| Light is one of the most limited resources in forest,influencing plant survival,growth and reproduction.Shade tolerance is a concept describing the ability of plants in tolerating low light stress.Studying impact of light availability on plants,which differs among species with varying shade tolerance,is of great importance in understanding structure and succession of forest comminities.I conducted a greenhouse experiment in Heishiding Natural Reserve in Guangdong by planting seedlings of 6 species under 3 different light environments.I measured light-response curves to study the effect of light intensity on photosynthetic physiology of seedlings.According to results from a mixed-effect model analysis,I found that low light availability reduced photosynthetic capacity(Gmax)and dark respiration(Rd)of seedlings while different species showed varied response to seasonal and ontogenetic variation.However,I found photosynthetic physiology and leaf traits of most species in the field had little relationship with light availability,and Gmax and Rd of saplings in the natural condition were significantly higher than the Gmax and Rd for the seedlings planted in greenhouse under similar light environments.I further collected 9 functional traits of 145 species in HSD plot to analyze the relationship between an index measuring spaling shade tolerance and functional traits.Standardized major axis regression analysis was used to analyze bivariate correlations.The results showed that there was a significant positive correlation between the light transmittance and the proportion of saplings(i.e.,those individuals with DBH <5 cm)for most species.This relationship becomes stronger with increasing shade tolerance when it was measured by a newly developped index of shade tolerance.Shade tolerance was found to significantly correlate with species photosynthetic physiology,wood density and asymptotic height but it had little correlation with leaf traits. |
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