We estimated nitrogen (N) use by trees of three poplar species exposed for 3 years to free air CO(2) enrichment (FACE) and determined whether the CO(2) treatment affected the future N availability of ...the plantation. Trees were harvested at the end of the first 3-year rotation and N concentration and content of woody tissues determined. Nitrogen uptake of fine roots and litter was measured throughout the first crop rotation. The results were related to previously published variations in soil N content during the same period. We estimated retranslocation from green leaves and processes determining N mobilization and immobilization, such as mineralization and nitrification, and N immobilization in litter and microbial biomass. In all species, elevated CO(2) concentration (CO(2)) significantly increased nitrogen-use efficiency (NUE; net primary productivity per unit of annual N uptake), decreased N concentration in most plant tissues, but did not significantly change cumulative N uptake by trees over the rotation. Total soil N was depleted more in elevated CO(2) than in ambient CO(2), although not significantly for all soil layers. The effect of elevated CO(2) was usually similar for all species, although differences among species were sometimes significant. During the first 3-year rotation, productivity of the plantation remained high in the elevated CO(2) treatment. However, we observed a potential reduction in N availability in response to elevated CO(2).
Abstract
The free air carbon dioxide enrichment (FACE) and N deposition experiments on four ombrotrophic bogs in Finland, Sweden, the Netherlands and Switzerland, revealed that after three years of ...treatment: (1) elevated atmospheric CO
2
concentration had no significant effect on the biomass growth of
Sphagnum
and vascular species; and (2) increased N deposition reduced Sphagnum growth, because it increased the cover of vascular plants and the tall moss
Polytrichum strictum
, while vascular plant biomass growth was not affected. This paper focuses on water chemistry, plant nutrient content, and litter decomposition rates. Potassium limitation, or low supply of K and P, may have prevented a significant increase of
Sphagnum
growth under elevated CO
2
and N deposition. Vascular plant growth under elevated CO
2
and N deposition was also limited by K, or by K in combination with P or N (N in CO
2
experiment). Elevated CO
2
and N deposition had no effect on decomposition rates of
Sphagnum
and vascular plant litter. Aside from a possible effect of N deposition on light competition between species, we expect that elevated atmospheric CO
2
and N deposition concentrations will not affect
Sphagnum
and vascular plant growth in bogs of north‐west Europe due to K‐, or K in combination with N‐ or P‐, limited growth. For the same reason we expect no effect of elevated CO
2
and N deposition on litter decomposition. Net primary production of raised ombrotrophic bogs that are at or close to steady state, is regulated by input of nutrients through atmospheric deposition. Therefore, we hypothesize that the expected increase of plant growth under elevated CO
2
and N deposition is diminished by current levels of K (and to some extent P and N) in atmospheric deposition.
Summary
Boreal and subarctic peatlands contain 20–30% of the world’s soil organic carbon, and if growing, they constitute sinks for atmospheric CO
2
. We hypothesized that even in the nutrient‐poor ...bog environment, elevated CO
2
would stimulate
Sphagnum
growth more than vascular plant growth, thereby improving
Sphagnum’s
competitive strength and enhancing carbon (C) sequestration.
Free‐air carbon dioxide enrichment (FACE) experiments took place on predominantly ombrotrophic peatbog‐lawns in Finland (FI), Sweden (SW), The Netherlands (NL), and Switzerland (CH).
After 3 yr of treatment, increased CO
2
concentration (560 ppm on volume basis) had no significant effect on
Sphagnum
or vascular plant biomass at either site.
This research suggests that, just as with other nutrient‐poor ecosystems, increased atmospheric CO
2
concentrations will have a limited effect on bog ecosystems.
The low decomposability of dead Sphagnum biomass makes this genus one of the most important among the plants that sequester carbon in temperate and northern bog ecosystems. The effects of ...experimentally increased atmospheric CO sub(2) levels and atmospheric N deposition rates on the growth of Sphagnum and other plants were studied in four bogs in Finland, Sweden, Switzerland, and the Netherlands. Contrary to expectations, elevated CO sub(2) did not cause increased Sphagnum biomass growth. Increased N deposition reduced Sphagnum biomass growth by stimulating the growth of vascular plants and the tall moss Polystichum strictum, which could overtop the Sphagnum. Carbon sequestration in Sphagnum-dominated bog ecosystems may thus be substantially reduced by increased N inputs.
Abstract
Part of the missing sink in the global CO
2
budget has been attributed to the positive effects of CO
2
fertilization and N deposition on carbon sequestration in Northern Hemisphere ...terrestrial ecosystems. The genus
Sphagnum
is one of the most important groups of plant species sequestrating carbon in temperate and northern bog ecosystems, because of the low decomposability of the dead material it produces. The effects of raised CO
2
and increased atmospheric N deposition on growth of
Sphagnum
and other plants were studied in bogs at four sites across Western Europe. Contrary to expectations, elevated CO
2
did not significantly affect
Sphagnum
biomass growth. Increased N deposition reduced
Sphagnum
mass growth, because it increased the cover of vascular plants and the tall moss
Polytrichum strictum
. Such changes in plant species composition may decrease carbon sequestration in
Sphagnum
‐dominated bog ecosystems.
This study focuses on the uncertainties in the ‘fate’ of nitrogen (N) in the Netherlands. Nitrogen inputs into the Netherlands in products, by rivers, and by atmospheric deposition, and microbial and ...industrial fixation of atmospheric N2 amount to about 4450 Gg N y(−1). About 60% of this N is transported out of the Netherlands in products. The fate of the remaining 40%, however, is less clear. We discuss uncertainties in losses to the atmosphere (as ammonia or through denitrification), by leaching and runoff, and in N accumulation in biomass and soils. These processes may account for the fate of about 40% of the N in the Netherlands, and for the fate of about 60% of the N in Dutch agricultural soils. Reducing uncertainties in the estimates of these fluxes is necessary for reducing the impact of excess N in the environment. In particular, monitoring the environmental effects of ammonia emissions and nitrate leaching to groundwater and aquatic systems requires an increased understanding of the fate of N. Uncertainties arise because (1) some N fluxes cannot be measured directly and are usually quantified indirectly as the balance in N budgets, (2) direct measurements of N fluxes have inevitable inaccuracies, (3) lack of experimental data and other information (e.g. statistics) needed for upscaling, (4) large spatial and temporal variability of fluxes, and (5) poor understanding of the processes involved. These uncertainties can be reduced by additional experimental studies and by further development of process-based models and N budget studies. We prioritize these future research needs according to a range of different criteria.
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