Short-term plant-decomposer feedbacks in grassland plants

Plant species differ in their effects on ecosystem productivity and it is recognised that these effects are partly due to plant species-specific influences on soil processes. Until recently, however, not much attention was given to the potential role played by soil biota in these species-specific effects. While soil decomposers are responsible for governing the availability of nutrients for plant production, they simultaneously depend on the amount of carbon provided by plants. Litter and rhizodeposition constitute the two basal resources that plants provide to soil decomposer food webs. While it has been shown that both of these can have effects on soil decomposer communities that differ among plant species, the putative significance of these effects for plant nitrogen (N) acquisition is currently understudied. My PhD work aimed at clarifying whether the species-specific influences of three temperate grassland plants on the soil microfood-web, through rhizodeposition and litter, can feed back to plant N uptake. The methods and approach used (15N labelling of plant litter in microcosm experiments) revealed to be an effective combination of tools in studying these feedbacks. Plant effects on soil organisms were shown to differ significantly between plant species and the effects could be followed across several trophic levels. The labelling of litter further permitted the evaluation of plant acquisition of N derived from soil organic matter. The results show that the structure of the soil microfood-web can have a significant role in plant N acquisition when the structure is experimentally manipulated, such as when comparing systems consisting of microbes to those consisting of microbes and their grazers. However, despite this, the results indicate that differences in N uptake from soil organic matter between different plant species are not related to the effects these species exert on the structure of the soil microfood-web. Rather, these differences in N uptake seem to be determined by other species-specific traits of live plants and their litter. My results thus indicate that different resources provided by different plant species may not induce species-specific decomposer feedbacks on plant N uptake from soil organic matter. This further suggests that the species-specific plant effects on soil decomposer communities may not, at least in the short term, have significant consequences on plant production.Ei saatavill

Climate-smart agriculture, agroecology and soil carbon: Towards winning combinations

Adaptation to climate change and its mitigation are some of the biggest challenges facing agriculture. In the global South, these challenges are associated with the need for food security. The arrival of climate change on the international agenda has prompted the recycling of a multitude of initiatives to address this problem, leading inevitably to the emergence of numerous controversies. However, although the scales and actors targeted may differ, all of these initiatives are trying in one way or another to provide technical, social, economic and political options to increase the climate resilience of agriculture. There is heated debate about three approaches, which focus on these relationships between agriculture and climate: climate-smart agriculture, agroecology and the 4 per 1000 Initiative on soil carbon. Beyond the conceptual differences and the sometimes partisan interpretations of these three approaches, agriculture in the Southern countries needs to take advantage of their potential synergies

Agriculture climato-intelligente, agroécologie et carbone du sol : vers des conjugaisons gagnantes

L'adaptation au changement climatique et son atténuation comptent parmi les principaux défis que doit relever l'agriculture. Au Sud, ces défis s'associent à un impératif de sécurité alimentaire. L'arrivée du changement climatique sur l'agenda international a favorisé le recyclage d'une multitude d'initiatives visant à y faire face avec, en corollaire, l'apparition de nombreuses controverses. Or, même si les échelles et les acteurs visés peuvent différer, toutes ces initiatives tentent d'une façon ou d'une autre de fournir des options techniques, sociales, économiques et politiques pour accroître la résilience de l'agriculture face au changement climatique. Trois approches sont fortement débattues et portent sur ces relations entre l'agriculture et le climat : l'agriculture climato-intelligente, l'agroécologie et l'initiative 4 pour 1000 relative au carbone du sol. Au-delà des divergences conceptuelles et des interprétations parfois partisanes entre ces trois approches, l'agriculture des pays du Sud doit pouvoir bénéficier de leurs synergies potentielles

Pest species diversity enhances control of spider mites and whiteflies by a generalist phytoseiid predator

To test the hypothesis that pest species diversity enhances biological pest control with generalist predators, we studied the dynamics of three major pest species on greenhouse cucumber: Western flower thrips, Frankliniella occidentalis (Pergande), greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and two-spotted spider mites, Tetranychus urticae Koch in combination with the predator species Amblyseius swirskii Athias-Henriot. When spider mites infested plants prior to predator release, predatory mites were not capable of controlling spider mite populations in the absence of other pest species. A laboratory experiment showed that predators were hindered by the webbing of spider mites. In a greenhouse experiment, spider mite leaf damage was lower in the presence of thrips and predators than in the presence of whiteflies and predators, but damage was lowest in the presence of thrips, whiteflies and predators. Whitefly control was also improved in the presence of thrips. The lower levels of spider mite leaf damage probably resulted from (1) a strong numerical response of the predator (up to 50 times higher densities) when a second and third pest species were present in addition to spider mites, and (2) from A. swirskii attacking mobile spider mite stages outside or near the edges of the spider mite webbing. Interactions of spider mites with thrips and whiteflies might also result in suppression of spider mites. However, when predators were released prior to spider mite infestations in the absence of other pest species, but with pollen as food for the predators, we found increased suppression of spider mites with increased numbers of predators released, confirming the role of predators in spider mite control. Thus, our study provides evidence that diversity of pest species can enhance biological control through increased predator densitie

Functional Neuroanatomy of Vertical Visual Perception in Humans

Vertical representation is central to posture control, as well as to spatial perception and navigation. This representation has been studied for a long time in patients with vestibular disorders and more recently in patients with hemispheric damage, in particular in those with right lesions causing spatial or postural deficits. The aim of the study was to determine the brain areas involved in the visual perception of the vertical. Sixteen right-handed healthy participants were evaluated using fMRI while they were judging the verticality of lines or, in a control task, the color of the same lines. The brain bases of the vertical perception proved to involve a bilateral temporo-occipital and parieto-occipital cortical network, with a right dominance tendency, associated with cerebellar and brainstem areas. Consistent with the outcomes of neuroanatomical studies in stroke patients, The data of this original fMRI study in healthy subjects provides new insights into brain networks associated with vertical perception which is typically impaired in both vestibular and spatial neglect patients. Interestingly, these networks include not only brain areas associated with postural control but also areas implied in body representation