南方型和北方型美洲黑杨幼苗光合作用的日季节变化

在自然条件下,采用Li-6400便携式光合作用测定系统研究了南方型和北方型美洲黑杨在5、7、9月的光合日变化。结果表明:南方型美洲黑杨在5月和9月的净光合速率日变化为单峰曲线,峰值分别为15.79、14.13 μmol·m^-2·s^-1,在7月为双峰曲线,最高峰值为22.03 μmol·m^-2·s^-1;北方型美洲黑杨在5、7、9月的净光合速率日变化一直为双峰曲线,最高峰值分别为13.46、18.08、12.91 μmol·m^-2·s^-1。南方型美洲黑杨仅在生长旺盛的7月存在光合"午休"现象;北方型美洲黑杨在整个生长季均存在光合"午休"现象;南北方型美洲黑杨净光合速率季节变化特点为:夏季(7月)>春季(5月)>秋季(9月);10月份,南方型美洲黑杨净光合速率达到12.70 μmol·m^-2·s^-1,北方型美洲黑杨已落叶。分别对南方型和北方型美洲黑杨5、7、9月的光合有效辐射、气温、空气相对湿度、空气CO₂浓度与净光合速率进行逐步多元回归、偏相关及通径分析,影响净光合速率的主要生态因子是光合有效辐射。

Studies on Photosynthetic Characteristics of South-and North-typed Populus deltoides Younglings

The results showed that: the curves of diurna1 variations of net photosynthetic rate for South-typed Populus deltoides had one single peak curve in May and September, the peak values were respectively 15.79 and 14.13 μmol·m~(-2)·s~(-1), while it showed two-peak curve in July, the biggest value was 22.03 μmol·m~(-2)·s~(-1). North-typed P. deltoides showed a two-peak curve in the three months, the biggest value was respectively 13.46, 18.08, 12.91 μmol·m~(-2)·s~(-1) and North-typed P. deltoides had the phenomenon of "photosynthetic midday depression"; while South-typed had the phenomenon only in July. The photosynthetic characteristics of North- and South-type P.deltoides in different months had a certain similarity, both was summer(July)> spring(May)> autumn(September), In October, the net photosynthetic rate of South-typed P. deltoides was 12.7 μmol·m~(-2)·s~(-1), while the North-typed P. deltoides had already no leaves left. By using the methods of stepwise multiple regression, partial correlation and path analysis, it analyzed photosynthetic active radiation, air temperature, air relative humidity, air CO_2 concentration and net photosynthetic rate of the south and north-type Populus deltoides respectively in May, July and September. PARo is the most important ecological factor influencing the net photosynthetic rate of P. deltoides.