Tertiary sewage treatment by a full-scale compact vertical flow constructed wetland.

A 208 m2 compact vertical flow treatment wetland (cVFTW) was studied, treating the rotating biological contactor (RBC) effluent of a busy UK visitor attraction, with widely varying daily sewage loads up to 111 resident population equivalent. Results are presented from monthly spot-sampling and analysis for inlet and outlet concentrations of BOD, SS, NH4-N and TN, including load rates, for the first four-and-a-half years of operation. From commissioning to 13 weeks, outlet BOD, SS and NH4-N were below 12 mg l-1, until a sudden outlet NH4-N spike, to 31.9 mg l-1, the reasons for which are discussed. Thereafter, final effluent quality was <3:<3:<0.5 mg l-1 BOD/SS/NH4-N almost without exception, regardless of the determinand load rates imposed. Recirculation of controlled proportions of cVFTW effluent to the RBC inlet eliminated foul odour emanating from the RBC, and considerably increased overall nitrogen removal via denitrification. Phragmites australis development was poor, with the majority of plants experiencing chlorosis, putatively owing to insufficient bioavailable iron. By year three, despite ongoing weed removal to select for Phragmites, the wetland was increasingly colonised by other species, predominantly Epilobium hirsutum. Glyceria maxima, planted in year three, outcompeted even Epilobium, recommending itself as an alternative to Phragmites in high redox potential treatment wetlands.

The influence of tetrad shape and intersporal callose wall formation on pollen aperture pattern ontogeny in two eudicot species.

BACKGROUND AND AIMS: In flowering plants, microsporogenesis is accompanied by various types of cytoplasmic partitioning (cytokinesis). Patterns of male cytokinesis are suspected to play a role in the diversity of aperture patterns found in pollen grains of angiosperms. The relationships between intersporal wall formation, tetrad shape and pollen aperture pattern ontogeny are studied. METHODS: A comparative analysis of meiosis and aperture distribution was performed within tetrads in two triporate eudicot species with contrasting aperture arrangements within their tetrads [Epilobium roseum (Onagraceae) and Paranomus reflexus (Proteaceae)]. KEY RESULTS AND CONCLUSIONS: Intersporal wall formation is a two-step process in both species. Cytokinesis is first achieved by the formation of naked centripetal cell plates. These naked cell plates are then covered by additional thick, localized callose deposits that differ in location between the two species. Apertures are finally formed in areas in which additional callose is deposited on the cell plates. The recorded variation in tetrad shape is correlated with variations in aperture pattern, demonstrating the role of cell partitioning in aperture pattern ontogeny.

Elevated carbon dioxide increases nectar production in Epilobium angustifolium L.

Effects of elevated CO2 and nutrient availability on nectar production and onset of flowering in five different seed families (genotypes) of Epilobium angustifolium were investigated in a greenhouse experiment. Elevated CO2 significantly increased nectar production per day (+51%, p < 0.01), total sugar per flower (+41%, p < 0.05), amino acid concentration (+65%, p < 0.05) and total amino acids per flower (+192%, p < 0.001). All other parameters tested, i.e., nectar sugar concentration, proportion of glucose/fructose and proportion of sucrose/(glucose + fructose), were not significantly affected by elevated CO2 and/or fertilization. However, elevated CO2 caused a marginally significant trend for earlier flowering in highly fertilized plants. No significant family x CO2 interaction was found in any of the tested parameters, but the response in nectar production varied considerably among seed families (+10 to +104%) and was significantly positive in two of the five seed families investigated. Our results are not consistent with earlier studies on effects of elevated CO2 on nectar production and flowering phenology in other plant species. It seems, on the other hand, that CO2 effects on nectar production are specific to species and genotype. Hence, no general conclusions about effects of elevated CO2 on these floral traits can be drawn at present, but it must be cautioned that elevated CO2 might not only increase floral rewards as in E. angustifolium, but might also lead to shifts or even disruptions in fine-tuned plant-pollinator interactions.