Dataset Information

Twenty-two years of warming, fertilisation and shading of subarctic heath shrubs promote secondary growth and plasticity but not primary growth.

ABSTRACT: Most manipulation experiments simulating global change in tundra were short-term or did not measure plant growth directly. Here, we assessed the growth of three shrubs (Cassiope tetragona, Empetrum hermaphroditum and Betula nana) at a subarctic heath in Abisko (Northern Sweden) after 22 years of warming (passive greenhouses), fertilisation (nutrients addition) and shading (hessian fabric), and compare this to observations from the first decade of treatment. We assessed the growth rate of current-year leaves and apical stem (primary growth) and cambial growth (secondary growth), and integrated growth rates with morphological measurements and species coverage. Primary- and total growth of Cassiope and Empetrum were unaffected by manipulations, whereas growth was substantially reduced under fertilisation and shading (but not warming) for Betula. Overall, shrub height and length tended to increase under fertilisation and warming, whereas branching increased mostly in shaded Cassiope. Morphological changes were coupled to increased secondary growth under fertilisation. The species coverage showed a remarkable increase in graminoids in fertilised plots. Shrub response to fertilisation was positive in the short-term but changed over time, likely because of an increased competition with graminoids. More erected postures and large, canopies (requiring enhanced secondary growth for stem reinforcement) likely compensated for the increased light competition in Empetrum and Cassiope but did not avoid growth reduction in the shade intolerant Betula. The impact of warming and shading on shrub growth was more conservative. The lack of growth enhancement under warming suggests the absence of long-term acclimation for processes limiting biomass production. The lack of negative effects of shading on Cassiope was linked to morphological changes increasing the photosynthetic surface. Overall, tundra shrubs showed developmental plasticity over the longer term. However, such plasticity was associated clearly with growth rate trends only in fertilised plots.

SUBMITTER: Campioli M

PROVIDER: S-EPMC3325270 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Twenty-two years of warming, fertilisation and shading of subarctic heath shrubs promote secondary growth and plasticity but not primary growth.

Campioli Matteo M Leblans Niki N Michelsen Anders A

PloS one 20120412 4

Most manipulation experiments simulating global change in tundra were short-term or did not measure plant growth directly. Here, we assessed the growth of three shrubs (Cassiope tetragona, Empetrum hermaphroditum and Betula nana) at a subarctic heath in Abisko (Northern Sweden) after 22 years of warming (passive greenhouses), fertilisation (nutrients addition) and shading (hessian fabric), and compare this to observations from the first decade of treatment. We assessed the growth rate of current ...[more]

PMID: 22511968

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Project description:Background and aimsClimate change is subjecting subarctic ecosystems to elevated temperature, increased nutrient availability and reduced light availability (due to increasing cloud cover). This may affect subarctic vegetation by altering the emissions of biogenic volatile organic compounds (BVOCs) and leaf anatomy. We investigated the effects of increased nutrient availability on BVOC emissions and leaf anatomy of three subarctic dwarf shrub species, Empetrum hermaphroditum, Cassiope tetragona and Betula nana, and if increased nutrient availability modifies the responses to warming and shading.MethodsMeasurements of BVOCs were performed in situ in long-term field experiments in the Subarctic using a dynamic enclosure system and collection of BVOCs into adsorbent cartridges analysed by gas chromatography-mass spectrometry. Leaf anatomy was studied using light microscopy and scanning electron microscopy.Key resultsIncreased nutrient availability increased monoterpene emission rates and altered the emission profile of B. nana, and increased sesquiterpene and oxygenated monoterpene emissions of C. tetragona. Increased nutrient availability increased leaf tissue thicknesses of B. nana and C. tetragona, while it caused thinner epidermis and the highest fraction of functional (intact) glandular trichomes for E. hermaphroditum. Increased nutrient availability and warming synergistically increased mesophyll intercellular space of B. nana and glandular trichome density of C. tetragona, while treatments combining increased nutrient availability and shading had an opposite effect in C. tetragona.ConclusionsIncreased nutrient availability may enhance the protection capacity against biotic and abiotic stresses (especially heat and drought) in subarctic shrubs under future warming conditions as opposed to increased cloudiness, which could lead to decreased resistance. The study emphasizes the importance of changes in nutrient availability in the Subarctic, which can interact with climate warming and increased cloudiness effects.

Project description:Traditionally, biogenic volatile organic compound (BVOC) emissions are often considered a unidirectional flux, from the ecosystem to the atmosphere, but recent studies clearly show the potential for bidirectional exchange. Here we aimed to investigate how warming and leaf litter addition affect the bidirectional exchange (flux) of BVOCs in a long-term field experiment in the Subarctic. We also assessed changes in net BVOC fluxes in relation to the time of day and the influence of different plant phenological stages. The study was conducted in a full factorial experiment with open top chamber warming and annual litter addition treatments in a tundra heath in Abisko, Northern Sweden. After 18 years of treatments, ecosystem-level net BVOC fluxes were measured in the experimental plots using proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS). The warming treatment increased monoterpene and isoprene emissions by ≈50%. Increasing temperature, due to diurnal variations, can both increase BVOC emission and simultaneously, increase ecosystem uptake. For any given treatment, monoterpene, isoprene, and acetone emissions also increased with increasing ambient air temperatures caused by diurnal variability. Acetaldehyde, methanol, and sesquiterpenes decreased likely due to a deposition flux. For litter addition, only a significant indirect effect on isoprene and monoterpene fluxes (decrease by ~50%-75%) was observed. Litter addition may change soil moisture conditions, leading to changes in plant species composition and biomass, which could subsequently result in changes to BVOC emission compositions. Phenological stages significantly affected fluxes of methanol, isoprene and monoterpenes. We suggest that plant phenological stages differ in impacts on BVOC net emissions, but ambient air temperature and photosynthetically active radiation (PAR) also interact and influence BVOC net emissions differently. Our results may also suggest that BVOC fluxes are not only a response to changes in temperature and light intensity, as the circadian clock also affects emission rates.

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Dataset Information

Twenty-two years of warming, fertilisation and shading of subarctic heath shrubs promote secondary growth and plasticity but not primary growth.

Publications

Twenty-two years of warming, fertilisation and shading of subarctic heath shrubs promote secondary growth and plasticity but not primary growth.

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