Nitrogen Transfer from Four Nitrogen-Fixer Associations to Plants and Soils

Rousk, Kathrin; Sørensen, Pernille Lærkedal; Michelsen, Anders

doi:10.1007/s10021-016-0018-7

Cited by 36 publications

(17 citation statements)

References 45 publications

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“…Relevant external nutrient inputs to the subarctic birch forests are atmospheric N deposition, which was estimated to ~0.05–0.1 g N m −2 yr −1 in the area for the period 2013–2015 (Alpfjord & Andersson, 2017), biological N fixation, which has been estimated to be 0.1–0.5 g N m −2 yr −1 (Jonasson & Michelsen, 1996; Rousk & Michelsen, 2017; Rousk et al., 2016) and P from mineral weathering, which has been estimated to contribute ~0.01 g P m −2 yr −1 (Akselsson et al., 2008). This shows that the external inputs of N were comparable to our estimates of what was recycled through the litter, but 1–2 orders of magnitude higher than the contribution by insect herbivores at background densities.…”

Section: Discussionmentioning

confidence: 99%

Background insect herbivory increases with local elevation but makes minor contribution to element cycling along natural gradients in the Subarctic

Kristensen

Michelsen

Metcalfe

2020

Ecology and Evolution

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Herbivores can exert major controls over biogeochemical cycling. As invertebrates are highly sensitive to temperature shifts (ectothermal), the abundances of insects in high‐latitude systems, where climate warming is rapid, is expected to increase. In subarctic mountain birch forests, research has focussed on geometrid moth outbreaks, while the contribution of background insect herbivory (BIH) to elemental cycling is poorly constrained. In northern Sweden, we estimated BIH along 9 elevational gradients distributed across a gradient in regional elevation, temperature, and precipitation to allow evaluation of consistency in local versus regional variation. We converted foliar loss via BIH to fluxes of C, nitrogen (N), and phosphorus (P) from the birch canopy to the soil to compare with other relevant soil inputs of the same elements and assessed different abiotic and biotic drivers of the observed variability. We found that leaf area loss due to BIH was ~1.6% on average. This is comparable to estimates from tundra, but considerably lower than ecosystems at lower latitudes. The C, N, and P fluxes from canopy to soil associated with BIH were 1–2 orders of magnitude lower than the soil input from senesced litter and external nutrient sources such as biological N fixation, atmospheric deposition of N, and P weathering estimated from the literature. Despite the minor contribution to overall elemental cycling in subarctic birch forests, the higher quality and earlier timing of the input of herbivore deposits to soils compared to senesced litter may make this contribution disproportionally important for various ecosystem functions. BIH increased significantly with leaf N content as well as local elevation along each transect, yet showed no significant relationship with temperature or humidity, nor the commonly used temperature proxy, absolute elevation. The lack of consistency between the local and regional elevational trends calls for caution when using elevation gradients as climate proxies.

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Section: Discussionmentioning

confidence: 99%

Background insect herbivory increases with local elevation but makes minor contribution to element cycling along natural gradients in the Subarctic

Kristensen

Michelsen

Metcalfe

2020

Ecology and Evolution

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“…, Rousk et al. ). In boreal forests, subarctic and arctic tundra, moss‐associated N 2 fixation can exceed N deposition rates, mostly due to the high coverage and biomass of mosses (Van Cleve et al.…”

Section: Introductionmentioning

confidence: 99%

“…While atmospheric N deposition is one major source of plant available N in many ecosystems, N deposition in pristine ecosystems, such as subarctic and arctic tundra, is low (<2 kg NÁha À1 Áyr À1 ; Van Cleve and Alexander 1981, Peñuelas et al 2013) and is likely not sufficient to cover plant-N demand. Here, fixation of atmospheric N 2 is a large source of plant available N and is performed by free-living N 2 fixing bacteria (diazotrophs), and diazotrophs associated with lichens and mosses (Hobara et al 2006, Rousk et al 2016. In boreal forests, subarctic and arctic tundra, moss-associated N 2 fixation can exceed N deposition rates, mostly due to the high coverage and biomass of mosses (Van Cleve et al 1983, Turetsky 2003, Gavazov et al 2010.…”

Section: Introductionmentioning

confidence: 99%

What drives biological nitrogen fixation in high arctic tundra: Moisture or temperature?

2018

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Biological nitrogen (N2) fixation is one of the main sources of available N for pristine ecosystems such as subarctic and arctic tundra. Although this has been acknowledged more than a decade ago, few attempts have been undertaken to identify the foremost driver of N2 fixation in the high Arctic. Here, we report results from in situ measurements of N2 fixation throughout the main growing period (June–August) in high arctic tundra, Greenland, in climate change treatments, shading and warming, and control. Nitrogen fixation was also measured in cores that received additional water prior to the measurements. The climate change field treatments did not lead to significant changes in any measured parameters; however, N2 fixation was promoted by adding water, and moisture was the most important factor influencing N2 fixation in all climate change field treatments. Maximum N2 fixation rates were measured below 14°C soil temperature, which is much lower than the theoretical and previously reported temperature optimum for the nitrogenase enzyme. Diazotroph (N2 fixing bacteria) communities are adapted to low temperatures in high arctic settings, and increased temperature in a future climate may lead to decreased N2 fixation rates, or to a shift in diazotroph communities.

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“…Nitrogen is the primary nutrient limiting net primary productivity in high-latitude ecosystems (LeBauer and Treseder 2008, Wang et al 2010, Kuypers et al 2018. In these ecosystems, a large fraction of "new" N comes from diazotrophs (N-fixing bacteria, free-living or associated with soil crusts, mosses, or lichens) fixing atmospheric N 2 into ammonia (Dickson 2000, Hobara et al 2006, Rousk et al 2016b. In these ecosystems, N fixation can be as high as 10 kgÁha À1 Áyr À1 (Cleveland et al, 1999, Gavazov et al 2010, Rousk et al 2015.…”

Section: Introductionmentioning

confidence: 99%

Faster nitrogen cycling and more fungal and root biomass in cold ecosystems under experimental warming: a meta‐analysis

Salazar

Rousk

Jónsdóttir

et al. 2019

Ecology

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esson. 2020. Faster nitrogen cycling and more fungal and root biomass in cold ecosystems under experimental warming: a meta-analysis. Ecology 101(2):Abstract. Warming can alter the biogeochemistry and ecology of soils. These alterations can be particularly large in high northern latitude ecosystems, which are experiencing the most intense warming globally. In this meta-analysis, we investigated global trends in how experimental warming is altering the biogeochemistry of the most common limiting nutrient for biological processes in cold ecosystems of high northern latitudes (>50°): nitrogen (N). For comparison, we also analyzed cold ecosystems at intermediate and high southern latitudes. In addition, we examined N-relevant genes and enzymes, and the abundance of belowground organisms. Together, our findings suggest that warming in cold ecosystems increases N mineralization rates and N 2 O emissions and does not affect N fixation, at least not in a consistent way across biomes and conditions. Changes in belowground N fluxes caused by warming lead to an accumulation of N in the forms of dissolved organic and root N. These changes seem to be more closely linked to increases in enzyme activity that target relatively labile N sources, than to changes in the abundance of N-relevant genes (e.g., amoA and nosZ). Finally, our analysis suggests that warming in cold ecosystems leads to an increase in plant roots, fungi, and (likely in an indirect way) fungivores, and does not affect the abundance of archaea, bacteria, or bacterivores. In summary, our findings highlight global trends in the ways warming is altering the biogeochemistry and ecology of soils in cold ecosystems, and provide information that can be valuable for prediction of changes and for management of such ecosystems.

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Nitrogen Transfer from Four Nitrogen-Fixer Associations to Plants and Soils

Cited by 36 publications

References 45 publications

Background insect herbivory increases with local elevation but makes minor contribution to element cycling along natural gradients in the Subarctic

Background insect herbivory increases with local elevation but makes minor contribution to element cycling along natural gradients in the Subarctic

What drives biological nitrogen fixation in high arctic tundra: Moisture or temperature?

Faster nitrogen cycling and more fungal and root biomass in cold ecosystems under experimental warming: a meta‐analysis

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