| Growth and metabolism of aquatic macrophytes stands(especially euhydrophytes) can be always affected by environmental factors of lakes inhabited. Composition of C-N stable isotopes in euhydrophytes tissues are found distinct among different lakes. The characteristics of stable isotope signatures in euhydrophytes can be obtained through analyzing these differences. Diverse characteristics of plant tissues(especially the most active parts, leaves) can be served as a stable and effective microscopic methodology for monitoring the environmental variations in lakes. If the methodology is applied to the study on the Poyang Lake, the biogenic elements(carbon and nitrogen) of euhydrophytes tissues and patterns of the changes in the environmental catastrophes can be easily detected and obtained.In the present study, 9 genera and 10 species of aquatic plants were collected in National nature Reserves of Poyang Lake Wetland(Wucheng, in Yongxiu County) and Nanji Wetland(Nanjishan, in Xinjian County) during the year of 2014. The dominant species of euhydrophytes in the lake zones was Potamogeton malaianus and Nymphoides peltatum. The factors affecting the distribution of carbon and nitrogen stable isotopes in Potamogeton malaianus and Nymphoides peltatum tissues were complicated and diverse. In this paper, the effects on their carbon and nitrogen stable isotopes were discussed in the scales of different tissues, water periods and lake zones. The results were as follows:(1) ?13C & ?15N values in stems, roots and leaves of P. malaianus were larger than those in N. peltatum, while the variation amplitude of ?13C values in N. peltatum were found much smaller than those in P. malaianus. The allocation of stable isotopes in different tissues of P. malaianus were in the following order: ?13C values in roots< stems < leaves, the same as ?15N. The allocation of stable isotopes in different tissues of N. peltatum were in order below: ?13C values in roots > stems > leaves, and ?15N values in roots < stems < leaves. The features were determined by the plant's own properties, various ecological functions and environmental components. Carbon and nitrogen stable isotope values in leaves of euhydrophytes were more steady and reliable, which was more valuable on study significance than roots and stems.(2) The ?13C values in the leaves of P. malaianus along the different water-periods were in order as follows: wet season of summer < dry season of winter < normal season of autumn(no samples collected in normal season of spring), while ?15N in the leaves of P. malaianus has no significant difference among the three water-periods. The stable isotope values in the leaves of N. peltatum along the different water-periods were in the following order: values of ?13C indry season of winter < normal season of spring < wet season of summer < normal season of autumn, and the values of ?15N in dry season of winter < wet season of summer < normal season of autumn< normal season of spring. The patterns of C-N stable isotope contents in the two life-form plants were determined by the factors e.g. life history of euhydrophytes, source of external C/N, water resource contents of lake zones and etc.(3) In contrast with non-bloom water, ?(Chl-a), ?(TN), ?(TP) and ?(NH4+-N) were apparently higher in water column of bloom areas in eutrophic state. In the lake zones with existence of algal bloom, lower ?13C(0.22‰-3.91‰) and lower ?15N(0.66‰-10.15‰) in the leaves of P. malaianus were detected, and higher ?13C(1.15‰-2.37‰) and lower ?15N(3.02‰-4.81‰) in the leaves of N. peltatum were found. Noteworthily, in the area of algal bloom, both of ?13C and ?15N values between P. malaianus and N. peltatum leaves were separately convergent, and the difference were both smaller(?13C: 3.53‰, ?15N: 0.37‰) than those in the clean-water areas(the difference of ?13C: 5.93‰-8.59‰, the difference of ?15N: 0.63‰-7.50‰). Research shows that P. malaianus is more sensitive to environmental disaster. |
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