Ecological consequences of carbon substrate identity and diversity in a laboratory study

Plants return a wide range of carbon (C) substrates to the soil system. The decomposition rate of these substrates is determined by their chemical nature, yet few studies have examined the relative ecological role of specific substrates (i.e., substrate identity) or mixtures of substrates. Carbon substrate identity and diversity may alter soil chemistry and soil community composition, resulting in changes in belowground ecosystem functions such as decomposition and nutrient transfer, creating feedbacks that may affect plant growth and the aboveground community. A laboratory experiment was set up in which eight C substrates of varying chemical complexity were added to a base soil singly, in pairs, fours, or with all eight together every four days over a 92-day period. After 92 days these soils were analyzed for changes in chemistry, microbial community structure, and components of ecosystem functioning. The identity of the added C substrates significantly affected soil chemistry, microbial basal and substrate-induced respiration, and soil microbial community structure measured by either the catabolic response profile (CRP) technique or phospholipid fatty acid composition. These belowground changes strongly affected the ability of the soil microflora to decompose cellulose paper, probably because of differential effects of the C substrates on soil energy supplies and enzyme activities. The addition of C substrates to soils also reduced plant growth compared to the unamended control soil, but less so in soils amended with a tannin than those amended with other substrates. Carbon substrate diversity effects saturated at low diversity levels, tended to have neutral or negative effects on ecosystem functions, and depended strongly on which C substrates were added. It increased CRP compound use but had little effect on other measures of the soil microbial community. Overall, results showed that the chemical nature of C substrates added to soil, and sometimes their diversity, can affect the soil microbial community and soil chemistry, which subsequently affect other ecosystem processes such as decomposition and plant growth. The identity and diversity of substrates that plants add to soil may therefore have important consequences for both above- and belowground ecosystem functions.     

Biotransformation of the flame retardant tetrabromo-bisphenol A by human and rat sub-cellular liver fractions

The comparative in vitro metabolism of the flame retardant tetrabromo-bisphenol A was studied in rat and human using a [(14)C]-radio-labelled molecule. Tetrabromo-bisphenol A is metabolised into the corresponding glucuronide (liver S9 fractions) and several other metabolites produced by cytochrome P450 dependent pathways (liver microsomes and liver S9 fractions). No major qualitative differences were observed between rat and human, regardless of the selected concentration, within the 20-200 microM range. Tetrabromo-bisphenol A undergoes an oxidative cleavage near the central carbon of the molecule, that leads to the production of hydroxylated dibromo-phenol, hydroxylated dibromo-isopropyl-phenol and glutathione conjugated dibromo-isopropyl-phenol. The main metabolites of tetrabromo-bisphenol A are two molecules of lower polarity than the parent compound, characterised as a hexa-brominated compound with three aromatic rings and a hepta-brominated dimer-like compound, respectively. Both structures, as well as the lower molecular weight metabolites resulting from the breakdown of the molecule, suggest the occurrence of chemically reactive intermediates formed following a first step oxidation of tetrabromo-bisphenol A.     

Sources of hydrocarbons in sediments of the Bay of Fort de France (Martinique)

Sedimentary hydrocarbons have been studied quantitatively and qualitatively in 16 stations of the Bay of Fort de France (Martinique). Hydrocarbon levels ranged from 54 to 1045 mg kg(-1) sed. dry weight. Origin of hydrocarbons are multiple: biogenic (terrestrial inputs), pyrolytic (residues of natural or anthropogenic combustions), diagenetic and anthropogenic (petroleum contamination). Generally high levels of hydrocarbons are not associated to a petroleum contamination. The main source of hydrocarbons in the mangrove coastal zones of the Bay of Fort de France seems to be the early diagenetic degradation products of 3-oxytriterpenoids. Excepted two stations, petroleum contamination is very low or absent.     

Recovery of a freshwater wetland from chemical contamination after an oil spill

In March 2009, a cargo ship spilled 250 tons of heavy fuel oil off the Queensland coast of Australia. The pristine National Park Moreton Island, seven nautical miles to the east of the spill site, was most affected by the oil slick. Contamination of the island's shoreline was widespread, with freshwater wetlands particularly slow to recover as clean-up needed to be carefully managed to avoid damage to this sensitive ecosystem. During the clean-up process on Moreton Island a monitoring program was initiated using traditional chemical analysis in combination with bioanalytical techniques to assess the extent and variability in contamination at sites on the shoreline and freshwater wetlands. Water accommodated fractions (WAF) of oil residues from samples taken directly after the spill on the shoreline showed the same level of toxic potency as samples from the wetland while baseline-toxicity equivalent concentrations (baseline-TEQ) and 2,3,7,8-tetrachlorodibenzodioxin equivalent concentrations (TCDDEQ) were much lower in oil collected from the sandy beach. The umuC assay for genotoxicity and the E-SCREEN assay for estrogenic effects indicated the extracts were not genotoxic or estrogenic. PAH concentrations and toxicity in grab water samples were below detectable levels, however, extracts from time integrated silicone passive samplers deployed for several weeks at the contaminated sites gave measurable responses in the bioassays with TCDDEQ levels increased relative to the control site. The low levels of baseline-TEQ and TCDDEQ present after 8 months had further decreased 6 months later indicating satisfactory recovery of this pristine ecosystem after an oil spill.     

The use of fetal MRI for renal and urogenital tract anomalies

Fetal anomalies are detected in approximately 2% of all fetuses and, among these, genitourinary tract abnormalities account for 30% to 50% of all structural anomalies present at birth. Although ultrasound remains the first line diagnostic modality, fetal MRI provides important additional structural and functional information, especially with the development of faster sequences and the use of functional sequences. The added value of MRI-based imaging is three-fold: (a) improvement of diagnostic accuracy by adequate morphological examination, (b) detection of additional anomalies, and (c) in addition, MRI has the potential to provide information regarding renal function. In this review, we describe the role of fetal MRI in the anatomical evaluation of renal and urogenital tract anomalies, and we also touch upon the contribution of functional MRI to the diagnostic workup of these conditions.     

Factors affecting vegetation establishment and development in a sand dune chronosequence at Newborough Warren,North Wales

Newborough Warren is a large calcareous west coast UK dune system, which has experienced rapid vegetation spread in the last 70 years. Information from two high resolution chronosequences for dry and wet dune habitats, 0–145 years, was used to answer the following questions: Does climate influence colonisation of vegetation on bare sand? What are the timescales and sequences of successional change in the vegetation? Analysis of aerial photographs showed that stabilisation of the dune system since 1945 has occurred in three main phases. The onset of stabilisation predated myxomatosis by 10 years; while stabilisation virtually halted during the period 1964–1978. Periods of rapid stabilisation were coincident with higher values of Talbot’s Mobility index (M)?>?0.3. Successional development was apparent in both dry and wet habitats. Fixed dune grassland started to replace earlier successional communities at around 40 years, and could persist to 145 years. Linear succession in dune slacks was less apparent, but a separation between communities typically regarded as ‘younger’ and ‘older’ occurred at around 40 years. Species richness in dry dune habitats increased with age to a maximum on soils around 60 years old, then declined again. Species richness was unrelated to age or soil development in wet dune slacks. The influence of climate suggests that conservation managers can only operate within the constraints imposed by natural climatic conditions. Vegetation growth and soil development are closely linked and maintaining some open areas is key to preventing soil development and over-stabilisation.     

A peaceful zone bordering two Argentine ant (Linepithema humile) supercolonies

In invasion areas, the Argentine ant (Linepithema humile) forms huge supercolonies with free exchange of individuals among nests. Two continental supercolonies on the French mediterranean coast, the Main European supercolony and the Corsican supercolony, are known to contain workers showing moderate to high levels of inter-supercolony aggression. We performed chemical and behavioral assays using workers from eight coastal sites in southeastern France covering a geographical zone that includes nests of the two supercolonies, to determine the nature of worker interactions in a supercolony boundary zone. We examined how the chemical and behavioral clines vary across the borders of the Main and Corsican supercolonies. Our results on Giens peninsula and Porquerolles island populations bordering the Main supercolony reveal the existence of a peaceful border zone with no aggression between workers of the Main supercolony and the Corsican supercolony. The chemical results, however, exhibited qualitative similarity to those observed in the Corsican supercolony and revealed both quantitative and qualitative chemical differences from those observed in the Main supercolony. These peaceful populations may result from fusion and/or genetic crosses between the two supercolonies, and we hypothesize that such peaceful border zones are instrumental in the evolution of supercolonies.     

Who’s where? Ecological uncertainty shapes neophobic predator avoidance in Trinidadian guppies

Behavioral Ecology and Sociobiology - Behavioural diversity is a basic component of biodiversity, with implications in ecological interactions at the intra- and interspecific levels. The...