Differential water-use and growth responses of Pinus densiflora and Larix kaempferi seedlings to microclimate manipulation

Our study assessed how physiological traits and the growth of seedlings of Pinus densiflora and Larix kaempferi, representative coniferous species of Korea, are affected by warming and precipitation manipulation. A warming and precipitation manipulation experiment was conducted with 1-and 2-year-old seedlings using infrared heaters, transparent panels, and an irrigation system. Plant physiological activities were monitored using a portable photosynthesis measurement system, and seedling growth was investigated by measuring the dry weight of harvested biomass. P. densiflora, an isohydric species, showed an overall decrease in physiological activities under the warming treatment in the first (germination) year. In particular, stomatal conductance decreased to prevent excessive water loss, with minimal decreases in photosynthetic activity, and increased the water-use efficiency in the first year. L. kaempferi, an anisohydric species, maintained stomatal conductance under the warming treatment. Both species maintained physiological activities with their distinct responses to heat in the second year, while the seasonal variation pattern changed in 2-year-old P. densiflora seedlings. The dry weight of L. kaempferi seedlings increased under warming; however, it decreased by warming combined with increased precipitation. These results can enhance the understanding of seedling responses to microclimate manipulation according to the different water-use by species and seedling age. Under the future climate change, these responses should be accounted for in management of seedlings in nurseries or newly afforested areas.