森林砍伐对苦槠种群遗传结构的影响

Effects of deforestation on the genetic structure of Castanopsis sclerophylla

人类活动严重干扰着自然生态系统,其中砍伐是对森林生态系统最常见的干扰之一,它导致森林退化,植物种群变小,甚至灭绝,遗传多样性也随之下降。当被破坏的森林未被转换性利用时,则会逐渐恢复,但由于瓶颈效应,恢复起来的生态系统中植物种群的遗传结构可能会改变。恢复种群遗传组成的改变一方面与干扰的强度、频度和持续时间有关,另一方面,也受植物生活史特点的深刻影响。然而,我国对于砍伐后恢复起来的森林生态系统中生物多样性的改变,尤其是遗传多样性的改变的研究并不多见。研究在浙江省宁波市天童国家森林公园及周边地区选择了5个苦槠种群,采用SSR微卫星标记来分析砍伐对苦槠种群遗传结构的影响。5对多态SSR引物共得到了29个等位基因。种群内维持了较高的遗传多样性,种群间遗传分化程度较低,基因流达8.68。恢复林和成熟林种群的遗传多样性相差不大,以阿育王寺地区恢复种群的最高;表明砍伐对于苦槠种群遗传多样性的影响不大,这与苦槠较强的萌条能力有关。尽管如此,在恢复种群中观察到近期的种群瓶颈,显示出砍伐对种群遗传组成的影响;而在一个成熟林中也观察到种群瓶颈,这是因片断化导致种群变小之故。植被保存最好的天童国家森林公园内苦槠种群的遗传多样性却较低,这可能与成熟林中苦槠优势度较低有关。

Human activities have vital impacts on ecosystems. Deforestation is one of the most common human activities. Deforestation leads to reduced population sizes of the remnant plants, or leads to local extinction. When deforestation stops, population size of remnant plants may increase gradually and some extinct species may appear via seed dispersal. However, genetic composition of the restored populations may be changed due to bottleneck effect or founder effect. Theoretical studies have proven that deforestation has negative impacts on genetic variation, and that rare alleles are especially vulnerable to loss. However, there are few empirical studies concerning the genetic consequences of deforestation on plant species. East China has suffered from serious deforestation, and there is hardly any pristine forest remaining. Zonal vegetation in subtropical areas of East China is constituted largely by evergreen broadleaved forests （EBLFs）. Castanopsis sclerophyUa is one of the dominant species of EBLFs and is also one of the earliest evergreen plants to recover during the restoration process that follows after deforestation. Therefore, it is an ideal species to check the effects of deforestation on genetic variation. To study the effects of deforestation on genetic variation of Castanopsis sclerophylla, a total of 138 individuals were collected from 5 populations, among them two were from mature forests and three were from restored forests. We used microsatellites to detect the genetic composition. After screening the mierosatellite primers available in congener species C. cuspidata var. sieboldii, we got five pairs of primer suitable for C. sclerophylla. Each individual was genotyped at the five microsatellite loci. The five loci revealed 29 alleles in the global population. Mean number of alleles per locus, effective number of alleles per locus and allelic richness of the global population were 5.80, 3.54 and 4.85 respectively. The observed heterozygosity （0.53） was significantly lower than the expected heterozygosity （0.72） （p 〈 0.01 ）. Withinpopulation genetic diversity was high, and no significant difference was found between populations from mature forests and from restored forests. Little genetic differentiation （ GST = 0. 028, FST = 0. 032） was observed among populations and the calculated gene flow was 8.68. Comparable genetic variation in populations from restored and mature forests indicated that deforestation in this region has not significantly reduced genetic diversity of C. sclerophylla, mainly due to its extensive sprouting. However, the software BOTTLENECK indicated a recent population bottleneck in 3 restored populations, a sign of distinct population decline in recent generations. A recent bottleneck was also observed in 1 mature population, mainly due to recent forest fragmentation.