Expansion of Sphagnum fallax in bogs: striking the balance between N and P availability

Abstract

Nitrogen deposition may cause shifts in the Sphagnum species composition of bogs, ultimately affecting the conservation value of these systems. We studied the effects of N and P on the expansion of S. fallax and S. flexuosum in bogs. We related historical census data of S. fallax, S. flexuosum, and four of their accompanying species to changes in N deposition. In addition, we conducted two fertilization experiments with N and P; one at a low deposition site with S. flexuosum and one at two high deposition sites with S. fallax. Finally, we related existing data on capitulum N and P concentrations of S. fallax to its abundance in the field.

A relative increase in observed frequency of S. fallax coincided with an historical increase in N deposition in the Netherlands. There was no indication that S. fallax consistently outcompeted one of the other five Sphagnum species; the observed frequency of the Sphagnum species analysed was rather stable with time. The census data on S. flexuosum did not indicate a response to N deposition, but the species expanded at the low N deposition site when extra N was applied. In contrast, the expansion of S. fallax at the high deposition sites was limited by P. Organic nutrient concentrations suggested that when S. fallax can maintain a capitulum N concentration of 7 mg g^-1 or higher and a P concentration of 0.7 mg g^-1 or higher the species can grow to dominate.

We conclude that S. fallax will gradually colonize an increasing number of new habitats in areas with a low, albeit increasing, N deposition, but will only grow to dominate when P supply is adequate. Then, the expansion of S. fallax may lead to ousting of the other Sphagnum species present.     

Growth reduction of<Emphasis Type="Italic"> Sphagnum magellanicum</Emphasis> subjected to high nitrogen deposition: the role of amino acid nitrogen concentration

We tested the relationship between Sphagnum growth and the amount of nitrogen stored in free amino acids in a fertilisation experiment with intact peat monoliths in an open greenhouse in The Netherlands. Three nitrogen deposition scenarios were used: no nitrogen deposition, field conditions and a doubling of the latter, corresponding to 0, 40 and 80 kg N ha(-1 )year(-1). Growth of Sphagnum as expressed by height increment was reduced in the 80 kg N treatment, but showed no correlation with the total nitrogen tissue concentration or with the concentration of individual or pooled free amino acids. The amount of nitrogen stored in free amino acids increased concomitantly with deposition, although it lagged more and more behind the total nitrogen concentration, the latter pointing to the accumulation of unmeasured nitrogen compounds. Asparagine clearly acted as the major storage compound for nitrogen in Sphagnum stem tissue, whereas arginine fulfilled this function to a lesser extent in the capitulum. It appears that nitrogen-induced growth inhibition of Sphagnum is related to acclimation rather than to certain threshold concentrations of amino nitrogen or total nitrogen. We propose that when Sphagnum is exposed to a step increase of nitrogen, its nitrogen metabolism does not adapt fast enough to keep up with the enhanced uptake rate. This imbalance between nitrogen uptake and assimilation may lead to an accumulation of toxic NH(4)(+ )in the cell and a subsequent reduction in growth.     

Microsite and regional variation in the potential decay rate of Sphagnum magellanicum in south Swedish raised bogs

In southern Sweden there are regional gradients in the rate of atmospheric deposition of nitrogen, and the rate of N deposition has increased in recent decades This may have caused a shift in the growth-limiting nutrient of Sphagnum growth from nitrogen to phosphorus In this study, the influence of N and P concentrations on the decay of litter peat formed by Sphagnum magellanicum was examined A total of 90 litter peat samples formed by this species was collected from 15 raised bogs (3 sites per bog, 2 microsites per site) Total N and P of samples were determined and the rate of decomposition (C0₂ release) was measured under aerated, laboratory conditions at 18°C Differences in decomposition rates, N and P concentrations were most pronounced among microsites within sites, whereas no significant differences were observed among bogs The results indicate that decomposition of 5 magellanicum litter peat is influenced more by P than by N Thus, it appears that the recent increase in atmospheric N deposition has not had a large direct effect on peat decomposition rates It is suggested that the efficient uptake of N and P by the Sphagnum plant may lead to a positive feedback mechanism, whereby more slowly growing Sphagnum produces more nutrient-enriched litter peat with a more rapid decay Such a mechanism could promote the development of microtopography (hummocks and hollows) on bogs     

Nutrient additions in pristine Patagonian Sphagnum bog vegetation: can phosphorus addition alleviate (the effects of) increased nitrogen loads

Sphagnum-bog ecosystems have a limited capability to retain carbon and nutrients when subjected to increased nitrogen (N) deposition. Although it has been proposed that phosphorus (P) can dilute negative effects of nitrogen by increasing biomass production of Sphagnum mosses, it is still unclear whether P-addition can alleviate physiological N-stress in Sphagnum plants. A 3-year fertilisation experiment was conducted in lawns of a pristine Sphagnum magellanicum bog in Patagonia, where competing vascular plants were practically absent. Background wet deposition of nitrogen was low (≈ 0.1-0.2 g · N · m(-2) · year(-1)). Nitrogen (4 g · N · m(-2) · year(-1)) and phosphorus (1 g · P · m(-2) · year(-1)) were applied, separately and in combination, six times during the growing season. P-addition substantially increased biomass production of Sphagnum. Nitrogen and phosphorus changed the morphology of Sphagnum mosses by enhancing height increment, but lowering moss stem density. In contrast to expectations, phosphorus failed to alleviate physiological stress imposed by excess nitrogen (e.g. amino acid accumulation, N-saturation and decline in photosynthetic rates). We conclude that despite improving growth conditions by P-addition, Sphagnum-bog ecosystems remain highly susceptible to nitrogen additions. Increased susceptibility to desiccation by nutrients may even worsen the negative effects of excess nitrogen especially in windy climates like in Patagonia.     

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

? 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 assessments-- diverged 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.     

Nutrient concentration in shape Sphagna at increased N-deposition rates and raised atmospheric CO2 concentrations

Sphagnum fuscum, S. magellanicum, S. angustifolium and S. warnstorfii were treated with N deposition rates (0, 10, 30 and 100 kg ha^-1 a^-1) and with four atmospheric CO₂ concentrations (350, 700, 1000 and 2000 ppm) in greenhouse for 71–120 days. Thereafter, concentrations of total N, P, K, Ca and Mg in the capitulae of the Sphagna were determined. The response of each species to N deposition was related to ecological differences. With increasing N deposition treatments, moss N concentrations increased and higher N:P-ratios were found, the increase being especially clear at the highest N load. Sphagnum fuscum, which occupies ombrotrophic habitats, was the most affected by the increased nitrogen load and as a consequence the other elements were decreased. Oligotrophic S. magellanicum, wide nutrient status tolerant S. angustifolium and meso-eutrophic S. warnstorfii tolerated better increased N deposition, though there were increased concentrations of Ca and Mg in S. warnstorfii and Mg in S. magellanicum. Nitrogen and P concentrations decreased with raised CO₂ concentrations, except for S. magellanicum. This seems to be the first time this kind of response in nutrient concentrations to enhanced CO₂ concentration has been shown to exist in bryophytes. The concentration of K clearly decreased in S. fuscum as did the concentration of Mg in the other Sphagna with increasing CO₂. Sphagnum angustifolium and S. magellanicum, which are the less specialized species, were the least affected by the CO₂ treatments.     

The interaction between epiphytic algae, a parasitic fungus and Sphagnum as affected by N and P

We report the effects of fertilisation with N and P on the infection of Sphagnum by its fungal parasite Lyophyllum palustre, the expansion of epiphytic algae and the interaction between the latter two from 1998 to 2001. We added 40 kg N ha⁻¹ yr⁻¹ or 3 kg P ha⁻¹ yr⁻¹ in a full factorial design at 4 field sites. In a greenhouse experiment we reinoculated Sphagnum to verify the identity of the fungus and its necrotic effect on Sphagnum .
Lyophyllum palustre was responsible for the necrosis of Sphagnum in our experiments. Adding N induced complete necrosis of Sphagnum cuspidatum by L. palustre , whereas adding P decreased the area of necrotic tissue. Disease severity was related to the N concentration in the Sphagnum capitula. In Sphagnum magellanicum and S. papillosum , infection with L. palustre resulted in defoliation of stem sections. Adding N stimulated the expansion of algae at all sites, reducing the volume of photosynthetic tissue in Sphagnum. The density of the film of algae in the treatments receiving N was a function of the frequency of defoliated Sphagnum stems.
We conclude that infection with parasitic fungi and, in humid environments, the expansion of epiphytic algae, may aggravate the impact of increased N deposition or of other ecosystem disturbances that affect nutrient availability.     

Potassium limits potential growth of bog vegetation under elevated atmospheric CO2 and N deposition

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 CO₂ 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 CO₂ and N deposition. Vascular plant growth under elevated CO₂ and N deposition was also limited by K, or by K in combination with P or N (N in CO₂ experiment). Elevated CO₂ 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 CO₂ 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 CO₂ 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 CO₂ and N deposition is diminished by current levels of K (and to some extent P and N) in atmospheric deposition.     

Interspecific and geographical differences of plant tissue nutrient concentrations along an environmental gradient in Southern Patagonia, Chile

Foliar nutrient concentrations of South Patagonian ombrotrophic peatland species were analyzed along a gradient of increasing continentality. We paid particular attention to nutrient demands of Sphagnum magellanicum, the dominant constituent of continental raised bogs, and to those of cushion-forming vascular plants such as Astelia pumila, dominating in western hyperoceanic blanket bogs. With exception of one graminoid species, nutrient concentrations in leaf tissues were generally low, but showed considerable variation. Extremely low concentrations were measured in S. magellanicum reflecting the unpolluted, pristine character of the investigated bog ecosystems. Nutrient concentrations in cushion plants showed remarkable variation. While nutrient concentrations in Donatia fascicularis were almost as low as in S. magellanicum, they were significantly higher in A. pumila. Variation in foliar nutrient concentrations was predominantly due to differences between species. Nevertheless, there was a significant shift within species along the considered west-to-east continental gradient. The stronger minerotrophic character of the western cushion bogs was reflected by higher Ca contents. N concentrations increased and P concentrations decreased westward in most species. Consequently, the most noticeable shift was an increasing N:P ratio indicating a higher degree of P limitation towards western cushion dominated blanket bogs.     

How litter quality affects mass loss and N loss from decomposing Sphagnum

Nitrogen (N) deposition may affect litter decomposition and may thus have an impact on the rate of carbon (C) sequestration in Sphagnum peatlands. We present results from four separate experiments aimed at delineating the effects of litter N-enrichment, Sphagnum species, stem part of Sphagnum , and place of incubation on decomposition rate and N release. We measured mass loss and N loss from litterbags incubated at 10-15 cm in the field for one year.
Mass loss was positively related to the N/C quotient of the litter, but depended strongly on the range in N/C quotients observed; only a distinct difference in N/C quotients affected mass loss. Although hummock species decayed at a slower rate than hollow species, the differences between the species became less pronounced for old stem parts and for N-enriched litter. Old stem parts decayed at a slower rate than young stem parts, except for S. papillosum . Neither position of incubation (low hummock or hollow), nor the inorganic N concentration of the incubation environment affected mass loss. N loss was mainly determined by, and positively related to, the N/C quotient of the litter; species and stem part had minor effects. Above a N/C quotient of about 0.015, net N loss was observed for all species.
We conclude that decomposition of Sphagnum is stimulated by N deposition. As the latter also affects litter N concentration and thus N release, we think that positive feedbacks through changing litter quality should be taken into account when modelling the effects of N deposition on Sphagnum peatlands and C sequestration in these systems.     

Competition between Sphagnum magellanicum and Eriophorum angustifolium as affected by raised CO2 and increased N deposition

The competition between peat mosses ( Sphagnum ) and vascular plants as affected by raised CO₂ and increased N deposition was studied in a glasshouse experiment by exposing peat monoliths with monocultures and mixtures of Sphagnum magellanicum and Eriophorum angustifolium to ambient (350 ppmv) or raised (560 ppmv) atmospheric CO₂ concentrations, combined with low (no N addition) or high (5 g m⁻² yr⁻¹ added) N deposition. Growth of the two species was monitored for three growing seasons.
The presence of Eriophorum did not affect Sphagnum biomass, because Eriophorum density did not become high enough to severely shade the moss surface. In contrast, Sphagnum had a negative effect on Eriophorum biomass, particularly on the number of flowering stems. Possibly, the presence of a living Sphagnum layer decreased nutrient availability to Eriophorum by immobilising nutrients mineralised from the peat.
Raised CO₂ and/or increased N deposition did not change these competitive relationships between Sphagnum and Eriophorum , but had independent effects. Raised CO₂ had a positive effect both on Sphagnum and Eriophorum biomass, though on Eriophorum the effect was transient, probably because of P limitation. Nitrogen addition had a direct negative effect on Sphagnum height growth in the first growing season, but by the third year an increased shoot density had cancelled this out, so no N effect on Sphagnum biomass was present at the end of the experiment. The response of Eriophorum to N addition was small; N availability appeared not to limit its growth.     

Climatic modifiers of the response to nitrogen deposition in peat-forming Sphagnum mosses: a meta-analysis

Peatlands in the northern hemisphere have accumulated more atmospheric carbon (C) during the Holocene than any other terrestrial ecosystem, making peatlands long-term C sinks of global importance. Projected increases in nitrogen (N) deposition and temperature make future accumulation rates uncertain. Here, we assessed the impact of N deposition on peatland C sequestration potential by investigating the effects of experimental N addition on Sphagnum moss. We employed meta-regressions to the results of 107 field experiments, accounting for sampling dependence in the data. We found that high N loading (comprising N application rate, experiment duration, background N deposition) depressed Sphagnum production relative to untreated controls. The interactive effects of presence of competitive vascular plants and high tissue N concentrations indicated intensified biotic interactions and altered nutrient stochiometry as mechanisms underlying the detrimental N effects. Importantly, a higher summer temperature (mean for July) and increased annual precipitation intensified the negative effects of N. The temperature effect was comparable to an experimental application of almost 4 g?N m(-2) yr(-1) for each 1°C increase. Our results indicate that current rates of N deposition in a warmer environment will strongly inhibit C sequestration by Sphagnum-dominated vegetation.     

Root decomposition and soil nutrient and carbon cycling in two temperate fen ecosystems

Although root litter contributes to a large extent to soil organic matter accumulation in peatlands, decomposition of root litter is often neglected in studies on litter decomposition and carbon and nutrient cycling in these ecosystems. In this study, decomposition of root and rhizome litter of Carex diandra and Carex lasiocarpa was determined in two temperate fens, one dominated by Sphagnum species ( Sphagnum fen; soil pH=4.4) and one without a Sphagnum cover ( Carex fen; soil pH=5.7). One-year mass loss increased in the order: roots Carex diandra 相似文献   

Water Supply Changes N and P Conservation in a Perennial Grass Leymus chinensis

Changes in precipitation can influence soil water and nutrient availability, and thus affect plant nutrient conservation strategies. Better understanding of how nutrient conservation changes with variations in water availability is crucial for predicting the potential influence of global climate change on plant nutrient-use strategy. Here, green-leaf nitrogen (N) and phosphorus (P) concentrations, N- and P-resorption proficiency (the terminal N and P concentration in senescent leaves, NRP and PRP, respectively), and N- and P-resorption efficiency (the proportional N and P withdrawn from senescent leaves prior to abscission, NRE and PRE, respectively) of Leymus chinensis (Trin.) Tzvel., a typical perennial grass species in northern China, were examined along a water supply gradient to explore how plant nutrient conservation responds to water change. Increasing water supply at low levels (< 9000 mL/year) increased NRP, PRP and PRE, but decreased green-leaf N concentration. It did not significantly affect green-leaf P concentration or NRE. By contrast, all N and P conservation indicators were not significantly influenced at high water supply levels (> 9000 mL/year). These results indicated that changes in water availability at low levels could affect leaf-level nutrient characteristics, especially for the species in semiarid ecosystems. Therefore, global changes in precipitation may pose effects on plant nutrient economy, and thus on nutrient cycling in the plant-soil systems.     

Nutrient concentrations in mire vegetation as a measure of nutrient limitation in mire ecosystems

Abstract. The above-ground standing crop and nutrient concentrations in plant material were examined in 45 stands of mire vegetation in the Biebrza peatland, Poland. The stands included flood-plains, rich fens, transitional fens and bogs. The pattern in nutrient concentrations in the above-ground plant material resembled the pattern in nutrient concentrations in peatwater and peat which had been investigated in an earlier study. Concentrations of N were quite uniform along the gradient. P-concentrations were highest in the transitional fen. Critical nutrient concentrations were defined on the basis of a review of nutrient concentrations in plant material from peatlands in which a fertilization experiment had been carried out. Defined critical values for phanerogams were: 13-14 and 0.7 mg/g dry wt for N and P respectively. Concentrations lower than these values indicate deficiency. P/N ratios ≥ 0.07 indicate N-deficiency and P/N ratios ≤ 0.04 — 0.05 indicate P-deficiency. According to these values the Biebrza fens and bogs appear to be primarily deficient in N. The growth of the flood-plain vegetation does not appear to be restricted by nutrients.     

High nitrogen : phosphorus ratios reduce nutrient retention and second-year growth of wetland sedges

Shifts from nitrogen (N)- to phosphorus (P)-limited growth due to high N deposition may alter the functioning of wetland vegetation. This experiment tested how N vs P deficiency affects the growth and nutrient use of wetland sedges. Five wetland Carex species were grown at nine N : P supply ratios (0.6-405) with two absolute levels of N and P. Biomass and nutrient concentrations were determined after one and two growing seasons. Shoot biomass was maximal at N : P supply ratios of 15-26 after one season but 5-15 after two seasons. Photosynthesis after the first season, second-year growth, leaf longevity, and the fraction of nutrient supply retained by plants over two seasons were all negatively related to N : P supply ratios, with small effects of absolute supply. The five Carex species responded similarly to N : P ratios but differed in nutrient resorption efficiency and biomass allocation. Plants treated with high N : P ratios appeared to lose nutrients below ground. Such losses may reduce plant performance in P-limited wetlands affected by high N deposition.     

Nutrient cycling strategies

This paper briefly reviews pathways by which plants can influence the nutrient cycle, and thereby the nutrient supply of themselves and of their competitors. Higher or lower internal nutrient use efficiency positively feeds back into the nutrient cycle, and helps to increase or decrease soil fertility. These tendencies are further enhanced by secondary effects (higher or lower rates of decomposition of litter and hence of nutrient mineralization) in resp. fertile and infertile soils. Such feedbacks may strongly increase the fitness of the plants involved. Plants can also influence the external inputs and outputs into the plant-soil system, by affecting the general hydrology of their environment. Sphagnum peat bogs exemplify an extreme degree of control of plants over the hydrological cycle, causing intense nutrient impoverishment by making the ecosystem dependent on nutrient supply from the atmosphere, apparently giving Sphagnum a competitive edge over other plants.     

氮磷添加对麦冬根部养分浓度及其化学计量比的影响

以城市地被植物麦冬(Ophiopogon japonicus(Thunb.)Ker-Gawl.)为研究对象,研究了土壤中添加氮(N)磷(P)后对植物根部N、P养分及其化学计量比的影响。结果表明,实验监测期间(10-12月),麦冬根部N浓度平均值表现为N(5gm-2) P(1gm-2)处理>N(5gm-2)处理=P(1gm-2)处理>对照,根部P浓度和N:P比差异不显著(P>0.1)。而监测期间的N、P月份动态结果表明,同对照相比,N处理、P处理和N P处理的麦冬根部N、P浓度和N:P比的差异性均表现为监测前期(10月)较大,中后期(11-12月)较小的变化趋势。这说明麦冬能保持其根部N、P水平的稳定性,具有较强的应对N沉降的能力,且补充P肥可增强这种能力。因此,麦冬可在大气沉降严重的地区应用和推广。     

Hydrological and biological processes modulate carbon,nitrogen and phosphorus flux from the St. Lawrence River to its estuary (Quebec,Canada)

Changes in atmospheric deposition, stream water chemistry, and solute fluxes were assessed across 15 small forested catchments. Dramatic changes in atmospheric deposition have occurred over the last three decades, including a 70% reduction in sulphur (S) deposition. These changes in atmospheric inputs have been associated with expected changes in levels of acidity, sulphate and base cations in streams. Soil retention of S appeared to partially explain rates of chemical recovery. In addition to these changes in acid–base chemistry we also observed unexpected changes in nitrogen (N) biogeochemistry and nutrient stoichiometry of stream water, including decreased stream N concentrations. Among all catchments the average flux of dissolved inorganic nitrogen (DIN) was best predicted by average runoff, soil chemistry (forest floor C/N) and levels of acid deposition (both S and N). The rate of change in stream DIN flux, however, was much more closely correlated with reductions in rates of S deposition rather than those of DIN. Unlike DIN fluxes, the average concentrations as well as the rates of decline in streamwater nitrate (NO₃) concentration over time were tightly linked to stream dissolved organic carbon/dissolved organic nitrogen ratios DOC/DON and DON/TP rather than catchment characteristics. Declines in phosphorus adsorption with increasing soil pH appear to contribute to the relationship between C, N, and P in our study catchments. Our observations suggest that catchment P availability and its alteration due to environmental changes (e.g. acidification) might have profound effects on N cycling and catchment N retention that have been largely unrecognized.     

Periodicity in growth,productivity, nutrient content and decomposition ofSphagnum recurvum var.mucronatum in a fen woodland

Summary Condition in the understory of aBetula-carr appeared to be favourable for the growth ofSphagnum recurvum. The estimates of annual productivity and nutrient accumulations forS. recurvum obtained in this wetland forest are in the high range of those reported for peatmosses. On an annual basis, the organic matter production, vegetative reproduction (forking), and accumulation of N, P and K were very much the same for a relatively dry and for a relatively wet year. Periodicity in growth and length increase of the plants, however, differed remarkably between these years, and fruiting was observed in the dry year only.S. recurvum was characterized by a distinct variation in nutrient concentrations both with time and with distance from the capitulum. Organic weight loss during breakdown ofS. recurvum in the wetland forest was low. Release of N, P and particularly K was larger than that of organic matter in decomposingS. recurvum. Nevertheless, a relatively large proportion of the original N and P stock remained associated with the peatmoss material after a 12 month decay period. Observations with the scanning electron microscope revealed that after a year the cells of deadS. recurvum were hardly damaged and only poorly colonized by microorganisms. The characteristics ofS. recurvum described here indicate its potency in directing succession in peatland forests.