Macrophyte beds in a subtropical reservoir shifted from a nutrient sink to a source after drying then rewetting

1. Macrophytes play a key role in assimilating and storing nutrients in shallow aquatic ecosystems, but their capacity to act as a long‐term nutrient sink can be affected by water level fluctuations. Water level drawdown in reservoirs followed by rewetting may mobilise a significant nutrient pool. These nutrients can be stored in the littoral zone in dead or dormant macrophytes, and in the desiccated sediments within the macrophyte beds. However, the contribution of desiccated macrophyte beds to nutrient release upon rewetting has not been well quantified.
2. Our study examined the effect of rewetting the previously desiccated waterlily Nymphoides indica (Menyanthaceae) in treatments (1) without sediments (N.i.?Sed), and (2) with sediments in N. indica beds (N.i.+Sed) on water quality.
3. We found that longer drying duration increased dissolved nutrients (nitrate/nitrite, ammonium and total dissolved organic nitrogen/phosphorus) and organic carbon release from N.i.+Sed and N.i.?Sed treatments after rewetting. In the N.i.+Sed treatment with <4 weeks of desiccation, all N. indica plants regenerated from roots after subsequent rewetting. In addition, the resulting nutrient/carbon release was not significantly different to the control treatment which did not have desiccation. A significant increase in dissolved nutrient and carbon concentrations in the water column was found in treatments with more than 10 weeks of desiccation followed by rewetting. This coincided with the sediment reaching its minimum moisture content. Furthermore, chlorophyll a (Chl‐a) concentrations in the overlying water also increased with more than 10 weeks of desiccation, presumably in response to the increased nutrient availability and the removal of competition for nutrients from macrophytes.
4. On the basis of our laboratory experiments, we calculated the potential effect of desiccated and rewetted N. indica beds on water quality in a local N. indica‐dominated reservoir after water level drawdown. We also separated the contribution of N. indica plants from their macrophyte beds on water quality changes. Fourteen days after rewetting, the total dissolved nutrients released from N. indica alone (N.i.?Sed) could contribute 0.5% of the total nitrogen and 29% of total phosphorus to the water column concentrations in the whole reservoir. In contrast, N. indica beds (N.i.+Sed) contributed more total dissolved nitrogen (4.3%) but less total dissolved phosphorus (0.3%) release into the water column. The higher nitrogen release for the N.i.+Sed treatment was likely due to the organic matter decomposition in the sediment in macrophyte beds. In contrast, the less dissolved phosphorus release, compared with the N. indica alone, was likely the result of phosphate adsorption by previously desiccated soil particles and/or assimilation by phytoplankton, since the phytoplankton biomass (as measured by Chl‐a concentrations) was significantly higher in the N.i.+Sed treatment.
5. This study highlights the importance of managing both the duration and rate of water level drawdown in reservoirs to prevent rooted macrophytes, like N. indica, from becoming a source of nutrients, which may cause deterioration in water quality.

     

The Customer Isn't Always Right—Conservation and Animal Welfare Implications of the Increasing Demand for Wildlife Tourism

Tourism accounts for 9% of global GDP and comprises 1.1 billion tourist arrivals per annum. Visits to wildlife tourist attractions (WTAs) may account for 20–40% of global tourism, but no studies have audited the diversity of WTAs and their impacts on the conservation status and welfare of subject animals. We scored these impacts for 24 types of WTA, visited by 3.6–6 million tourists per year, and compared our scores to tourists’ feedback on TripAdvisor. Six WTA types (impacting 1,500–13,000 individual animals) had net positive conservation/welfare impacts, but 14 (120,000–340,000 individuals) had negative conservation impacts and 18 (230,000–550,000 individuals) had negative welfare impacts. Despite these figures only 7.8% of all tourist feedback on these WTAs was negative due to conservation/welfare concerns. We demonstrate that WTAs have substantial negative effects that are unrecognised by the majority of tourists, suggesting an urgent need for tourist education and regulation of WTAs worldwide.     

Effect of magnesium on the growth and cell cycle of transformed and non-transformed epithelial rat liver cells in vitro

The effects of magnesium (Mg) restriction on cell growth and the cell cycle were determined in transformed (TRL-8) and non-transformed (TRL-12-15) epithelial-like rat liver cells. Cells were cultured in RPMI 1640 medium in which the Mg concentration was reduced to 0.5, 0.1, and 0 × the concentration in the regular RPMI 1640 media (100mg/l). Cell growth in the transformed cells was not influenced by the Mg restriction as greatly as in the non-transformed cell line. Transit through the cell cycle also exhibited an independence of the Mg in the medium in the transformed cells. When transformed cells were grown for two generations in Mg-limited medium, the growth rate slowed to a rate similar to that demonstrated by the non-transformed cells. Analysis by flow cytometry showed that transit through the cell cycle was minimally slowed in Mg deficient transformed cells; however, transit through the G₁ and S phases in the non-transformed cells was slowed. The TRL-8 cells in Mg-limited medium resulted in fewer nuclei in G₁ with subsequent increases in the percentages of S-phase nuclei. The TRL 12-15 cells reacted oppositely with the number of G₁ nuclei increased and the number of S-phase nuclei decreased. In respect to growth, these results show that epithelial cells respond in a similar manner to Mg-limitation as do fibroblast cells. The transformed cells exhibited a level of independence from Mg in respect to growth, reproduction, and cell-cycle kinetics.     

Trichoderma Synthesizes Cytokinins and Alters Cytokinin Dynamics of Inoculated Arabidopsis Seedlings

Journal of Plant Growth Regulation - Trichoderma is an important genus of symbiotic fungi, commonly used around the world as biocontrol agents and as biofertilizer. Although their beneficial...     

Improving Smear Technics by the Use of Enzymes

A method for securing spreading of large meiotic chromosomes is described. It consists in treating a piece of fixed anther in a 1% solution of Clarase, a proprietary enzyme complex, or in an extract prepared by grinding the contents of flask cultures of certain fungi (Aspergillus niger, Chaetomium globosum, Metarrhizium sp.) with quartz sand in a mortar containing 10 ml. of a sodium acetate buffer, pH 5.0. The fixed anthers are thoroughly washed in H₂O prior to the enzyme treatment. Length of treatment may vary from as little as 10 minutes to several hours. The usual aceto-carmine or propionic-carmine smear technic may then be used. The treatment destroys some of the elasticity of the cytoplasm so that the chromosomes remain spread out when light pressure is exerted on the cover slip.     

The Indigenous People of the Caribbean

The Indigenous People of the Caribbean. Samuel M. Wilson. ed. Gainesville: University of Florida Press, 1997.254 pp.