Abstract
With the rise of water level, the construction of the Three-Gorges Dam may have significant impacts on plant carbon-water relation and ecosystem properties in this region. To understand how the plants in this region adapt to the changes in water environments, we measured gas exchange, water potential and δ 13 C of sapling and mature trees of three co-occurring coniferous and deciduous species: Pinus massoniana, Quercus variabilis and Q. aliena, all are dominant tree species in this region. The two deciduous broad-leaf trees (Q. variabilis and Q. aliena) exhibited higher photosynthetic (P-n) and stomatal conductance (G-s) than the evergreen conifer species (P. massoniana). The predawn water potential (ψ- pd ) of P. massoniana was lower than that of the two broad-leaf species. Intrinsic water use efficiency (WUE-i, P-n/G-s) of P. massoniana was higher than those of Q. variabilis and Q. aliena. However, the differences in carbon isotope ratio (δ 13 C) of leaves among species, which gives integrative information of WUE in growing season period, were not statistically significant. We also compared eco-physiological parameters between saplings and mature trees of these three species. The P-n and G-s values of the mature trees were significantly lower than those of the saplings. The mature trees showed lower ψ- pd value, but the difference between the mature trees and the saplings was not statistically significant. However, the WUE-i values of all mature trees were significantly higher than those of the saplings. The δ 13 C values of mature trees showed more positive than those of corresponding saplings, indicating also higher WUE in the mature trees. From these results, we concluded that 1) P. massoniana showed different water use strategies from two Quercus trees species, and 2) the mature trees of these three dominant tree species showed lower photosynthetic rate but higher WUE than those of their corresponding saplings.
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