热带季节雨林冠层树种绒毛番龙眼的光合生理生态特性

采用Li-6400便携式光合作用测定仪，对西双版纳热带季节雨林冠层树种绒毛番龙眼成树树冠上、中、下3层叶片进行了测定，分析西双版纳热带季节雨林冠层树木的光合作用.结果表明，绒毛番龙眼成树具有喜光的光合特性，光饱和点较高(1 000～1 500 μmol·m^-2·s^-1)，而光补偿点较低(7.7～15.3 μmol·m^-2·s^-1)，对光环境有较强的适应和调节能力，光合有效辐射是影响绒毛番龙眼光合日进程的关键因子；12月，叶片处于成熟期，生长良好，光合能力较强，树冠上层净光合速率（P_n）日变化为单峰型，最大净光合速率（A_max）约为8.9 μmol CO₂·m^-2·s^-1；4月处于新老树叶更替期，光合能力下降，树冠上层P_n日变化为双峰型，中午出现“午休”现象，树冠上层A_max约为4.3 μmol CO₂·m^-2·s^-1；7月上、中层叶片P_n为单峰型，下层出现“午休”.如人为使CO₂浓度在短期内迅速升高，则绒毛番龙眼的P_n会增加，而气孔导度和蒸腾速率降低；CO₂浓度从400 μmol·mol^-1升高到800 μmol·mol^-1时，干季水分利用效率（WUE）提高约50%～100％，雨季WUE较低.

Physiology and ecology of Pometia tomentosa photosynthesis in tropical seasonal rain forest

Pometia tomentosa is a dominant uppermost canopy tree in Xishuangbanna tropical seasonal rain forest. In this paper, the photosynthetic characteristics of the three layers of P. tomentosa canopy were measured with Li-6400 portable photosynthesis system, and the results showed that P. tomentosa had the characteristics of high light saturation point (1 000 - 1 500 micromol x m(-2) x s(-1)) and low compensation point (7.7 - 15.3 micromol x m(-2) x s(-1)). Its leaf photosynthesis had the adaptive responses when the high irradiance changed. PAR was the main factor affecting the diurnal changes of net photosynthesis. In December, the leaf grew well, and had a high ability of photosynthesis, with the diurnal change of P. for upper layer exhibiting single-peaked pattern and the maximum value being 8.9 micromol CO2 x m(-2) x s(-1). April was the alternative period of old and young leaves, and the ability of photosynthesis was dropped, with the diurnal change of P(n) for upper layer following double-peaked curve and the maximum value being 4.3 micromol CO2 x m(-2) x s(-1). The highest net photosynthesis rate was observed in July, with the diurnal change of P. for upper and middle layers exhibiting single-peaked pattern and that for lower layers being double-peaked. Short-term enriched CO2 concentration could evidently increase the photosynthesis of P. tomentosa, while the stomatic conductance and transpiration would be inhibited. When the CO, concentration increased from 400 micromol x mol(-1) to 800 micromol x mol(-1), water use efficiency (WUE) was increased by 50% - 100% in dry season, but rather low in wet season.