18年生杉木不同部位和叶龄针叶光响应研究

在最适温度(30±1℃)、适宜湿度(70%±5％)和正常大气CO2浓度（350±10×10-6V/V）向下，采用活体测定方法，测定了18年生杉木不同部位和叶龄针叶对光照的稳态和动态响应。结果表明，不同部位和叶龄针叶净光合速率（Pn）的光响应特征有明显差异，从上部到下部、从当年生到1年生至2年生，针叶Pn、饱和光强（PSLI）和光补偿点（LCP）降低，表观量子效率（α）提高。经一定时间暗处理后，针叶需要一定光诱导才能获得相应光强下的最大Pn。光诱导期长短与猝发性光强以及叶龄和针叶在树冠中所处的部位有关。猝发性光照越强，所需的光诱导期越长；下部针叶光诱导期短于中部针叶；而1年生针叶短于当年生针叶。不同部位针叶对稳态和动态光照的响应与针叶长期适应所处的光环境有关，而不同叶龄的差异除与生理活性有关外，也可能与所处的光环境有关。

Light responses of 18-year-old China fir shoots in relation to shoot ages and positions within crown

Stable and dynamic light responses for net photosynthetic rate of 18-year-old China fir shoots with different age and position within the tree crown were measured under optimum temperature(30±10℃) and humidity(70%±5％) for photosynthesis and normal ambient CO2（350±10×10-6V/V）. Results showed that Pn, photosynthetic saturated light intensity (PSLI) and light compensation point (LCP) of shoots decreased from upper crown through mid-crown to lower-crown while apparent photo utilization efficiency (α) increased. With the aging of shoots, Pn, PSLI and LCP also decreased while α increased too. After a certain period of darkness treatment, a photo induction process was required to get maximum Pn. However the length of induction period depended on sudden light intensity, shoot age and position within the tree crown. The higher the sudden light intensity, the longer the induction period. The induction period of shoots at lower crown was shorter than mid-crown, and that of current shoots was longer than 1-year-old shoots. It is suggested that different stable and dynamic responses between different positions were related to micro-light environment which shoots acclimated in a long term, while the differences between different shoot ages were associated not only to physiological activities of shoots but also resulted from acclimated micro-light environment.