五指山不同林型土壤对金钟藤幼苗生长的影响

Effects of soil from different forest types in Wuzhi Mountain on the seedling growth of Merremia boisiana

金钟藤在海南和广州的爆发成灾严重威胁着当地的森林生态系统。不同林型被金钟藤入侵的程度不一样,干扰严重、透光度较高的次生林容易被入侵,而自然林则不易被入侵。本研究比较金钟藤幼苗在海南五指山干扰林及自然林下土壤上生长的差别,以说明是否土壤性状的差别可部分解释金钟藤入侵性的差别。于2011年11月在五指山自然林和干扰林山坡分别取土及表层凋落物,带回实验室放入花盆中。一半的花盆中加入活性炭以检验凋落物可能释放的化感物质对金钟藤幼苗生长的影响。金钟藤种子经萌发后种入花盆中。在14.72%的透光度及排除地上部分天敌的条件下,于2011年11月至2012年7在大棚内种植8个月后收获、烘干并称重。结果表明:自然林土壤的全氮、全磷、有效氮含量高于干扰林土壤,而有效磷含量低于干扰林土壤,说明土壤资源并不是在干扰林下更高。在自然林土壤生长的金钟藤幼苗地下、地上部分生物量分别为1.496±0.14 g、3.22±0.31 g,比在干扰林土壤生长的生物量略大(1.129±0.135 g、2.93±0.357 g),但两者的差异并不显著(地下:t=1.881,P=0.072。地上:t=0.662,P=0.539);添加活性炭以吸附凋落物化感物质并不显著改变金钟藤地下、地上部分生物量。本实验说明,在一定的光照及排除地上部分天敌的条件下,仅是自然林下的土壤本身并不能抵抗金钟藤的入侵。然而,在野外观察到金钟藤种子可以在自然林下萌发但幼苗却难以存活,说明其他因素造成了金钟藤幼苗的死亡。未来研究这些因素对于保护生物多样性、维护森林生态系统健康具有重要意义。

The invasion and explosion of Merremia boisiana in Hainan and Guangzhou significantly threaten forest ecosystems. Different forest types show the varieties in the degree of invasion by M. boisiana, in which severely disturbed secondary forests with high light levels at the ground are more prone to invasion, as compared to natural forests. This study compared the growth of M. boisiana seedlings on soils of disturbed and natural forests in Wuzhi Mountain of Hainan, so as to elucidate if differences in soil properties might partly explain this pattern. Soil samples of disturbed and natural forests and the litter on their surface in Wuzhi Mountain were collected and then placed into pots after taking back to the laboratory. Half of the pots were added with activated carbon to examine the influence of allelopathic substances potentially released from litter on the seedling growth of M. boisiana. Seeds of M. boisiana were germinated and then planted into the pots. Under a light penetration ratio of 14.72%, the seedlings of M. boisiana were allowed to grow without aboveground natural enemies from November 2011 to July 2012. After that, the seedlings were harvested, dried and weighed. The results showed that the contents of soil total nitrogen, total phosphorus, and available nitrogen in the natural forest were higher than those in the disturbed forest, whereas the opposite trend was observed in the soil available phosphorus content, indicating that soil resources were not higher under the disturbed forest. The belowground biomass and aboveground biomass of M. boisiana seedlings grown on soils of the natural forest were 1.496±0.14 g and 3.22±0.31 g, respectively, which were slightly higher than those of seedlings grown on soils of the disturbed forest （1.129±0.135 g and 2.93±0.357 g, respectively）. But the values of biomass of M. boisiana seedlings grown on soils of these two forest types did not differ significantly （belowground biomass： t = 1.881, P= 0.072; aboveground biomass： t = 0.662, P= 0.539）. The activated carbon addition did not significantly change the belowground and aboveground biomass of M. boisiana seedlings. These findings suggest that soils of natural forests alone cannot resist the invasion of M. boisiana under a specific light level and exclusion of aboveground natural enemies. However, it was observed that seeds of M. boisiana could germinate but seedlings could not survive in the natural forest understory, indicating that some other factors caused the death of M. boisiana seedlings. Future studies to examine the factors contributing to the resistance of natural forests to M. boisiana invasion would be important for protection of biodiversity and maintenance of forest health.