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There is a heated debate over the necessity of nitrogen (N) reduction, in addition to phosphorus (P) reduction, for the control of eutrophication. Whole-lake fertilization experiments and lake restoration practices in high latitudes have demonstrated that P is the primary factor regulating total phytoplankton. Recognizing the limited large-scale evidence in warmer climatic zones, a fertilization experiment was conducted in four ponds located in the subtropical Yangtze River Basin, China. Total phytoplankton abundance in a pond receiving P (+P) was similar to that in a pond receiving both N and P (+N+P). Both had higher phytoplankton than a pond receiving no additional nutrient (Control). Total nitrogen concentration (TN) in the +P pond increased with the appearance of N-fixing cyanobacteria. Total phytoplankton abundance was similar in the ponds without P addition (+N, Control), and both ponds had lower phytoplankton levels than the +N+P pond. These results showed that P, not N, determines total phytoplankton abundance and that N deficiency is offset by N fixation in subtropical lakes. This experiment supports the idea that attention should be mainly focused on P reduction in mitigating eutrophication. Un debat existe concernant la necessite de reduire l'azote (N), en plus du phosphore (P), pour controler l'eutrophisation. Des experiences de fertilisation a l'echelle des lacs et les pratiques de restauration des lacs a hautes latitudes ont demontre que le P est le principal facteur de regulation du phytoplancton total. Reconnaissant le caractere limite des donnees a grande echelle pour les zones climatiques plus chaudes, nous avons mene une experience de fertilisation dans quatre etangs situes dans le bassin subtropical du fleuve Yangzi (Chine). L'abondance du phytoplancton total dans un etang recevant du P (+P) etait semblable a celle d'un etang recevant du N et du P (+N+P). Les deux avaient plus de phytoplancton qu'un etang ne recevant aucun ajout de nutriment (temoin). La concentration d'azote total (TN) dans l'etang +P augmentait avec l'apparition de cyanobacteries fixatrices de N. L'abondance du phytoplancton total etait semblable pour les etangs sans ajout de P (+N, temoin), et l'abondance de phytoplancton dans ces deux etangs etait plus faible que dans l'etang +N+P. Ces resultats montrent que le P, et non le N, determine l'abondance de phytoplancton total et que la fixation de N compense les deficiences en N dans les lacs subtropicaux. Cette experience appuie la notion voulant que les efforts d'attenuation de l'eutrophisation devraient principalement porter sur la reduction du P. [Traduit par la Redaction], Introduction Eutrophication of lakes is a global environmental problem, associated with algal blooms, fish kills, ecosystem degeneration, and toxic algae, and hence represents a hazard to drinking water supplies. Many [...]

The management of water levels in wetlands is of great importance for the wetland ecosystem, including the conservation and revitalization of plants. However, the water level requirements (WLRs) of wetland plants have not been well investigated. In this study, Typha angustifolia was selected as an experimental plant species. Combining field investigation and simulation experiments, the relationship between the development status of this species and water level fluctuations (WLFs) in different life-history stages were analyzed. The results show that populations in the Yangtze floodplain, China, had two phenotypic forms 'tall' and 'short', and that these were distributed in lakes with intermittent or quasi-natural fluctuations and reservoir-like fluctuations, respectively. Lakes with high amplitude (>3.2 m) water fluctuations did not contain T. angustifolia. We investigated the distribution and growth of T. angustifolia in lakes of varying hydrology across the Yangtze floodplain, seeking to define its tolerance of water-level fluctuations and submergence at different stages in its life cycle. The upper tolerance limit of static submerged water depth was bounded by 1.5 times the height of plants in the seedling stage, and the upper tolerance limit of the submergence rate in the seedling stage was the average growth rate of seedling, 1.5 cm/d. The plant height had a positive linear correlation with amplitude and water depth from June to July. The autumn biomass was significantly negatively correlated with amplitude and water depth from January to May. This paper is perhaps the first case study on water level fluctuation requirements (WLFRs) of emergent macrophytes. It systematically assessed the WLFRs of T. angustifolia in each life-history stage, and established a comprehensive WLFR conceptual model. The results of this study could provide a quantitative operational basis for the protection and restoration of this species in Yangtze floodplain lakes. [ABSTRACT FROM AUTHOR]

Objective: To investigate the expression of 17 beta-hydroxysteroid dehydrogenase type 1 (17β-HSD1) in the kidney of rats and explore the capacity of the kidney for synthesizing sex hormones., Methods: The expressions of 17-HSD1 and sex hormones were detected by Western blotting and radioimmunoassay in rat renal cells in primary cultured for 24 and 48 h in the presence or absence of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)., Results: After cell culture for 24 h, the primary rat renal cells expressed a low level of 17β-HSD1 (0.1843±0.076), which increased to 1.6651±0.044 (P<0.01) in response to co-stimulation by FSH and LH. Low levels of estradiol, progesterone and testosterone were also detected in rat renal cells (3.30±3.78, 62.60±12.33, and 22.12±3.36, respectively), and co-stimulation of FSH and LH significantly increased their levels to 8.50±2.64, 117.80±9.79, and 45.04±4.39, respectively (P<0.05). The levels of these hormones showed no significant differences between cells cultured for 24 h and 48 h (P>0.05)., Conclusion: The rat renal cells express 17β-HSD1 and are capable of stably secreting sex hormones in response to co-stimulation with FSH and LH, suggesting the capacity of the rat kidneys for synthesizing sex hormones. These findings enrich the understanding of the endocrine function of the kidney.