Degradation of native and exotic riparian plant leaf litter in a floodplain pond

1. A litter‐bag experiment was undertaken in a pond on the margins of a large temperate floodplain in south‐western France to assess the potential influence of the replacement of native by exotic riparian species on organic matter degradation. We determined initial litter chemical composition, breakdown rates and the invertebrate assemblages associated with the litter for five pairs of native dominant and exotic invasive species co‐occurring at different stages along a successional gradient. 2. Litter chemical composition, breakdown rates and abundance and diversity of detritivorous invertebrates were similar for the exotic and native species overall. No overall changes in organic matter degradation can thus be predicted from the replacement of dominant natives by exotic invasives. Breakdown rates were primarily driven by the C/N ratio. 3. One invasive species (Buddleja davidii) showed significantly higher breakdown rates than its native counterpart (Populus nigra), resulting in the disappearance of leaf litter 6 months prior to the next litterfall. In some cases, therefore, invasion by exotic species may result in discontinuity of resource supply for decomposers.     

Studies in the Nutrition of Apple Rootstocks: 1. Effects of Deficiencies of Iron and Magnesium on Growth

Plants of the apple rootstock M.VII were grown for a singleseason by spraying their roots continuously with nutrient solutions:(a) complete, (b) low iron, (c) low magnesium, and (d) low ironand low magnesium. Detailed records were taken throughout theseason of fresh weight, shoot length, diameter, and leaf area,while the fresh and dry weights of component parts were determinedon harvested samples. The leaves of the iron-deficient plants were chlorotic and hada lower dry weight and higher water content per unit area thanthose of the control plants. Growth and net assimilation ratewere both reduced but the distribution of assimilates was similarto that in the controls. Total growth was also markedly reduced by the low-magnesiumtreatment, but the leaf symptoms were different and the plantswere morphologically distinct from the control plants. Verylittle chlorosis occurred, but necrosis and severe defoliation,progressing up the shoot, reduced the leaf area ratio and probablylargely accounted for the low net assimilation rate and relativegrowth rate. The diameter of the shoot was affected much morethan its length and the shoot/root ratio was greatly increased. Plants deficient in both iron and magnesium showed less defoliationthan when magnesium alone was low. More dry matter accumulatedin the old stem and less in the new shoot than would have occurredwith a simple combination of the single deficiencies.     

A Screening Level Mass Balance Model of Sediment Remediation Options

It is suggested that dynamic mass balance models can provide valuable support information when sediment remediation activities, such as dredging, are contemplated. A model with sufficient credibility and accuracy can be used to compare and contrast the results of various remediation actions and the effect of natural remediation processes. A food web model can also be included. The information provided by the model can be summarized in periodic (e.g. annual) “Report Cards” documenting the status of the contaminated system during and after the remediation process. Time plots of relevant properties of the system, such as contaminant masses, concentrations and levels in water, sediment and biota, can convey the essential information required for decision-making. This approach is illustrated by applying it with screening level accuracy to the remediation activities currently being undertaken in the St. Clair River, which flows from Lake Huron to Lake St. Clair near Sarnia, Ontario, Canada. The effects of dredging to reduce concentrations of hexachlorobenzene in sediment, water and biota are explored.     

<Emphasis Type="Italic">De novo</Emphasis> Synthesis of Transfer and 55 RNA<Superscript>1f</Superscript> in Cleaving Sea Urchin Embryos

SIGNIFICANT changes in RNA metabolism have been described during early sea urchin development. Until recently the only detectable class of RNA synthesized during cleavage stages was that with a low G + C base composition and heterogeneous sedimentation properties (DNA-Jike RNA)¹. The genes for nucleolar ribosomal RNA (26S and 18S) were believed to become active only following gastrulation^2–4 and the products of nuclear transfer RNA (4S) genes were first detected at the mesenchyme blastula stage⁵. Any label in the 4S region of sucrose gradients of RNA from the cleavage stages of embryogenesis was interpreted as reflecting the turnover of the pCpCpA region of pre-existing transfer RNA (tRNA) molecules.     

The use of open burrows to estimate abundances of intertidal estuarine crabs

Estimation of absolute (or true) abundances of intertidal burrowing crabs is a difficult problem in some estuarine habitats because the nature of the substratum and behaviour of crabs can restrict researchers to the use of sampling methods which at best estimate only apparent, or relative, abundances. One method that has been used is to count open burrows to estimate population densities. This paper discusses the results of a test examining the validity of using burrows to estimate apparent abundances of a temperate ocypodid crab, Heloecius cordiformis. inhabiting mangrove forests of south-eastern Australia. Under appropriate circumstances, this method may provide a quick and reliable estimate of abundance of crabs.     

A TWO-HOUR, SINGLE-STEP RT-PCR PROTOCOL FOR DETECTION OF RNA-VIRUS

A rapid protocol of RT-PCR for the detection of RNA-Virus, Mouse Hepatitis Virus , was developed. An Idaho Air-Thermal Cycler was used with 5 mM Mg CI₂ in the buffer so that both RT and PCR steps can be run in one tube and the total detection time is less than two hours.