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Above- and below-ground herbivory effects on below-ground plant–fungus interactions and plant–soil feedback responses
No full textSummary
Feeding by insect herbivores can affect plant growth and the concentration of defense compounds in plant tissues. Since plants provide resources for soil organisms, herbivory can also influence the composition of the soil community via its effects on the plant. Soil organisms, in turn, are important for plant growth. We tested whether insect herbivores, via their effects on the soil microbial community, can influence plant-soil feedbacks.
We first examined the effects of above-ground (AG) and below-ground (B) insect herbivory on the composition of pyrrolizidine alkaloids (PAs) in roots and on soil fungi in roots and rhizosphere soil of ragwort (Jacobaea vulgaris). The composition of fungal communities in roots and rhizosphere soil was affected by both AG and BG herbivory, but fungal composition also differed considerably between roots and rhizosphere soil. The composition of PAs in roots was affected only by BG herbivory.
Thirteen different fungal species were detected in roots and rhizosphere soil. The presence of the potentially pathogenic fungus Fusarium oxysporum decreased and that of Phoma exigua increased in presence of BG herbivory, but only in soil samples.
We then grew new plants in the soils conditioned by plants exposed to the herbivore treatments and in unconditioned soil. A subset of the new plants was exposed to foliar insect herbivory. Plant-soil feedback was strongly negative, but the feedback effect was least negative in soil conditioned by plants that had been exposed to BG herbivory. There was a negative direct effect of foliar herbivory on plant biomass during the feedback phase, but this effect was far less strong when the soil was conditioned by plants exposed to AG herbivory. AG herbivory during the conditioning phase also caused a soil feedback effect on the PA concentration in the foliage of ragwort.
Synthesis. Our results illustrate how insect herbivory can affect interactions between plants and soil organisms, and via these effects how herbivory can alter the performance of late-growing plants. Plant-soil feedback is emerging as an important theme in ecology and these results highlight that plant-soil feedback should be considered from a multitrophic AG and BG perspective.
Methylocystis bryophila sp. nov., a Novel Facultatively Methanotrophic Bacterium from Acidic Sphagnum Peat, and Emended Description of the Genus Methylocystis (ex Whittenbury et al. 1970) Bowman et al. 1993
No full textA new species is proposed for two facultatively methanotrophic representatives of the genus Methylocystis, strains H2sT and S284, which were isolated from an acidic (pH 4.3) Sphagnum peat bog lake (Teufelssee, Germany) and an acidic (pH 3.8) peat bog (European North Russia), respectively. Cells of strains H2sT and S284 are aerobic, Gram-negative, non-motile, curved coccoids or short rods that contain an intracytoplasmic membrane system typical of type II methanotrophs. They possess both a soluble and a particulate methane monooxygenase (MMO); the latter is represented by two isozymes, pMMO1 and pMMO2. The preferred growth substrates are methane and methanol. In the absence of C1 substrates, however, these methanotrophs are capable of slow growth on acetate. Atmospheric nitrogen is fixed by means of an aero-tolerant nitrogenase. Strains H2sT and S284 develop between pH 4.2 and 7.6 (optimum pH 6.0-6.5), and at temperatures between 8 and 37°C (optimum 25-30°C). The major fatty acids are C18:1w8c, C18:1w7c, and C16:1w7c; the major quinone is Q-8. The DNA G+C content is 62.0-62.3 mol%. Strains H2sT and S284 share identical 16S rRNA gene sequences, which displayed 96.6-97.3% similarity to sequences of other taxonomically characterized members of the genus Methylocystis. Therefore, strains H2sT and S284 are classified as a novel species, for which the name Methylocystis bryophila sp. nov. is proposed. Strain H2sT (=DSM 21852T = VKM B-2545T) is the type strain of Methylocystis bryophila.
Quantifying measures to limit wind driven resuspension of sediments for improvement of the ecological quality in some shallow Dutch lakes
Get PDFAlthough phosphorus loadings are considered the main pressure for most shallow lakes, wind-driven resuspension can cause additional problems for these aquatic ecosystems. We quantified the potential effectiveness of measures to reduce the contribution of resuspended sediments, resulting from wind action, to the overall light attenuation for three comparable shallow peat lakes with poor ecological status in the Netherlands: Loosdrecht, Nieuwkoop, and Reeuwijk (1.8–2.7 m depth, 1.6–2.5 km fetch). These measures are: 1. wave reducing barriers, 2. water level fluctuations, 3. capping of the sediment with sand, and 4. combinations of above. Critical shear stress of the sediments for resuspension (Vcrit), size distribution, and optical properties of the suspended material were quantified in the field (June 2009) and laboratory. Water quality monitoring data (2002–2009) showed that light attenuation by organic suspended matter in all lakes is high. Spatial modeling of the impact of these measures showed that in Lake Loosdrecht limiting wave action can have significant effects (reductions from 6% exceedance to 2% exceedance of Vcrit), whereas in Lake Nieuwkoop and Lake Reeuwijk this is less effective. The depth distribution and shape of Lake Nieuwkoop and Lake Reeuwijk limit the role of wind-driven resuspension in the total suspended matter concentration. Although the lakes are similar in general appearance (origin, size, and depth range) measures suitable to improve their ecological status differ. This calls for care when defining the programme of measures to improve the ecological status of a specific lake based on experience from other lakes.
Late child acquisition and identity construction. Variation in use of the Dutch definite determiners 'de' and 'het'
No full textVariation in herbivore-induced plant volatiles corresponds with spatial heterogeneity in the level of parasitoid competition and parasitoid exposure to hyperparasitism
No full textReproductive success for species in which offspring are confined to a distinct resource depends on the ability of parents to locate reproductive sites as well as the quality of these sites in terms of the food source, risk of predation and competition. To locate hosts for their offspring, parasitic wasps, or parasitoids, use plant odour blends induced by herbivore feeding. These herbivore-induced plant volatiles (HIPVs) may also be used by competitors and predators. Therefore, offspring of parasitoids that respond to the most conspicuous odours may find themselves more frequently involved in competition or predation risk.
We studied cultivars of Brassica oleracea that are known to differ in volatile production that underlies attractiveness to parasitoids and asked whether variation in this parameter is associated with a heterogeneous distribution of intrinsic competition among parasitoid larvae and predation risk by hyperparasitoids that parasitize parasitoid larvae or pupae. We inoculated field-grown plants with Pieris caterpillars and, thereafter, exposed them to the natural parasitoid community. We measured the frequency of multiple incidences of parasitism in these herbivores. Cocoons of the parasitoids were collected to identify the degree of hyperparasitism associated with different Brassica cultivars.
Pieris caterpillars on cultivars that were more attractive to Cotesia parasitoids were more commonly parasitized by several females of the same (superparasitism) or different wasp species (multiparasitism) than caterpillars on less attractive plants. Cocoons of parasitoids on attractive plants also more frequently produced hyperparasitoids.
Our results show that there is heterogeneity in intrinsic competition and risk of hyperparasitism for parasitoids on different cabbage cultivars and that this heterogeneity is likely generated by variation in attraction of parasitoids to HIPVs of these cultivars. We conclude that parasitoids may find themselves between a rock and a hard place as cues for host presence may also predict high levels of competition and risk of predation. We speculate that this affects selection on parasitoid responses to plant odours and enhances selection on traits that make wasps better intrinsic or extrinsic competitors as well as selection for adaptive traits – such as crypsis – that protect them against hyperparasitoids.
Local variation in conspecific plant density influences plant-soil feedback in a natural grassland
No full textSeveral studies have argued that under field conditions plant–soil feedback may be related to the local density of a plant species, but plant–soil feedback is often studied by comparing conspecific and heterospecific soils or by using mixed soil samples collected from different locations and plant densities. We examined whether the growth of the early successional species Jacobaea vulgaris in soil collected from the field is related to the local variation in plant density of this species. In a grassland restoration site, we selected eight 8 m × 8 m plots, four with high and four with low densities of J. vulgaris plants. In 16 subplots in each plot we recorded the density and size of J. vulgaris, and characteristics of the vegetation and the soil chemistry. Soil collected from each subplot was used in a greenhouse pot-experiment to study the growth of J. vulgaris, both in pure field soil and in sterile soil inoculated with a small part of field soil.
In the field, flowering J. vulgaris plants were taller, the percentage of rosette plants was higher and seed density was larger in High- than in Low-density plots. In the pot experiment, J. vulgaris had a negative plant–soil feedback, but biomass was also lower in soil collected from High- than from Low-density plots, although only when growing in inoculated soil. Regression analyses showed that J. vulgaris biomass of plants growing in pure soil was related to soil nutrients, but also to J. vulgaris density in the field.
We conclude that in the field there is local variation in the negative plant–soil feedback of J. vulgaris and that this variation can be explained by the local density of J. vulgaris, but also by other factors such as nutrient availability.
The Construction of HISCAM: A Stratification Scale Based on Social Interactions for Historical Comparative Research
No full textA new occupational stratification scale, “HISCAM” (historical CAMSIS), has been developed to facilitate the analysis of data coded to the Historical International Standard Classification of Occupations. This article describes the derivation and properties of the HISCAM measure. The scale was derived using patterns of inter-generational occupational connections, replicating a method of “social interaction distance” analysis which is widely used in contemporary sociology. Analysis was performed on data for the period of 1800–1938, principally derived from marriage registers covering Belgium, Britain, Canada, France, Germany, the Netherlands, and Sweden, and encompassing over two million inter-generational relationships. Researchers report how several different HISCAM scales were evaluated and show how this approach can explain social stratification and inequality in the past.
