Effects of water-level changes in the hydro-fluctuation zone of Three Gorges Reservoir on carbon, nitrogen and phosphorus stoichiometry of Taxodium distichum

After completion of the Three Gorges Dam, its special hydrological scheduling caused the extinction of some original plants in hydro-fluctuation zone of Three Gorges Reservoir(TGR). It also led to the ecological and environmental problems including soil erosion, biodiversity loss, landslide, collapse and so on. The suitable plants selection for vegetation reconstruction is considered as one of the effective methods to solve these problems. The previous study has been proved that Taxodium distichum was a good choice for vegetation reconstruction in the TGR. In March 2012, we selected the section at an altitude of 165 to 175 meters above sea level. According to the hydrological characteristics of the TGR, two-year-old T. distichum that grew evenly at a row spacing of 1 meter multiplying 1 meter were planted in Ruxi River vegetation reconstruction demonstration base. After four years of in-situ flooding cycle, T. distichum showed good adaptability. In order to further understand its adaptive mechanism to the water-level changes in the TGR, the leaf, branch and root samples were collected from control check(CK; 175 m ASL), moderate submergence(MS; 170 m ASL), and deep submergence(DS; 165 m ASL) in mid-September 2016 before impoundment of TGR. The contents of carbon(C), nitrogen(N), and phosphorus(P) in the roots, branches, and leaves were determined. The effects of water-level changes on C, N and P stoichiometry and growth were analyzed. The results showed that:(1) In the TGR, T. distichum reduced the growth rate to adapt water-level changes. The overall growth state of the plants was good.(2) The distribution of C content in various organs of T. distichum was relatively balanced. N was concentrated in the leaves and P was mainly stored in the roots. There was no serious lack of elements.(3) The water-level changes significantly increased the leaf C content of DS group plants. The water-level changes significantly reduced the root P content of the MS group plants, but significantly increased the leaf P content. Those resulted in C∶P and N∶P ratios of leaf in the MS group plants decreased significantly and the root C∶P increased significantly. The results indicated that T. distichum in hydro-fluctuation zone of the TGR could maintain a reasonable elemental distribution among organs to ensure their growth needs, showing good adaptability to the water-level changes.