Species specific physiological responses of Pinus densiflora and Larix kaempferi seedlings to open-field experimental warming and precipitation manipulation

Physiological responses of 1-year-old Pinus densiflora and Larix kaempferi seedlings were measured under open-field warming and precipitation manipulation. Air temperature of warming plots was 3 °C higher, while precipitation manipulation plots received ±40% of the precipitation than control plots. Seedlings were planted in May, and temperature and precipitation were manipulated from June 2017. Total chlorophyll content (Chl_t), net photosynthetic rate (P_n), transpiration rate (E), and stomatal conductance (g_s) were measured between July and September 2017. For P. densiflora and L. kaempferi, Chl_t increased by 11.75% and 11.64%, and P_n decreased by 9.14% and 2.17% under warming, respectively. E and g_s were lower under warming in P. densiflora, but higher in L. kaempferi. The lower P_n in P. densiflora resulted from stomatal closure, while that of L. kaempferi resulted from reduced vitality. Lower precipitation increased Chl_t and P_n by 11.64% and 2.66% for P. densiflora, and by 6.40% and 4.32% for L. kaempferi, respectively. Conversely, higher precipitation decreased P_n of P. densiflora by 5.72%, and decreased Chl_t and P_n of L. kaempferi by 8.24% and 4.55%, respectively. These results can be attributed to concentrated precipitation. In this study, two species responded differently even when they were exposed to the same environmental conditions, and this was due to the species-specific mechanisms to water stress derived from the high temperature.