Differences in metal concentrations in juniper (Juniperus communis) and bilberry (Vaccinium myrtillus) shoots collected from northern and southern Finland

The average metal concentrations in all juniper samples (n=19) originating from Finnish Lapland north from polar circle were lower than in southern samples (n=28). For bilberry, situation was different

Gender Dimorphism Does Not Affect Secondary Compound Composition in Juniperus communis After Shoot Cutting in Northern Boreal Forests

Due to a difference in plant resource allocation to reproduction, the males of dioecious plants may be more growth-orientated, whereas females may allocate more resources for synthesizing secondary compounds. This mechanism is considered to cause gender-specific differences in the plant responses to the loss of plant biomass. Here, we tested gender dimorphism in the responses of common juniper (Juniperus communis) to shoot cutting in four juniper populations located in northern boreal forests in Finland. We collected shoots from uncut junipers and from junipers subjected to shoot cutting in the previous year, and analyzed them for their shoot growth as well as phenolic and terpenoid concentrations. There were no differences in foliar phenolic or terpenoid concentrations between the males and the females. Shoot cutting increased phenolic but not terpenoid concentrations, similarly, in both males and females. Our study reveals that the nature of gender dimorphism may differ among species and locations, which should be considered in theories on plant gender dimorphism. Given the similar phenolic and terpene concentrations in both genders, the different sexes in the northern juniper populations might experience equal levels of herbivory. This lack of gender dimorphism in biotic interactions could result from the high need of plant secondary metabolites (PSM) against abiotic stresses, which is typical for juniper at high latitudes

Urine is an important nitrogen source for plants irrespective of vegetation composition in an Arctic tundra:insights from a 15N-enriched urea tracer experiment

1. Mammalian herbivores can strongly influence nitrogen (N) cycling and herbivore urine could be a central component of the N cycle in grazed ecosystems. Despite its potential role for ecosystem productivity and functioning, the fate of N derived from urine has rarely been investigated in grazed ecosystems. 2. This study explored the fate of 15N-enriched urea in tundra sites that have been either lightly or intensively grazed by reindeer for more than 50 years. We followed the fate of the 15N applied to the plant canopy, at 2 weeks and 1 year after tracer addition, in the different ecosystem N pools. 3. 15N-urea was rapidly incorporated in cryptogams and in aboveground parts of vascular plants, while the soil microbial pool and plant roots sequestered only a marginal proportion. Further, the litter layer constituted a large sink for the 15N-urea, at least in the short term, indicating a high biological activity in the litter layer and high immobilization in the first phases of organic matter decomposition. 4. Mosses and lichens still constituted the largest sink for the 15N-urea 1 year after tracer addition at both levels of grazing intensity demonstrating their large ability to capture and retain N from urine. Despite large fundamental differences in their traits, deciduous and evergreen shrubs were just as efficient as graminoids in taking up the 15N-urea. The total recovery of 15N-urea was lower in the intensively grazed sites, suggesting that reindeer reduce ecosystem N retention. 5. Synthesis The rapid incorporation of the applied 15N-urea indicates that arctic plants can take advantage of a pulse of incoming N from urine. In addition, δ 15N values of all taxa in the heavily grazed sites converged towards the δ 15N values for urine, bringing further evidence that urine is an important N source for plants in grazed tundra ecosystems

Historical Reindeer Corrals as Portraits of Human-Nature Relationships in Northern Finland

Reindeer herding has been practised in northern boreal and subarctic regions of Fennoscandia for several centuries. The gathering and separation of reindeer for slaughter and calf marking are significant and cyclical activities of reindeer herding that are commonly carried out in reindeer corrals composed of circular-shaped fences of wood or stone construction leading into the corral. Using archaeological databases, we mapped historical reindeer corrals in northern Finland dating from the late 1800s to the 1960s for the entire reindeer herding area and characterized the legacies of their past use on present-day vegetation in Peräpohjola. In total, 94 corrals were located. Reindeer separations created a niche for novel plant communities with increasing graminoids in relation to dwarf shrubs and formation of a dense birch grove. Corrals have also preserved old rare trees left standing inside the corral to provide shelter for reindeer. The positioning of the corrals in the landscape was usually planned in a way that utilized man-made constructions and natural barriers, such as peatlands, and the typical behaviour of the reindeer in combination with both. When the wooden constructions had collapsed and decomposed, only the different vegetation indicates their past existence. L’élevage des rennes est pratiqué dans les régions boréales et subarctiques nordiques de la Fennoscandie depuis des siècles. Le rassemblement et la séparation des rennes à des fins d’abattage et de marquage des veaux sont d’importantes activités cycliques de l’élevage des rennes. Elles s’effectuent généralement dans des enclos à rennes composés de clôtures circulaires en bois ou de constructions en pierre menant aux enclos. À l’aide de bases de données archéologiques, nous avons dressé la carte historique des enclos à rennes du nord de la Finlande de la fin des années 1800 jusqu’aux années 1960 pour l’ensemble de la zone d’élevage des rennes, puis nous avons caractérisé l’héritage de leur utilisation antérieure sur la végétation actuelle de Peräpohjola. Nous avons localisé 94 enclos en tout. Les séparations employées pour les rennes ont donné lieu à la création d’un créneau favorable à l’établissement de nouvelles associations végétales contenant plus de graminiformes par rapport aux arbustes nains et à la formation de boulaies denses. Les enclos ont également permis de préserver d’anciens arbres rares qui sont restés à l’intérieur des enclos en guise d’abri pour les rennes. En général, l’emplacement des enclos était planifié de sorte à tirer parti des constructions artificielles et des obstacles naturels, comme les tourbières, et du comportement typique des rennes à l’égard de ces deux caractéristiques. Une fois les constructions en bois effondrées et décomposées, seule la végétation différente témoigne de leur existence.

Herbivore-Induced Effects on Arctic Soil Carbon Storage

Permafrost degradation and organic matter decomposition in the terrestrial Arctic are strongly depending on soil temperature throughout the year. These temperatures are affected in numerous ways by activity of large herbivorous animals. We identified snow compaction and animal-induced vegetation changes as key elements. Therefore, we analysed soil parameters along transects following grazing intensity in both a permafrost environment (northeastern Siberia) and seasonally frozen ground (norther Finland). Parameters included TOC, C/N ratio, d13C, bulk density and radiocarbon age. While we observed a strong increase in soil carbon storage with high grazing intensity under permafrost conditions, this effect does not show in seasonally frozen ground. However, an obvious animal-induced change in both areas was a shift in vegetation composition and structure, following the grazing gradient. We conclude that material and water fluxes in seasonally frozen ground outweigh the animals’ effects, contrary to permafrost environments, but state that on permafrost, animals could help maintaining low soil temperatures and hence reduce organic material decomposition

Consequences of grazer-induced vegetation transitions on ecosystem carbon storage in the tundra

1. Large herbivores can control plant community composition and, under certain conditions, even induce vegetation shifts to alternative ecosystem states. As different plant assemblages maintain contrasting carbon (C) cycling patterns, herbivores have the potential to alter C sequestration at regional scales. Their influence is ofparticular interest in the Arctic tundra, where a large share of the world’s soil C reservoir is stored.2. We assessed the influence of grazing mammals on tundra vegetation and C stocks by resampling two sites located along pasture rotation fences in northern Norway. These fences have separated lightly grazed areas from heavily grazed areas (in close proximity to the fences) and moderately grazed areas (further away from the fences) for the past 50 years. Fourteen years earlier, the lightly and moderately grazed areas were dominated by dwarf shrubs, whereas heavy grazing had promoted the establishment of graminoid-dominated vegetation. Since then, bothreindeer densities and temperatures have increased, and more time has passed for transient dynamics to be expressed. We expected that the vegetation and C stocks would have changed under all grazing intensities, but not necessarily in the same way. 3. At the site where relative reindeer numbers and trampling intensity had increasedthe most, graminoid-dominated vegetation was now also found in the moderately grazed area. At the other site, the dominant vegetation types under all grazing intensities were the same as 14 years earlier.4. We show that the heavily grazed, graminoid-dominated areas stored less C abovegroundthan the lightly grazed, shrub-dominated areas. Yet, the below-ground consequencesof grazing-induced grassification varied between the sites: Grazing did not alter organic soil C stocks at the site where both evergreen and deciduous shrubs were abundant in the lightly grazed area, whereas heavy grazing increasedorganic soil C stocks at the site where the deciduous shrub Betula nana was dominant. 5. Our results indicate that, despite the negative impacts of grazers on above-ground C storage, their impact on below-ground C may even be positive. We suggest that the site-specific responses of organic soil C stocks to grazing could be explained bythe differences in vegetation under light grazing. This would imply that the replacement of deciduous shrubs by graminoids, as a consequence of grazing could be beneficial for C sequestration in tundra soils. K E Y W O R D Scarbon stocks, grazing, herbivory, plant functional types, plant–soil interactions, Rangifer tarandus, reindeer, soil carbon</div

Reindeer grazing history determines the responses of subarctic soil fungal communities to warming and fertilization

Composition and functioning of arctic soil fungal communities may alter rapidly due to the ongoing trends of warmer temperatures, shifts in nutrient availability and shrub encroachment. In addition, the communities may also be intrinsically shaped by heavy grazing, which may locally induce an ecosystem change that couples with increased soil temperature and nutrients and where shrub encroachment is less likely to occur than in lightly grazed conditions. We tested how four years of experimental warming and fertilization affected organic soil fungal communities in sites with decadal history of either heavy or light reindeer grazing using high-throughput sequencing of ITS2 rDNA region. Grazing history largely overrode the impacts of short-term warming and fertilization in determining the composition of fungal communities. The less diverse fungal communities under light grazing showed more pronounced responses to experimental treatments when compared to the communities under heavy grazing. Yet, ordination approaches revealed distinct treatment responses under both grazing intensities. If grazing shifts the fungal communities in Arctic ecosystems to a different and more diverse state, this shift may dictate ecosystem responses to further abiotic changes. This inclines that the intensity of grazing cannot be left out when predicting future changes in fungi-driven processes in the tundra