Author: isabel

To what extent herbivores concomitantly alter silicon-based defence and nutrient levels in tundra grasses will ultimately determine changes in the quality of their pastures. In this study, we asked to what extent keystone tundra herbivores, small rodents and reindeer, affect silicon content and silicon:nutrient ratios of grasses found in tundra-grasslands.

Herbivores did not promote a net silicon accumulation in grasses, but rather enhanced their quality by increasing leaf nitrogen and phosphorus levels, thus decreasing silicon:nutrient ratios. Yet, the magnitude of these quality increments varied depending on the herbivore(s) involved and differed between inherently silicon-rich and silicon-poor grasses, ultimately leading to the formation of a fine-scale mosaic of tundra-patches with different nutrient values. In tundra-patches utilised by both herbivores, the quality of inherently silicon-rich grasses was further decreased relative to that of the already more palatable silicon-poor grasses. This could provide an advantage against herbivory, potentially being one of the pathways through which tundra-grassland vegetation states dominated by silicon-rich grasses are generally maintained by herbivores.

Reference: Petit Bon, M., Inga, K.G., Utsi, T.A., Jónsdóttir, I.S. and Bråthen, K.A. (2022), Forage quality in tundra grasslands under herbivory: Silicon-based defences, nutrients, and their ratios in grasses. Journal of Ecology 110(1): 129-143. https://doi.org/10.1111/1365-2745.13790

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Text: Matteo Petit Bon, Czech Academy of Sciences.

Picture: The fence built in the 1950s at Ifjordfjellet, Finnmark, separates spring/fall migratory and summer pasture ranges for semi-domesticated reindeer (Photo: Matteo Petit-Bon).

As vegetation and soil jointly regulate whole-ecosystem processes, differential sensitivity and magnitude of their carbon and nitrogen responses to environmental perturbations may have implications for the functioning of tundra ecosystems. In this study, we addressed sensitivity and magnitude of short-term carbon and nitrogen responses of vascular plants, mosses, and soil to simulated goose disturbance and warming across three habitats that differ in soil moisture in a high-Arctic ecosystem in Svalbard.

Though the system’s total carbon and nitrogen contents were relatively resistant to both perturbations, the three studied ecosystem compartments still differed in their chemical responses (vascular plants > soil > mosses), and such differential sensitivity was further exacerbated by their different responses across habitats (mesic > moist > wet).

These findings highlight the potential for environmental perturbations to have small, yet differential short-term impacts on the carbon and nitrogen contents of vascular plants, mosses, and soil, both within and between tundra-habitats. They also imply that assessments of a single ecosystem compartment in a given context cannot be extrapolated to the whole ecosystem, suggesting that addressing vegetation and soil chemical responses in different habitats can advance our predictive capability of how the biogeochemistry of tundra ecosystems respond to environmental changes.

Reference: Petit Bon, M., Böhner, H., Bråthen, K. A., Ravolainen, V. T., and Jónsdóttir, I. S.. 2021. Variable responses of carbon and nitrogen contents in vegetation and soil to herbivory and warming in high-Arctic tundra. Ecosphere 12( 9):e03746. https://doi.org/10.1002/ecs2.3746

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Text: Matteo Petit Bon, Czech Academy of Sciences.

Picture: Pink-footed geese after their arrival in Svalbard (Photo: Matteo Petit-Bon).

Insect herbivory is a significant source of plant stress and, due to climate change, the herbivory stress is continuously increasing. In the Arctic, where climate warming proceeds with the rate twice of the global average, insect herbivory stress to vegetation is expected to become more severe. In response to herbivory, plants produce specialized metabolites to fulfil physiological and ecological functions, which include volatile organic compounds (VOCs). VOCs are highly reactive and play an important role in biosphere-atmosphere interactions. Various biotic and abiotic stressors, including insect herbivory, can enhance and/or induce the production of many VOCs and alter the composition of the overall VOC blend emitted from the plants.

Due to lack of the empirical studies in the Arctic, it is unclear how the effects of insect herbivory and changing climate such as warming and increased cloudiness, which are both predicted conditions for the future Arctic, will affect VOC emissions in the changing Arctic.

Therefore, in this study we assessed how experimental manipulations of temperature and light availability in subarctic tundra, that had been maintained for 30 years at the time of the measurements, affect the VOC emissions from a widespread dwarf birch when subjected to herbivory by local geometrid moth larvae, the autumnal moth and the winter moth.

Our study showed that whether the future subarctic tundra in Northern Fennoscandia experiences rising temperatures or increasing cloudiness, and therefore milder temperature increases, matter very little for herbivory-related VOC emissions. Under both conditions, we showed strong interactions with herbivory effects on VOC emissions with potentially positive feedbacks on cloud formation. We also show that acclimation of plants to long-term climate treatments, which has resulted in changes in anatomical traits, might strongly interact with volatile responses to insect herbivory. This finding further complicates predictions of how climate change, together with interacting biotic stresses, affects VOC emissions in the Arctic.

Full article here:  https://doi.org/10.1111/gcb.15773

Reference: Rieksta, J., Li, T., Michelsen, A., & Rinnan, R. (2021). Synergistic effects of insect herbivory and changing climate on plant volatile emissions in the subarctic tundra. Global Change Biology, 27(20), 5030-5042.

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Text: Jolanta Rieksta, University of Copenhagen.

Picture: Measuring volatile organic compound (VOC) emissions from dwarf birch in the field using branch enclosure method where VOC are collected using custom built pull-push systems. (Photo: Jolanta Rieksta).