Two distinct AFLP types in three populations of marram grass (Ammophila arenaria in Wales)

The genetic structure of marram grass populations at coastal and inland locations, 200 m apart, was investigated at three sites by means of amplified fragment length polymorphism (AFLP) DNA markers. We expected a genetic differentiation between coastal and inland populations and more genetic variation in the coastal areas as a result of different events of colonization by different plant materials. An assignment test showed that the sampled Ammophila arenaria could be assigned to two groups based on AFLP data. The spatial distribution of the two AFLP types of A. arenaria varied with sampling location. In two of the three locations, mainly one type (1) was found in the newly formed dunes. This type did also occur further landward, but the second type (2) was preferentially found in inland populations. Genetic diversity was very low and of similar value in both coastal and inland populations. For each site, outlier loci with respect to FST value were identified, which may be indicative of different selection pressures in coastal compared with inland clusters. However, no identical outlier loci were found at all three sites. Possible explanations for the observed difference in distribution of type 1 and 2 populations between coastal and inland sites are discusse

Competition increases sensitivity of wheat (Triticum aestivum) to biotic plant-soil feedback

Plant-soil feedback (PSF) and plant competition play an important role in structuring vegetation composition, but their interaction remains unclear. Recent studies suggest that competing plants could dilute pathogenic effects, whereas the standing view is that competition may increase the sensitivity of the focal plant to PSF. In agro-ecosystems each of these two options would yield contrasting outcomes: reduced versus enhanced effects of weeds on crop biomass production. To test the effect of competition on sensitivity to PSF, we grew Triticum aestivum (Common wheat) with and without competition from a weed community composed of Vicia villosa, Chenopodium album and Myosotis arvensis. Plants were grown in sterilized soil, with or without living field inoculum from 4 farms in the UK. In the conditioning phase, field inocula had both positive and negative effects on T. aestivum shoot biomass, depending on farm. In the feedback phase the differences between shoot biomass in T. aestivum monoculture on non-inoculated and inoculated soils had mostly disappeared. However, T. aestivum plants growing in mixtures in the feedback phase were larger on non-inoculated soil than on inoculated soil. Hence, T. aestivum was more sensitive to competition when the field soil biota was present. This was supported by the statistically significant negative correlation between shoot biomass of weeds and T. aestivum, which was absent on sterilized soil. In conclusion, competition in cereal crop-weed systems appears to increase cereal crop sensitivity to soil biota

Doodtroetelen - een plant bestrijden door ze te bemesten

Kun je onkruiden bestrijden door ze te bemesten? Het lijkt onlogisch, maar in theorie kun je van onkruiden af komen door ze flink te bemesten. De planten groeien dan natuurlijk harder, maar worden ook eerder gevonden en opgegeten door insecten. Bemeste planten bevatten immers meer stikstof, een belangrijke limiterende voedingsstof voor insecten. En het mooiste: de concentratie afweerstoffen in de plant wordt lager. Op de universiteit van Leiden is dit aangetoond voor Jakobskruiskruid, een plant die bekend staat om zijn giftige alkaloïden. Vooral paarden hebben te lijden onder deze geelgebloemde weidedecoratie. Door bemesting groeit de plant sneller dan dat hij alkaloïden produceert en daardoor worden de afweerstoffen als het ware verdund. Ideaal voer voor insecten dus. Alleen is het niet zo simpel als het lijkt, want bemeste planten herstellen zich ook weer sneller van vraat

Zeldzame bacteriën moeten beschermd worden

De bescherming van zeldzame bacteriën lijkt volledig overbodig. Bijna iedereen heeft een negatieve associatie met bacteriën en gaat ze met zeep en ontsmettingsmiddelen te lijf. Maar wat gebeurt er als zeldzame bacteriën verdwijnen? Zou het WNF zich ook moeten richten op de bescherming van bacteriën? Onderzoek op het Nederlands Instituut voor Ecologie heeft aangetoond dat de verdwijning van zeldzame bodembacteriën wel degelijk uitmaakt. Planten groeiden minder goed op bodems met zeldzame soorten, maar hadden ook minder last van luis. Luizen waren namelijk het kleinst op planten die groeiden op bodems met zeldzame bacteriën. Niet meteen een reden om zeldzame bacteriën te beschermen, maar het toont wel aan dat kleine verschuivingen grote gevolgen kunnen hebben. Toch maar een beetje voorzichtig zijn dus..

Pyrrolizidine alkaloids from Senecio jacobaea affect fungal growth

We investigated the growth-reducing effects of pyrrolizidine alkaloids (PAs) from Senecio jacobaea on nine plant-associated fungi (five strains of Fusarium oxysporum, two of F. sambucinum, and two of Trichoderma sp). Fungal growth was monitored on water agar media containing different concentrations of monocrotaline, retrorsine, or a purified extract of PAs from S. jacobaea. The growth rate of six strains was inhibited by PAs at the highest test concentration (3.33 mM), with the magnitude of the inhibition (7-35%) being dependent upon the specific fungus-PA interaction. In general, the PA extract caused the largest inhibition. However, the fungi isolated from S. jacobaea were positively affected by the PA extract (7-9%). Retrorsine N oxide was as effective as retrorsine in its inhibition of mycelium growth. [KEYWORDS: Senecio jacobaea, pyrrolizidine alkaloids, anti fungal activity, retrorsine, N oxide, monocrotaline]

Getting the ecology into the interactions between plants and the plant-growth promoting bacterium Pseudomonas fluorescens

Plant growth-promoting rhizobacteria (PGPR) are increasingly appreciated for their contributions to primary productivity through promotion of growth and triggering of induced systemic resistance in plants. Here we focus on the beneficial effects of one particular species of PGPR (Pseudomonas fluorescens) on plants through induced plant defense. This model organism has provided much understanding of the underlying molecular mechanisms of PGPR-induced plant defense. However, this knowledge can only be appreciated at full value once we know to what extent these mechanisms also occur under more realistic, species-diverse conditions as are occurring in the plant rhizosphere. To provide the necessary ecological context, we review the literature to compare the effect of P. fluorescens on induced plant defense when it is present as a single species or in combination with other soil dwelling species. Specifically, we discuss combinations with other plant mutualists (bacterial or fungal), plant pathogens (bacterial or fungal), bacterivores (nematode or protozoa), and decomposers. Synergistic interactions between P. fluorescens and other plant mutualists are much more commonly reported than antagonistic interactions. Recent developments have enabled screenings of P. fluorescens genomes for defense traits and this could help with selection of strains with likely positive interactions on biocontrol. However, studies that examine the effects of multiple herbivores, pathogens, or herbivores and pathogens together on the effectiveness of PGPR to induce plant defenses are underrepresented and we are not aware of any study that has examined interactions between P. fluorescens and bacterivores or decomposers. As co-occurring soil organisms can enhance but also reduce the effectiveness of PGPR, a better understanding of the biotic factors modulating P. fluorescens–plant interactions will improve the effectiveness of introducing P. fluorescens to enhance plant production and defense.

Nutrients decrease pyrrolizidine alkaloid concentrations in Senecio jacobaea

Changes in the defence compounds pyrrolizidine alkaloids (PAs) in roots and shoots of Senecio jacobaea are reported in response to nutrient addition in order to investigate whether changes in concentration are adaptive. PA concentrations were examined in leaves and roots of 40 vegetative ragwort plants, subjected to four nutrient treatments in a climate chamber study. Roots from 10 plants were subdivided into main root cortex, main root vascular cylinder, lateral roots and root tips and analysed for PA concentrations. Increasing nutrients lead to a significant reduction in total PA concentration of both roots and shoots. All individual PAs except jacobine decreased in concentration. The total amount of PA produced in the whole plant was not influenced by nutrient supply. Root tips contained a three times lower concentration than the main and lateral roots. The concentrations in the main root cortex were five times higher than concentrations in the vascular cylinder. Changes in biomass rather than changes in production rates can explain alterations in PA concentration of S. jacobaea in response to nutrients.

Idiosyncrasy in ecology - what's in a word?

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