Response of photosynthetic capacity of Larix gmelinii needles to climate warming

Larix gmelinii seedlings were transplanted from Tahe, Songling, Heihe and Dailing to a common garden in Mao'ershan, near the southern edge of its natural distribution range in China. Two decades after the transplantation, we measured the photosynthetic capacity of needles in four transplanting locations (control) and common garden (climate warming treatment) simultaneously, and analyzed the response mechanism of needle photosynthetic capacity to climate warming. The results showed that climate warming significantly increased the maximum net photosynthetic rate (P_{n max}), total nitrogen content (N_area), chlorophyll content (Chl_m), the activities of ribulose-1,5-diphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC), as well as the content and proportion of nitrogen in photosynthetic system. Climate warming significantly increased P_{n max} by 23.5%, 34.4%, 37.5% and 45.8%, increased Rubisco activity by 11.1%, 30.1%, 36.3% and 56.7%, and increased nitrogen content in photosynthetic system by 19.0%, 51.0%, 67.8% and 70.4% for Dailing, Heihe, Songling and Tahe, respectively. The P_{n max} was significantly positively associated with Rubisco activity, PEPC activity and the content of nitrogen in photosynthetic system. Climate warming did not affect photosynthetic nitrogen use efficiency. The significant increase in photosynthetic capacity of L. gmelinii needles under climate warming was resulted from the interaction of increased nitrogen content in the photosynthetic system and enhanced photosynthetic enzyme activity.