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Stable isotopic turnover with isotopic change due to growth and metabolic tissue replacement associated with a change in environmental conditions is a critical aspect of the use of stable isotope analyses as time-integrating tracers of resource-consumer interactions. However, stable isotopic turnover in plants remains poorly understood compared with those of animals, and here we used continuous flow elemental analyzer-isotopic ratio mass spectrometry (EA-IRMS) to analyse the turnover of stable carbon and nitrogen isotopes in a submersed macrophyte (Vallisneria natans) after transplantation to hypereutrophic and mesoeutrophic treatments in a field mesocosm experiment. The direction and magnitude of the isotopic shifts of V. natans were suggested to be determined by the inorganic nutrient availability and its isotopic content in the different treatments. Based on the modelling results of turnover, the contribution of growth to the isotopic turnover was as high as those observed in various aquatic ectotherms. However, the contribution of metabolism was also considerable, especially for nitrogen in the hypereutrophic treatment, which was argued to be a response, co-occurring with growth inhabitation and biochemical disorder of V. natans, to the stress induced by the eutrophication. Our results indicated that isotope turnover in a macrophyte is a feasible technique for estimating its ecophysiological conditions in the natural environment, and that it may facilitate understanding of isotopic data in field studies of food web and habitat restoration under eutrophic conditions., (Copyright © 2011 John Wiley & Sons, Ltd.)

Some environmental factors, such as brownification and eutrophication, may influence the successful invasions of non-native submerged macrophytes. However, few studies have focused on how interactions between these factors influence the performance of exotic submerged plants. Here, we conducted an experiment in 60 indoor containers (170 l) over 68 days using the native species Hydrilla verticillata (L. f.) Royle and the non-native species Elodea nuttallii (Planch.) St. John to test the effects of brownification, eutrophication and their interactions on the growth and competition of native and non-native aquatic plants. Our results showed that the biomass of both H. verticillata and E. nuttallii increased in the brown water treatment and that eutrophication and water brownification did not lead to a shift from a native species-dominated system to a non-native-dominated system. However, brown water treatment decreased the relative competitive ability of E. nuttallii, and this decrease was exacerbated when brown water and nutrient treatments were combined. Our results indicated that some environmental factors, such as water brownification, eutrophication and their interactions, may not benefit the competition of some non-native submerged macrophytes. Further studies with more species are needed to corroborate these conclusions. [ABSTRACT FROM AUTHOR]

We examined the stable carbon and nitrogen isotope variation in the submersed macrophyte Vallisneria natans in several shallow Chinese lakes relative to physicochemical parameters of the lake water and V. natans tissue. Of the parameters examined, the δ15N values of V. natans were correlated only with different inorganic nitrogen concentrations in the water column, suggesting that V. natans could be a sensitive bioindicator for monitoring nitrogen input into lakes. The δ 13C of V. natans varied widely and was correlated only with the inorganic carbon concentration of the water, possibly reflecting complex photosynthetic fixation and adaptations of V. natans to utilize inorganic carbon sources of different types. [ABSTRACT FROM AUTHOR]

Abstract: Decline of submersed macrophytes under low light and high nutrient stresses in eutrophic waters has been increasing worldwide. Many studies have examined the effects of low light and high nutrient alone on the decline of submersed macrophytes. Some studies have also examined the combined effects of low light and high nutrient on seagrass, but very few on freshwater macrophytes. In the present study, a factorial design of three sunlight intensities (100%, 42% and 11% full sunlight) with two nutrient levels in water (mesotrophic water and eutrophic water) was used to examine the combined effects of low light and high nutrient stresses of the water column on submersed macrophyte. Specifically, we examined the changes by testing the changes of the carbohydrate and nitrogen metabolisms, and response of antioxidant enzymes in a submersed macrophytes Potamogeton crispus. The results showed that plants tended to reduce tissue soluble protein, soluble carbohydrates (SC) contents, and SC/FAA ratios both in nutrient-enriched waters and shaded conditions, while plants accumulated free amino acids (FAA), promoted superoxide dismutase (SOD) and guaiacol peroxidase (POD) activities under these conditions. The potential mechanisms may involve the following aspects: (1) FAA was formed to transfer the accumulated NH4 +–N in the plant; (2) Carbohydrates and protein contents of the plants decreased due to the decline of photosynthesis in shaded condition; (3) Carbohydrates were also consumed significantly due to their transformation into the carbon skeleton of FAA; (4) Antioxidant enzymes SOD and POD were found to closely collaborate with each other in responding to low light and high nutrient stresses. The present study indicated that low light and high nutrient in water column could aggravate the carbon consumption and nitrogen accumulation metabolisms, and caused oxidative stress in the submersed plant. These findings contributed to the mechanisms for submersed macrophytes’ decline in eutrophic lakes. [Copyright &y& Elsevier]