Svalbard reindeer winter diets: Long-term dietary shifts to graminoids in response to a changing climate

Arctic ecosystems are changing dramatically with warmer and wetter conditions resulting in complex interactions between herbivores and their forage. We investigated how Svalbard reindeer (Rangifer tarandus platyrhynchus) modify their late winter diets in response to long-term trends and interannual variation in forage availability and accessibility. By reconstructing their diets and foraging niches over a 17-year period (1995–2012) using serum δ13C and δ15N values, we found strong support for a temporal increase in the proportions of graminoids in the diets with a concurrent decline in the contributions of mosses. This dietary shift corresponds with graminoid abundance increases in the region and was associated with increases in population density, warmer summer temperatures and more frequent rain-on-snow (ROS) in winter. In addition, the variance in isotopic niche positions, breadths, and overlaps also supported a temporal shift in the foraging niche and a dietary response to extreme ROS events. Our long-term study highlights the mechanisms by which winter and summer climate changes cascade through vegetation shifts and herbivore population dynamics to alter the foraging niche of Svalbard reindeer. Although it has been anticipated that climate changes in the Svalbard region of the Arctic would be detrimental to this unique ungulate, our study suggests that environmental change is in a phase where conditions are improving for this subspecies at the northernmost edge of the Rangifer distribution

Global Distribution of Human Protoparvoviruses

Development of next-generation sequencing and metagenomics has revolutionized detection of novel viruses. Among these viruses are 3 human protoparvoviruses: bufavirus, tusavirus, and cutavirus. These viruses have been detected in feces of children with diarrhea. In addition, cutavirus has been detected in skin biopsy specimens of cutaneous T-cell lymphoma patients in France and in 1 melanoma patient in Denmark. We studied seroprevalences of IgG against bufavirus, tusavirus, and cutavirus in various populations (n = 840), and found a striking geographic difference in prevalence of bufavirus IgG. Although prevalence was low in adult populations in Finland (1.9%) and the United States (3.6%), bufavirus IgG was highly prevalent in populations in Iraq (84.8%), Iran (56.1%), and Kenya (72.3%). Conversely, cutavirus IgG showed evenly low prevalences (0%-5.6%) in all cohorts, and tusavirus IgG was not detected. These results provide new insights on the global distribution and endemic areas of protoparvoviruses

Location of studies and evidence of effects of herbivory on Arctic vegetation: a systematic map

Herbivores modify the structure and function of tundra ecosystems. Understanding their impacts is necessary to assess the responses of these ecosystems to ongoing environmental changes. However, the effects of herbivores on plants and ecosystem structure and function vary across the Arctic. Strong spatial variation in herbivore effects implies that the results of individual studies on herbivory depend on local conditions, i.e., their ecological context. An important first step in assessing whether generalizable conclusions can be produced is to identify the existing studies and assess how well they cover the underlying environmental conditions across the Arctic. This systematic map aims to identify the ecological contexts in which herbivore impacts on vegetation have been studied in the Arctic. Specifically, the primary question of the systematic map was: “What evidence exists on the effects of herbivores on Arctic vegetation?”

Ecosystem-level consequences of climate warming in tundra under differing grazing pressures by reindeer

Abstract Grazing by reindeer (Rangifer tarandus L.) affects vegetation and soil microbial processes in tundra ecosystems. It is considered that grazing can induce two alternative vegetation states that differ in plant species composition and the rate of nutrient cycling. I hypothesised that these alternative vegetation states differ in ecosystem responses to climate warming. I tested the hypothesis using a factorial warming and fertilisation experiment on long-term lightly grazed (LG) and heavily grazed (HG) tundra. The reindeer grazing induced vegetation shift from dwarf shrubs to graminoids increased microbial activities for SOM decomposition. The grazer-induced shifts in vegetation and microbial activities in combination with the fertilisation via urine and faeces had important consequences on soil N availability and soil C quality that determined the ecosystem-level consequences of climate warming. Due to higher soil N availability, warming increased plant productivity (GEP) on HG but not on LG tundra, where N limitation prevented the warming-increased plant production. The varying effects of warming on GEP at different grazing intensities determined the effects of warming on ecosystem net C sink, which was unaffected by warming on HG but decreased on LG tundra. Reindeer grazing reduced the soil C quality, as soils under LG stored a higher proportion of carbohydrates vulnerable to microbial decomposition than soils under HG. According to laboratory soil incubations, the grazer-induced reduction in soil C quality mitigated the responses of soil microbial activity to prolonged warming. Warming caused a stronger decrease in concentrations of phenolics, an important means of plant defence against biotic and abiotic stresses, in Empetrum nigrum ssp. hermaphroditum under HG than LG. Grazing history by reindeer, with the associated vegetation shift from dwarf shrubs to graminoids, can significantly alter the ecosystem-level consequences of climate warming. Overall, this thesis highlights that the effects of reindeer grazing on soil properties, soil N availability and C quality, are important determinants of the ecosystem responses to climate warming. Therefore, future research on climate warming should take into account herbivores and aim towards a more holistic approach that includes both aboveground and belowground components of the ecosystem.Tiivistelmä Tundralla porolaidunnus vaikuttaa kasvillisuuteen ja maaperän mikrobien toimintaan. Porolaidunnus voi aikaansaada kaksi vaihtoehtoista kasvillisuuden tilaa, jotka eroavat toisistaan paitsi kasvilajiston myös ravinnekierron suhteen. Esitin hypoteesin, jonka mukaan ilmaston lämpenemisen vaikutukset eroavat tundratyypeillä, jotka edustavat vaihtoehtoisia kasvillisuustiloja. Testasin hypoteesia faktoriaalisen lämmitys- ja lannoituskokeen avulla tundra-alueilla, joilla poron laidunnuspaine on ollut pitkäaikaisesti joko kevyttä tai voimakasta. Poron aiheuttama kasvillisuusmuutos varpuvaltaisesta heinävaltaiseksi lisäsi maaperän mikrobien hajotusaktiivisuutta. Poron aiheuttamat erot kasvillisuudessa ja mikrobiaktiivisuuksissa yhdessä virtsan ja papanoiden lannoittavan vaikutuksen kanssa muuttivat maaperän typen saatavuutta sekä hiilen laatua. Erot maaperän ominaisuuksissa puolestaan ohjasivat ilmaston lämpenemisen ekosysteemitason vaikutuksia. Lämmitys kasvatti ekosysteemituotantoa ravinteikkaalla voimakkaasti laidunnetulla tundralla mutta ei kevyesti laidunnetulla tundralla, joka oli typpirajoitteinen. Lämmityksen erilaiset vaikutukset ekosysteemituotantoon eri laidunpaineissa määrittivät lämmityksen vaikutuksen ekosysteemin hiilinieluun, joka pysyi muuttumattomana voimakkaasti laidunnetulla tundralla mutta pieneni kevyesti laidunnetulla tundralla. Porolaidunnus alensi maaperän hiilen laatua, ja kevyesti laidunnetulla tundralla maaperässä oli enemmän mikrobien hajotukselle alttiita hiilihydraatteja kuin voimakkaasti laidunnetulla tundralla. Laboratoriossa suoritetun inkubaatiokokeen perusteella maaperän hiilen alhaisempi laatu lievensi mikrobien hajotusaktiivisuuden vastetta pitkäaikaiseen lämmitykseen. Lämmitys vähensi pohjanvariksenmarjan fenoliyhdisteiden, jotka ovat tärkeä osa kasvien puolustusta bioottisia ja abioottisia stressitekijöitä vastaan, pitoisuuksia enemmän voimakkaasti kuin kevyesti laidunnetulla tundralla. Poron laidunnushistoria yhdessä kasvillisuusmuutoksen kanssa voi merkittävästi vaikuttaa ilmaston lämpenemisen ekosysteemitason seurauksiin. Tämän väitöstyön tulokset osoittavat, että poron vaikutukset maaperän typpeen ja hiileen määrittävät lämpenemisen vaikutukset ekosysteemissä. Tulevaisuudessa ilmastonmuutostutkimuksen pitäisikin kokonaisvaltaisemmin huomioida sekä herbivorian että ekosysteemin eri osien merkitys

Plant and soil nitrogen in oligotrophic boreal forest habitats with varying moss depths:does exclusion of large grazers matter?

The boreal forest consists of drier sunlit and moister-shaded habitats with varying moss abundance. Mosses control vascular plant–soil interactions, yet they all can also be altered by grazers. We determined how 2 decades of reindeer (Rangifer tarandus) exclusion affect feather moss (Pleurozium schreberi) depth, and the accompanying soil N dynamics (total and dissolvable inorganic N, δ(15)N), plant foliar N, and stable isotopes (δ(15)N, δ(13)C) in two contrasting habitats of an oligotrophic Scots pine forest. The study species were pine seedling (Pinus sylvestris L.), bilberry (Vaccinium myrtillus L.), lingonberry (V. vitis-idaea L.), and feather moss. Moss carpet was deeper in shaded than sunlit habitats and increased with grazer exclusion. Humus N content increased in the shade as did humus δ(15)N, which also increased due to exclusion in the sunlit habitats. Exclusion increased inorganic N concentration in the mineral soil. These soil responses were correlated with moss depth. Foliar chemistry varied due to habitat depending on species identity. Pine seedlings showed higher foliar N content and lower foliar δ(15)N in the shaded than in the sunlit habitats, while bilberry had both higher foliar N and δ(15)N in the shade. Thus, foliar δ(15)N values of co-existing species diverged in the shade indicating enhanced N partitioning. We conclude that despite strong grazing-induced shifts in mosses and subtler shifts in soil N, the N dynamics of vascular vegetation remain unchanged. These indicate that plant–soil interactions are resistant to shifts in grazing intensity, a pattern that appears to be common across boreal oligotrophic forests. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00442-021-04957-0

Plant and soil nitrogen in oligotrophic boreal forest habitats with varying moss depths:does exclusion of large grazers matter?

Abstract The boreal forest consists of drier sunlit and moister-shaded habitats with varying moss abundance. Mosses control vascular plant–soil interactions, yet they all can also be altered by grazers. We determined how 2 decades of reindeer (Rangifer tarandus) exclusion affect feather moss (Pleurozium schreberi) depth, and the accompanying soil N dynamics (total and dissolvable inorganic N, δ¹⁵N), plant foliar N, and stable isotopes (δ¹⁵N, δ¹³C) in two contrasting habitats of an oligotrophic Scots pine forest. The study species were pine seedling (Pinus sylvestris L.), bilberry (Vaccinium myrtillus L.), lingonberry (V. vitis-idaea L.), and feather moss. Moss carpet was deeper in shaded than sunlit habitats and increased with grazer exclusion. Humus N content increased in the shade as did humus δ¹⁵N, which also increased due to exclusion in the sunlit habitats. Exclusion increased inorganic N concentration in the mineral soil. These soil responses were correlated with moss depth. Foliar chemistry varied due to habitat depending on species identity. Pine seedlings showed higher foliar N content and lower foliar δ¹⁵N in the shaded than in the sunlit habitats, while bilberry had both higher foliar N and δ¹⁵N in the shade. Thus, foliar δ¹⁵N values of co-existing species diverged in the shade indicating enhanced N partitioning. We conclude that despite strong grazing-induced shifts in mosses and subtler shifts in soil N, the N dynamics of vascular vegetation remain unchanged. These indicate that plant–soil interactions are resistant to shifts in grazing intensity, a pattern that appears to be common across boreal oligotrophic forests

Contrasting impacts of short- and long-term large herbivore exclusion on understory net CO₂ exchange in a boreal forest

Abstract Across boreal forests, trees are the main living biomass carbon (C) stock, but the understory vegetation can contribute significantly to the C cycling and net forest carbon dioxide (CO₂) balance. The patchy understory vegetation, which consists of sunlit (i.e. lichen-like) and shaded habitats (i.e. dwarf shrub-like), is often altered by ungulate grazers. Grazers may influence understory CO₂ exchange and, consequently, the forest CO₂ balance. Grazing affects differently the biomass of slow-growing lichens compared to the faster-growing mosses and dwarf shrubs, and therefore the effects of grazing on CO₂ exchange in the patchy understory vegetation may vary temporally. We studied how excluding grazing for short and long periods affects the CO₂ exchange and vegetation biomass in the understory of an oligotrophic Scots pine forest. We measured growing season (2019, 2020) CO₂ exchange across sunlit and shaded habitats inside fences that had excluded large grazers for 0–1 and 25–26 years and in the adjacent grazed area. In addition, we measured the height of understory vegetation. We found that short-term grazer exclusion increased ecosystem CO₂ source fluxes only in the shaded habitats. However, long-term exclusion of grazing decreased CO₂ net release regardless of the habitat type. Furthermore, grazer exclusion increased moss depth immediately, which coincided with an abrupt intensification of CO₂ net release. Considering the impacts of grazing over both short- and long-term periods may help to forecast C fluxes more accurately, which may be relevant for informed climate solutions regionally and even on a larger scale

Resistance and change in a High Arctic ecosystem, NW Greenland:differential sensitivity of ecosystem metrics to 15 years of experimental warming and wetting

Abstract Dramatic increases in air temperature and precipitation are occurring in the High Arctic (>70 °N), yet few studies have characterized the long-term responses of High Arctic ecosystems to the interactive effects of experimental warming and increased rain. Beginning in 2003, we applied a factorial summer warming and wetting experiment to a polar semidesert in northwest Greenland. In summer 2018, we assessed several metrics of ecosystem structure and function, including plant cover, greenness, ecosystem CO₂ exchange, aboveground (leaf, stem) and belowground (litter, root, soil) carbon (C) and nitrogen (N) concentrations (%) and pools, as well as leaf and soil stable isotopes (δ¹³C and δ¹⁵N). Wetting induced the most pronounced changes in ecosystem structure, accelerating the expansion of S. arctica cover by 370% and increasing aboveground C, N, and biomass pools by 94–101% and root C, N, and biomass pools by 60–122%, increases which coincided with enhanced net ecosystem CO₂ uptake. Further, wetting combined with warming enhanced plot-level greenness, whereas in isolation neither wetting nor warming had an effect. At the plant level the effects of warming and wetting differed among species and included warming-linked decreases in leaf N and δ¹⁵N in Salix arctica, whereas leaf N and δ¹⁵N in Dryas integrifolia did not respond to the climate treatments. Finally, neither plant- nor plot-level C and N allocation patterns nor soil C, N, δ¹³C, or δ¹⁵N concentrations changed in response to our manipulations, indicating that these ecosystem metrics may resist climate change, even in the longer term. In sum, our results highlight the importance of summer precipitation in regulating ecosystem structure and function in arid parts of the High Arctic, but they do not completely refute previous findings of resistance in some High Arctic ecosystem properties to climate change

Long-term grazing intensity by reindeer alters the response of the soil micro-food web to simulated climate change in subarctic tundra

Abstract 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