不同透光环境下红松光合色素含量的季节变动及应对策略

Seasonal variation of photosynthetic pigment content in Pinus koraiensis:the role of different light-induced strategies

研究了辽东山区天然次生林内3种不同透光环境(强度透光、中度透光和弱度透光)下红松针叶光合色素(叶绿素a(Chl a)、叶绿素b(Chl b)、类胡萝卜素(Car)和叶绿素总量(Chl T))应对光环境季节变动做出的适应性调整。结果表明,随季节的变动(从春季至秋季),林分透光孔隙度逐渐减小。春季,透光度越大,红松叶绿素含量越高,Chl a/b值升高,Car/Chl T值降低;夏季,不同透光条件对红松光合色素含量无影响;秋季,各类透光条件下红松光合色素含量总体表现为升高的趋势,强度透光与中度透光条件红松针叶Chl a/b显著大于弱度透光,3种透光条件下红松Car/Chl T均降低。在春季红松开始生长前进行适当抚育,能提高光合色素含量,增强光合作用能力,促进生长。

Broad-leaved Korean pine forest （BKPF） is one of several zonal climax vegetation types dominated by Korean pine （Pinus koraiensis） in the temperate forest region of Northeast China. Unfortunately, intense human activities and extreme natural disturbances have continuously affected the succession of the BKPFs for the past century. Most of the historic areas of BKPFs have succeeded into secondary forests that are not dominated by Korean pine. As a result, since the 1960s, P. koraiensis seedlings have been planted under the canopy of secondary forests in an effort to restore the BKPFs. The status of the survival and growth of P. koraiensis saplings under the canopy of secondary forests has been considered to be an important indicator demonstrating the success of these efforts. Many reports suggested that light was one of the most important environmental factors affecting the regeneration and growth of P. koraiensis. Generally, P. koraiensis is considered to be both a tolerant and intolerant species, having a dual response to light conditions in forest communities depending on its habitat and age classes. P. koraiensis seedlings are able to survive under closed canopy conditions; canopy openness ranging from 0.5 to 0.6 is optimal for the survival and growth of P. koraiensis seedlings. However, as the saplings grow, they need more and more light and finally become intolerant to shaded conditions. For example, compared with seedlings, slightly more mature trees will grow under a forest canopy with a canopy openness of 0.7 for the long-term, but they grow poorly and eventually die under those conditions over an extended period of time. Selective thinning is almost always carried out when P. koraiensis saplings reach an age of 8 to 10 years. However, the needles of P. koraiensis may turn yellow after the selective thinning indicating that the type and quantity of photosynthetic pigments in needles changes in response to the selective thinning. This study was conducted to analyze the response of the photosynthetic pigments in P. koraiensis needles to selective thinning in an effort to understand the relationships between the light environment and the regeneration of P. koraiensis. The experiments were conducted at Qingyuan Experimental Station of Forest Ecology, Chinese Academy of Sciences, located in Changsha, Qingyuan County, Fushun City, Liaoning Province, China. We compared the content of chlorophyll a （Chl a）, chlorophyll b （Chl b）, carotenoids （Car）, and total chlorophyll （Chl T） in P. koraiensis needles under three light environments： low-, mid- and high light levels in a secondary forest. The results showed that canopy openness decreased from a high-level light to low-level light environment from spring through summer to autumn. In spring, the chlorophyll content and the ratio of Chl a/b increased, but the ratio of Car/Chl T decreased as the light levels changed from a low-level to high-level light environment. However, the Car content did not change significantly during spring. In summer, no significant differences in pigment content were observed among the three light levels, but the pigment content was higher than that in spring for all pigments analyzed here. In autumn, the ratio of Chl a/b was higher in the high-level and mid-level light environments than that in the low-level light environment. The photosynthetic pigment content increased in all three light levels from spring to summer, but the ratio of Car/Chl T decreased significantly during the same time period. In summary, these results suggest that thinning management designed to increase light-transmittance should be conducted in spring and a mid-level thinning intensity is suitable for improving the photosynthetic capability and for accelerating growth of P. koraiensis under the canopy of secondary forests.