湿地松幼树冠层光合作用日变化及其影响因素

Diurnal variation and effective factors of photosynthesis on the canopy layer of young Pinus elliottii forest

以四川盆地北部低山区湿地松Pinus elliottii幼林为研究对象，对冠层顶部不同年龄针叶光合作用、叶片温度以及冠层顸部空气温度和相对湿度、光照强度和二氧化碳摩尔分数的日变化进行测定，并测定针叶叶绿素质量分数。结果表明：1年生针叶和当年生针叶净光合速率随光照强度增强而增大，均未出现光合午休现象；叶片温度除了在12：00～14：00略高于气温外，其他时间均低于气温；气孔导度与蒸腾速率随时间变化规律相同，最大值出现在14：00；空气相对湿度呈“U”型变化；二氧化碳摩尔分数在8：00～16：00逐渐减小，并在18：00开始回升。1年生针叶净光合速率始终低于当年生针叶，而前者叶绿素质量分数低于后者。相关性分析表明，叶片温度、空气相对湿度、光照强度和气孔导度是引起湿地松光合日变化的主要因素。

Diurnal variation of photosynthesis, leaf temperature, air temperature, relative humidity, light intensity and CO2 concentration on the canopy layer of young Pinus elliottii forest in the low hilly area of northern Sichuan basin and their chlorophyll content of leaf were measured. The results showed that the net photosynthesis rate of 1- year-old leaf and 0-year-old leaf increased with the enhanced light intensity; the phenomenon of midday depression of photosynthetic rate wasn＇t found. The leaf temperature was lower than air temperature all the time except between 12： 00- 14： 00. The variation regularity of stomatal conductance and transpiration rate was similar, their max value both emerged at 14： 00. The diurnal variation of air relative humidity was in a ＂U＂ curve. The CO2 concentration was gradually decreased from 8： 00 to 16： 00, and it started to increase at 18： 00. The net photosynthesis rate of 1-year-old leaf was always lower than that of 0-year-old leaf, however, chlorophyll content of the former was higher than the latter. Through the correlation analysis, we found the main factors causing the diurnal variation of photosynthesis included leaf temperature, air relative humidity, light intensity and stomatal conductance. [Ch, 3 fig. 1 tab. 17 ref. ]