气候变暖下干旱对森林生态系统的影响

人类活动显著影响着全球大气循环格局,全球平均温度升高导致干旱事件发生幅度、频度和持续时间增加,这对森林生态系统带来更多的是负面影响.本文基于已有研究,系统总结了干旱事件对森林生态系统地理分布格局、群落结构重建、植物生长和生理特性、死亡和灭绝、植物生产力以及碳循环功能的影响及其机理,并对未来干旱事件对森林生态系统长期效应以及在不同时间尺度上作用机理的研究提出建议.本研究对开展全球变化背景下森林生态系统对干旱事件响应机制的研究具有重要指导意义.     

Mechanisms of Enhancement of Photocatalytic Properties and Activity of Nd^3＋ -Doped TiO2 for Methyl Orange Degradation

Nd^3 -doped TiO2 powders were prepared by the sol-gel method. Their crystal pattern and parameter, the specific surface area, the surface chemical state of Ti and the ratio of O/Ti were characterized. The results show that Nd impurity hinders the crystal transformation, and decreases the relative intensity of (101) peak. The crystallite sizes of Nd^3 -doped TiO2 powders decrease while their specific surface area increase owing to the Nd^3 doping. The XPS measurement shows that the content of Ti (Ⅲ) and ratio of O/Ti on their surfaces increase significantly with the increase of Nd^3 dosage. The adsorption and photodegradation experiments show that the optimum molar content of Nd^3 is 1.2%.