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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]

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]

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]

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]