热带雨林林内小生境对木奶果和染木种子萌发与幼苗存活的影响

Seed Germination and Seedling Survival of Baccaurea ramiflora and Saprosma ternatain Xishuangbanna Tropical Rainforests under Habitat Heterogeneity

森林生态系统中小生境的差异可能影响种子萌发与幼苗的建立,并形成物种不同的分布格局。为探讨生境异质性对植物分布的影响,该研究在西双版纳热带季节性雨林中选取5个具有不同海拔和地形的小生境,人工散布木奶果与染木种子,定期监测种子萌发与幼苗存活,同步记录小生境的近地面（距地面3cm）温度、近地面（3cm）空气湿度和表层土壤（5cm）含水量变化,并在实验室开展种子脱水和不同水势条件下的种子萌发实验。结果表明：（1）实验所选的5个小生境中,沟底地带的土壤水分含量在一年中始终都高于其他小生境;5个小生境的空气相对湿度在雨季与雾凉季都接近饱和,只有在干热季出现明显的差别,即随海拔的升高,空气湿度下降。同时,在旱季,近地面温度随海拔的升高而升高,出现1～2个月的山地逆温现象。（2）木奶果与染木具有不同的种子传播与萌发规律,而且染木种子在不同生境下,其种子萌发率和幼苗存活率有显著的差异。其中：木奶果种子在雨季成熟散布并快速萌发,以幼苗的形式度过干热季,其种子可以在相对较低的水势下萌发;染木种子在雨季末期成熟并进入休眠期,以种子的形式度过干热季,其种子相对较抗脱水。研究认为,地形是决定西双版纳热带季节性雨林生境异质性的重要因子,小生境在温度和水分方面的差异在干热季时尤为明显,并对木奶果和染木种子的萌发或幼苗存活产生了重要影响,而木奶果与染木种子自身的特性使其对于西双版纳季节性的干旱具有不同的适应对策。

Difference at micro-habitats in forest ecosystems may affect seed germination and seedling establishment,lead to various species distribution patterns.In order to explore effects of habitat heterogeneity on plant distribution pattern,we dispersed seeds of Baccaurea ramifloraand Saprosma ternataat five microhabitats which have difference in elevation and topography,in a Xishuangbanna tropical seasonal rainforest.The dynamics of seed germination and seedling survival were monitored.The corresponding land surface（3cm above the ground）temperature,air humidity（3cm above the ground）and topsoil（5cmdeep）water content at micro-habitat were also recorded.Meanwhile,seed desiccation under ambient regime and germination under water stress were performed.It was found：（1）at five micro-habitats,soil water content at valley bottom kept the highest all the year round;Air relative humidity was saturated on rainy season and fogy season.Only on dry season there is obvious difference,namely with the increase of altitude,the air humidity dropped;Mountain temperature inversion which last one or two months occured on dry season.（2）In addition,B.ramifloraand S.ternataseeds had different dispersal and germination pattern.S.ternata seed had significant difference in seed germination and seedling survival at different habitats.B.ramiflora had seed dispersed and quickly germinated on rainy season,and its seed had the ability to germinate under relatively lower water potential,so it spent dry season by seedling;While S.ternata dispersed seed in the end of rainy season,which was dormant and relatively desiccation resistant,it pass spent through dry season by seed.In conclusion,topographical condition is a critical factor to effect micro-habitats heterogeneity in Xishuangbanna tropical seasonal rainforest,and the difference in temperature and water regime among these five micro-habitats is most obvious on dry season,which had important effect on seed germination and seedling survival of B.ramiflora and S.ternata.On the other hand,B.ramifloraand S.ternataseeds have different strategy to cope with drought in Xishuangbanna tropical seasonal rainforest because of their seed traits.