Response of chlorophyll fluorescence of Pinus tabulaeformis Carr. needles in growing seasons to temperature changes.

Pinus tabulaeformis Carr. is a species of evergreen plants with the characteristics of heat and cold resistance in north China. The changing patterns of its needles chlorophyll fluorescence parameters after various temperatures were investigated in order to find out how the needles photosynthetic institution respond to unusual temperatures. The data showed that when needles were subjected to 30 and 35 ℃, the minimal fluorescence (F0) and the nonphotochemical quenching coefficient (qN) increased by degrees, while the maximal quantum yield of PSⅡ(Fv/Fm), the maximum quanta yield (Yield), and the electron transport rate (ETR) decreased gradually as the temperature went up. Whereas, all the data varied within a small range, indicating that common high temperature in summer had effects on the PSⅡ reaction centre activity, but cause slight damage. However, when dealt with over 40 ℃ high temperatures, F0, qN ascended and Yield, ETR descended sharply, meanwhile, Fv/Fm reduced to the value below 08. This suggested that the PSⅡ reaction centre might have suffered severe damage. When subjected to low temperatures above zero (ranged from 0 to 15 ℃), parameters didnt have notable changes. That is to say, PSⅡ reaction centres activity of the needles in growing seasons can be stable to the above freezing temperatures influence. Under subzero temperatures, Fv/Fm, ETR and qN decreased considerably while F0 increased visibly, and didnt have significant recovery in the next 12 hours, which implied that subzero temperatures have done irreversible harm to the photosynthetic institution of P. tabulaeformiss needles.