ALBERT

Notes: Throughout the world there is a trend towards retaining crop residues rather than burning them. For this reason, changes in soil chemistry and aggregation in a Vertisol induced by 59 years of burning or green cane harvesting with or without annual fertilizer applications were investigated. Crop residues were either burnt prior to harvest with the harvest residues raked off (R1), burnt prior to harvest with the harvest residues left on the soil surface (R2), or left unburnt with all the trash left on the soil surface (R3). Concentrations of organic C in the surface 10 cm of soil increased with fertilizer applications and with increasing amounts of crop residue returned in the order R1 〈 R2 〈 R3. Fertilizer applications caused an accumulation of residual P in both inorganic (Pi) and organic (Po) forms. A sequential P fractionation showed that fertilizer P accumulated in both labile and recalcitrant Pi and Po forms, and trash retention caused an accumulation of recalcitrant Po. Concentrations of K decreased in the unfertilized R1 and R2 treatments because K reserves were depleted. By contrast, there was an increase in the concentrations of K in the fertilized R3 treatment. The soil became more acid on the fertilized and, to a lesser extent, trash retention plots. We attribute this to nitrification and subsequent nitrate leaching. Acidification resulted in a loss of exchangeable Ca and Mg, a decrease in ECEC, and an increase in the concentrations of total and monomeric Al in soil solution, in exchangeable Al3+ and in the buffering reserve of non-exchangeable Al associated with organic matter. Aggregate stability was increased by increasing crop residues but decreased by fertilizer applications. The decrease was attributed to an increase in the proportion of exchangeable cations present in monovalent form due to applications of fertilizer K and leaching of Ca and Mg. We conclude that trash retention and annual fertilizer applications have substantial long-term effects on both organic matter status and soil pH and therefore on other soil chemical and physical properties.

Notes: A method is presented for the prediction and attenuation of long-period water-layer multiples based on an adaptive multichannel lattice algorithm. The multichannel approach can be viewed as a generalization of two-dimensional linear prediction. The multichannel linear least-squares prediction problem is reviewed briefly and the performance and limitations of the algorithm are demonstrated on two different marine data sets with different properties of the simple and peg-leg multiple system. The algorithm works well even on problematic data sets and is very easy to apply.

Notes: The dynamics of water flow in soils influences the transport behaviour of solutes. Transport of bromide and herbicides through undisturbed soil columns was investigated under conditions of unsaturated steady-state and transient water flow. Effective transport parameters were obtained from fitting the convection–dispersion equation to curves of concentration against cumulative drainage, and these enabled us to interpret the observed behaviour. Under both steady-state and transient flow bromide and herbicides were transported through similar parts of the pore volume of a homogeneous single grain soil (Bv horizon). However, in aggregated Ah and Ap horizons preferential transport occurred during transient flow but not during steady-state flow. For preferential flow the mean transport volume seemed to depend on the prevailing pore system and the fraction of preferentially flowing water. Solute leaching was more efficient under steady-state than under transient flow for bromide in all soils and for herbicides in the Bv horizon. However, when transient flow caused preferential transport, herbicide loss was greater under transient flow than during steady-state flow. Under preferential flow conditions a three-step herbicide concentration development recurred in successive drainage events. This behaviour was not observed for the non-reactive tracer. It seemed to be caused by sorption. A steady-state model with cumulative drainage as independent variable instead of time can predict the transport of non-reactive and adsorbed solutes in homogeneous soils without features of preferential flow. Otherwise constant effective input parameters cannot be assessed a priori.

Notes: 1. Although the crucial point of disturbance experiments in streams is the extent to which they can simulate an actual spate, this aspect has been widely neglected in the design of such studies. Similarly, the influence of the specific hydrological disturbance regime of a stream on its benthic community has received much theoretical attention in recent years, but hypotheses have rarely been tested in the field.2. Our field experiment compared the structure of the benthic invertebrate community in the prealpine River Necker in north-eastern Switzerland with predictions of the patch dynamics concept about the faunal composition of frequently disturbed streams. We also compared the resistance and resilience of the invertebrates between two sites in the River Necker. A similar substratum composition at both sites, but higher shear stress values both at baseflow and bankfull discharge at site 2, implied a higher disturbance frequency at the latter site. Five patches of stream bed of ≈ 9 m2 were disturbed by kicking and raking at each site, while five similar areas served as controls. From each plot, six Surber samples were taken: the first immediately after the disturbance, and the following five 1, 3, 6, 10 and 30 days later.3. Resilience of the total benthic invertebrate fauna was high. The total number of individuals recovered to undisturbed densities within 30 days at site 1 and 6 days at site 2. Taxon richness recovered within 3 days. In accordance with theory, taxa with high recolonization rates made up a major percentage of the total number of individuals, especially in disturbed plots. However, this percentage was lower at site 2 in spite of the higher disturbance frequency at this site. Rhithrogena spp., Leuctra spp. and the Simuliidae recovered faster to undisturbed densities at site 2. In contrast, absolute recolonization rates of these taxa were higher at site 1, where total invertebrate densities were more than twice as high as at site 2.4. Our results suggest that the time since the last disturbance should be considered as an important factor in studies of benthic invertebrate communities in prealpine rivers, because disturbances can alter the community structure. In frequently disturbed streams, very short sampling intervals may be needed to detect differences in taxon-specific colonization rates. The specific hydrological disturbance regime of such streams is also important, because even within-stream differences in the resilience of the benthic invertebrate community are possible.

Notes: 1. The Lotic Intersite Nitrogen eXperiment (LINX) was a coordinated study of the relationships between North American biomes and factors governing ammonium uptake in streams. Our objective was to relate inter-biome variability of ammonium uptake to physical, chemical and biological processes.2. Data were collected from 11 streams ranging from arctic to tropical and from desert to rainforest. Measurements at each site included physical, hydraulic and chemical characteristics, biological parameters, whole-stream metabolism and ammonium uptake. Ammonium uptake was measured by injection of 15N-ammonium and downstream measurements of 15N-ammonium concentration.3. We found no general, statistically significant relationships that explained the variability in ammonium uptake among sites. However, this approach does not account for the multiple mechanisms of ammonium uptake in streams. When we estimated biological demand for inorganic nitrogen based on our measurements of in-stream metabolism, we found good correspondence between calculated nitrogen demand and measured assimilative nitrogen uptake.4. Nitrogen uptake varied little among sites, reflecting metabolic compensation in streams in a variety of distinctly different biomes (autotrophic production is high where allochthonous inputs are relatively low and vice versa).5. Both autotrophic and heterotrophic metabolism require nitrogen and these biotic processes dominate inorganic nitrogen retention in streams. Factors that affect the relative balance of autotrophic and heterotrophic metabolism indirectly control inorganic nitrogen uptake.

Notes: SUMMARY 1. We examined the relationship between catchment land cover, sediment regime and fish assemblage structure in four small streams in the upper Little Tennessee River basin of North Carolina. Study streams drained similar sized catchments (17–31 km2) with different fractions of non-forested land cover. Non-forested land cover was 〈3% in two ‘reference’ streams, whereas it was 13 and 22% in two ‘disturbed’ streams. Land cover data were compared with sediment transport data (suspended and bedload), benthic habitat data (embeddedness, substratum composition and coverage of fines) and fishes collected in autumn 1997.2. Suspended sediment concentration was significantly higher in disturbed streams during both baseflow and stormflow. During baseflow disturbed streams nearly always exceeded 10 nephelometric turbidity units (NTU), whereas reference streams never exceeded this threshold. The difference in suspended sediment concentration between reference and disturbed streams was more consistent at baseflow than at stormflow. Therefore, baseflow turbidity may be a useful indicator of potential stream degradation.3. Disturbed sites had five- to nine-fold more bedload transport than reference sites. Both embeddedness and streambed instability increased with increasing non-forested land cover.4. Relative abundance of fishes requiring clean cobble/gravel substratum for spawning was lower in disturbed streams, whereas relative abundance of mound-building cyprinids, their nest associates and fishes that excavate nests in soft sediments (centrarchids) was higher. Relative abundance of fishes spawning in benthic crevices and gravel (BC + G) declined as the proportion of non-forested land cover increased. This study supports growing evidence that human-induced sedimentation alters stream fish assemblages.

Notes: In this study a method was designed to assess non-destructively the type of UV-screening compounds present in the leaf epidermis. The method is based on the recording and calculation of the ratio of UV-excitation spectra of chlorophyll fluorescence (FER) from the adaxial and abaxial sides of bifacial leaves, or from older and younger segments of monocotyledonous leaves. The logarithm of this ratio (logFER) matched the absorption spectrum of the UV-absorbers present in the leaf, as confirmed by its overlap with the absorption spectrum of the methanolic extract of the leaf or of the isolated epidermis. By using the logFER approach, it was possible to demonstrate that the concentration but not the classes of compounds present in the epidermis that are responsible for UV-screening is affected by the side and the age of the leaves. In contrast, measurements from the leaves of seven dicots and one monocot indicated large difference in the classes of these compounds between species. Finally, it was shown that the logFER in the UV is independent of the emission wavelength, and that the method can be used for quantitative measurements. This method expands to the spectral domain the use of ChlF for the estimation of the leaf epidermal transmittance.

Notes: The level of glutathione (GSH) in plants is important in defence reactions against biotic and abiotic stresses and can place considerable demand of the sulphur assimilation pathway. Enzymes involved in sulphur assimilation and GSH metabolism are not evenly distributed between different subcellular compartments or between different cell types in leaves or roots; however, there is little information on the effect that such asymmetries have on the actual GSH concentration in each compartment or cell type. In the present study in situ labelling with monochlorobimane (MCB) in combination with confocal laser scanning microscopy was used to quantify GSH in each of the main cell types of poplar leaves from fluorescence of the GSB conjugate formed. Comparison of results from the in situ approach with total GSH levels measured in vitro by high-performance liquid chromatography suggested that only the cytosolic GSH pool was labelled using this approach. This suggests that an appropriate GST was not present within the chloroplasts to catalyse the conjugation reaction and that chloroplastic GSH does not rapidly exchange with the cytoplasmic pool under the conditions of the assay. Cytosolic GSH levels were between 0.2 and 0.3 mm for both photosynthetic and non-photosynthetic (epidermal) cell types in wild-type poplar leaves. Cytosolic levels increased by around two-fold in transgenic poplars over-expressing bacterial γ-glutamylsynthetase (γ-ECS) in the cytosol of all cell types, but there was no concomitant increase in the chloroplastic GSH pool.

Notes: 〈list style="custom"〉1The streams of French Polynesia contain several species of Neritidae and Thiaridae (Mollusca: Gastropoda). The neritids are dioecious and amphidromous with a freshwater adult stage and a poorly known, marine larval stage. The thiarids are parthenogenetic and viviparous, and rely on passive dispersal for colonisation of new habitats.2Populations of the neritid Clithon spinosus and the thiarids Melanoides tuberculata and Thiara granifera were analysed using mitochondrial DNA sequences from COI to compare the population structure of the snails at three different scales: between streams (N = 9), between islands (N = 4), and between age and distance of paired islands.3The amphidromous C. spinosus showed no evidence of genetic isolation at any of the scales tested (Fst values 〈inlineGraphic alt="leqslant R: less-than-or-eq, slant" extraInfo="nonStandardEntity" href="urn:x-wiley:00465070:FWB599:les" location="les.gif"/〉 0.02). Parsimony analyses resulted in two haplotype clusters separated by a three-step segment, which were not linked to geographic isolation. The larval phase of C. spinosus is most likely a long-lived planktotroph and a very effective disperser.4Two haplotypes of M. tuberculata, separated by 16 base pairs, were found. Both haplotypes were found in snails on all islands, and individuals representing both were often collected in the same habitat. One haplotype of T. granifera was found. M. tuberculata has the characteristics of the ‘general-purpose genotype’ of clonal population structure and although it relies on passive dispersal, it has colonised nearly all freshwater habitats on the islands.

Notes: 1. Rhododendron (Rhododendron maximum) is a common evergreen shrub in riparian areas of the southern Appalachians, where its leaves can comprise a large proportion of leaf litter in streams. However, they are relatively refractory and generally considered a low quality food resource for detritivores.2. Our objective was to assess whether macroconsumers [primarily crayfish (Cambarus bartonii)] influence rhododendron leaf breakdown in a forested southern Appalachian stream in both summer (when leaves other than rhododendron are relatively scarce) and autumn (when other leaves are relatively abundant). We conducted two leaf decay experiments, one in summer and one in autumn, using pre-conditioned leaves. Macroconsumers were excluded from the benthos of a fourth-order stream using electric ‘fences’; we predicted that excluding macroconsumers would reduce the decay rate of rhododendron leaves in both summer and autumn.3. In both experiments, breakdown rate was lower in exclusion treatments. Macroconsumers accounted for approximately 33 and 54% of rhododendron decay in summer and autumn, respectively. We attribute this effect to direct shredding of rhododendron by crayfish. Biomass of insect shredders, insect predators and fungi did not differ between control and exclusion treatments, indicating that insectivorous sculpins (Cottus bairdi) had no effect on rhododendron decay and that omnivorous crayfish did not exert an indirect effect via alteration of insect or fungal biomass.4. The influence of shredding insects varied between summer and autumn. In summer, when other, more palatable leaf types were not available, rhododendron leaf packs appeared to provide ‘resource islands’ for insect shredders. There was a significant inverse relationship between insect shredders and leaf pack mass in the summer exclusion treatment: insects were the only organisms eating leaves in this treatment and, as shredder biomass increased, remaining leaf pack mass decreased. In the control treatment, however, we did not see this relationship; here, the effect of insect shredders was presumably swamped by the impact of crayfish. In autumn, when other leaves were abundant, insect shredder biomass in rhododendron leaf packs was less than one-third of summer values.5. Even at low density (approximately 2 m–2) crayfish were able to influence an ecosystem process such as leaf decay in both summer and autumn. Given the threatened status of many crayfish species in the United States, this finding is especially relevant. Even small alterations in crayfish assemblages, whether via loss of native species and/or introduction of exotic species, may have significant repercussions for ecosystem function.