| The riparian zone of the Three Gorges Reservoir Area is the most Constructed wetland in China. Due to the anti season flooding, environmental in reservoir area changed, causing lots of ecological and environmental problems, such as more frequent geological disasters, silted river, river floats, larger non-point source pollution, and biodiversity reduction and so on. In the Three Gorges Reservoir area ecosystem is very fragile, in need of repair. Plant ecological restoration is an effective approach, which can increase the reservoir biodiversity, improve the stability of the ecological system and ability of self-repair. In present experiment, therefore, Morus alba L., Betula nigra and Salix fragilis L. with characteristics of tolerance to both flood and drought were chosen as experimental materials, planted in the reservoir area of the Three Gorges at 170~175 m altitude in spring, 2014, to study the effect of waterlogged time on wood plants growth, and select suitable woody plants in reservoir area, by measuring growth(plant height, diameter, crown) and photosynthetic characteristics(chlorophyll, fluorescence dynamic parameters, and gas exchange parameters). Main results as follows:(1) M. alba, B. nigra and S. fragili were flooded for 135 days at 170 m altitude and 2 days at 175 m altitude. The survival rate of M. alba, B. nigra and S. fragili were 47%, 64% and 88% at 170 m altitude, and 91%, 95%, 98% at 175 m altitude respectively. So waterlogged time had significant difference on plant growth. Annual growth of M. alba height, ground diameter and crown were respectively 7.71%(P >0.05), 36.81%(P<0.05), 37.51%(P<0.05) at 170 m altitude lower than that at 175 m altitude. Annual growth of B. nigra height, ground diameter and crown were respectively 45.93%(P<0.05), 55.28%(P<0.05), 58.12%(P<0.05) at 170 m altitude lower than that at 175 m altitude; Annual growth of S. fragilis height, ground diameter and crown were respectively 18.96%(P>0.05), 8.53%(P>0.05), 6.26%(P>0.05) at 170 m altitude lower than that at 175 m altitude. Therefore, waterlogged time had much impact on height, ground diameter and crown of M. alba and B. nigra while it had low effect on height, ground diameter and crown of S. fragile, which meant S. fragile had higher adaptability to heterogeneity biotope changes in the reservoir area.(2) In spring dew period, summer drainage period and before autumn flooding, photosynthetic characteristics were different between plants in long-term-flooding(plants at 170 m altitude) and non-long-term-flooding(plants at 175 m altitude), without significant difference as a whole.1) Chlorophyll content. The average chlorophyll content of M. alba for at 170 m and 175 m altitude in three periods, were respectively 2.78 mg·g-1 and 2.55 mg·g-1(P>0.05). The average chlorophyll content of B. nigra for at 170 m and 175 m altitude in three periods, were respectively 2.36 mg·g-1 and 2.35 mg·g-1(P > 0.05). The average chlorophyll content of S. fragile for at 170 m and 175 m altitude in three periods, were respectively 1.60 mg·g-1 and 1.92 mg·g-1(P<0.05). The chlorophyll content of B. nigra and S. fragili increased over time at different altitudes. Therefore, flooding time had little effect on chlorophyll content of M. alba, and B. nigra, but much effect on S. fragile.2) Chlorophyll fluorescence dynamic parameters. During the exposed period in spring, the actual photochemical efficiency(ΦPSⅡ), electron transfer rate(ETR), and photochemical quenching coefficient(q P) of long-term flooding M. alba were 0.56, 41.98 μmol·m-2·s-1, 0.79, respectively, which were significantly higher than that of onlong-term-flooding M. alba(P<0.05), and there was no significant difference of them in the non photochemical quenching coefficient(q N), and energy conversion efficiency(Fv/Fm). In the summer drainage period, There was no significant difference in ΦPSⅡand ETR. Compared with non-term-flooding M. alba, long-term-flooding M. alba had lower Fv/Fm(0.71) and q N(0.05), while its q P(0.87) were higher. Before autumn flooding, ΦPSⅡ, ETR and q P of long-term-flooding M. alba were 0.59, 47.59 μmol·m-2·s-1, and 0.87 respectively, which were higher than that of non-long-term flooding M. alba, but lower q N. There was no significant difference in Fv/Fm.In spring dew period, q P and q N of long-term-flooding B. nigra were 0.81 and 0.21, that were lower in both, while Fv/Fm of long-term-flooding B. nigra was 0.75, which was higher, without significant difference(P>0.05). In the summer drainage period, ΦPSⅡ, ETR, q P, and q N of non-long-term-flooding B. nigra were 0.65, 47.92 μmol·m-2·s-1, 0.93, 0.27, which were bigger than that of long-term-flooding B. nigra, while Fv/Fm of nonlong-term-flooding B. nigra was lower, all without significant difference(P > 0.05). Berofe autumn flooding, changes of ΦPSⅡ, ETR and q P were the same with that in summer drainage period. Fv/Fm of long-term-flooding B. nigra was 0.70, which was lower, while its q N was higher, all without significant difference(P>0.05).In spring dew period, ΦPSⅡ, ETR, q P, Pn and q N of the long-term-flooding S. fragilis were 0.61, 48.91 μmol·m-2·s-1, 0.86, and 0.26 respectively, that were higher in both, without significant difference(P>0.05). In summer drainage period, ΦPSⅡ, ETR, q P of long-term-flooding S. fragilis were 0.59, 47.33 μmol·m-2·s-1, 0.89 respectively, that were smaller than that at 175 m altitude, while its q N and Fv/Fm were higher, with significant difference in q N(P<0.05). Berofe autumn flooding, there was no significant difference in ΦPSⅡ, ETR, q P and Fv/Fm(P>0.05), while q N of long-term-flooding S. fragilis was 0.18, which was significantly higher than that of the other(P<0.05).3) Gas exchange parameters. net photosynthetic rate(Pn), stomatal conductance(Gs), transpiration rate(Tr), intercellular CO2 concentration(Ci), water use efficiency(WUE) of long-term flooding M. alba were 13.69 μmol·m-2·s-1, 0.13 mol H2O·m-2·s-1, 2.13 mmol·m-2·s-1, 282.92 umol·mol-1, and 6.51 mmol·mol-1 respectively, and Pn, Gs, Tr, Ci, WUE of non-long-term flooding M. alba were 15.78 μmol·m-2·s-1, 0.12 mol H2O·m-2·s-1, 1.92 mmol·m-2·s-1, 282.41 umol·mol-1, and 8.10 mmol·mol-1 respectively. There were significant differences in WUE. Pn, Gs, Tr, Ci, WUE of long-term-flooding B. nigra were16.18 μmol·m-2·s-1, 0.14 mol H2O·m-2·s-1, 2.52 mmol·m-2·s-1, 290.82 umol·mol-1, and 6.10 mmol·mol-1 in turn, and Pn, Gs, Tr, Ci, WUE of non-long-term-flooding B. nigra were, 16.84 μmol·m-2·s-1, 0.16 mol H2O·m-2·s-1, 2.58 mmol·m-2·s-1, 293.98 umol·mol-1, and 5.83 mmol·mol-1 in turn, without significant difference. Pn, Gs, Tr, Ci, WUE of longterm-flooding S. fragilis were 22.06 μmol·m-2·s-1, 0.16 mol H2O·m-2·s-1, 2.69 mmol·m-2·s-1, 274.80 umol·mol-1, and 7.65 mmol·mol-1 respectively, and those of non-long-termflooding S. fragile were 19.50 μmol·m-2·s-1、0.17 mol H2O·m-2·s-1, 3.09 mmol·m-2·s-1, 294.44 umol·mol-1, and 5.94 mmol·mol-1 successively, what’s more, there were significant diferences in WUE.Thus, compared with plants planted at 175 m altitude, survival rate and growth of plants planted at 170 m altitude was poorer, due to the long time of winter flooding. However, M. alba, B. nigra and S. fragili could maintain relatively high growth rate by keeping better chlorophyll fluorescence parameters, higher chlorophyll content and net photosynthetic rate, to adapt to the environment in the reservoir area. |
PDF Full Text Request