甜橙密植果园光合特性研究

STUDIES ON PHOTOSYNTHETIC PROPERTIES OF SWEET ORANGE TREES IN DENSELY PLANTING ORCHARDS

甜橙净光合速率的季节性变化,春梢叶片呈双峰形,高峰出现在6月和9月,光合值为19.5953mgCO_2/dm^2·h 和25.1490mgCO_2/dm^2·h;秋叶净光合速率也呈双峰形,第一次高峰出现在10月上旬,第二次高峰在次年5月中旬,光合值分别是17.9051mgCO_2/dm^2·h 和17.4264mgCO_2/dm^2·h。叶片光合产物输出率的变化趋势与叶片的光合速率基本一致,一般占总光合量的30～50%左右。叶绿素含量的季节性变化与光合速率相似,春叶呈极显著相关,r=0.8937^(**)。甜橙密植果园树冠各部位的相对光照强度随树高的增加而增大,随叶幕层的加深而急剧减弱,栽植密度主要影响叶幕层的光照强度。

The photosynthetic rate of densely planted orange (Citrus sinensis)trees was studied using a modified“half method”.The seasonal fluctuationof net photosynthetic rate (Pn) of spring leaves presented a double-peakpattern with the peaks appearing in June and September,Pn being 19.59and 25.15 mg CO_2/dm^2·h,respectively.The seasonal fluction in autumnleaves also exhibited a double-peak pattern:the first peak appeared inearly October and the second in mid-May,with Pn being 17.91 and 17.43mg CO_2/dm^2.h,respectiely.The seasonal fluctuation pattern of photos-ynthate transport rate seemed to be similar to that of leaf Pn.The ratewas generally in the range of 25-50% of the total Pn.Pn levels increasedwith chlorophyll contents (r=0.8987^(**)).The relative intensity of photos-ynthetically active radiation (PAR) at every location of the canopyincreased with tree height.As the green-leaf layer thickened,the relativeintensity of PAR reduced sharply.Planting density mainly influenced therelative intensity of PAR in the outer sections of the green-leaf layer ofthe tree canopy.