自毒和森林凋落物化感作用对极小种群野生植物大树杜鹃种子萌发的影响

Effect of Autotoxicity and Litter Allelopathy on Seed Germination of Rhododendron protistum var.giganteum,a Plant Species with Extremely Small Populations in China

为了探讨立地条件对极小种群野生植物大树杜鹃的种子萌发和种群自然更新的作用机制,该试验对大树杜鹃鲜叶、枯叶和植株冠幅下不同距离(0、2、5和10m)的森林凋落物以及林下苔藓等浸提液对其种子萌发的影响,以及自毒与森林凋落物的化感作用对大树杜鹃种群自然更新的影响进行分析。结果表明:(1)大树杜鹃鲜叶和枯叶浸提液对种子萌发均具有抑制作用,但枯叶浸提液对其种子萌发率和萌发的抑制强度较小;而种子萌发率和萌发指数均随鲜叶浸提液浓度增加而显著降低,当鲜叶浸提液浓度为10%时,种子萌发率仅为8%,表明大树杜鹃具有较强的自毒作用。(2)大树杜鹃植株冠幅下不同距离的森林凋落物对其种子的萌发具有化感作用,但不同距离的影响不同;距离冠幅5m的凋落物对其种子萌发的抑制作用最强,在该距离下的凋落物浸提液浓度为2%时大树杜鹃种子萌发率和萌发指数分别显著降低为77.33%和21.35,较对照分别显著降低18.32%和20.5%。(3)大树杜鹃林下苔藓对大树杜鹃种子萌发有一定的抑制作用,但作用并不明显。研究认为,大树杜鹃具有较强的自毒作用,可能进一步影响其种群自然更新;森林凋落物对大树杜鹃种子萌发具有一定的化感抑制效应,推测立地条件可能会通过影响其种子萌发而进一步影响种群的自然更新。

In order to elucidate the effect mechanism of stand characteristics on seed germination and natural regeneration of Rhododendron protistum var.giganteum, we investigated the effect of fresh and litter leaf, forest litter and forest moss aqueous extracts on its seed germination percentage and germination index.We also discussed the autotoxicity and litter allelopathy effects on the species natural regeneration.The results indicated that： （1） both fresh and litter leaf aqueous extracts inhibited seed germination, the inhibiting effect of litter leaf aqueous extracts is relatively lower than that of fresh leaf.Seed germination percentage and germination index dramatically decreased with increasing fresh leaf aqueous extracts concentrations.When the fresh leaf aqueous extracts concentration reached 10%, seed germination percentage decreased to only 8%.Thus, the species has obvious autotoxicity effect on its germination.（2） Forest litters collected under the plant canopy with different distance （0, 2, 5 and 10 m） to adult individuals have allelopathic effects on seed germination.However, the effect varied among different distances and forest litter aqueous extracts concentrations.Forest litters collected from canopy 5 m distance have the strongest allelopathic effects on seed germination percentage and germination index.When the concentration of forest litter aqueous extracts reached to 2%, seed germination percentage and germination index decreased to 77.33% and 21.35, respectively.These indictors significantly reduced 18.32% and 20.5% compared to control, respectively.（3） The aqueous extracts of moss which collected under the plant canopy also inhibited seeds germination percentage of R.protistum var.giganteum.Based on above results, we concluded that the plant has autotoxicity effects on its seed germination, which may further influence its natural regeneration.The forest litters also have inhibited allelopathic effects on seed germination.Thus, we can reasonable to assume that the autotoxicity and allelopathic effects would affect the natural regeneration of R.protistum var.giganteum populations.