Biomass and nutrient responses of a clonal tundra sedge to climate warming

Jónsdóttir, Ingibjörg S.; Khitun, Olga KhitunO.; Stenström, Anna

doi:10.1139/b05-129

Cited by 29 publications

(25 citation statements)

References 58 publications

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“…In addition, arctic plants that respond to warming with earlier development tend to have lower N and P pools after 3 years of treatment (Michelsen et al ., ; Welker et al ., ), although there have also been reports of the converse (e.g. Carex bigelowii , Jónsdóttir et al ., ). This latter point may explain why phenology was less advanced in 2005, the third consecutive year of warming, than in 2004 (0.14 phenology index units difference vs. 0.08 units).…”

Section: Discussionmentioning

confidence: 97%

Aphid–willow interactions in a high Arctic ecosystem: responses to raised temperature and goose disturbance

Gillespie

Jónsdóttir

Hodkinson

et al. 2013

Global Change Biology

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Recently, there have been several studies using open top chambers (OTCs) or cloches to examine the response of Arctic plant communities to artificially elevated temperatures. Few, however, have investigated multitrophic systems, or the effects of both temperature and vertebrate grazing treatments on invertebrates. This study investigated trophic interactions between an herbivorous insect (Sitobion calvulum, Aphididae), a woody perennial host plant (Salix polaris) and a selective vertebrate grazer (barnacle geese, Branta leucopsis). In a factorial experiment, the responses of the insect and its host to elevated temperatures using open top chambers (OTCs) and to three levels of goose grazing pressure were assessed over two summer growing seasons (2004 and 2005). OTCs significantly enhanced the leaf phenology of Salix in both years and there was a significant OTC by goose presence interaction in 2004. Salix leaf number was unaffected by treatments in both years, but OTCs increased leaf size and mass in 2005. Salix reproduction and the phenology of flowers were unaffected by both treatments. Aphid densities were increased by OTCs but unaffected by goose presence in both years. While goose presence had little effect on aphid density or host plant phenology in this system, the OTC effects provide interesting insights into the possibility of phenological synchrony disruption. The advanced phenology of Salix effectively lengthens the growing season for the plant, but despite a close association with leaf maturity, the population dynamics of the aphid appeared to lack a similar phenological response, except for the increased population observed.

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Section: Discussionmentioning

confidence: 97%

Aphid–willow interactions in a high Arctic ecosystem: responses to raised temperature and goose disturbance

Gillespie

Jónsdóttir

Hodkinson

et al. 2013

Global Change Biology

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“…N:P RE values <1 demonstrate higher efficiency in resorbing P with respect to N, as observed in most studies (Jiang et al, ; Vergutz et al, ). A possible explanation resides in the different mobility of N and P, with a larger proportion of N than of P locked in structural compounds (Jónsdóttir, Khitun, & Stenström, ). While at the global scale N:P resorption ratios reflect soil N and P stoichiometry (Reed, Townsend, Davidson, & Cleveland, ), we did not observe any significant relationship between N:P RE and soil N:P. This suggests that at the local scale, the differential efficiency in resorbing nutrients is determined more by the relative cost of resorbing nutrients than by the absolute soil nutrient levels and their stoichiometric ratio (Tang et al, ; Wright & Westoby, ).…”

Section: Discussionmentioning

confidence: 99%

Differential effects of soil chemistry on the foliar resorption of nitrogen and phosphorus across altitudinal gradients

2019

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Nutrient resorption from senescing leaves prior to litterfall is a strategy for nutrient conservation in vascular plants. However, the mechanisms through which soil fertility and/or foliar nutrient status affect nutrient resorption are not yet fully known. We used two 1,000‐m‐wide altitudinal gradients on two different bedrock types (carbonate and silicate) for analysing the interactive effects of temperature and soil chemistry on the resorption efficiency of two major nutrients, nitrogen (N) and phosphorus (P). Our objective was to assess how nutrient resorption varied across the gradients through the adaptation of individual species to changing environmental conditions rather than through changes in species composition. Both N and P resorption efficiency increased across the altitudinal gradients independent of bedrock type. The main process regulating nutrient resorption was a negative feedback to nutrient availability in the soil. The negative feedback of nutrient resorption efficiency to soil nutrient status was unrelated to total soil nutrient contents but depended on concentrations of organic N forms for nitrogen resorption efficiency (NRE) and on inorganic P forms for phosphorus resorption efficiency (PRE), respectively. While we hypothesized that the resorption of P, as a principally rock‐derived nutrient, depended on physical–chemical processes affected by soil chemistry, our results showed that microbial P mineralization was the main source of inorganic P supply to the plants. Both NRE and PRE were effective to improve the growth potential of plants, but there was no evidence of stoichiometric adaptations of N:P RE‐to‐nutrient ratio in the soil. A plain language summary is available for this article.

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“…To better visualize this relationship, we used our LMMs to project values of N on the coastal plain across the growing season for different dates of peak NDVI (Fig. Warmer summer temperatures and accelerated phenology have been associated with increases in plant biomass, but reductions in concentrations of forage nitrogen (J onsd ottir et al 2005(J onsd ottir et al , Doiron et al 2014, although the responses of individual species are mixed (Welker et al 2005) and can exhibit complex dynamics (Zamin et al 2017). Earlier dates of peak NDVI were associated with earlier seasonal declines in forage N, resulting in particularly low N values late in the summer when female caribou need to amass body stores for future reproduction Parker 2008, Gustine et al 2017).…”

Section: Discussionmentioning

confidence: 99%

NDVI exhibits mixed success in predicting spatiotemporal variation in caribou summer forage quality and quantity

Johnson

Gustine²,

Golden

et al. 2018

Ecosphere

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The satellite-derived Normalized Difference Vegetation Index (NDVI) is commonly used by researchers and managers to represent ungulate forage conditions in landscapes across the globe, despite limited information about how it compares to empirical measurements of forage quality and quantity. The application of NDVI as a forage metric is particularly appealing for studying migratory caribou (Rangifer tarandus) in remote Arctic ecosystems, where field assessments are logistically and financially prohibitive, and climate-mediated changes in vegetation have been hypothesized to influence population declines. To determine the utility of NDVI for adequately representing caribou forage conditions, we compared NDVI derived from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery to empirical measures of caribou forage biomass, nitrogen, digestible nitrogen, and digestible energy within the summer range of the Central Arctic Caribou Herd on the North Slope of Alaska. Specifically, we determined the strength of forage-NDVI relationships at the start of the growing season and across the summer, assessed the efficacy of NDVI variables for modeling spatiotemporal variation in field measurements of different forage components, and used long-term MODIS data to estimate temporal changes in forage between 2000 and 2016. We found that NDVI values were weakly correlated with caribou forage quality at the start of the growing season and throughout the summer. Although linear models of forage-NDVI relationships performed poorly, NDVI variables (NDVI and the number of days from when NDVI reached its maximum value) were useful for modeling spatiotemporal variation in empirical measurements of forage components across the growing season, but only when we incorporated nonlinear forage-NDVI relationships and other habitat covariates. Phenological advances in the date of peak NDVI were associated with significant changes in forage conditions, particularly nitrogen, which exhibited earlier seasonal declines. Using long-term MODIS data, predicted values of forage nitrogen declined between 2000 and 2016, driven by exceedingly low values in 2014 and 2015. Given our results, we caution the application of NDVI as a general (linear) proxy of caribou forage conditions across the growing season, and encourage practitioners to use NDVI variables to model spatiotemporal variation in specific forage conditions from empirical field data, accounting for nonlinear forage-NDVI relationships.

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Biomass and nutrient responses of a clonal tundra sedge to climate warming

Cited by 29 publications

References 58 publications

Aphid–willow interactions in a high Arctic ecosystem: responses to raised temperature and goose disturbance

Aphid–willow interactions in a high Arctic ecosystem: responses to raised temperature and goose disturbance

Differential effects of soil chemistry on the foliar resorption of nitrogen and phosphorus across altitudinal gradients

NDVI exhibits mixed success in predicting spatiotemporal variation in caribou summer forage quality and quantity

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