Abstract:

The spruce stand was classified into four age classes i.e. age classⅠ (0～20 years), Ⅱ (20～40 years), Ⅲ (40～60 years), and Ⅳ (≥60 years). The basic photosynthetic characteristics of this species in the natural stands have never been studied. In this paper we investigated the variation of net photosynthetic rate among Picea schrenkiana var. tianschanica trees in the different age classes growing in its natural stand with a portable photosynthesis system of Li-6400. The result showed that the light compensation point of different age needles of trees in different age classes was in a range of 10～25 μmol·m^-2s^-1, and the light saturation was 870～1220 μmol·m^-2s^-1. The diurnal change of net photosynthetic rate of sunny needles in the different ages all exhibited the uni-modal curves with their peakvalues occurring at 10:00, 12:00 and 13:00, respectively. There was variation in maximum net photosynthetic rate value of the same age needles among the different stand ages, and the order was: age class Ⅲ＞age class Ⅳ＞age class Ⅱ＞age class Ⅰ. The diurnal changes of net photosynthetic rate of the shady needles revealed the bimodal curves in all stand ages except for the ageⅠ, which had a uni-modal curve of change. The value of maximum net photosynthetic rate of the same age class was in an order of current year needles＞1-year-old needle＞2-year-old needle. The regression analysis indicated that Pn of sunny needles was positively correlated with PAR, T air, T leaf and H2O-S, while its correlations with CO₂-S, RH-R and CO₂-R were significantly negative. The P n of shady needles had significantly positive correlation with PAR, and negative correlation with RH-R.

Key words: Picea schrenkiana var. tianschanica, photosynthesis, natural stand, leaf age