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DeLuca T.H.,University of Washington | DeLuca T.H.,Bangor University | DeLuca T.H.,Institute for Subarctic Landscape Research | Zewdie S.A.,Bangor University | And 3 more authors.
Plant and Soil | Year: 2013

Background and Aims: In spite of the broad array of studies conducted on the ecology of bracken fern (Pteridium aquilinum (L.) kuhn), there is currently only a limited understanding of how P. aquilinum alters the soil environment in which it succeeds. P. aquilinum is one of the world's most aggressive invasive species and is known to effectively invade conservation priority habitats such as Calluna vulgaris (L.) heathland. The aim of this study was to evaluate differences in soil properties between intact stands of C. vulgaris and neighboring P. aquilinum to assess how P. aquilinum alters soil N transformations in a manner that might promote its success. Methods: Replicate plots in five independently paired stands of P. aquilinum and C. vulgaris were established on land in which P. aquilinum is actively invading. Soils under the two plant types were evaluated for total N, mineralisable N, net nitrification, nitrifier activity, denitrification enzyme activity, polyphenol N complexing capacity, and resin sorption of inorganic N. Results: Soils under P. aquilinum were consistently higher in NO3 - and NH4 + concentrations compared to C. vulgaris. Extractable organic and inorganic N concentrations for soil under P. aquilinum were respectively 65 %, 77 % and 358 % greater in amino N NH4 +-N and NO3 --N compared to that under C. vulgaris. In-situ net nitrification (NO3 - sorption to ionic resins) was found to be nearly 300 times greater under P. aquilinum than under C. vulgaris. Conclusions: P. aquilinum alters the soil environment as to create an inorganic N-rich environment that is favorable to its growth and development. © 2012 Springer Science+Business Media Dordrecht. Source


DeLuca T.H.,University of Washington | DeLuca T.H.,Institute for Subarctic Landscape Research | Zackrisson O.,Institute for Subarctic Landscape Research | Bergman I.,Institute for Subarctic Landscape Research | And 2 more authors.
PLoS ONE | Year: 2013

There is currently limited understanding of the contribution of biological N2 fixation (diazotrophy) to the N budget of large river systems. This natural source of N in boreal river systems may partially explain the sustained productivity of river floodplains in Northern Europe where winter fodder was harvested for centuries without fertilizer amendments. In much of the world, anthropogenic pollution and river regulation have nearly eliminated opportunities to study natural processes that shaped early nutrient dynamics of large river systems; however, pristine conditions in northern Fennoscandia allow for the retrospective evaluation of key biochemical processes of historical significance. We investigated biological N2 fixation (diazotrophy) as a potential source of nitrogen fertility at 71 independent floodplain sites along 10 rivers and conducted seasonal and intensive analyses at a subset of these sites. Biological N2 fixation occurred in all floodplains, averaged 24.5 kg N ha-1 yr-1 and was down regulated from over 60 kg N ha-1 yr-1 to 0 kg N ha-1 yr -1 by river N pollution. A diversity of N2-fixing cyanobacteria was found to colonize surface detritus in the floodplains. The data provide evidence for N2 fixation to be a fundamental source of new N that may have sustained fertility at alluvial sites along subarctic rivers. Such data may have implications for the interpretation of ancient agricultural development and the design of contemporary low-input agroecosystems. © 2013 DeLuca et al. Source


Deluca T.H.,University of Washington | Deluca T.H.,Institute for Subarctic Landscape Research | Zackrisson O.,Institute for Subarctic Landscape Research | Bergman I.,Institute for Subarctic Landscape Research | Hornberg G.,Institute for Subarctic Landscape Research
Anthropocene | Year: 2013

Historical and repeated use of fire is thought to be responsible for poor forest regeneration on Norway spruce (Picea abies L.)-lichen (Cladina spp.) forests of subarctic Sweden; however, the role of nutrient limitation in this process has not been studied. Studies were performed on three paired stands of open spruce-Cladina forests and un-disturbed, Norway spruce-Scots pine (Pinus sylvestris L.)-feathermoss forests to evaluate whether repeated use of fire in ancient times led to depletion of nutrient resources which altered forest regeneration. All pairs were analyzed for vegetative composition, soil nutrient capital and availability, and total soil organic matter. Peat cores collected in neighboring bogs were used for pollen analyses. Spruce-Cladina forests were found to have significantly reduced N capital and little N2 fixation capacity. Spruce-Cladina forests had lower concentrations of mineral soil P compared to reference forests. Pollen records suggest that these sites were historically mixed spruce, pine forests, but under the influence of recurrent fire exhibited a marked peak in charcoal occurrence at about 550 calibrated years BP and a decrease in tree pollen accumulation at circa 500 calibrated years BP. Carbon dating of charcoal in hearths located on the three sites place regular human occupation of this from circa 600-300 calibrated years BP. The open spruce-Cladina forests of subarctic Sweden are likely a product of recurrent use of fire by humans. By adopting a long-term perspective it is possible to understand land-use legacies even in remote ecosystems that are considered "natural" today. © 2013 Elsevier Ltd. Source


Josefsson T.,Swedish University of Agricultural Sciences | Josefsson T.,Institute for Subarctic Landscape Research | Ramqvist P.H.,Institute for Subarctic Landscape Research | Ramqvist P.H.,Umea University | Hornberg G.,Institute for Subarctic Landscape Research
Vegetation History and Archaeobotany | Year: 2014

The age of the introduction of cereal cultivation in northern Europe has long been debated by researchers from many disciplines, in particular archaeology and palaeoecology. Over the past 40 years extensive palynological data have been collected concerning pre-industrial land use in northern Fennoscandia. This paper reviews palynological studies that include records of fossil cereal pollen from northernmost Sweden, Finland and Norway at latitudes north of 63°N. The geographical extent of known early cultivation sites is constantly expanding, with more than 100 records of cereal pollen pre-dating ad 1700. The oldest records of scattered cereal pollen derive from Neolithic times. Periods of continuous cultivation, indicated by cereal pollen recorded recurrently in the sediment profiles, derive from the Late Neolithic and Early Bronze Age. Collectively, the reviewed pollen records indicate that cereal cultivation was first introduced into areas close to the coast and later to the interior, and that it may have been practiced locally long before sedentary settlements based on intensive cultivation were established during medieval times. The data do not indicate a latitudinal spread of cultivation from south to north. However, methodological problems relating to pollen morphology of cereals, site characteristics and lack of connections to archaeologically excavated sites imply that the value of many early cereal pollen finds remains unclear. To increase our understanding of the context in which cereal cultivation was introduced in northernmost Fennoscandia, multidisciplinary studies integrating palaeoecology, archaeology and history are needed. © 2014, Springer-Verlag Berlin Heidelberg. Source


Bay G.,Swedish University of Agricultural Sciences | Nahar N.,University of Stockholm | Oubre M.,University of Stockholm | Whitehouse M.J.,Swedish Museum of Natural History | And 4 more authors.
New Phytologist | Year: 2013

The mechanistic basis of feather moss-cyanobacteria associations, a main driver of nitrogen (N) input into boreal forests, remains unknown. Here, we studied colonization by Nostoc sp. on two feather mosses that form these associations (Pleurozium schreberi and Hylocomium splendens) and two acrocarpous mosses that do not (Dicranum polysetum and Polytrichum commune). We also determined how N availability and moss reproductive stage affects colonization, and measured N transfer from cyanobacteria to mosses. The ability of mosses to induce differentiation of cyanobacterial hormogonia, and of hormogonia to then colonize mosses and re-establish a functional symbiosis was determined through microcosm experiments, microscopy and acetylene reduction assays. Nitrogen transfer between cyanobacteria and Pleurozium schreberi was monitored by secondary ion mass spectrometry (SIMS). All mosses induced hormogonia differentiation but only feather mosses were subsequently colonized. Colonization on Pleurozium schreberi was enhanced during the moss reproductive phase but impaired by elevated N. Transfer of N from cyanobacteria to their host moss was observed. Our results reveal that feather mosses likely secrete species-specific chemo-attractants when N-limited, which guide cyanobacteria towards them and from which they gain N. We conclude that this signalling is regulated by N demands of mosses, and serves as a control of N input into boreal forests. See also the Commentary by Sprent and Meeks. © 2013 New Phytologist Trust. Source

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