Nutritional constraints in ombrotrophic Sphagnum plants under increasing atmospheric nitrogen deposition in Europe

Bragazza, Luca; Tahvanainen, Teemu; Kutnar, Lado; Rydin, Håkan; Limpens, Juul; Hájek, Michal; Grosvernier, Philippe; Hájek, Tomáš; Hájková, Petra; Hansen, Ina; Iacumin, Paola; Gerdol, Renato

doi:10.1111/j.1469-8137.2004.01154.x

Cited by 175 publications

(186 citation statements)

References 56 publications

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“…At each study bog, litter peat samples were collected in similar plant communities and microtopographic positions (hummocks and lawns) as previously described (35). The sampling was performed in areas with a dense cover of healthy Sphagnum plants and a very sparse, if any, cover of vascular plants.…”

Section: Methodsmentioning

confidence: 99%

“…However, Sphagnum productivity has only been shown to respond positively to atmospheric N deposition until a critical threshold of Ϸ1 g of N⅐m Ϫ2 ⅐yr Ϫ1 , beyond which productivity is reported to decrease (30,(33)(34)(35). Moreover, increased N deposition may also give a competitive advantage to vascular plants (30,36) whose litter is more easily decomposed (37).…”

Section: Figmentioning

confidence: 99%

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Atmospheric nitrogen deposition promotes carbon loss from peat bogs

Bragazza

Freeman

Jones

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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383

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Peat bogs have historically represented exceptional carbon (C) sinks because of their extremely low decomposition rates and consequent accumulation of plant remnants as peat. Among the factors favoring that peat accumulation, a major role is played by the chemical quality of plant litter itself, which is poor in nutrients and characterized by polyphenols with a strong inhibitory effect on microbial breakdown. Because bogs receive their nutrient supply solely from atmospheric deposition, the global increase of atmospheric nitrogen (N) inputs as a consequence of human activities could potentially alter the litter chemistry with important, but still unknown, effects on their C balance. Here we present data showing the decomposition rates of recently formed litter peat samples collected in nine European countries under a natural gradient of atmospheric N deposition from Ϸ0.2 to 2 g⅐m ؊2 ⅐yr ؊1 . We found that enhanced decomposition rates for material accumulated under higher atmospheric N supplies resulted in higher carbon dioxide (CO2) emissions and dissolved organic carbon release. The increased N availability favored microbial decomposition (i) by removing N constraints on microbial metabolism and (ii) through a chemical amelioration of litter peat quality with a positive feedback on microbial enzymatic activity. Although some uncertainty remains about whether decay-resistant Sphagnum will continue to dominate litter peat, our data indicate that, even without such changes, increased N deposition poses a serious risk to our valuable peatland C sinks.decomposition ͉ global change ͉ litter peat ͉ CO2 P eatlands cover 2-3% of the land's surface, store approximately one-third of all soil carbon (C) (390-455 Pg), and currently act as sinks for atmospheric C (1, 2). The ability of peatlands to sequester atmospheric C resides in the long-term accumulation of partially decomposed organic matter (i.e., peat). Indeed, acidic water conditions, low soil temperature, frequent waterlogging, and low nutrient quality of plant litter impair decomposition of plant litter, favoring its accumulation (3). In peatlands exclusively fed by atmospheric deposition (i.e., bogs) (1), the accumulated peat is dominated by the remnants of the mosses of the genus Sphagnum, which produce a litter poor in nutrients and highly enriched in organochemical compounds such as uronic acids (4) and polyphenols (5) with a strong inhibitory effect on microbial activity and vascular plants (3). As such, Sphagnum plants form the bulk of living and dead biomass in bog ecosystems (3).Because of the strict dependence of bogs on atmospheric deposition as a source of nutrients (1), the increasing availability of biologically reactive nitrogen (N) from industrial and agricultural activities (6) could potentially alter the chemical quality of plant litter with consequent effects on the amount of C released during litter decomposition. Accordingly, an understanding of the mechanisms of bog soil C response to changing N availability is essential for assessing the capa...

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Section: Methodsmentioning

confidence: 99%

Section: Figmentioning

confidence: 99%

Atmospheric nitrogen deposition promotes carbon loss from peat bogs

Bragazza

Freeman

Jones

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

383

260

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show abstract

“…As the N:P ratios were already relatively high at the start of our experiment, with values of 25 or higher, this might indicate that Sphagnum was already P limited, since P limitation occurs at high N:P ratios ([15 according to Aerts et al 1992; [30 according to Bragazza et al 2004). Bragazza et al (2004) suggest that the critical load of N deposition in Europe is 1 g N m -2 year -1 , above which Sphagnum plants change from being N-limited to being P and K co-limited at N:P [ 30 and N:K [ 3. This would indicate that Sphagnum was P-limited in all treatments in our study and colimited by P and K in the high N treatment.…”

Section: Nitrogenmentioning

confidence: 97%

“…Atmospheric N deposition in Europe varies from 0.1 to 2 g N m -2 year -1 (Bragazza et al 2004), although higher values up to 5 g N m -2 year -1 are reported for the Netherlands (RIVM 2004). Our N addition of 4 g N m -2 year -1 is therefore already relatively high, but actual N availability might have been even higher because of nutrient mineralisation from the Sphagnum and peat in containers.…”

Section: Nitrogenmentioning

confidence: 99%

Response of Sphagnum species mixtures to increased temperature and nitrogen availability

et al. 2009

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To predict the role of ombrotrophic bogs as carbon sinks in the future, it is crucial to understand how Sphagnum vegetation in bogs will respond to global change. We performed a greenhouse experiment to study the effects of two temperature treatments (17.5 and 21.7°C) and two N addition treatments (0 and 4 g N m -2 year -1 ) on the growth of four Sphagnum species from three geographically interspersed regions: S. fuscum, S. balticum (northern and central Sweden), S. magellanicum and S. cuspidatum (southern Sweden). We studied the growth and cover change in four combinations of these Sphagnum species during two growing seasons. Sphagnum height increment and production were affected negatively by high temperature and high N addition. However, the northern species were more affected by temperature, while the southern species were more affected by N addition. High temperature depressed the cover of the 'wet' species, S. balticum and S. cuspidatum. Nitrogen concentrations increased with high N addition. N:P and N:K ratios indicated P-limited growth in all treatments and co-limitation of P and K in the high N treatments. In the second year of the experiment, several containers suffered from a severe fungal infection, particularly affecting the 'wet' species and the high N treatment. Our findings suggest that global change can have negative consequences for the production of Sphagnum species in bogs, with important implications for the carbon sequestration in these ecosystems.

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“…Peat mosses (Sphagnum spp.) function as a filter that very effectively absorbs particularly ammonium (NH + 4 ) but also nitrate (NO − 3 ) from atmospheric deposition, leading to N limitation in the rhizosphere of vascular plants (Lamers et al, 2000;Bragazza et al, 2004;Fritz et al, 2014). Since the availability of N determines primary production, there appears to be a close link between the N and C cycles (Hungate et al, 2003;Vitousek et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Symbiosis revisited: phosphorus and acid buffering stimulate N2 fixation but not Sphagnum growth

et al. 2017

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Abstract. In pristine Sphagnum-dominated peatlands, (di)nitrogen (N 2 ) fixing (diazotrophic) microbial communities associated with Sphagnum mosses contribute substantially to the total nitrogen input, increasing carbon sequestration. The rates of symbiotic nitrogen fixation reported for Sphagnum peatlands, are, however, highly variable, and experimental work on regulating factors that can mechanistically explain this variation is largely lacking. For two common fen species (Sphagnum palustre and S. squarrosum) from a high nitrogen deposition area (25 kg N ha −1 yr −1 ), we found that diazotrophic activity (as measured by 15−15 N 2 labeling) was still present at a rate of 40 nmol N gDW −1 h −1 . This was surprising, given that nitrogen fixation is a costly process. We tested the effects of phosphorus availability and buffering capacity by bicarbonate-rich water, mimicking a field situation in fens with stronger groundwater or surface water influence, as potential regulators of nitrogen fixation rates and Sphagnum performance. We expected that the addition of phosphorus, being a limiting nutrient, would stimulate both diazotrophic activity and Sphagnum growth. We indeed found that nitrogen fixation rates were doubled. Plant performance, in contrast, did not increase. Raised bicarbonate levels also enhanced nitrogen fixation, but had a strong negative impact on Sphagnum performance. These results explain the higher nitrogen fixation rates reported for minerotrophic and more nutrient-rich peatlands. In addition, nitrogen fixation was found to strongly depend on light, with rates 10 times higher in light conditions suggesting high reliance on phototrophic organisms for carbon. The contrasting effects of phosphorus and bicarbonate on Sphagnum spp. and their diazotrophic communities reveal strong differences in the optimal niche for both partners with respect to conditions and resources. This suggests a trade-off for the symbiosis of nitrogen fixing microorganisms with their Sphagnum hosts, in which a sheltered environment apparently outweighs the less favorable environmental conditions. We conclude that microbial activity is still nitrogen limited under eutrophic conditions because dissolved nitrogen is being monopolized by Sphagnum. Moreover, the fact that diazotrophic activity can significantly be upregulated by increased phosphorus addition and acid buffering, while Sphagnum spp. do not benefit, reveals remarkable differences in optimal conditions for both symbiotic partners and calls into question the regulation of nitrogen fixation by Sphagnum under these eutrophic conditions. The high nitrogen fixation rates result in high additional nitrogen loading of 6 kg ha −1 yr −1 on top of the high nitrogen deposition in these ecosystems.

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Nutritional constraints in ombrotrophic Sphagnum plants under increasing atmospheric nitrogen deposition in Europe

Cited by 175 publications

References 56 publications

Atmospheric nitrogen deposition promotes carbon loss from peat bogs

Atmospheric nitrogen deposition promotes carbon loss from peat bogs

Response of Sphagnum species mixtures to increased temperature and nitrogen availability

Symbiosis revisited: phosphorus and acid buffering stimulate N<sub>2</sub> fixation but not <i>Sphagnum</i> growth

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Nutritional constraints in ombrotrophic Sphagnum plants under increasing atmospheric nitrogen deposition in Europe

Cited by 175 publications

References 56 publications

Atmospheric nitrogen deposition promotes carbon loss from peat bogs

Atmospheric nitrogen deposition promotes carbon loss from peat bogs

Response of Sphagnum species mixtures to increased temperature and nitrogen availability

Symbiosis revisited: phosphorus and acid buffering stimulate N&lt;sub&gt;2&lt;/sub&gt; fixation but not &lt;i&gt;Sphagnum&lt;/i&gt; growth

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Symbiosis revisited: phosphorus and acid buffering stimulate N<sub>2</sub> fixation but not <i>Sphagnum</i> growth