Abstract
Submergence-tolerant trees are essential for vegetation restoration of the hydro-fluctuation zone of the Three Gorges Dam Reservoir (TGDR) area. Thus, it is of great significance to select the submergence-tolerant plant species by conducting in situ studies. To restore degraded riparian vegetation under the circumstances of dynamic impoundment of the TGDR, Salix matsudana Koidz., a flooding-tolerant native tree species, was introduced to conduct an in situ practical study to test its performance in re-vegetating and restoring the hydro-fluctuation zone of the TGDR. Effects of periodic moderate submergence (MS) and deep submergence (DS) on photosynthesis and growth of Salix matsudana Koidz. were investigated after three water cycles compared to a control (i.e., shallow submergence, abbreviated as SS) in order to specifically assess its application prospects in vegetation restoration under such extreme environment. Results showed that net photosynthetic rate (Pn), intrinsic water use efficiency (WUEi) and limiting value of stomata (Ls) of S. matsudana were significantly reduced in DS. However, pigment content had no significant change in all submergence treatments. Diameter at breast height (DBH) and tree height of S. matsudana were significantly decreased in both MS and DS when compared to that of SS, respectively. In contrast, the primary branch number of S. matsudana was significantly increased as submergence increased. In addition, relative diameter and height growth rates of S. matsudana were also reduced under submergence. Considering the sustained growth of this species, S. matsudana saplings are tolerant to long-term periodic submergence and can be applied to the vegetative restoration of the hydro-fluctuation zone of the TGDR region.
Highlights
The Three Gorges Dam (TGD) is the largest dam ever built in the world [1], which is located in the upper reaches of the Yangtze River
Based on the performance presented in the literature on Salix species that we studied, we hypothesized that the growth and photosynthesis of S. matsudana saplings would recover to control level after such extreme submergence
Pigment contents of S. matsudana had no significant difference among the three submergence treatments. These results suggested that S. matsudana could recover its pigment content after submergence
Summary
The Three Gorges Dam (TGD) is the largest dam ever built in the world [1], which is located in the upper reaches of the Yangtze River. The TGD had totally reversed the submergence season and increased the submergence depth and duration when compared to the original hydrological regime [4,5] This artificial regime has totally changed the habitat of the natural vegetation. Vegetation degradation of the hydro-fluctuation zone of the Three Gorges Dam Reservoir (TGDR) caused serious degradation of its ecosystem function, resulting in many serious environmental problems [7], such as soil erosion, water pollution, etc. These problems have posed a serious threat to the long-term security operation of the TGDR and need to be solved
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