Sphagnum Mosses - Masters of Efficient N-Uptake while Avoiding Intoxication

Fritz, Christian; Lamers, Leon P. M.; Riaz, Muhammad; Berg, Leon J.L. van den; Elzenga, J. Theo M.

doi:10.1371/journal.pone.0079991

Cited by 76 publications

(68 citation statements)

References 69 publications

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“…These high N uptake rates, especially for NH + 4 , from surface water or rainwater are indeed typical for Sphagnum spp. (Fritz et al, 2014). Simultaneously, the associated diazotrophs were still fixing N 2 at appreciable rates under these N-rich conditions, even though N 2 fixation is an energy demanding process (Vitousek et al, 2002).…”

Section: Diazotrophic Activity Under High N Conditionsmentioning

confidence: 95%

“…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%

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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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Section: Diazotrophic Activity Under High N Conditionsmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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“…NH4 + is preferentially taken up by Sphagnum (Fritz et al, 2014;Liu et al, 330 2013; Wiedermann et al, 2009) because Sphagnum has a high cation exchange capacity 331 (Bates, 1992;Gunnarsson & Rydin, 2000). In addition, NH4 + has greater toxicity 332 (Gerendás et al, 1997;Krupa, 2003;Stevens et al, 2011).…”

Section: Science Of the Total Environment Chiwa Et Al Revised Msmentioning

confidence: 99%

“…(NH4 + ) versus oxidized (NO3 -) N on the N status of the Sphagnum moss and the (Manninen et al, 2011;Sheppard et al, 2014), possibly due to the greater toxicity of 97 NH4 + (Gerendás et al, 1997;Krupa, 2003;Stevens et al, 2011;Limpens and Berendse, 98 2003) coupled to preferential uptake of NH4 + by Sphagnum (Fritz et al, 2014;Liu et al, 99 2013; Wiedermann et al, 2009). For example, Manninen et al (2011) found that NH4 + 100 addition increased shoot N concentration of Sphagnum and decreased photosynthetic 101 variables (Fv/Fm) and shoot dry weight of Sphagnum.…”

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Sphagnum can ‘filter’ N deposition, but effects on the plant and pore water depend on the N form

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Sheppard

Leith

et al. 2016

Science of The Total Environment

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“…>10 kg N ha −1 year −1 ; Lamers et al 2000) on plants, since plants are assumed to be the main consumers of NH 4 + and NO 3 − in terrestrial ecosystems. Sphagnum mosses have been shown to be very efficient in retaining nitrogenous compounds from N deposition, preferentially taking up N in the form of NH 4 + (Fritz et al 2014). The effects of high N deposition on Sphagnum moss productivity are dependent on the level, where at low deposition levels, up to about 10 kg N ha −1 year −1 , mosses might still benefit from the additional N input (Lamers et al 2000;Berg et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Effects of nitrogen fertilization on diazotrophic activity of microorganisms associated with Sphagnum magellanicum

et al. 2016

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Background and aims In pristine ombrotrophic Sphagnum-dominated peatland ecosystems nitrogen (N) is often a limiting nutrient, which is replenished by biological N 2 fixation and atmospheric N deposition. It is, however, unclear which impact long-term N deposition has on microbial N 2 fixing activity and diazotrophic diversity, and whether phosphorus (P) modulates the response. Therefore, we studied the impact of increased N deposition and N depletion on microbial N 2 fixation and diazotrophic diversity associated with the peat moss Sphagnum magellanicum, and their interaction with P availability. Methods Nitrogenase activities of S. magellanicumassociated microorganisms were determined by acetylene reduction assays (ARA) and 15 N 2 tracer methods on mosses from two geographically distinct locations with different N deposition histories, high or low N deposition, and in samples depleted in N (grown 3 years in the greenhouse) versus recent field samples. The short-term response to increased N deposition was tested for mosses differing in N and P fertilization histories. In addition, diversity of diazotrophic microorganisms was assessed by nifH gene amplicon sequencing of N-depleted mosses. Results We showed distinct and persistent differences in diazotrophic communities and their activities associated with S. magellanicum from sites with high versus low N deposition. Initially, diazotrophic activity was six times higher for the low N site. During incubation and repeated ARA, however, this activity strongly decreased, while it remained stable for the high N site. Activity for the high N site could not be increased by long-term experimental N deprivation. Short-term, experimental N application had an inhibitory effect on N 2 fixation for both sites, which was not observed in mosses with high indirect P availability. Conclusions We conclude that although N deposition negatively affects N 2 fixation as also shown in previous studies, long-term effects of N deprivation on the diazotrophic activity and community are more complex. Furthermore, our results indicated that P availability might be an important factor in modulating the response of Sphagnum-associated diazotrophs to N deposition.

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Sphagnum Mosses - Masters of Efficient N-Uptake while Avoiding Intoxication

Cited by 76 publications

References 69 publications

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

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

Sphagnum can ‘filter’ N deposition, but effects on the plant and pore water depend on the N form

Effects of nitrogen fertilization on diazotrophic activity of microorganisms associated with Sphagnum magellanicum

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Sphagnum Mosses - Masters of Efficient N-Uptake while Avoiding Intoxication

Cited by 76 publications

References 69 publications

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

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

Sphagnum can ‘filter’ N deposition, but effects on the plant and pore water depend on the N form

Effects of nitrogen fertilization on diazotrophic activity of microorganisms associated with Sphagnum magellanicum

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

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