Microclimatic response to increasing shrub cover and its effect on <i>Sphagnum</i> CO<sub>2</sub> exchange in a bog

Chong, Mandy; Humphreys, Elyn; Moore, Tim R.

doi:10.2980/19-1-3489

Cited by 26 publications

(25 citation statements)

References 61 publications

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“…The initial trend of increasing ecosystem CO 2 uptake under the highest NPK load with increases in vascular plant biomass was reversed after 5 years when Sphagnum was out‐competed due to shading, litter burial, and possibly toxic effects (Bubier et al ., ). After 8 years, the treatment differences in mid‐season photosynthesis remained small and the vascular plant biomass shifted to more woody than foliar components, presumably due to competition for light (Juutinen et al ., ; Chong et al ., ). At Whim Bog, wet N deposition did not significantly disrupt the main shrub Calluna, but reduced the cover of Sphagnum (Sheppard et al ., ) and increased Sphagnum gross photosynthesis after 8 years compared with unfertilized controls (Kivimäki et al ., ).…”

Section: Introductionmentioning

confidence: 99%

Vegetation feedbacks of nutrient addition lead to a weaker carbon sink in an ombrotrophic bog

Larmola

Bubier

Kobyljanec

et al. 2013

Global Change Biology

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To study vegetation feedbacks of nutrient addition on carbon sequestration capacity, we investigated vegetation and ecosystem CO2 exchange at Mer Bleue Bog, Canada in plots that had been fertilized with nitrogen (N) or with N plus phosphorus (P) and potassium (K) for 7-12 years. Gross photosynthesis, ecosystem respiration, and net CO2 exchange were measured weekly during May-September 2011 using climate-controlled chambers. A substrate-induced respiration technique was used to determine the functional ability of the microbial community. The highest N and NPK additions were associated with 40% less net CO2 uptake than the control. In the NPK additions, a diminished C sink potential was due to a 20-30% increase in ecosystem respiration, while gross photosynthesis rates did not change as greater vascular plant biomass compensated for the decrease in Sphagnum mosses. In the highest N-only treatment, small reductions in gross photosynthesis and no change in ecosystem respiration led to the reduced C sink. Substrate-induced microbial respiration was significantly higher in all levels of NPK additions compared with control. The temperature sensitivity of respiration in the plots was lower with increasing cumulative N load, suggesting more labile sources of respired CO2 . The weaker C sink potential could be explained by changes in nutrient availability, higher woody : foliar ratio, moss loss, and enhanced decomposition. Stronger responses to NPK fertilization than to N-only fertilization for both shrub biomass production and decomposition suggest that the bog ecosystem is N-P/K colimited rather than N-limited. Negative effects of further N-only deposition were indicated by delayed spring CO2 uptake. In contrast to forests, increased wood formation and surface litter accumulation in bogs seem to reduce the C sink potential owing to the loss of peat-forming Sphagnum.

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Section: Introductionmentioning

confidence: 99%

Vegetation feedbacks of nutrient addition lead to a weaker carbon sink in an ombrotrophic bog

Larmola

Bubier

Kobyljanec

et al. 2013

Global Change Biology

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“…While several studies assessed solar radiation transmittance below Arctic shrubs (Bewley et al, 2007;Chong et al, 2012;Juszak et al, 2014;Williams et al, 2014), this study compared shrub shading with shading by other vegetation types. Furthermore, the radiation and soil heat flux budget of Arctic tundra has been more extensively studied in Alaska, Canada, and Europe than in the vast Siberian lowlands.…”

Section: Introductionmentioning

confidence: 99%

Contrasting radiation and soil heat fluxes in Arctic shrub and wet sedge tundra

et al. 2016

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Abstract. Vegetation changes, such as shrub encroachment and wetland expansion, have been observed in many Arctic tundra regions. These changes feed back to permafrost and climate. Permafrost can be protected by soil shading through vegetation as it reduces the amount of solar energy available for thawing. Regional climate can be affected by a reduction in surface albedo as more energy is available for atmospheric and soil heating. Here, we compared the shortwave radiation budget of two common Arctic tundra vegetation types dominated by dwarf shrubs (Betula nana) and wet sedges (Eriophorum angustifolium) in North-East Siberia. We measured time series of the shortwave and longwave radiation budget above the canopy and transmitted radiation below the canopy. Additionally, we quantified soil temperature and heat flux as well as active layer thickness. The mean growing season albedo of dwarf shrubs was 0.15 ± 0.01, for sedges it was higher (0.17±0.02). Dwarf shrub transmittance was 0.36 ± 0.07 on average, and sedge transmittance was 0.28 ± 0.08. The standing dead leaves contributed strongly to the soil shading of wet sedges. Despite a lower albedo and less soil shading, the soil below dwarf shrubs conducted less heat resulting in a 17 cm shallower active layer as compared to sedges. This result was supported by additional, spatially distributed measurements of both vegetation types. Clouds were a major influencing factor for albedo and transmittance, particularly in sedge vegetation. Cloud cover reduced the albedo by 0.01 in dwarf shrubs and by 0.03 in sedges, while transmittance was increased by 0.08 and 0.10 in dwarf shrubs and sedges, respectively. Our results suggest that the observed deeper active layer below wet sedges is not primarily a result of the summer canopy radiation budget. Soil properties, such as soil albedo, moisture, and thermal conductivity, may be more influential, at least in our comparison between dwarf shrub vegetation on relatively dry patches and sedge vegetation with higher soil moisture.

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“…Glasshouse experiments underestimated the (indirect) effect of adding N compared to field experiments when vascular plant shoots are present, indicating that the vascular plant effect found in field experiments at sparse cover is not so much a consequence of competitive interaction, but, rather, it is more likely to be mediated through other factors controlled for in glasshouse experiments. The presence of vascular plant shoots in the field could potentially aggravate the effect of N by increasing interception of snow (Dorrepaal et al, 2003) dry N deposition (Limpens et al, 2004) or, perhaps, enable more intensive competition with algae (Gilbert et al, 1998) by altering the microclimate (Chong et al, 2012). Why the direct effect of adding N in the absence of vascular plant shoots was overestimated in the glasshouse compared to the field remains speculative.…”

Section: Why Do Glasshouse Experiments Give Different Results?mentioning

confidence: 99%

“…, 2004) or, perhaps, enable more intensive competition with algae (Gilbert et al. , 1998) by altering the microclimate (Chong et al. , 2012).…”

Section: Discussionmentioning

confidence: 99%

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Glasshouse vs field experiments: do they yield ecologically similar results for assessing N impacts on peat mosses?

et al. 2012

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Summary• Peat bogs have accumulated more atmospheric carbon (C) than any other terrestrial ecosystem today. Most of this C is associated with peat moss (Sphagnum) litter. Atmospheric nitrogen (N) deposition can decrease Sphagnum production, compromising the C sequestration capacity of peat bogs. The mechanisms underlying the reduced production are uncertain, necessitating multifactorial experiments.• We investigated whether glasshouse experiments are reliable proxies for field experiments for assessing interactions between N deposition and environment as controls on Sphagnum N concentration and production. We performed a meta-analysis over 115 glasshouse experiments and 107 field experiments.• We found that glasshouse and field experiments gave similar qualitative and quantitative estimates of changes in Sphagnum N concentration in response to N application. However, glasshouse-based estimates of changes in production -even qualitative assessmentsdiverged from field experiments owing to a stronger N effect on production response in absence of vascular plants in the glasshouse, and a weaker N effect on production response in presence of vascular plants compared to field experiments.• Thus, although we need glasshouse experiments to study how interacting environmental factors affect the response of Sphagnum to increased N deposition, we need field experiments to properly quantify these effects.

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Microclimatic response to increasing shrub cover and its effect on Sphagnum CO₂ exchange in a bog

Cited by 26 publications

References 61 publications

Vegetation feedbacks of nutrient addition lead to a weaker carbon sink in an ombrotrophic bog

Vegetation feedbacks of nutrient addition lead to a weaker carbon sink in an ombrotrophic bog

Contrasting radiation and soil heat fluxes in Arctic shrub and wet sedge tundra

Glasshouse vs field experiments: do they yield ecologically similar results for assessing N impacts on peat mosses?

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Microclimatic response to increasing shrub cover and its effect on Sphagnum CO2 exchange in a bog

Cited by 26 publications

References 61 publications

Vegetation feedbacks of nutrient addition lead to a weaker carbon sink in an ombrotrophic bog

Vegetation feedbacks of nutrient addition lead to a weaker carbon sink in an ombrotrophic bog

Contrasting radiation and soil heat fluxes in Arctic shrub and wet sedge tundra

Glasshouse vs field experiments: do they yield ecologically similar results for assessing N impacts on peat mosses?

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Microclimatic response to increasing shrub cover and its effect on Sphagnum CO₂ exchange in a bog