Responses Of Three Herbs To Flooding-drying Habitat Changes In Hydro-fluctuation Belts Of Three Gorges Reservoir

Hydro-fluctuation belt of Three Gorges Reservoir with area of 349 km² and vertical drop 30m is rare at home and abroad, which is the most unstable ecotone where the matter, energy and information between water ecosystem and terrestrial ecosystem translate and converse most actively. Three Gorges are greatly concerned with focus on its Ecological environment changes.Vegetation construction in hydro-fluctuation belt is an important measurement to ecological environment treatment, and screening suitable plant plays the vital role on the success. With operating mode"winter storage while summer row", the habitats in hydro-fluctuation belt of Three Gorges Reservoir are in water in winter and into land in summer alternately. Therefore, screening plants that have the tolerance to flooding and draught is urgent in vegetation construction of hydro-fluctuation belt of Three Gorges Reservoir.Located monitoring sample plots of vegetation construction experiment and demonstration areas which were set up during the"11^th five year plan"period were set up in-between different elevation sections of the hydro-fluctuation belts of the Three Gorges Reservoir at Wushan section, where population density, morphological characters, biomass and photosynthetic physiology of Cyperus rotundus, Cynodon dactylon and Vetiveria zizanioioles responding to changing flooding-drying habitats were observed. The main conclusions are as follows:(1)Compared with no flooding area, after flooding-drying habitat changes, the population density, root length, root number, the number of shooting plant per tuber, total biomass, aboveground biomass, underground biomass and underground and aboveground biomass ratio of Cyperus rotundus increased significantly. In July, Cyperus rotundus in shallow water area increased by 102.95%, 24.19%, 45.85%, 86.96%, 89.57%, 49.73%, 108.93% and 39.76% separately, while in the deep water area increased by 412.19%, 55.63%, 71.80%, 175.36%, 244.67%, 162.10%, 284.80% and 46.84% separately.(2)Compared with no flooding area, after flooding-drying habitat changes, the root diameter, root length and underground and aboveground biomass ratio of Cynodon dactylon increased significantly. In July, root diameter, root length and underground and aboveground biomass ratio of Cynodon dactylon in the shallow water area increased by 141.37%, 37.16% and 13.19% separately, and in the deep water area 160.72%, 41.80% and 48.49% separately. In the shallow water area, the population density and internode lengths of primary and secondary branching nodes increased significantly, while in the deep water area, the population density decreased significantly and number of the primary and secondary branches increased significantly.(3)Compared with no flooding area, after flooding-drying habitat changes, the average leaf length, maximum leaf length, underground biomass and underground and aboveground biomass ratio of Vetiveria zizanioioles increased by 10.37%, 5.34%, 30.04% and 151.71% separately in the shallow water area in July, while total cluster number, average plant height, maximum plant height, leaf number per cluster, total biomass, aboveground biomass decreased by 41.70%, 15.61%, 9.34%, 0.36%, 10.58% and 48.46% separately.(4)Compared with no flooding area, after flooding-drying habitat changes, Pn, Cond, Tr of Cyperus rotundus increased significantly. In July, Pn, Cond, Tr of Cyperus rotundus increased by 23.52%, 40.67% and 40.67% in the shallow water area and 72.74%, 55.07% and 31.54% in the deep water area. WUE, CUE, LUE(June to July), LSP of Cyperus rotundus increased, LCP in the shallow water area declined significantly and in the deep water area increased significantly. There was no obvious changes in P_max of Cyperus rotundus and AQY and Rd of Cyperus rotundus declined significantly.(5)Compared with no flooding area, after flooding-drying habitat changes, Pn, Cond, Tr of Cynodon dactylon increased by 106.80%, 68.03% and 228.75% in the shallow water area and 81.63%, 64.81% and 200.80%in the deep water area. WUE and LUE of Cynodon dactylon was significantly higher in June and significantly lower in July. CUE, P_max, AQY and Rd of Cynodon dactylon increased and LSP and LCP declined significantly.(6)Compared with no flooding area, after flooding-drying habitat changes, Pn of Vetiveria zizanioioles increased by 7.23%, Cond of Vetiveria zizanioioles decreased by 9.19%, but they both did not reach the significant level. Tr of Vetiveria zizanioioles decreased significantly by 20.75%. WUE, CUE, LUE and LCP of Vetiveria zizanioioles increased. P_max, AQY and Rd of Vetiveria zizanioioles had no significantly changes, LSP decreased significantly.(7)Compared with no flooding area, after flooding-drying habitat changes, Cyperus rotundus, Cynodon dactylon and Vetiveria zizanioioles had high population density and biomass, which indicated that the 3 herbs had good adaptability to flooding-drying habitat changes which improved the restoration growth to some extent. All three herbst showed increasing in underground growth and underground biomass allocation, which indicated that flooding-drying habitat changes promoted the root growth and tillering. Increasing underground biomass allocation preparing nutrition and energy for the regrowth after flooding was the common policy of 3 herbs to flooding-drying habitat changes.(8)Increasing of Pn of Cyperus rotundus and Cynodon dactylon were the results of stomatal and nonstomatal factors. Flooding-drying habitat changes led to the Cond and the degree of stomatal opening increasing that caused the increase of external CO₂ into the leaf cells, while Ci decreased as external CO₂ into the leaf cells increase. This indicated nonstomatal factors(improving of photosynthetic function)were the main factors of improvement of Pn. Pn of Vetiveria zizanioioles increased , while the decrement of Cond and Ci of Vetiveria zizanioioles indicated nonstomatal factors(improving of photosynthetic function)were the reason of improving of Pn。(9)After flooding-drying habitat changes, the adaptability of high light intensity of Cyperus rotundushad and the efficiency of low light intensity of Cynodon dactylon was improved. Although the scope of available light of Vetiveria zizanioioles was reduced, it did not affect the high Pn. Flooding-drying habitat changes did not cause significant changes to potential production of Cyperus rotundus, while the potential production of Cynodon dactylon was improved.