Fluctuations of nematode populations in pine forest soil : influence by clear-cutting

La dynamique des populations de nématodes après coupes claires dans une forêt de pins du centre de la Suède a été suivie pendant deux périodes : de 1 à 5 ans et de 14 à 19 ans après la coupe. Les effets de l'enlèvement des abattis ont été pris en compte dans cette étude. Les fluctuations de l'abondance animale sont importantes pendant la première période et plusieurs espèces croissent en nombre, notamment dans les endroits sous abattis. Au cours de la seconde période, de nombreux taxons sont présents en abondance moindre dans les zones de coupe que dans une zone boisée de référence. Les taux de croissance ou de décroissance des différentes espèces et genres ont été comparés à un classement des nématodes (échelle c-p) utilisé pour le calcul de l'indice de maturité (IM), lequel est en usage pour indiquer les perturbations du sol. Il en est conclu que la coupe claire constitue une sorte de perturbation qui favorise les espèces tolérant des conditions climatiques rudes. Plusieurs espèces et genres dont les populations croissent après d'autres sortes de perturbations - telle la fertilisation de la forêt - décroissent au contraire à la suite de coupes claires. Cela conduit dans les coupes claires à un type de réaction de l'IM ne correspondant pas aux prédictions du modèle. (Résumé d'auteur

Changes in Plant Species Richness Induce Functional Shifts in Soil Nematode Communities in Experimental Grassland

Changes in plant diversity may induce distinct changes in soil food web structure and accompanying soil feedbacks to plants. However, knowledge of the long-term consequences of plant community simplification for soil animal food webs and functioning is scarce. Nematodes, the most abundant and diverse soil Metazoa, represent the complexity of soil food webs as they comprise all major trophic groups and allow calculation of a number of functional indices.We studied the functional composition of nematode communities three and five years after establishment of a grassland plant diversity experiment (Jena Experiment). In response to plant community simplification common nematode species disappeared and pronounced functional shifts in community structure occurred. The relevance of the fungal energy channel was higher in spring 2007 than in autumn 2005, particularly in species-rich plant assemblages. This resulted in a significant positive relationship between plant species richness and the ratio of fungal-to-bacterial feeders. Moreover, the density of predators increased significantly with plant diversity after five years, pointing to increased soil food web complexity in species-rich plant assemblages. Remarkably, in complex plant communities the nematode community shifted in favour of microbivores and predators, thereby reducing the relative abundance of plant feeders after five years.The results suggest that species-poor plant assemblages may suffer from nematode communities detrimental to plants, whereas species-rich plant assemblages support a higher proportion of microbivorous nematodes stimulating nutrient cycling and hence plant performance; i.e. effects of nematodes on plants may switch from negative to positive. Overall, food web complexity is likely to decrease in response to plant community simplification and results of this study suggest that this results mainly from the loss of common species which likely alter plant-nematode interactions

Anhydrobiosis and Freezing-Tolerance:Adaptations That Facilitate the Establishment of Panagrolaimus Nematodes in Polar Habitats

<div><p>Anhydrobiotic animals can survive the loss of both free and bound water from their cells. While in this state they are also resistant to freezing. This physiology adapts anhydrobiotes to harsh environments and it aids their dispersal. <i>Panagrolaimus davidi</i>, a bacterial feeding anhydrobiotic nematode isolated from Ross Island Antarctica, can survive intracellular ice formation when fully hydrated. A capacity to survive freezing while fully hydrated has also been observed in some other Antarctic nematodes. We experimentally determined the anhydrobiotic and freezing-tolerance phenotypes of 24 <i>Panagrolaimus</i> strains from tropical, temperate, continental and polar habitats and we analysed their phylogenetic relationships. We found that several other <i>Panagrolaimus</i> isolates can also survive freezing when fully hydrated and that tissue extracts from these freezing-tolerant nematodes can inhibit the growth of ice crystals. We show that <i>P. davidi</i> belongs to a clade of anhydrobiotic and freezing-tolerant panagrolaimids containing strains from temperate and continental regions and that <i>P. superbus</i>, an early colonizer at Surtsey island, Iceland after its volcanic formation, is closely related to a species from Pennsylvania, USA. Ancestral state reconstructions show that anhydrobiosis evolved deep in the phylogeny of <i>Panagrolaimus</i>. The early-diverging <i>Panagrolaimus</i> lineages are strongly anhydrobiotic but weakly freezing-tolerant, suggesting that freezing tolerance is most likely a derived trait. The common ancestors of the <i>davidi</i> and the <i>superbus</i> clades were anhydrobiotic and also possessed robust freezing tolerance, along with a capacity to inhibit the growth and recrystallization of ice crystals. Unlike other endemic Antarctic nematodes, the life history traits of <i>P. davidi</i> do not show evidence of an evolved response to polar conditions. Thus we suggest that the colonization of Antarctica by <i>P. davidi</i> and of Surtsey by <i>P. superbus</i> may be examples of recent “ecological fitting” of freezing-tolerant anhydrobiotic propagules to the respective abiotic conditions in Ross Island and Surtsey.</p></div

Fluctuations of nematode populations in pine forest soil : influence by clear-cutting

La dynamique des populations de nématodes après coupes claires dans une forêt de pins du centre de la Suède a été suivie pendant deux périodes : de 1 à 5 ans et de 14 à 19 ans après la coupe. Les effets de l'enlèvement des abattis ont été pris en compte dans cette étude. Les fluctuations de l'abondance animale sont importantes pendant la première période et plusieurs espèces croissent en nombre, notamment dans les endroits sous abattis. Au cours de la seconde période, de nombreux taxons sont présents en abondance moindre dans les zones de coupe que dans une zone boisée de référence. Les taux de croissance ou de décroissance des différentes espèces et genres ont été comparés à un classement des nématodes (échelle c-p) utilisé pour le calcul de l'indice de maturité (IM), lequel est en usage pour indiquer les perturbations du sol. Il en est conclu que la coupe claire constitue une sorte de perturbation qui favorise les espèces tolérant des conditions climatiques rudes. Plusieurs espèces et genres dont les populations croissent après d'autres sortes de perturbations - telle la fertilisation de la forêt - décroissent au contraire à la suite de coupes claires. Cela conduit dans les coupes claires à un type de réaction de l'IM ne correspondant pas aux prédictions du modèle. (Résumé d'auteur

Occurrence of nematodes, tardigrades and rotifers on ice-free areas in East Antarctica

Nematodes, rotifers and tardigrades were collected on three nunataks (mountain peaks penetrating the ice sheet) in Vestfjella, on six nunataks; in Heimefrontfjella and on the Schirmacher Oasis in East Antarctica in the austral summers of 1996/97 and 2001/02. Most samples were taken on the nunatak Basen in Vestfjella where the Swedish station Wasa is located. The microfauna was patchily distributed and the highest densities of animals were found on sites with visible vegetation of mosses, lichens or algae. Thirty-four taxa of nematodes and tardigrades were found. Only seven of these occurred regularly in apparently actively reproducing populations. Other occasional records of nematodes had very few specimens. The highest number of species was found on the nunatak Basen. Rotifers, found in 66% of the samples, were the most frequent animal group. Nematodes occurred in 37% of the samples and tardigrades in 42%. The most frequent nematodes were Plectus and Panagrolaimus, occurring in 26% and 5% of the samples, respectively. Macrobiotus, Hebesuncus and Acutuncus were the most frequent and abundant tardigrades. The pattern of animal distribution can be related to both habitat characteristics and to the geographic position of the nunatak. The communities are little organised and the distribution of the fauna has similarities with an early phase of colonisation. (C) 2004 Elsevier GmbH. All rights reserved

Preliminary description of tardigrade species diversity and distribution pattern around coastal Syowa Station and inland Sør Rondane Mountains, Dronning Maud Land, East Antarctica.

Tardigrades are important members of the simple terrestrial ecosystems in the extreme environments in Antarctica. This study provides a baseline description of tardigrade species diversity and distribution pattern within the terrestrial and lake environments of the coastal regions around Syowa Station and the neighbouring inland Sør Rondane Mountains, Dronning Maud Land. We combined data obtained from new and previously described collections and updated data available in the existing literature. We recorded five tardigrade species, three of which (Echiniscus pseudowendti Dastych 1984, Hebesuncus ryani Dastych and Harris 1994, Pseudechiniscus sp.) have not previously been reported from the area, increasing the total recorded tardigrade diversity for this region of continental Antarctica to ten species. The results of our study indicate that tardigrades have been and are major components of the lake environment community in continental Antarctica, with Acutuncus antarcticus (Richters 1904) the most common and dominant species. Our data confirm that the tardigrade species diversity in the vicinity of Syowa Station is very low and suggest potential relationships between individual tardigrade species and terrestrial moss species and depth in freshwater ecosystems