Studies On Growth And Gas Exchange Characteristics Of The Main Afforestation Tree Species In Beijing

The net photosynthetic rate,water transpiration rate and water use efficiency of the main green tree species in Beijing have been studied in this paper. The article also discusses characteristics in different tree species. Morphological characteristics of Pinus provenances have been studied in this paper, which provide theoretical foundation for vegetation construction and management in Beijing.Study showed:the net photosynthetic rate of Pinus tabulaeformis is lower in spring, compared with summer and autumn. Pinus tabulaeformis and Platycladus orientalis have highest net photosynthetic rate in September,but their photosynthetic rate is lowest in April. Quercus variabilis has highest photosynthetic rate in July, but its photosynthetic rate is lowest in April. The net photosynthetic rate of Platycladus orientalis is higher than Pinus tabulaeformis in dry season, which confirmed that the drought tolerance of Platycladus orientalis is stronger than Pinus tabulaeformis. The soil water content of Pinus tabulaeformis and Platycladus orientalis.has the similar trend.The water transpiration rate of the main green tree species in Beijing is higher in summer and autumn. The water transpiration rate of Pinus tabulaeformis is higher in June and July, but lower in April, May and October. The change trend of the water transpiration rate of Pinus tabulaeformis is different,compared with sap flow fluctuation. The water transpiration rate of Pinus tabulaeformis is highest in September, lowest in April. The water transpiration rate of Quercus variabilis is highest in September, the value is 2.2 times as much as it is in May. The water transpiration rate in different tree species is: Quercus variabilis> Platycladus orientalis> Pinus tabulaeformis. Soil water content and light radiation of Platycladus orientalis have strong relationship with water transpiration rate.The water use efficiency of Pinus tabulaeformis in different season is autumn > summer > spring. The water use efficiency of Platycladus orientalis is:autumn> Summer> Spring. The water use efficiency of Quercus variabilis is: Summer >autumn > Spring. Quercus variabilis has higher water use efficiency than other tree species. Theδ13C value in different tree species is: Pinus tabulaeformis.> Platycladus orientalis> Quercus variabilis. Theδ13C value of Pinus tabulaeformis is: 32a>18a>1a.WUE has negative relationship with intercellular CO2 concentration. But the Correlation coefficient is variable significantly in different tree species.Morphological characteristics of Pinus provenances varies significantly. Tree Height doesn't has significant relationship with blade length, for they are controlled by different genetic factors. According to tree height and blade length, Pinus provenances are divided into four ecotypes: short-needle, low-tree-height type; Short-needle, high-tree-height type; long-needle, low-tree -height type; long-needle, Low-tree-height type.