Altered morphologies and physiological compensation in a rapidly expanding dwarf bamboo in alpine ecosystems.
Dwarf bamboos are evergreen woody grasses that produce large clonal patches and dominate the understories of the montane to subalpine zones of northern Japan. Recently, dwarf bamboos have expanded their distribution to above the treeline and into alpine meadows. To clarify the mechanism of rapid invasion into the alpine, we compared the morphological performance, biomass allocation, photosynthetic activity, CO2 fixation ability, and sensitivity to temperature of dwarf bamboos in their native montane and expanding alpine sites in the Taisetsu Mountains. Alpine bamboo produced shorter but denser aboveground structures, where leaves were smaller and branching was more frequent. The total biomass of alpine bamboo was nearly half of that produced by montane bamboo. Montane bamboo produced more stems, while alpine bamboo invested more carbon in belowground structures. CO2 fixation per land area by alpine bamboo was 1.3 times higher than rates observed in montane bamboo. Optimal temperatures for photosynthesis were lower in alpine bamboo (15-20°C) than in montane bamboo (20-25°C), probably because of the rapid decrease in stomatal conductance at higher temperatures (>20°C) observed in the alpine site. Overall, leaf transpiration rates were higher in alpine bamboo, but water-use efficiency was similar between sites. A high flexibility in both morphological and physiological characteristics enabled dwarf bamboos to expand into alpine environments in response to recent climate change.