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Soil amendment with biochar increases the competitive ability of legumes via increased potassium availability
No full textSoil amendment with biochar is currently proposed as a management strategy to improve soil quality and enhance plant productivity. Relatively little is known about how biochar affects plant competition, although it has been suggested that it can increase the competitive ability of legumes. This study tested the impact of a biochar on the competitive ability of legumes through alterations to soil pH and/or nutrient availability. Biochar was produced from aboveground plant biomass from a species-rich semi-natural grassland pyrolysed at 400 °C. In a greenhouse experiment, a legume (red clover, Trifolium pratense L.); a grass (red fescue, Festuca rubra L.); and a forb (plantain, Plantago lanceolata L.) were grown in (1) monocultures, (2) in a mixed culture of red fescue and red clover, and (3) in a mixture of all three species. Soil treatments included fertilisation with nitrogen (N), potassium (K), phosphorus (P), or micronutrient fertiliser in the presence or absence of biochar; a pH-adjusted control soil; and a control (i.e. with no amendment). The competitive ability of red clover was quantified as the proportion of aboveground biomass of this species within the mixtures. Both biochar amendment and K fertilisation significantly (P < 0.001) increased red clover biomass, and increased the competitive ability of red clover when grown with red fescue and plantain. Application of N fertiliser, irrespective of biochar amendment, resulted in significantly (P < 0.001) greater red fescue and plantain biomass and eliminated the competitive advantage of red clover. The biochar-mediated pH increase did not affect red clover biomass or its competitive ability. We conclude that biochar has a beneficial effect on red clover under N limiting conditions due to an increase in K availability. Our results suggest a potential role for biochar to maintain the proportion of forage legumes in agricultural pastures or semi-natural grasslands.
Beneficial interactions in the rhizosphere
No full textProduction of plant biomass is one of the main ecosystem services delivered by soil. The area closely surrounding the root surface, the rhizosphere, is where plants interact with soil organisms. The interaction of a plant with soil microorganisms may result in several benefits to the plant, including improved nutrient availability or uptake, protection against pests and pathogens, improved tolerance to abiotic stress and growth promotion via hormones. Those relationships between plant and microorganisms determine plants growth and competitiveness. Ultimately the microbial community may determine plant community composition and succession. In this chapter we give an overview of fungal and bacterial microbial rhizosphere species that benefit plants, namely plant growth promoting bacteria, mycorrhizal fungi and other beneficial fungi. The aim is to summarize the current knowledge on mechanisms underlying plant-microbe interaction and to discuss the role of species identity and diversity for both microorganisms and plants. For each group (plant growth promoting bacteria, mycorrhiza, other beneficial fungi) we highlight the latest developments and promising future directions. At the end of the chapter the microbial groups are viewed as part of the soil ecosystem and interactions between the groups are discussed.
Arbeidsparticipatie ouderen weer op niveau door vrouwen
No full textNadat decennialang oudere werknemers de arbeidsmarkt vooral hebben verlaten door vroegpensioen of door met de VUT te gaan, lijkt thans een einde te zijn gekomen aan wat wel de ‘cultuur van vervroegd uittreden’ werd genoemd. Mede doordat de gemiddelde leeftijd waarop ouderen het arbeidsproces verlaten toeneemt, stijgt ook de arbeidsparticipatie van deze groep. Het UWV kopte vorig jaar dat de arbeidsdeelname van ouderen (55-64 jarigen), die een dieptepunt kende in de jaren negentig van de vorige eeuw, weer terug is op het niveau van de jaren zestig. Daarbij werd voorzichtig gemeld dat natuurlijk ook het veranderde arbeidsmarktgedrag van vrouwen een rol speelde. Dat is zeker het geval! Zonder die vrouwen zou helemaal geen sprake zijn van een herstel.
Effect of redox conditions on bacterial community structure in Baltic Sea sediments with contrasting redox conditions
No full textPhosphorus release from sediments can exacerbate the effect of eutrophication in coastal marine ecosystems. The flux of phosphorus from marine sediments to the overlying water is highly dependent on the redox conditions at the sediment-water interface. Bacteria are key players in the biological processes that release or retain phosphorus in marine sediments. To gain more insight in the role of bacteria in phosphorus release from sediments, we assessed the effect of redox conditions on the structure of bacterial communities. To do so, we incubated surface sediments from four sampling sites in the Baltic Sea under oxic and anoxic conditions and analyzed the fingerprints of the bacterial community structures in these incubations and the original sediments. This paper describes the effects of redox conditions, sampling station, and sample type (DNA, RNA, or whole-cell sample) on bacterial community structure in sediments. Redox conditions explained only 5% of the variance in community structure, and bacterial communities from contrasting redox conditions showed considerable overlap. We conclude that benthic bacterial communities cannot be classified as being typical for oxic or anoxic conditions based on community structure fingerprints. Our results suggest that the overall structure of the benthic bacterial community has only a limited impact on benthic phosphate fluxes in the Baltic Sea.
Are the specialized bird ticks, Ixodes arboricola and I. frontalis, competent vectors for Borrelia burgdorferi sensu lato?
No full textOur study tested whether two European bird-specialized ticks, Ixodes arboricola and I. frontalis, can act as vectors in the transmission cycles of Borrelia burgdorferi s.l. The ticks have contrasting ecologies but share songbird hosts (such as the great tit, Parus major) with the generalist I. ricinus which may therefore act as a bridging vector. In the first phase of the experiment, we obtained Borrelia-infected ornithophilic nymphs by exposing larvae to great tits that had previously been exposed to I. ricinus nymphs carrying a community of genospecies (Borrelia garinii, valaisiana, afzelii, burgdorferi s.s., spielmanii). Skin samples showed that birds selectively amplified B. garinii and B. valaisiana. The spirochetes were transmitted to the ornithophilic ticks and survived moulting, leading to infection rates of 16% and 27% in nymphs of I. arboricola and I. frontalis respectively. In the second phase, pathogen-free great tits were exposed to the Borrelia-infected ornithophilic nymphs. None of these ticks were able to infect the birds, as indicated by the tissue samples. Analysis of xenodiagnostic I. ricinus larvae found no evidence for co-feeding or systemic transmission of B. burgdorferi s.l. These outcomes do not support the occurrence of enzootic cycles of Borrelia burgdorferi s.l. involving songbirds and their specialized ornithophilic ticks.
