Study On The Photosynthetic Characteristics Of Leymus Chinensis In Hulunber Meadow Under Different Soil Moistures

In order to understand the influence of drought stress on Hulunber grassland productivity, many photosynthetic characteristics of Leymus chinensis with four soil moisture grades were measured with Li-6400 Portable Photosynthesis System in hulunber prairie, such as diurnal and seasonal variations in net photosynthetic rate , transpiration rate , stomatal conductance and intercellular CO2 concentration , the effect of photosynthetic active radiation , the changes of Chlorophyll content under different soil moisture grades. Explore the Photosynthesis law of Leymus chinensis in hulunber prairie, studied the photosynthetic characteristics of Leymus chinensis systematically. The results were showed as follows:1. The diurnal patterns of net photosynthetic rate (Pn) of Leymus chinensis presented two peaks curve under moisture treatments of 40%, 20% and 10%. The first peak appeared at 8:00 and the sub-peak at 16:00, with an obvious mid-depression. Under drought stress conditions (5%), the net photosynthetic rate reduced greatly with unobvious diurnal variation.2. The diurnal variations of transpiration rate and stomatal conductance presented double peak curves. The diurnal variation of intercellular CO2 concentration was opposite with that of net photosynthetic rate.3. The study of photosynthetic response indicated that under soil water stress conditions, maximum photosynthetic rate, light saturation point, apparent quantum yield and water use efficiency of Leymus chinensis decreased, and light compensation point increased.4. The seasonal variations of net photosynthetic rate, transpiration rate and stomatal conductance presented double peak curves. The net photosynthetic rate started rising from late May, the first peak appeared in mid-June, and the sub-peak in mid-August. At the end of growing season in September, the leaves of Leymus chinensis was turning yellow, due to the decline of photosynthetic organ and chlorophyll content gradually, the net photosynthetic rate reached the lowest point.5. The chlorophyll content (Chl) of Leymus chinensis reduced with the dedcline of soil moisture. Under drought stress conditions the chlorophyll content was the lowest, which indicated that drought stress reduced the chlorophyll content and photosynthetic capacity of Leymus chinensis.6. The drought stress could reduce the photosynthetic ability of grassland vegetation, and resulted in a remarkeble decline of Hulunber meadow ecosystem productivity.