Effects Of Different Soil Nitrogen And Moisture Content On The Photosythetic Characteristics Of Syringa Oblate And Rhus Typhina Under Urban Environment

A experiment on the leaf daily dynamics of photosynthesis rate (Pn), transpiration rate (Tr),stomata conductance (Gs) , water use efficiency (WUE) of Syringa oblate, Rhus typhina and their relationships with environmental factors were conducted in the urban environment by using Li-6400 portable photosynthesis system. And through the way of simulation environment, the influence of photosynthetic eco-physiological of different soil nitrogen and the moisture content to Syringa oblata and Rhus typhina were studied in the urban environment. The results indicated:(1) The curves of diurnal variation in Pn of Syringa oblata and Rhus typhina in August had double peaks, with an obvious midday depression of photosynthesis, the curves of Pn in September to November had single peak,and the photosynthesis rate (Pn) reduced gradually along with the change of season. The curves of diurnal variation in Gs of them were as same as the curves of Pn in August to November, and they had a remark-able positive correlation.(2) The main factors that affect the diurnal variation of photosynthesis rate (Pn), stomata conductance (Gs) and transpiration rate (Tr) were different in different months. From August to November, the water use efficiency (WUE) of Syringa oblata and Rhus typhina increased gradually, implying that as the season changes, the photosynthesis rate (Pn) of them decreases, but the transpiration rate (Tr) reduces even more,in order to adapt to the change of environmental factors.(3)The t test indicated that Rhus typhina's Pn, Tr, Gs, Ci, LUE and CUE are higher than the Syringa oblata's and the differences are highly significant, the Rhus typhina has advantages in competition with Syringa oblata's.(4)The different soil moisture has the obvious influence to the leaf daily dynamics of photosynthetic of Syringa oblata and Rhus typhina. Along with the reduction of soil moisture content, the diurnal variation curve of photosynthetic rate of Rhus typhina shifted from a typical single peaked curve gradually to a double peaked one that signifies midday depression of photosynthesis. At the same time, according to the criteria suggested by Farquhar and Sharkey, the main factors affected midday photosynthesis rate reduces changed from stomatal limitation to non-stomatal limitation.The data mean of photosynthesis rate (Pn), stomata conductance (Gs) , transpiration rate (Tr) and intercellular CO2 concentration (Ci) of Rhus typhina reduced with the strengthen of drought stress. With the increase of water stress, the water use efficiency (WUE) of Rhus typhina has improved, implying that under the arid environment, Rhus typhina can through reduced the photosynthesis rate, stomata conductance and transpiration rate, in order to raised the water use efficiency, adapt to the arid environment.(5)The influences of different soil nitrogen and the moisture content to the photosynthesis physiology of Syringa oblata and Rhus typhina,, indicated that under the same nitrogen level condition, along with the drop of soil moisture content, the photosynthesis rate of them were remarkable drop, the leaf content of chlorophyll a, chlorophyll b and the chlorophyll a+b with the drop tendency, but the decline is different. Being suitable increases the nitrogen content of the city soil can improve the photosynthesis speed, stomata conductance, intercellular CO2 concentration and the water use efficiency and chlorophyll content of leaves, this can alleviate the drought stress of the plants of urban areas in some extent.