崇明岛东滩湿地芦苇光合作用对土壤水盐因子的响应

Responses of Photosynthesis of Phragmites australis to Water-salt Indicators of Soil in Dongtan Wetlands,Chongming Island

2015年3-10月,在崇明岛东滩湿地设置7块采样地,以不同水盐条件下生长的芦苇（Phragmites australis）为材料,应用便携式光合系统分析仪（Li-6400）,对芦苇的光响应特征进行实地测定,探讨芦苇光合过程对干旱和盐胁迫的响应机理。结果表明：1各月采样日的水位与土壤电导率显著负相关（n=420,p〈0.01）,适当增加土壤水位,有利于降低土壤电导率,从而缓解植物盐胁迫伤害;28月21日的芦苇叶片净光合速率、蒸腾速率和气孔导度与水位显著正相关（n=42,p〈0.01）,而与土壤电导率显著负相关（n=42,p〈0.01）;胞间CO2浓度与水位和土壤电导率不相关。当水位高于-50 cm,净光合速率随着水位下降而降低,非气孔因素可能是净光合速率下降的主要原因;当水位低于-50 cm时,土壤电导率高于10 m S/cm,叶片蒸腾速率快速降低,水分利用效率不断提高,芦苇叶片以较低的净光合速率来适应干旱胁迫和盐胁迫;芦苇叶片通过降低最大净光合速率、暗呼吸速率、光补偿点和光饱和点等光合生理特征来适应干旱胁迫和盐胁迫;芦苇叶片净光合速率和最大净光合速率对土壤水盐因子具有高度相关性,可以作为土壤水盐胁迫程度的反应指标。因此,在芦苇快速生长阶段,合理调控水位,对芦苇光合作用具有重要意义。

Phragmites australis is native dominant specie in the Yangtze Estuary, which plays a key role in the structure and function of wetland ecosystem. Wetlands is characteristic by changing soil water table and salinity, whereas little is known about the photosynthetic performance and consequent growth of Phragmites australis under varying soil water table and salinity, which has implication for the management of wetlands to sustain its structure and function. In this work, 7 sampling sites were chosen with different soil water table and salinity in Dongtan wetlands, Chongming Island, the soil water table and salinity were recorded across a year in2015, and measured the photosynthetic parameters during the growing season by using portable photosynthesis system（Li-6400）. The results showed that：（1） water table was negatively correlated with soil electrical conductivity（n=420,p〈0.01）, which an increasing water table could decreased the soil electrical conductivity and alleviate plant salt stress;（2） the net photosynthetic rate, transpiration rate and stomatal conductance of Phragmites australis had a significant positive correlation with water table（n=420,p〈0.01）, respectively, and had a significant negative correlation with soil electrical conductivity（n=420,p〈0.01） on August 21. Intercellular CO2 concentration had no significant correlation with water table and soil electrical conductivity. When water table was higher than-50 cm, the net photosynthetic rate decreased with the decrease of water table.The main reason for the decrease of net photosynthetic rate was non-stomatal limitation. When water table was lower than-50 cm and the soil electrical conductivity was higher than 10 m S/cm, the transpiration rate decreased rapidly, whereas the water use efficiency increased continuously, and the reed leaves adapted to drought stress and salt stress with low net photosynthetic rate. We concluded that Phragmites australis adapted to decreased water table accompanied by a higher soil electrical conductivity with lower maximum net photosynthetic rate, dark respiration, light compensation point and light saturation point. We suggested that net photosynthetic rate and maximum net photosynthetic rate could be used as the indicator of the degree of soil water-salt stress. Therefore, the influence of water table appeared to be crucial for the photosynthetic performance and consequent growth of Phragmites australis in the Yangtze Estuary.