencing the net photosynthetic efficiency. By calculating the stomatal limitation value, we know that the stomatal limitation results in the decline of photosynthetic rate.5、 PAR(PARi),leaf temperature(Tleaf),ambient humidity are major ecological factors influencing the net photosynthetic efficiency. Based on the photosynthetic model, we can know that the increase of PAR, leaf temperature and ambient humidity will result in the increase of photosynthetic rate, but it will have the opposite effect after the limitation, the mature leaves have the most high-temperature and high-intensity resistance.Combining the comparative analysis on each photosynthetic parameter, mature leaves have the most complete leaf functions, and they are main contributors to the photosynthesis. The order of new leaves and old leaves may be differ based on the leaf-selected and season, but generally, new leaves have the higher stability and vitality.