内蒙古半干旱草原区沙地植物群落光合特征的动态研究

PHOTOSYNTHETIC CHARACTERISTICS OF A SEMI-ARID SANDY GRASSLAND COMMUNITY IN INNER MONGOLIA

沙蒿（Ａｒｔｅｍｉｓｉａ ｉｎｔｒａｍｏｎｇｏｌｉｃａ）群落是半干旱草原地区沙地的重要植被类型，分别在植物的生长前期、中期、盛期和后期采用便携式光合测定仪和大型同化分析仪测定了沙蒿叶片和沙蒿群落的光合动态。单叶和群落的光合速率日进程类型随气候的不同而异，瞬时光合速率主要决定于光合有效辐射强度（ＰＡＲ）。土壤干旱大大降低了单叶和群落的光合能力，晴天土壤湿润时气温和空气湿度控制着叶片的光合速率，午间大气湿度降低是光合午休的主要外因。叶片的蒸腾速率与气温呈显著线性相关，植物的光能和水分利用效率也主要取决于ＰＡＲ和气温，随着ＰＡＲ和气温的升高利用效率下降。沙蒿叶片光能利用效率在后期也能保持较高水平。沙蒿对土壤干旱和高温具有一定的适应性，在土壤湿润时能迅速提高光合速率，形成较大的生物量。但是沙蒿的蒸腾速率高，水分利用效率低。研究认为，沙蒿通过对土壤干旱和高温的忍耐机制而保持长时间较高的光能利用效率，并在土壤湿润时迅速提高光合能力和积累干物质来适应半干旱的沙地环境，而且依靠高蒸腾速率和强的水分吸收能力来竞争性抑制其他植物的生长。

Photosynthesis of Artemisia intramongolica leaves and communities were studied at different developing stages. The diurnal course of photosynthetic rates of leaves and communities changed with climate conditions, with the instantaneous photosynthetic rate depending logistically on PAR (Photosynthetically active radiation). Low soil moisture content greatly depressed light use capacity of plant leaves and communities. On clear days photosynthetic rates mainly depended on air temperature and humidity under favorable soil water condition. Low mid-day air humidity was the critical environmental factor in observed contributing to 'mid-day depression' of photosynthesis. The transpiration rate of leaves was linearly correlated with air temperature. Moreover, the light use efficiency (LUE) and water use efficiency (WUE) of plants were both closely associated with PAR and air temperatures in a negative linear relationship. A. intramongolica maintained relatively high CO2 fixation capability under dry soil and high air temperature conditions, though, once soil water content increased, photosynthetic rate and biomass were observed to also increase greatly. These results suggested that the photosynthetic strategy of A. intramongolica is adapted to the conditions of sandy soils in the semi-arid regions where it occurs through its ability to maintaining a certain degree of LUE for a long time under water stress and high temperature and then to resume high photosynthetic rate when soil moisture status improves. It competitively inhibits other species through its high water harvesting capacity and its high transpiration rate.