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Aims: The release of the major greenhouse gas N2O from peatlands may be affected by current global change. We tried to answer how N2O emission from peatlands responds to phosphorus (P) addition and the co-addition of P and nitrogen (N). Methods: We investigated the long-term (12 years) effects of N (50 and 100 kg ha−1 yr−1) and P (5 kg ha−1 yr−1) additions and their interaction on N2O fluxes in Hani peatland during the 2019 growing season. Results: The addition of P, a low level of N or their co-addition had no effect on the source/sink function of N2O in the peatland. However, a high level of N addition turned the peatland into a sink of N2O with a cumulative flux of −164 ± 51 g m−2 during the growing season. This was probably due to the acceleration of plant litter decomposition, stimulation of hydrolase activity, and changes in the stoichiometric ratio of the peat soil. The co-addition of P and a high level of N turned the peatland into a source of N2O with a cumulative flux of 144 ± 54 g m−2 during the growing season by relieving nutrient limitation, accelerating the growth of vascular plants, and altering the litter input. Conclusions: We suggest that the increase in nutrient availability caused by N deposition and agriculture fertilization can alter the N2O source/sink function of peatlands. These changes may have significant implications for the overall balance of greenhouse gas emissions and the role of peatlands in mitigating climate change. [ABSTRACT FROM AUTHOR]

Drainage is known to reduce carbon sequestration in peatlands, but its effect on the stability of carbon pool and changes in recalcitrant organic carbon fractions remain relatively unknown, especially in temperate montane peatlands. We investigated the effect of drainage on physicochemical properties and organic carbon fractions of six peat cores from drained and near-pristine areas of Baijianghe peatland, NE China, basing on 210Pb and AMS 14C dating. The vegetation biomass and biomass-C sequestration were also measured in both areas. The loss of total soil carbon accumulation due to drainage was 7.5 kg m−2 (− 25%), equivalent to a complete consumption of carbon accumulated for nearly 170 years in the near-pristine area. Vegetation succession after drainage had a little positive effect on ecosystem carbon sequestration, with an increase of 0.26 kg m−2, which compensated for only 3.5% of the peat soil carbon loss. Notably, over 80% of the total carbon loss after drainage was attributed to the loss of the recalcitrant carbon fraction. The study emphasizes the crucial impact of drainage on carbon sequestration in temperate peatlands. Our findings suggest that continuous water table drawdown induced by drainage, together with drought driven by climate warming, will further reduce carbon sequestration in drained peatlands. There is an urgent need to restore hydrology of peatlands in order to mitigate the long-lasting negative effect of drainage. [ABSTRACT FROM AUTHOR]

Background and aims: Changes in morphological traits of fine roots indicate shift in adaptive strategies. However, it remains unclear how nitrogen (N) and phosphorus (P) depositions change fine root adaptive strategies in peatlands, both in the growing and non-growing seasons. Methods: We collected fine roots from shrubs and herbaceous plants after 2-year N and P additions and measured key morphological traits to evaluate different adaptive strategies. Results: During the growing season, P addition significantly increased shrub fine root production (FRP) by decreasing fine root length (FRL) under ambient N condition, while the effect was diminished when P was added in combination with N. Phosphorus addition significantly increased FRP by increasing FRL and fine root diameter (FRD) of herbaceous plants irrespective of N addition rate. Fine roots of shrub and herbaceous plants adopted contrasting adaptive strategies after fertilization. Fine roots of both shrub and herbaceous plants still grew in the non-growing season, but only shrub FRP was significantly decreased after N addition by decreasing root tissue density (RTD). Conclusion: Shrub FRP was more responsive to N addition whereas P addition had a stronger impact on herbaceous FRP. Nitrogen and P additions may have led to a shift towards the "outsourcing" strategy for herbaceous fine roots, whereas shrub fine roots tended to adopt the "fast" conservation strategy under P addition. Overall, N addition was disadvantageous to shrubs to survive cold winter. Our findings can advance the understanding of changes in fine root adaptation in northern peatlands under imbalanced N and P deposition. [ABSTRACT FROM AUTHOR]

Peatlands are limno-terrestrial habitats that support rich microscopic algae, whereas algal distribution is poorly known in peaty environments. This study aims to explore diatom diversity patterns and underlying driving forces in Sphagnum peatlands of central and northeastern China. A total of 200 diatom species were observed in 138 living Sphagnum samples collected from 8 peatlands in northeastern and central China, suggesting that diatoms are more prevalent in these limno-terrestrial environments than generally considered. The Simpson index was negatively correlated with dissolved organic carbon (DOC) in central China, while it was negatively correlated with water table depth (WTD) in northeastern China. Distance–decay rate of diatom community similarity was faster in central China than in northeastern China, probably due to strong dispersal limitation in these enclosed montane peatlands of central China. For diatom composition in the two regions, the pure effect of environmental variables explained more variance than that of regional climate or spatial factors, suggesting that niche-based processes primarily determined diatom composition in these peatlands. Our results highlight the importance of WTD and DOC in constraining diatom diversity patterns in Sphagnum peatlands. [ABSTRACT FROM AUTHOR]

Peatlands are important nutrient-limited, carbon (C)-accumulating ecosystems where phosphorus (P) is one major limiting nutrient. An increase in P input to peatlands has been observed close to agricultural areas. However, the effects of P input on gross primary productivity (GPP), ecosystem respiration (ER) and net ecosystem exchange (NEE) of peatlands, especially in temperate Asia, have been rarely studied. We selected the P addition plots of a 12-year experiment simulating environmental change in a peatland in northeastern China to evaluate the effect of P addition (5 and 10 kg ha−1 y−1) on carbon dioxide fluxes. Our results showed that the growth of Sphagnum was inhibited but that of vascular plants was facilitated by P addition, resulting in an unchanged GPP. P addition increased ER due to the increased activity potentials of N-acetyl-β-glucosaminidase (NAG) and polyphenol oxidase (POX) that might, in turn, increase the metabolic rate of soil microbes and enhance the decomposition of peat. During the growing season, a mean net CO2 absorption of 0.002 mg m−2 s−1 was observed at high levels of P addition, which was much lower than that of 0.063 mg m−2 s−1 in the controls. The results suggest that long-term P addition will greatly weaken the C sequestration in peatlands by enhancing ER rather than reducing GPP. Our study highlights the importance of the response of vegetation and soil enzyme activities to P addition regarding peatland respiration and C sink function. [ABSTRACT FROM AUTHOR]

Litter decomposition is a key process controlling carbon (C) sequestration in Sphagnum dominated peatlands. Peatland drainage lowers the water table, increases vascular plant richness, and alters species evenness. We hypothesized that abiotic and biotic changes following peatland drainage would greatly accelerate litter decomposition. This hypothesis was tested by a litter decomposition experiment in an undrained and a drained area of a peatland which was partially drained 30 years ago. Litter bags filled with shoots of the peat moss Sphagnum magellanicum and leaves of the dwarf shrub Potentilla fruticosa as single species and species mixtures with three evenness treatments were placed at the surface of the peatland. After 6 months (from August onwards) of decomposition, the single species litter of Potentilla fruticosa, with low initial C/N ratio, decomposed much faster than S. magellanicum litter, with high initial C/N ratio in both undrained and drained areas. Overall, mixed litter produced antagonistic effects (observed values less than expected) on decomposition and C/N ratio. Litter mixtures dominated by S. magellanicum showed lower mass loss than other mixtures. Contrary to our expectation, the undrained area showed higher decomposition than the drained area. Our study suggests that drainage-induced alteration in plant diversity slows down litter decomposition in a short term. However, in drained peatlands, lower C/N ratio of mixed litter may enhance decomposition and reduce C sequestration over time. [ABSTRACT FROM AUTHOR]

Background and aims: Plant carbon (C), nitrogen (N), phosphorus (P) levels and their stoichiometry and N uptake strategies are important aspects influencing vegetation composition and C dynamics in boreal peatlands. However, C, N and P levels and N sources of different plants remain poorly understood, which prevents a better assessment of plant responses to projected increasing N availability in boreal ecosystems with climate warming and increasing N deposition. Methods: We investigated differences of leaf C, N and P concentrations and C and N isotopes (δ13C and δ15N) between graminoids and shrubs in 18 peatlands in northeastern China. Results: Ericoid mycorrhizal (ERM) and ectomycorrhizal (ECM) shrubs have higher C and P while lower C/N and C/P than nonmycorrhizal (NM) graminoids. Shrubs and graminoids have similar leaf N/P, mainly exhibiting N limitation or N and P co-limitation. ECM shrubs show higher N and lower δ15N than NM graminoids despite having similar rooting depths, indicating higher N availability and more uptake of 15 N-depleted organic N of ECM shrubs. However, deep-rooted ECM shrubs show slightly higher N than shallow-rooted ERM shrubs, and their δ15N differences are insignificant. Shallow-rooted ERM shrubs have higher N and lower δ15N than deep-rooted NM graminoids. Conclusions: Our results imply lower N and P use efficiencies of shrubs than graminoids, and the important role of mycorrhizal association in differentiating N availabilities and sources between shrubs and graminoids. These findings are useful for understanding peatland plant responses to environmental changes. [ABSTRACT FROM AUTHOR]

Spore production of bryophytes is common in subalpine ecosystems, but how spore banks of bryophytes vary with elevations is unknown. We used peat cores from two Sphagnum dominated peatlands, a low- (780 m a.s.l.) and a high-elevation (1480 m a.s.l.) site to test the hypotheses that spore concentration, accumulation rate, germinability and longevity are lower at a high-elevation peatland than those at lower elevation due to the assumed climatic limitations at high elevation. Along the cores, Sphagnum spores were extracted, burial time of spores was dated and spore germinability was tested layer by layer. Sphagnum spore concentration, accumulation rate and germinability were greater at the high-elevation peatland than at the low-elevation site. Both peatlands had long-term persistent Sphagnum spore banks with a predicted longevity (the burial time when 1% spores are viable) of c. 390 and 140 years for the low- and high-elevation sites, respectively. Our study suggests that Sphagnum, the ecological engineer of peatlands, by regulating spore production and longevity can maintain relatively constant spore banks which may be of great importance in population regeneration and persistence in a changing world. [ABSTRACT FROM AUTHOR]

Aims: Separating the effect of resource competition from allelopathy in plants is challenging and it has never been attempted in closely related co-occurring bryophytes. In peatlands, peat mosses (Sphagnum spp.) show niche differentiation along water table level (WTL) gradient. Our aim was to evaluate whether the hummock species, S. magellanicum would be a winner at low WTL due to its allelopathic advantage and the hollow species, S. angustifolium would win by virtue of its superior competitive ability but not of allelopathy at high WTL due to dilution of its allelochemicals. Methods: We used a nested, field experimental design, with two WTL treatments—low WTL (hummock habitat) and high WTL (hollow habitat)—and three different inter-specific interactions: 1) monoculture; 2) mixed culture without activated charcoal; and 3) mixed culture with activated charcoal added to the neighbor. We measured growth and biochemical traits of the two species and compared the index of relative neighbor effect on each other. Results: We discovered a trade-off between biomass production (competitive outcome) and phenolic content (allelopathy) in these species. At low WTL, allelopathy of the hummock species is the main mechanism to suppress the hollow species, whereas at high WTL, competition is the main driver to suppress the hummock species. Conclusions: Competitive advantage in Sphagnum is mediated by both resource competition and allelopathy of the co-occurring species through niche differentiation along a WTL gradient. Unlike vascular plants, Sphagnum mosses can serve as excellent model organisms in studying allelopathic interaction since they bypass the complexity of plant-soil interactions. [ABSTRACT FROM AUTHOR]

Aims: To test the effects of characteristic ecological gradients in peatlands including oxygen-deficiency and allelopathy on Sphagnum spore persistence.Methods: We determined the initial viability of Sphagnum spores and then stored the spores for 60 days, either dry, in ultrapure water, peatland surface water or Sphagnum water leachate (the latter two solutions rich in allelochemicals from Sphagnum). We varied oxygen concentration by injecting air at three different concentrations during the storage experiment. After retrieval from experimental storage, spore germinability index was assessed.Results: Germinability index after air injection was lower than under oxygen-deficiency. Germinability index in the peatland surface water and Sphagnum leachate water was higher than in ultrapure water, under oxygen-deficiency. Overall, dissolved oxygen and high pH negatively affected spore germinability and, consequently, viability.Conclusions: These results indicate that once dispersed onto bryophyte substrates or waterlogged hollows, Sphagnum spores can maintain viability better than when exposed to dry conditions or in water without allelochemicals. Extreme longevity of Sphagnum spores may be attributed to the oxygen-deficient, waterlogged and acidic Sphagnum-dominated peatland habitat with allelopathic substrates. [ABSTRACT FROM AUTHOR]

The dynamics of polycyclic aromatic hydrocarbon (PAH) degradation in Sphagnum litters and the decomposition of the litters were investigated. PAH concentration decreased to approximately half of the initial concentration as Sphagnum litters decayed. The initial PAH concentration was 489.2 ± 72.2 ng g−1, and the concentration after 120 days of incubation was 233.0 ± 5.8 ng g−1. The different PAH compositions changed concentrations at different times. The low-molecular-weight (LMW) and high-molecular-weight (HMW) PAHs started to be degraded after incubation and after 40 days of incubation, respectively. PAH concentrations in the Sphagnum litters correlated with the total organic carbon (TOC) content (p < 0.05), indicating that PAHs were associated with the TOC of the Sphagnum litters and were degraded as organic matter decayed. The positive relationship between LMW PAH concentration and the soluble carbohydrate content (p < 0.05) indicated that LMW PAHs and the readily decomposed organic carbon fractions were cometabolized, or that LMW PAHs were mainly absorbed by soluble carbohydrate. The weak negative correlation between fulvic acid (FA) and PAH concentrations (p < 0.1) indicated that FA may enhance PAH degradation. Redundancy analysis suggested that the contents of both soluble carbohydrate and cellulose significantly affected the changes in PAH concentrations (p < 0.05), and that FA content and C/N ratios may also contribute to the changes in PAH concentrations (p < 0.1). However, the polyphenol that was related to microbial activities was not associated with changes in PAH concentrations. These results suggested that litter quality is more important than microbial activities in PAH degradation in Sphagnum litters. [ABSTRACT FROM AUTHOR]

Burial depth within soil affects the survival of seeds and spores in ecosystems. However, burial depth effect on germinability of Sphagnum spores received little attention. In a peatland in Northeast China, we conducted a spore burial experiment using two hollow dwelling species, Sphagnum squarrosum and S. fallax. We hypothesised that i) S. squarrosum would show lower spore germinability than S. fallax because of its limited distribution in open area and ii) for both species there would be increased spore germinability along burial depth gradient because greater depth provides better conditions for spore preservation. After one-year spore burial, we conducted a laboratory germination bioassay to test spore germinability, determined by germination percentage (GP) and germination index (GI). Spore germinablity of S. squarrosum was >60% lower than S. fallax. Both species showed at least 40% higher germinability when buried in hollows than in hummocks. Overall spore germinability increased with burial depth with maximum germinability at 30 and 20 cm below the surface of hummocks and hollows respectively, where water table fluctuation occurred. We conclude that although hollows are better habitats for spore storage, continuous waterlogging may not be favourable for maintaining high germinability of Sphagnum spores. [ABSTRACT FROM AUTHOR]

Age structure of a plant population carries important information on population dynamics. The traditional age classification of individuals by development phases could not explain the generation relationship neither between individuals nor between modules, and it could not accurately predict the future of population or the tendency of peatland evolution. In a peatland of the Xiao Hinggan Mountains, China, at the middle of the growth season, the age structures of 3 modules, ramets, active buds and rhizomes of a Carex middendorffii clonal population were investigated, with the method of classifying age classes of ramets and active buds by counting generation quantity of tiller nodes, and classifying age classes of rhizomes by their real survival time. The quantity of vegetative ramets was dominant. Tiller nodes of ramets can propagate vegetatively for a maximum of 3 generations. The population of ramets consisted of 3 age classes of ramets at the middle of the growth season, and showed a stable age structure. In the two sampling events, there was no significant difference between quantities and age structure of the population. The maximum age of an excavated rhizome was 12 years old. Rhizomes were classified in 8 age classes, and age classes 4–6 contributed most to the total biomass. There was no significant difference in total length and total biomass per unit area, or in biomass per unit length in rhizomes between the two samplings. Four age classes of active buds were recognized, and their number increased from July to August. The Carex middendorffii clonal population achieved regeneration by budding from the tiller nodes of ramets. The age structures of the 3 modules suggested that the Carex middendorffii clonal population could persist in the early development phase of the oligotrophic peatland in the Xiao Hinggan Mountains, but it could not be dominant. It also faces the risk to disappear from the community as the peatland develops further. [ABSTRACT FROM AUTHOR]