Exoenzyme activities as indicators of dissolved organic matter composition in the hyporheic zone of a floodplain river

1. We measured the hyporheic microbial exoenzyme activities in a floodplain river to determine whether dissolved organic matter (DOM) bioavailability varied with overlying riparian vegetation patch structure or position along flowpaths. 2. Particulate organic matter (POM), dissolved organic carbon (DOC), dissolved oxygen (DO), electrical conductivity and temperature were sampled from wells in a riparian terrace on the Queets River, Washington, U.S.A. on 25 March, 15 May, 20 July and 09 October 1999. Dissolved nitrate, ammonium and soluble reactive phosphorus were also collected on 20 July and 09 October 1999. Wells were characterised by their associated overlying vegetation: bare cobble/young alder, mid‐aged alder (8–20 years) and old alder/old‐growth conifer (25 to >100 years). POM was analysed for the ash‐free dry mass and the activities of eight exoenzymes (α‐glucosidase, β‐glucosidase, β ‐N‐acetylglucosaminidase, xylosidase, phosphatase, leucine aminopeptidase, esterase and endopeptidase) using fluorogenic substrates. 3. Exoenzyme activities in the Queets River hyporheic zone indicated the presence of an active microbial community metabolising a diverse array of organic molecules. Individual exoenzyme activity (mean ± standard error) ranged from 0.507 ± 0.1547 to 22.8 ± 5.69 μmol MUF (g AFDM)^?1 h^?1, was highly variable among wells and varied seasonally, with the lowest rates occurring in March. Exoenzyme activities were weakly correlated with DO, DOC and inorganic nutrient concentrations. 4. Ratios of leucine aminopeptidase : β‐glucosidase were low in March, May and October and high in July, potentially indicating a switch from polysaccharides to proteins as the dominant component of microbial metabolism. 5. Principal components analysis indicated that there were patch effects and that these effects were strongest in the summer. 6. DOM degradation patterns did not change systematically along hyporheic flowpaths but varied with overlying forest patch type in the Queets River hyporheic zone, suggesting that additional carbon inputs exist. We hypothesise that the most likely input is the downward movement of DOM from overlying riparian soils. Understanding this movement of DOM from soils to subsurface water is essential for understanding both the hyporheic metabolism and the carbon budget of streams and rivers.     

Temperature-independent diel variation in soil respiration observed from a temperate deciduous forest

The response of soil respiration (R_s) to temperature depends largely on the temporal and spatial scales of interest and how other environmental factors interact with this response. They are often represented by empirical exponential equations in many ecosystem analyses because of the difficulties in separating covarying environmental responses and in observing below ground processes. The objective of this study was to quantify a soil temperature‐independent component in R_s by examining the diel variation of an R_s time series measured in a temperate deciduous forest located at Oak Ridge, TN, USA between March and December 2003. By fitting 2 hourly, continuous automatic chamber measurements of CO₂ efflux at the soil surface to a Q₁₀ function to obtain the temperature‐dependent respiration (R_t) and plotting the diel cycles of R_t, R_s, and their difference (R_i), we found that an obvious temperature‐independent component exists in R_s during the growing season. The diel cycle of this component has a distinct day/night pattern and agrees well with diel variations in photosynthetically active radiation (PAR) and air temperature. Elevated canopy CO₂ concentration resulted in similar patterns in the diel cycle of the temperature‐independent component but with different daily average rates in different stages of growing season. We speculate that photosynthesis of the stand is one of the main contributors to this temperature‐independent respiration component although more experiments are needed to draw a firm conclusion. We also found that despite its relatively small magnitude compared with the temperature‐dependent component, the diel variation in the temperature‐independent component can lead to significantly different estimates of the temperature sensitivity of soil respiration in the study forest. As a result, the common practice of using fitted temperature‐dependent function from night‐time measurements to extrapolate soil respiration during the daytime may underestimate daytime soil respiration.     

Transformation by Polyoma Virus affects Adhesion of Fibroblasts

WHEN freshly trypsinized hamster fibroblasts (BHK 21, Clone 13¹) are shaken in suspension, intercellular adhesions are rapidly formed and there is some support for the view that this process is the expression of an adhesive property of the cells in culture which has survived the procedures used to separate them and is not simply an artefact of the use of trypsin². Transformation of animal cells in culture by tumour viruses alters the cell surfaces, as various techniques have shown^3–9 and we have investigated whether intercellular adhesiveness, as defined by the particular assay we have been using, is also affected.     

Landscapes of Settlement in Northern Iceland: Historical Ecology of Human Impact and Climate Fluctuation on the Millennial Scale

Early settlement in the North Atlantic produced complex interactions of culture and nature. The sustained program of interdisciplinary collaboration is intended to focus on ninth- to 13th-century sites and landscapes in the highland interior lake basin of Mývatn in Iceland and to contribute a long-term perspective to larger issues of sustainable resource use, soil erosion, and the historical ecology of global change.     

The incidence of viruses in wild Brassica rapa ssp. sylvestris in southern England

Using enzyme‐linked immunosorbent assays, the frequency of occurrence of six viruses was determined in Brassica rapa ssp. sylvestris collected from two Thameside sites (Abingdon and Culham) in Oxfordshire and one near the Avon (Claverton) in Bath & North East Somerset. During 2000–2001, the viruses detected were: Beet western yellows virus (genus Polerovirus) (BWYV), Cauliflower mosaic virus (genus Caulimovirus) (CaMV), Turnip crinkle virus (genus Carmovirus) (TCV), Turnip rosette virus (genus Sobemovirus) (TRoV), and Turnip yellow mosaic virus (genus Tymovirus) (TYMV). BWYV and TYMV were the most frequently detected viruses at the Oxford shire sites, both as single infections (20/1743 and 66/1743 respectively) and as dual infections (7/1743). Turnip mosaic virus (genus Potyvirus) (TuMV) was not detected in the field‐grown plants assayed from any of the sites. There was a highly significant (x²_[1]=30.07, P<0.001) difference in the proportion of plants at each Oxfordshire site in which one or more viruses were detected, and essentially the same pattern of virus infection was observed in tests on B. rapa from the site near Claverton. At least one representative isolate of each detected virus was tested for its morphological and serological effects on glasshouse‐grown individuals from different half‐sib families of B. rapa from both Oxfordshire sites. Except for TRoV, where there was a large difference in the frequency of successful infection in B. rapa from the two locations (1/15 vs 11/15), no clear evidence of resistance or immunity to challenge was observed, although tolerance (virus invasion without symptoms) was frequent. Fewer of the plants from Abingdon were infected than those from Culham, when mechanically challenged with TRoV, but the two B. rapa populations were not otherwise consistently different, either in their infectibility by this virus or in their responses to challenge. However, with TCV, viral antigen concentration was closely linked to the severity of disease and the B. rapa from both Oxfordshire sites segregated into two classes: those with symptoms and most viral antigen, and those without symptoms and least viral antigen. These results suggest that generic risk assessments cannot be made due to differences in the way distinct B. rapa populations react to virus challenge.     

Innate aversion to ants (Hymenoptera: Formicidae) and ant mimics: experimental findings from mantises (Mantodea)

Field data suggest that ants may be important predators of mantises which, in turn, may be important predators of jumping spiders (Salticidae). Using a tropical fauna from the Philippines as a case study, the reactions of mantises to ants, myrmecomorphic salticids (i.e. jumping spiders that resemble ants) and ordinary salticids (i.e. jumping spiders that do not resemble ants) were investigated in the laboratory. Three mantis species ( Loxomantis sp., Orthodera sp., and Statilia sp.) were tested with ten ant species, five species of Myrmarachne (i.e. myrmecomorphic salticids), and 23 ordinary salticid species. Two categories of the myrmecomorphic salticids were recognized: (1) 'typical Myrmarachne ' (four species with a strong resemblance to ants) and (2) Myrmarachne bakeri (a species with less strong resemblance to ants). Ants readily killed mantises in the laboratory, confirming that, for the mantises studied, ants are dangerous. In alternate-day testing, the mantises routinely preyed on the ordinary salticids, but avoided ants. The mantises reacted to myrmecomorphic salticids similarly to how they reacted to ants (i.e. myrmecomorphic salticids appear to be, for mantises, Batesian mimics of ants). Although myrmecomorphic salticids were rarely eaten, M . bakeri was eaten more often than typical Myrmarachne . Because the mantises had no prior experience with ants, ant mimics or ordinary salticids, our findings suggest that mantises have an innate aversion to attacking ants and that this aversion is generalized to myrmecomorphic salticids even in the absence of prior experience with ants. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 23–32.     

Lower Devonian coalified sporangia from Shropshire: Salopella Edwards & Richardson and Tortilicaulis Edwards

A diverse assemblage of coalified sporangia from Lochkovian/Gedinnian, fluvial rocks imicrornatus-newportensis Spore Biozone) contains fusiform forms assignable to Salopella Edwards & Richardson and Tortilicaulis Edwards. Both show bifurcation within some sporangia. In specimens assigned to Salopella cf. marcensis , longitudinal dehiscence produces two equal valves revealing spores resembling Aneurospora , although trilete marks may be difficult to distinguish. The spores are in two forms with distal ornament of either coarse or fine coni, each occurring in separate sporangia. A further sporangium of Salopella shape contains distally apiculate, hilate cryptospores. Elongate sporangia exhibiting spiralling of superficial cells and sometimes gross twisting, are placed in a new species of Tortilicaulii, T. offaeus. Anatomical data include details of irregularly thickened epidermal cells, sporangial wall and in situ spores. The latter are trilete, equatorially thickened and highly distinctive, because the entire exospore surface is covered with grana, a feature not common in dispersed spores of this age. The nomenclatural and curatorial problems associated with these small, coalified fossils, whose anatomical examination by scanning electron microscope necessitates elimination of gross morphology, are discussed.