A Study On The Photosynthetic Physioecology Of Oriental Oak

Oriental oak is one of the most important afforestation tree species. The diurnal and seasonal dynamics of its photosynthesis, the response of its photosynthesis to elevated CO₂ concentration, the light distribution in oriental oak forest and the photosynthetic characteristics of main plant species in the forest were measured with Licor-6400 photosynthesis system and LI-188B integrating quantum/radiometer/photometer. Furthermore, the photosynthetic characteristics of oriental oak were compared to other tree species growing in the same area and the relationship between photosynthesis and eco-physiological factors was analyzed with principal analysis and path analysis. Finally, through potted seedling experiment, the response of oriental oak seedlings to water stress was determined. The study provided the foundation for predicting the production and making carbon budget of oriental oak forest, realizing the integrity of oriental community, understanding the response of forest to global changes and managing seedlings and young forest of oriental oak. The main results were as follows:1. The oriental oak had high CO₂ compensation point and high light saturation point, which showed that it was a light-demanding C₃ plant.2. Its daily course of net photosynthetic rate (Pn) in early growing season and fast growing season was single peaked, which during late growing season was double peaked. Its Pn in fast growing season is highest and its Pn in early growing was higher than that in late growing season.3. Its daily course of dark respiration (Rd) in early and late growing seasons was single peaked, which in fast growing season was double peaked.4. Its transpiration rate (Tr) in fine day is clearly higher than that in overcast day. Its Tr in fast growing season was clearly higher than that in early and late growing seasons. Its water use efficiency(WUE) in fast growing season is lowest, and its WUE in early season was higher than that in late growing season.5. The factor limiting the Pn of oriental oak in early growing season was temperature. The leading factors aifecting Pn in fast growing and late growing seasons were photosynthetic active radiation (PAR) and inter-cellular CO₂ concentration (Ci). In fast growing season ,the leading factors in fine day were PAR and Ci, which in cloudy day were PAR and conductance to H₂O (COND), which in overcast day were PAR and vapor pressure deficit based on temperature (VPD).6. The leading factor affecting Rd was temperature and other factors such as VPD, humidity and Ci also affected the Rd.7. Tr was regulated directly by COND and indirectly by PAR, temperature and relative humidity.8. The capacity of Pn was sawtooth oak>oriental oak >beautiful sweetgum >Chinese fir. The rank of light-demanding was sawtooth oak >oriental oak> Chinese fir > beautiful sweetgum.9. The daily courses of Pn of sawtooth oak and beautiful sweetgum in fast growing season weresingle peaked, these of Chinese fir and oriental oak were double peaked. The rank of thoes plant species WUE was Chinese fir >oriental oak> beautiful sweetgum > sawtooth oak10. Compared with the intensity of light above the crown, the light intensity under the crown clearly decreased. The PAR under the crown decreased most greatly. The light saturation point (LCP) and the light compensation point (LCP) were tree>shrub>herb.11. The Pn,WUE and LSP of oriental oak increased and the COND,Tr and Rd decreased under elevated CO2 concentration.12. The Pn ,Tr, the height, diameter at foot and biomass of oriental oak seedlings decreased when the soil water content was reduced, however, the WUE increased in the same process.