Climate warming is increasing fire severity in boreal forests and can alter forest structure and carbon (C) dynamics in Cajander larch (Larix cajanderi) forests of Siberia, which occur over C and ice-rich yedoma permafrost. Altered forest structure may impact understory vegetation through changing canopy cover, permafrost thaw depth, and soil temperatures. The primary objective of this study was to assess the long-term impacts of fire-driven changes in tree density on understory composition, diversity, and C pools and the underlying soil organic layer (SOL). Shrubs dominated low density stands, likely from reduced canopy cover and thaw depth, while mosses dominated high density stands. Consequently, understory C pools decreased from 415.46 to 158.87 g C m-2. Total SOL C pools remained unchanged as tree density increased. These findings suggest that fire-driven changes in tree density may alter understory composition and C pools, which could impact nutrient/water cycling and permafrost stability.

No description available.

Mangrove stands and oyster reefs are two common coastal habitats in the Indian River Lagoon. Each habitat provides diverse ecosystem services, including carbon sequestration and carbon storage. A decrease in freeze events and an increase in sea levels are leading to mangrove habitat expansion, including encroachment onto live oyster reefs in the IRL’s northernmost portion, Mosquito Lagoon. This study investigates how the encroachment of black mangroves (Avicennia germinans) and red mangroves (Rhizophora mangle) on eastern oyster reefs (Crassostrea virginica) impacts the abundance and stability of soil carbon relative to each habitat alone. Soil and sediment samples (0-10cm) were collected from three locations in Mosquito Lagoon, each containing a mangrove-only, oyster-only, and mangrove-encroached oyster reef habitat. Total and active carbon were quantified, and stable carbon was determined through physical and density fractionation that isolates persistent mineral-associated organic matter (MAOM). Results showed total, active, and MAOM-carbon averaged 2-3 times greater in mangroves than oyster reefs, while mangrove-encroached oyster reefs were intermediate in concentration. However, mangrove-oyster soils have the highest proportion of the total carbon pool protected as MAOM (54.9%), compared to each habitat alone (mangrove-only, 35.3%, oyster-only, 30.3%). This research is the first to provide data on blue carbon storage in areas where mangroves encroach on oyster reefs, including differentiating total carbon based on its stability in the soil.

Dans la dernière décennie, plusieurs hectares de terre agricole ont été convertis à la culture intensive sur courtes rotations (CICR) de saules dans le sud du Québec (Canada). Peu d’études ont été réalisées afin de déterminer comment se comporte la dynamique du carbone organique (Corg) dans le sol suivant cette conversion. Nous avons donc comparé la quantité du Corg et de deux pools labiles de carbone (carbone extractible à l’eau chaude et les sucres aminés) entre des CICR en phase initiale d’établissement (1-2 ans) et des parcelles appariées représentant le système de culture qui prévalait avant la transformation en culture de saules (culture fourragère) et d’autres cultures d’intérêt. La même chose a été faite pour une CICR en exploitation (depuis 9 ans) à un autre site. La quantité de Corg du sol n’était pas différente entre les CICR et les parcelles sous culture fourragère. Une plus haute concentration de sucres aminés dans le Corg total des CICR en établissement, par rapport aux autres parcelles sur le même site, permet de soupçonner que les perturbations liées à l’établissement ne mènent pas à une minéralisation accrue du Corg à court terme. La proportion de sucres aminés fongiques, qui diminue théoriquement lors de perturbations, était aussi plus élevée sous la plus jeune culture. Sous la CICR de neuf ans, le Corg était redistribué dans le profil vertical et les pools labiles étaient de plus petite taille (à une profondeur de 20-40 cm) comparativement à une parcelle témoin. La conversion d’une culture fourragère en plantation de saules en CICR n’a pas mené à la formation d’un puits de carbone. L’étude laisse entrevoir qu’un tel puits pourrait être créé si la conversion se faisait à partir d’un aménagement impliquant la culture en rotation de plantes annuelles et des labours. / Over the last ten years, many hectares of short-rotation willow coppice (SRWC) have been established on abandoned agricultural lands in southern Quebec (Canada). However, few studies were conducted to determine if these changes from a conventional crop to SRWC of willows would affect the soil carbon dynamic. A preliminary paired-site study was conducted to assess the impact of this land-use conversion on soil carbon stocks and dynamics shortly after they were established (1-year and 2-year) at one site and after multiple rotations (9-year) at another site. Apart from the total soil organic carbon pool, two labile carbon pools were investigated: the hot-water extractable carbon (HWC) pool and the amino sugars (AS) pool. Willow establishment and exploitation for nine years did not bring any changes in total organic carbon compared to an abandoned hay culture. The mature SRWC displayed a redistribution of TSOC in the vertical soil profile. We also measured a higher proportion of AS, compared to other plots on the same site, in total organic carbon under the 1-year-old SRWC; especially the proportion in AS of fungi origin that theorically decrease with perturbation intensity. Proportion of AS was also elevated under 2-year-old SRWC. A possible interpretation is that establishment-linked perturbations did not shift carbon dynamic toward an increased mineralization. The mature willow plantation exhibited depletion of HWC and the more labile amino sugar (muramic acid) in the deeper soil layer (20-40cm). This case study shows that conversion from an abandoned hay culture to a SRWC did not create a carbon sink. It was also found that the 9- year old willow plantation contained higher TSOC and had better soil quality than an adjacent short-term no-till crop rotation culture.

Dans la dernière décennie, plusieurs hectares de terre agricole ont été convertis à la culture intensive sur courtes rotations (CICR) de saules dans le sud du Québec (Canada). Peu d’études ont été réalisées afin de déterminer comment se comporte la dynamique du carbone organique (Corg) dans le sol suivant cette conversion. Nous avons donc comparé la quantité du Corg et de deux pools labiles de carbone (carbone extractible à l’eau chaude et les sucres aminés) entre des CICR en phase initiale d’établissement (1-2 ans) et des parcelles appariées représentant le système de culture qui prévalait avant la transformation en culture de saules (culture fourragère) et d’autres cultures d’intérêt. La même chose a été faite pour une CICR en exploitation (depuis 9 ans) à un autre site. La quantité de Corg du sol n’était pas différente entre les CICR et les parcelles sous culture fourragère. Une plus haute concentration de sucres aminés dans le Corg total des CICR en établissement, par rapport aux autres parcelles sur le même site, permet de soupçonner que les perturbations liées à l’établissement ne mènent pas à une minéralisation accrue du Corg à court terme. La proportion de sucres aminés fongiques, qui diminue théoriquement lors de perturbations, était aussi plus élevée sous la plus jeune culture. Sous la CICR de neuf ans, le Corg était redistribué dans le profil vertical et les pools labiles étaient de plus petite taille (à une profondeur de 20-40 cm) comparativement à une parcelle témoin. La conversion d’une culture fourragère en plantation de saules en CICR n’a pas mené à la formation d’un puits de carbone. L’étude laisse entrevoir qu’un tel puits pourrait être créé si la conversion se faisait à partir d’un aménagement impliquant la culture en rotation de plantes annuelles et des labours. / Over the last ten years, many hectares of short-rotation willow coppice (SRWC) have been established on abandoned agricultural lands in southern Quebec (Canada). However, few studies were conducted to determine if these changes from a conventional crop to SRWC of willows would affect the soil carbon dynamic. A preliminary paired-site study was conducted to assess the impact of this land-use conversion on soil carbon stocks and dynamics shortly after they were established (1-year and 2-year) at one site and after multiple rotations (9-year) at another site. Apart from the total soil organic carbon pool, two labile carbon pools were investigated: the hot-water extractable carbon (HWC) pool and the amino sugars (AS) pool. Willow establishment and exploitation for nine years did not bring any changes in total organic carbon compared to an abandoned hay culture. The mature SRWC displayed a redistribution of TSOC in the vertical soil profile. We also measured a higher proportion of AS, compared to other plots on the same site, in total organic carbon under the 1-year-old SRWC; especially the proportion in AS of fungi origin that theorically decrease with perturbation intensity. Proportion of AS was also elevated under 2-year-old SRWC. A possible interpretation is that establishment-linked perturbations did not shift carbon dynamic toward an increased mineralization. The mature willow plantation exhibited depletion of HWC and the more labile amino sugar (muramic acid) in the deeper soil layer (20-40cm). This case study shows that conversion from an abandoned hay culture to a SRWC did not create a carbon sink. It was also found that the 9- year old willow plantation contained higher TSOC and had better soil quality than an adjacent short-term no-till crop rotation culture.

No description available.

In der vorliegenden Arbeit wurden die Einflüsse der landwirtschaftlichen Nutzung auf die Struktur und Biomasse von Nematoden entlang eines Tiefengradientens und innerhalb zweier Vegetationsperioden an einem Ackerstandort untersucht. Die Freilandanalyse der Nematodengemeinschaft wies auf ein mit Nährstoffen angereichertes und gestörtes Ökosystem, mit einer geringen Diversität, hin. Entlang des Tiefengradienten bildeten die Nematoden Metacommunities, welche Umweltgegebenheiten wie Nahrungsquellen und abiotischen Faktoren widerspiegeln. Signifikant höhere Biomassen wurden unter Weizen im Vergleich zu Mais als Ackerfrucht beobachtet. Die Streuapplikation induzierte einen „bottom-up“ Effekt mit größeren Biomassen in den niedrigen als in den höheren trophischen Stufen. Die Nematoden Biomassen sowie die faunistischen Indizes (Channel Index, Enrichment Index) zeigten, dass der Kohlenstofffluss im Bakterienkanal des Bodens dominierte. Allerdings deckte das 13C Pulse-Labelling Experiment im Feld auf, dass der Kohlenstofffluss durch die Pilzgemeinschaft sowie die pilzfressenden Nematoden wesentlich höhere Umsatzraten aufweist. In einem 14C-Laborexperiment wurde ein vollständiges Budget des Flusses von wurzelbürtigem Kohlenstoff in das Nahrungsnetz der Nematoden bestimmt. Hierbei wiesen die pflanzenparasitären Nematoden die höchsten 14C-Gehalte innerhalb weniger Tage auf, da sie direkt an den Wurzeln fressen und über die Herbivorenkette den Nährstoffzyklus im Boden eröffnen. / The present research considered the effects of agricultural management practice on the nematode community structure and biomass in three different depths and two successive vegetation periods at an arable field site. The resource quality was manipulated by crop plant and organic amendment, to investigate the major soil carbon pathways based on roots, bacteria and fungi. The nematode community analysis pointed to a highly enriched and disturbed ecosystem with low biodiversity. Along the depth gradient the nematodes formed distinct metacommunities, reflecting resource availability and abiotic environmental factors. Wheat supported significantly greater nematode biomass than maize. The litter amendment induced bottom-up effects, with greater biomass allocation at lower than at higher trophic levels. The biomass of nematode families as well as faunal indices (Channel Index, Enrichment Index) revealed a predominance of the bacterial carbon channel in the arable soil. A 13C pulse-labelling experiment investigating the flux of root- derived C into the soil food web revealed high turnover rates in the fungal carbon pathway. This was evident for soil fungi as well as for fungal-feeding nematodes and contradicts general assumptions of a more active bacterial pathway in arable soils. A laboratory experiment with 14C isotope was used to compile a complete budget for the root-derived carbon in the nematode food web. Here plant-feeding nematodes, which feed on living plant roots, thereby opening the root C cycling into the food web, showed highest amounts of 14C allocation within a few days.