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Arctic ecosystems are threatened by pollution from recently detected extreme atmospheric nitrogen (N) deposition events in which up to 90% of the annual N deposition can occur in just a few days. We undertook the first assessment of the fate of N from extreme deposition in High Arctic tundra and are presenting the results from the whole ecosystem 1...
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The present study provides new information about the diversity of freshwater and terrestrial cyanoprokaryotes of the western part of the Oscar II Land, Spitsbergen (Svalbard) archipelago. Altogether, and 51 taxa were found in different habitats (29 species was found on wet rocks, 21 on the seepages, 18 on the lakes, 11 on the moss tundra), mainly i...
In High Arctic tundra ecosystems, seabird colonies create nitrogen cycling hotspots because of bird-derived labile organic matter. However, knowledge about the nitrogen cycle in such ornithocoprophilous tundra is limited. Here, we determined denitrification potentials and in-situnitrous oxide (N2O) emissions of surface soils on plant-covered taluse...
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... Plant NO 3 À preference was higher in the alpine and Arctic zones than in lower latitudes (Fig. 2). This result is consistent with some previous studies (Choudhary et al., 2016;Liu et al., 2018) that emphasize the important role of soil NO 3 À in plant N uptake in the Arctic tundra, but in contrast to other studies that reported a low soil nitrification rate associated with undetectable soil NO 3 À , which is unfavorable for plant NO 3 À uptake (McKane et al., 2002;Nordin et al., 2004). These conflicting results suggest that factors other than soil NO 3 À availability play a dominant role in driving plant NO 3 À preference. ...
Elucidating plant nitrogen (N) acquisition is crucial for understanding plant N strategies and ecosystem productivity. However, the variation in plant N uptake preference and its controlling factors on a global scale remain unclear.
We conducted a global synthesis to explore plant N preference patterns and driving factors.
Globally, the average contributions of ammonium (NH4⁺), nitrate (NO3⁻), and glycine N to the total plant N uptake were 41.6 ± 1.1%, 32.8 ± 1.2%, and 25.6 ± 0.9%, respectively. However, plant N uptake preferences differed significantly among climatic regions and vegetation types. Soil NH4⁺ was the most preferred N form by plants in (sub)tropical regions, whereas NO3⁻ preference was significantly higher in high‐latitude than low‐latitude regions. Plant functional type was one of the most important factors driving NO3⁻ preference, with significantly higher NO3⁻ preference of nonwoody species than broadleaf‐evergreen, conifer, and shrub species. Organic N preference was lowest in (sub)tropics and significantly lower than that in temperate and alpine regions.
This study shows clear climatic patterns and different influencing factors of plant NH4⁺ and NO3⁻ preference, which can contribute to the accurate prediction of N constraints on ecosystem productivity and soil carbon dynamics.
... Enhanced soil nutrient availability induced by climate warming (Jiang et al. 2016;McLaren and Buckeridge 2021;Pold et al. 2021;Salazar et al. 2020), atmospheric nitrogen (N) deposition (Choudhary et al. 2016), and human-induced disturbances (Wang and Friedl 2019) are increasingly modifying subarctic ecosystems. These anthropogenic perturbations occur in combination with natural disturbances such as herbivory (Jepsen et al. 2013;Sundqvist et al. 2019;Tuomi et al. 2021). ...
Subarctic ecosystems are subjected to increasing nitrogen (N) enrichment and disturbances that induce particularly strong effects on plant communities when occurring in combination. There is little experimental evidence on the longevity of these effects. We applied N-fertilization (40 kg urea-N ha⁻¹ year⁻¹ for 4 years) and disturbance (removal of vegetation and organic soil layer on one occasion) in two plant communities in a subarctic forest-tundra ecotone in northern Finland. Within the first four years, N-fertilization and disturbance increased the share of deciduous dwarf shrubs and graminoids at the expense of evergreen dwarf shrubs. Individual treatments intensified the other’s effect resulting in the strongest increase in graminoids under combined N-fertilization and disturbance. The re-analysis of the plant communities 15 years after cessation of N-fertilization showed an even higher share of graminoids. 18 years after disturbance, the total vascular plant abundance was still substantially lower and the share of graminoids higher. At the same point, the plant community composition was the same under disturbance as under combined N-fertilization and disturbance, indicating that multiple perturbations no longer reinforced the other’s effect. Yet, complex interactions between N-fertilization and disturbance were still detected in the soil. We found higher organic N under disturbance and lower microbial N under combined N-fertilization and disturbance, which suggests a lower bioavailability of N sources for soil microorganisms. Our findings support that the effects of enhanced nutrients and disturbance on subarctic vegetation persist over decadal timescales. However, they also highlight the complexity of plant–soil interactions that drive subarctic ecosystem responses to multiple perturbations across varying timescales.
Supplementary Information
The online version contains supplementary material available at 10.1007/s00442-024-05524-z.
... Nutrient fertilization and atmospheric deposition played a crucial role in the Holocene in enhancing the productivity of the Arctic vegetation (Galloway et al., 2004;Choudhary et al., 2016). A prolonged growing season due to a warmer climate and shorter ice coverage further contributes to an upsurge in carbon turnover within lakes (Walther et al., 2002;Vuglinsky and Valatin, 2018;Sharma et al., 2019;Sharma et al., 2020). ...
Introduction: Rising industrial emissions of carbon dioxide and methane highlight the important role of carbon sinks and sources in fast-changing northern landscapes. Northern lake systems play a key role in regulating organic carbon input by accumulating carbon in their sediment. Here we look at the lake history of 28 lakes (between 50°N and 80°N) over the past 21,000 years to explore the relationship between carbon accumulation in lakes and temperature changes.
Method: For this study, we calculated organic carbon accumulation rates (OCAR) using measured and newly generated organic carbon and dry bulk density data. To estimate new data, we used and evaluated seven different regression techniques in addition to a log-linear model as our base model. We also used combined age-depth modeling to derive sedimentation rates and the TraCE-21ka climate reanalysis dataset to understand temperature development since the Last Glacial Maximum. We determined correlation between temperature and OCAR by using four different correlation coefficients.
Results: In our data collection, we found a slightly positive association between OCAR and temperature. OCAR values peaked during warm periods Bølling Allerød (38.07 g·m⁻²·yr⁻¹) and the Early Holocene (40.68 g·m⁻²·yr⁻¹), while lowest values occurred during the cold phases of Last Glacial Maximum (9.47 g·m⁻²·yr⁻¹) and Last Deglaciation (10.53 g·m⁻²·yr⁻¹). However, high temperatures did not directly lead to high OCAR values.
Discussion: We assume that rapid warming events lead to high carbon accumulation in lakes, but as warming progresses, this effect appears to change as increased microbial activity triggers greater outgassing. Despite the complexity of environmental forcing mechanisms affecting individual lake systems, our study showed statistical significance between measured OCAR and modelled paleotemperature for 11 out of 28 lakes. We concluded that air temperature alone appears to drive the carbon accumulation in lakes. We expected that other factors (catchment vegetation, permafrost, and lake characteristics) would influence accumulation rates, but could not discover a conclusive factor that had a statistical significant impact. More data available on long-term records from northern lake systems could lead to more confidence and accuracy on the matter.
... A typical biotic driver in tundra ecosystems is grazing by the reindeer Rangifer tarandus (caribou in North America) with effects on plant species composition and biomass (Oksanen 1990, Eskelinen et al. 2012, soil microbial activity and community composition (Tuomi et al. 2021), and soil abiotic properties such as nutrient availability and temperature Väisänen 2014, Stark et al. 2015). These grazing-mediated controls intertwine with the contemporary anthropogenic abiotic changes through global climate warming and increasing nitrogen deposition (Choudhary et al. 2016, Hoegh-Guldberg et al. 2018). Yet, although some studies have examined the effect of reindeer grazing on soil nematode communities (Stark et al. 2008, Virtanen et al. 2008, Francini et al. 2014, none have combined grazing with the changing tundra environment. ...
Top–down control by nematodes over soil microorganisms – considered to be stronger over bacteria than over fungi – may dampen microbial responses to global changes in tundra. To test whether large grazers alter the responses of belowground trophic networks to global changes, we employed factorial warming and nitrogen fertilization treatments in adjacent sites with different reindeer grazing intensities for the past 50 years. Lightly grazed tundra is dominated by dwarf shrubs and a more fungal‐based microbial community, while in heavily grazed tundra the high reindeer densities during autumn migration have induced a shift into graminoids and a more bacterial‐based microbial community. We analysed the soil micro‐food web (i.e. the nematode density, trophic structure and species composition) as well as fungal, bacterial and total phospholipid fatty acids (PLFAs) after four growing seasons of warming and fertilization both before and during reindeer migration. We predicted that bacterivore densities are higher and fungivore densities lower under heavy than light grazing (i.e. nematode populations before migration reflect grazing effects via the base of the food web), whereas reindeer migration induces a negative impact on nematode densities under heavy grazing (disturbance by trampling is the driving factor). We further predicted that nematodes negate treatment effects on microbial biomass to a stronger extent in the bacterial‐based heavily grazed tundra than in the fungal‐based lightly grazed tundra. Fungivore densities were higher under light than under heavy grazing, but nematodes did not respond to trampling. Warming increased fungivores and the fungal PLFAs irrespective of grazing and timing but, under heavy grazing, it increased bacterivores while the bacterial PLFAs remained steady. Fertilization increased carnivores and influenced nematode species composition, diversity and maturity interactively with warming. Our data suggest that large grazers affect tundra soil nematodes via bottom–up effects through microbial community composition and biomass, which in turn may alter the strength of their top–down control over soil bacteria under climate warming.
... Bryophytes are conspicuous and critical elements in northern ecosystems (Chapin et al. III 1992;Daniëls et al. 2013;Choudhary et al. 2016) and maintain symbiotic associations and help summarize potential ecological interactions (e.g., Barberán et al. 2012;Ma et al. 2020). These bacterial community variations are crucial to understanding how environmental changes may affect the abundance of key groups and would help to predict potential shifts in ecosystem dynamics (Alvarenga and Rousk 2021;Klarenberg et al. 2021). ...
Bryophytes maintain symbiosis with bacteria influencing the local nutrient budget. Moss bacterial communities are composed of a core microbiome and bacteria recruited from environmental sources. Notably, symbiotic N2-fixing bacteria contribute to the N budget in northern ecosystems through biological nitrogen fixation. This process may be affected by the abundance of diazotrophs and moss nutrient content. We used the abundant moss Racomitrium lanuginosum in a forest tundra and shrub tundra in Northern Quebec, Canada, to investigate the bacterial and diazotrophic communities associated with habitat type using amplicon sequencing of the bacterial 16S rRNA and nifH genes and test whether the moss core microbiome has recruitment from the soil bacteria community. The nifH amplicons and element analysis were used to test the effect of diazotrophic abundance and moss nutrient content on N2-fixation activity estimated by acetylene reduction assays. Moss microbial communities between tundra types hosted similar bacterial diversity but differentially abundant groups and characteristic microbial interaction patterns. The core microbiome of R. lanuginosum is composed of bacteria strongly associated with northern mosses with no significant recruitment from the soil. The relative abundances of dominant diazotrophs are significantly correlated with acetylene reduction rates. In contrast, the moss nutrient content did not significantly drive N2-fixation. The proteobacterial genera Azorhizobium and Rhodomicrobium represent newly reported bacteria associated with N2-fixation rates in the tundra. We identified critical bacterial groups related to moss-bacterial symbiosis and N2-fixation in the forest-tundra transition zone, a changing environment susceptible to climate warming.
... Meanwhile, once mosses occur on the rock surface, the duration of available water holding on the surface against runoff is greatly prolonged, thereby increasing the time of rock hydrochemical action and promoting the transformation of rock surface nutrients (Cao and Yuan 1999). Bryophytes lack leaf surface cuticle and have many cation exchange sites, which can adsorb many kinds of cations, which results in the bryophyte being able to absorb nutrients from atmospheric deposition more freely (Dong et al. 2017;Varela et al. 2023) and efficiently utilize atmospheric deposited nitrogen (Chamizo et al. 2012;Choudhary et al. 2016;Koranda and Michelsen 2021). Because these cations could be converted into inorganic salts, organic salts, and other forms of compounds stored in the tissues of the bryophyte. ...
Since natural restoration combined with artificial auxiliary measures may achieve a relatively rapid restoration effect at a lower cost, it has become an essential measure for the ecological restoration of rock slopes. Previous studies have focused heavily on the relationship between substrate nutrients and water conditions and the development of mosses on the rock surface, but quantitative characterization of substantial effect of rock surface texture (e.g., microrelief) on moss growth is absent. The undulating microrelief on the rock surface can increase the heterogeneity of the microhabitat, which may be an important factor affecting the development of moss-dominated biocrusts. In this study, the roughness of rock surfaces, moss coverage and biomass, weight and major nutrient contents of soils within the biocrusts were measured in the western mountainous area of Sichuan Province, Southwest China to further examine the role of rock surface microrelief in the biocrusts. The results showed that three main factors affecting the development of the biocrusts were bryophyte emergence, soil accumulation, and lithology. The presence of moss accelerates soil formation on rock surfaces and lead to the accumulation of nutrients so that all parts of the moss-dominated biocrusts system can develop synergistically. It was found that a microrelief structure with a roughness between 1.5 and 2.5 could gather soil and bryophyte propagules effectively, which may have a strong relationship with the angle of repose. When the roughness is 1.5, the corresponding undulation angle is very close to the theoretical minimum value of the undulation angle calculated according to the relationships between the undulation angle of the protrusion, slope and angle of repose. Influence of surface roughness on the development of moss-dominated biocrusts on mountainous rock-cut slopes in West
... Even with the same annual deposition flux, the changes of atmospheric nitrogen deposition at a smaller time scale (episodic events occurring within a few days), occurring at different growth stages of plants in different seasons, can have distinct ecological effects. 17 Here we present the annual variations of nitrogen aerosols at the Qomolangma monitoring station (QOMS), Central Himalayas, from March 2017 to March 2018, with a focus on an intensive spring wildfire episode (10th to 14th April 2017). Based on the combined analysis of major ions, black carbon (BC), levoglucosan, δ 15 N isotope compositions, and satellite observations (MODIS and CALIOP), we investigated the sources and controlling factors of the nitrogen aerosols in the HTP. ...
Himalayas and Tibetan Plateau (HTP) is important for global biodiversity and regional sustainable development. While numerous studies have revealed that the ecosystem in this unique and pristine region is changing, their exact causes are still poorly understood. Here, we present a year-round (23 March 2017 to 19 March 2018) ground- and satellite-based atmospheric observation at the Qomolangma monitoring station (QOMS, 4276 m a.s.l.). Based on a comprehensive chemical and stable isotope (15N) analysis of nitrogen compounds and satellite observations, we provide unequivocal evidence that wildfire emissions in South Asia can come across the Himalayas and threaten the HTP's ecosystem. Such wildfire episodes, mostly occurring in spring (March-April), not only substantially enhanced the aerosol nitrogen concentration but also altered its composition (i.e., rendering it more bioavailable). We estimated a nitrogen deposition flux at QOMS of ∼10 kg N ha-1 yr-1, which is approximately twice the lower value of the critical load range reported for the Alpine ecosystem. Such adverse impact is particularly concerning, given the anticipated increase of wildfire activities in the future under climate change.
... Atmospheric nitrogen (N) deposition is a global threat to biodiversity and ecosystem function, and despite policy measures, nitrogen deposition rates keep increasing (Ackerman et al., 2019) with noticeable biotic responses (Ardyna et al., 2022;Bergström & Jansson, 2006). Critically, even low-dose N deposition (5-10 kg N ha À1 year À1 ) may lead to eutrophication and affect plant communities (Bobbink & Hettelingh, 2011;Choudhary et al., 2016). Cryptogams typically reflect the nitrogen status of their environment due to the lack of specialised tissue to regulate this (Asplund & Wardle, 2014;Palmqvist et al., 2002), and are known to capture a large proportion of the deposited N (Bokhorst, van Logtestijn, et al., 2019;Choudhary et al., 2016). ...
... Critically, even low-dose N deposition (5-10 kg N ha À1 year À1 ) may lead to eutrophication and affect plant communities (Bobbink & Hettelingh, 2011;Choudhary et al., 2016). Cryptogams typically reflect the nitrogen status of their environment due to the lack of specialised tissue to regulate this (Asplund & Wardle, 2014;Palmqvist et al., 2002), and are known to capture a large proportion of the deposited N (Bokhorst, van Logtestijn, et al., 2019;Choudhary et al., 2016). ...
Arctic ecosystems are increasingly exposed to extreme climatic events throughout the year, which can affect species performance. Cryptogams (bryophytes and lichens) provide important ecosystem services in polar ecosystems but may be physiologically affected or killed by extreme events. Through field and laboratory manipulations, we compared physiological responses of seven dominant sub-Arctic cryptogams (3 bryophytes, 4 lichens) to single events and factorial combinations of mid-winter heatwave (6°C for 7 days), re-freezing, snow removal and summer nitrogen addition. We aimed to identify which mosses and lichens are vulnerable to these abiotic extremes and if combinations would exacerbate physiological responses. Combinations of extremes resulted in stronger species responses but included idiosyncratic species-specific responses. Species that remained dormant during winter (March), irrespective of extremes, showed little physiological response during summer (August). However, winter physiological activity, and response to winter extremes, were not consistently associated with summer physiological impacts. Winter extremes affect cryptogam physiology, but summer responses appear mild, and lichens affect the photobiont more than the mycobiont. Accounting for Arctic cryptogam response to multiple climatic extremes in ecosystem functioning and modelling will require a better understanding of their winter eco-physiology and repair capabilities. This article is protected by copyright. All rights reserved.
... Present-day (2015) global simulations indicate substantial regional variation in the N r budget, reflecting the impact of regional activities and meteorology (Ge et al., 2022). The increasing importance of reduced N is likely to impact future N deposition budgets and the competitive nature among plants with varying affinities for the different forms of nitrogen (Choudhary et al., 2016;Kahmen et al., 2006). ...
Atmospheric deposition of nitrogen (N) and sulfur (S) compounds from human activity has greatly declined in the United States (US) over the past several decades in response to emission controls set by the Clean Air Act. While many observational studies have investigated spatial and temporal trends of atmospheric deposition, modeling assessments can provide useful information over areas with sparse measurements, although they usually have larger horizontal resolutions and are limited by input data availability. In this analysis, we evaluate wet, dry, and total N and S deposition from multiyear simulations within the contiguous US (CONUS). Community Multiscale Air Quality (CMAQ) model estimates from the EPA's (Environmental Protection Agency) Air QUAlity TimE Series (EQUATES) project contain important model updates to atmospheric deposition algorithms compared to previous model data, including the new Surface Tiled Aerosol and Gaseous Exchange (STAGE) bidirectional deposition model which contains land-use-specific resistance parameterization and land-use-specific deposition estimates needed to estimate the differential impacts of N deposition to different land use types. First, we evaluate model estimates of wet deposition and ambient concentrations, finding underestimates of SO4, NO3, and NH4 wet deposition compared to National Atmospheric Deposition Program observations and underestimates of NH4 and SO4 and overestimates of SO2 and TNO3 (HNO3+NO3) compared to the Clean Air Status and Trends Network (CASTNET) ambient concentrations. Second, a measurement–model fusion approach employing a precipitation and bias correction to wet-deposition estimates is found to reduce model bias and improve correlations compared to the unadjusted model values. Model agreement of wet deposition is poor over parts of the West and Northern Rockies, due to errors in precipitation estimates caused by complex terrain and uncertainty in emissions at the relatively coarse 12 km grid resolution used in this study. Next, we assess modeled N and S deposition trends across climatologically consistent regions in the CONUS. Total deposition of N and S in the eastern US is larger than the western US with a steeper decreasing trend from 2002–2017; i.e., total N declined at a rate of approximately -0.30 kg N ha-1 yr-1 in the Northeast and Southeast and by -0.02 kg N ha-1 yr-1 in the Northwest and Southwest. Widespread increases in reduced N deposition across the Upper Midwest, Northern Rockies, and West indicate evolving atmospheric composition due to increased precipitation amounts over some areas, growing agricultural emissions, and regional NOx/SOx emission reductions shifting gas–aerosol partitioning; these increases in reduced N deposition are generally masked by the larger decreasing oxidized N trend. We find larger average declining trends of total N and S deposition between 2002–2009 than 2010–2017, suggesting a slowdown of the rate of decline likely in response to smaller emission reductions. Finally, we document changes in the modeled total N and S deposition budgets. The average annual total N deposition budget over the CONUS decreases from 7.8 in 2002 to 6.3 kg N ha-1 yr-1 in 2017 due to declines in oxidized N deposition from NOx emission controls. Across the CONUS during the 2002–2017 time period, the average contribution of dry deposition to the total N deposition budget drops from 60 % to 52 %, whereas wet deposition dominates the S budget rising from 45 % to 68 %. Our analysis extends upon the literature documenting the growing contribution of reduced N to the total deposition budget, particularly in the Upper Midwest and Northern Rockies, and documents a slowdown of the declining oxidized N deposition trend, which may have consequences on vegetation diversity and productivity.
... The N1, N3, and N5 treatments were designed to test the direct fertilizing effect of N deposition via N addition alone on vegetation and its variability. In comparison, current N deposition rate in the Arctic is around 0.1 to ~1 g N m −2 year −1 [29] and is around 0.75 to ~4 g N m −2 year −1 in the alpine tundra of Europe [53]. Therefore, although the N level used here may seem high, it could reflect extreme levels to be encountered Table 1. ...
... The N1, N3, and N5 treatments were designed to test the direct fertilizing effect of N deposition via N addition alone on vegetation and its variability. In comparison, current N deposition rate in the Arctic is around 0.1 to~1 g N m −2 year −1 [29] and is around 0.75 to~4 g N m −2 year −1 in the alpine tundra of Europe [53]. Therefore, although the N level used here may seem high, it could reflect extreme levels to be encountered locally in the future in the context of increasing N deposition worldwide [54]. ...
... We simulated the anticipated increase in nutrient availability in the Arctic tundra due to increasing atmospheric N deposition in the Canadian High-Arctic [29,83] with our N addition treatments. We also simulated an overall increase in nutrient availability due to the indirect effect of global warming with our combined N/P addition treatments, as warming should lead to greater soil mineralization [64,84]. ...
Nutrient availability for tundra vegetation could change drastically due to increasing temperatures and frequency of nitrogen deposition in the Arctic. Few studies have simultaneously examined the response of plant communities to these two pressures over a long period. This study aims to assess which driver between increasing nitrogen (N) and phosphorus (P) availability through global warming and increasing N availability alone via N deposition is more likely to transform arctic wetland vegetation and whether there is a time lag in this response. An annual fertilization experiment simulating these nutrient inputs was conducted for 17 years in the Canadian High-Arctic to assess the impact on aboveground net primary productivity, floristic composition, and plant nutrient concentration. While the primary productivity of mosses remains unchanged by fertilization after 17 years, productivity of graminoids was increased slightly by N addition (36% increase at the highest dose). In contrast, the primary productivity of graminoids increased strongly with N/P addition (over 227% increase). We noted no difference in graminoid productivity between the 2nd and 5th year of the experiment, but we observed a 203% increase between the 5th and 17th year in the N/P addition treatments. We also noted a 49% decrease in the total moss cover and an 155% increase in the total graminoid cover between the 2nd and 17th year of N/P addition. These results indicate that the impact of warming through increased N/P availability was greater than those of N deposition alone (N addition) and promoted the transition from a moss-dominated tundra to a graminoid-dominated tundra. However, this transition was subject to a time lag of up to 17 years, suggesting that increased productivity of graminoids resulted from a release of nutrients via the decomposition of lower parts of the moss mat.
