Abstract: Longer growth season has been confirmed due to the elevated temperature in recent decades. Though the changes in the duration of growth season could affect tree productivity, it’s unclear how the growth season with different initiating temperature affects the radial growth of tree. In order to investigate the effects of growth season’s variability in temperature to the radial growth of Masson pine (Pinus massoniana) and search for the sensitive temperature to the growth, old Masson pine stands in Hanzhong, the northwest margin of north subtropical region, were chosen as test objects, with their tree ring width index chronology from 1945 to 2009 measured by dendrochronology method. The air temperatures on the first day, last day, and in the whole growth season as well as the active accumulative temperature during growth season were determined based on the daily mean temperature of Hanzhong, and the relationships between the temperatures and chronology were analyzed. The results showed that the growth season with initiating temperature 6.0 ℃-7.5 ℃ had negative effects on the tree ring width index chronology, with 6.0 ℃ being most significant. 10.5 ℃ on the last day had significant positive effects on tree ring growth. 10.0 ℃ and 10.5 ℃ in growth season were significantly positively correlated with the tree ring growth, and the active accumulative temperature during growth season was also significantly positively correlated with the growth. These sensitive temperatures were respectively corresponding to the onset of photosynthesis, needle emergence in spring, and shutting down of cambium activity in autumn. Our study suggested that elevated temperature led to the changes in phenophase, and thereby, affected the radial growth of P. massoniana in Hanzhong.

Key words: Nitrate nitroge, Ammonium nitrogen, Nitrogen nutrition, Lettuce