Photosynthesis And Physiological Features Of Different Desert Species In Horqin Sandland

The four species of xerophytes Artemisia scoparia, Caragana microphylla Lam, Artemisia halodendrom Turcz .exBess and Pennisetum centrasiaticum are respectively the dominant species of the different vegeration forms in dry sand environment in Horqin sandland. And they have strong capabilities adapting to the desert climate. The research of the photosynthesis and ecophysiology features of these plants is helpful to understand the characters of them and the differences between them. It is significant to reveal the mechanism of their tolerence to drought and provide the theoretical and practical foundations of desertification control.Artemisia scoparia, Caragana microphylla Lam,Artemisia halodendrom Turcz .exBess and Pennisetum centrasiaticum are selected as experimental materials. The features of four species, including light response curves, CO₂ response curves, daily changes of the photosynthesis and contents of cholorophyll, were measured by Li-6400 photosynthesis measurement system in both pot and field experiments.The following conclusions in this study are made out through the pot experiments and field experiments in the different water conditions and different growing seasons:1. The photosynthesis characters of different plantsIn the field experiments, the photosynthetic rate of P. centrasiaticum was highest in the daily changes of photosynthesis rate. In the course of light responses, the photosynthetic rate of P. centrasiaticum was highest and A. scoparia, A. halodendrom and C. microphylla were following in turn. The photosynthetic rate of A. scoparia and P. centrasiaticum was similar. In the course of CO₂ responses, the photosynthetic rate of A. halodendrom was highest and P. centrasiaticum, C. microphylla, A. scoparia were following in turn. The photosynthetic rate of C. microphylla and P. centrasiaticum was similar.The effect of light radiation to these plants' photosynthesis was strongest in the factors of micro-climates while the temperature of atmosphere was impactive to A. scoparia and P. centrasiaticum. The influence of relative humidity of atmosphere to these species was less than other environmental factors.2. The influence of water to photosynthesisThe photosynthesis of A. scoparia changed greatly under different water conditions, and the photosynthetic rate was higher in good water condition. As A. scoparia is herb and its' root system is shallow, leaves of the plant were wilt and its photosynthetic rate decreased heavily at noon when it was extremely out of water.The photosynthesis of C. microphylla changed in a large scope ofwater conditions. In normal water situation, its' abilities of photosynthesis was much stronger. However, in bad water conditions, the abilities of photosynthesis descended quickly and the contents of proline rised rapidly.The photosynthesis of A. halodendrom was strong in normal water conditions. Under the condition of water stress, its' photosynthesis didn't change much more and the contents of proline didn't rise obviously. A. halodendrom has the tolerance to drought in a certain extent.3 The influence of carbon dioxide to photosynthesisComparing to the pot experiments, the field experiments indicated that the photosynthesis of A. halodendrom changed obviously most when the concentration of carbon dioxide rised. P. centrasiaticum, A. scoparia and C. microphylla were following in turn and the photosynthesis of them was very similar. The photosynthesis of P. centrasiaticum and C. microphylla kept rising when the concentration of carbon dioxide was 1000μmolm^-2s^-1. It can be concluded that the concentration of carbon dioxide was their important restricted factor to the potential of photosynthesis.4 The changes of water use efficiencyIn the field experiments, the transpiration rate of A. scoparia and A. halodendrom was much higher and the changes of the transpiration rate of A. scoparia was complex. The transpiration rate of C. microphylla waslow and the capability of keeping stable water contents was much better than other species. The water use efficiency of C. microphylla was best comparing with A. scoparia and A. halodendrom.In the pot experiments, the changes of transpiration rate of plants in different water gradients were obvious. The water use efficiency of plants in different water gradients was relative to water conditions. The water use efficiency was high in suitable water conditions. 5 The content of chlorophyll and prolineIn the field experiments, the contents of plants' chlorophyll and proline were not directly combining to the rate of photosynthesis. The photosynthetic rates of A. scoparia and C. microphylla were not high in serious water stress. The photosynthetic rates of P. centrasiaticum and A. halodendrom were high in slight water stress.In the pot experiments, the contents of chlorophyll of C. microphylla were highest, and A. scoparia was following in turn. The contents of chlorophyll of A. halodendrom was lowest comparing with other species. Based on the differences of the proline contents and the photosynthetic rates, it could be concluded that the tolerance of A. halodendrom to water stress was highest, and A. scoparia and C. microphylla were following in turn.