Seed Germination Traits and High-Temperature Tolerance of Three Species from Xishuangbanna, SW China

Germination traits and high-temperature tolerance are critical seed traits for species to respond to habitat changes through seed germination and population dynamics in tropical areas. This study investigated germination under temperature, water and NaCl stress and the seed high-temperature tolerance of three species growing in Xishuangbanna, i.e., one native vine species, Clematis subumbellata, and two introduced tree species, Handroanthus chrysanthus and Melaleuca viminalis. The results were compared with our previous studies in this region to assess the threatened status of C. subumbellata and invasion risk of H. chrysanthus and M. viminalis, in combination with their other traits. These three species are all characterized by the production of numerous small seeds with high viability every year, having the ability to increase their population rapidly under favorable conditions, though they all suffered viability loss and germination inhibition under high temperature and water stresses. The two introduced species, both H. chrysanthus and M. viminalis, produced seeds with wider germination temperature ranges and better high-temperature tolerance than the native C. subumbellata, but their seed heat tolerance was markedly lower than that of typical invasive weeds in this region. On the contrary, C. subumbellata seeds exhibited rather poor high-temperature tolerance, comparable to some rare and endangered species reported previously in the region; however, this species primarily grows on forest margins, slopes, and scrub and produces plumose achenes with good wind dispersal capacity. Thus, it was concluded that H. chrysanthus and M. viminalis may possess only low-to-moderate invasion risks, and their most probable invasive habitats are mainly forest edges. C. subumbellata can be regarded as not threatened currently, without urgent conservation demand. This information is useful for biodiversity conservation in Xishuangbanna.