Study on characteristics of net photosynthetic rate of two kinds of tree shape and Impact Factors in Korla fragrant pear

The objective of this study was to investigate the diurnal variation curves of the net photosynthetic rate (Pn) and relationship between diurnal changes of Pn and the impact factors in open center shape and delayed-open central leader system in Korla fragrant pear. Diurnal changes of Pn and effect of environmental factors (i, e. photosynthetic available radiation, temperature and relative humidity) and physiology factors (i.e. stomatal conductance, transpiration rate and intercellular CO sub(2) concentration) on Pn in leaves of Korla fragrant pear were measured using LI-6400 portable photosynthesis system. The relationship between Pn and environmental factors were analyzed by regression analysis and correlative analysis. In order to investigate the effects of tree shape on net photosynthetic rate, we analyzed the relationship between chlorophyll content, specific leaf weight, other photosynthetic parameters and Pn between delayed-open central leader system and open center shape in this study. The results showed that the Pn under two different tree shapes indicated a bimodal curve of the asymmetry, and the midday depression of photosynthesis phenomenon appeared at 14:00. During the full fruit period, the delayed-open central leader system tree had obviously higher net photosynthetic rate than the open center shape tree in each stage. This phenomenon maight be double impacted by stomatal and non-stomatal factors. Diurnally, photosynthesis increased gradually with increasing light intensity and then decreased at noon. The peak of delayed-open central leader system tree leaves occurred at 11:00 and 15:30. The peak of open center shape tree leaves occurred at 11:00 and 17:00. The seasonal variation on Pn indicated the Pn is least in June in two shapes of Korla fragrant pear. The Pn increased with leaf chlorophyll (chl) content and specific leaf weight (SLW) increasing. There are positive relations, the correlation index of leaf chlorophyll (chl) content and Pn were 0.9438 and 0.8952 in two shapes of Korla fragrant pear. The photosynthetic pigment index of different kinds of tree shapes also had great differences. There were significant correlations between Pn and SLW in delayed-open central leader system and open center shape, but the later is higher than the former. Stomatal conductance (Gs), transpiration rate (Tr) and relative humidity (RH) increased in response to increasing Pn in all the treatments. Sample CO sub(2) concentration (Cs) and intercellular CO