Native habitats and salt stress responses of wild Hydrangea macrophylla

Abstract

Hydrangea shrubs, developed from wild Hydrangea macrophylla endemic to Japan, are very important plants for landscaping and horticulture. H. macrophylla, likely speciated from H. serrata growing in the mountainous zone, have migrated into coastal zone. However, there is still a lack of information about the habitats of wild H. macrophylla and its adaptative responses to salt-stressed coastal environments. Therefore, in this study we conducted a survey of wild H. macrophylla populations and its native habitats. The results of the habitat survey showed that H. macrophylla is mainly distributed in coastal zones that have a saline atmosphere, triggered by high wind speed, high soil EC1:5 and large soil sodium contents, capable of causing severe damage to many plant species. Additionally, we confirmed some inland populations in a part of the Izu Peninsula and on the Izu islands. Several of these inland H. macrophylla populations inhabited mountain vegetation areas favored by H. serrata, and had thinner leaves than the coastal populations. We also found H. macrophylla individuals growing in oligotrophic environments such as on rocky surfaces and in volcanic ash scoria. Leaf cation analysis suggests that H. macrophylla adapts to salt stress by regulating Na+ allocation and preventing high leaf Na+ concentrations. The findings of this fundamental investigation of native habitats and adaptation to coastal zone should help facilitate further studies on H. macrophylla ecosystem, abiotic stress and conservation.