[1] Forested peatlands represent an important global carbon pool, storing 48.0 Pg of carbon within continental western Canada alone. Peatland hydrology regulates the carbon dynamics and future stability of this carbon store and provides a critical control on regional water dynamics. Drying associated with land-use change and climate change has the potential to increase tree growth, modifying the density, size, and spatial arrangement of trees. This can reduce peatland evaporation and offset the associated increase in transpiration. To determine the magnitude of this negative ecohydrological feedback, we simulated spatial variations in radiation, turbulent energy fluxes, and temperatures in peatlands with real and idealized tree densities and distributions. For a random tree distribution, an increase in tree density from 0 to 4 trees per m 2 reduced available energy at the peat surface, decreasing average evaporation by 25%. At higher tree densities, feather moss species covered a larger fraction of the ground because of lower light availability. In combination with the lower energy availability, this change in moss composition reduced evaporation by~70%. The reduction in evaporation was greater (83%) when the effects of increased canopy cover on peatland aerodynamic properties were incorporated. Additionally, we found that evaporation was dependent on the spatial arrangement of trees, with evaporation being higher when trees were clustered. Overall, our model showed that the trade-off between reduced evaporation and increased transpiration with increasing tree densities reduced landscape variation in evapotranspiration, with simulated evapotranspiration remaining approximately constant across a broad range of peatland ecosystems despite varying canopy densities.

Snow amount is expected to decline in the Northern hemisphere as an effect of climate warming. However, snow amount in alpine regions will probably undergo stronger interannual fluctuations than elsewhere. We set up a short-term (1 year) experiment in which we manipulated snow cover in an alpine bog, with the following protocol: snow removal at the end of winter; snow removal in spring; snow addition in spring; removal of all aboveground plant tissues with no snow manipulation; no manipulation at all. We measured, at different dates from late spring to early autumn: ecosystem respiration (ER), and concentrations of carbon (C), nitrogen (N) and phosphorus (P) in the soil and in microbes. We hypothesized that longer duration of snow cover will lead to: i) higher ER rates associated with increased microbial biomass; and ii) decreased soil nutrient availability. Contrary to our first hypothesis, ER and microbial C content were unaffected by the snow cover manipulations, probably because ER was decoupled from microbial biomass especially in summer, when CO 2 efflux was dominated by autotrophic respiration. Our second hypothesis also was partially contradicted because nutrient content in the soil and in plants did not vary in relation to snow cover. However, we observed unexpected effects of snow cover manipulations on the N : P ratio in the microbial biomass, which declined after increasing snow cover. This probably depended on stimulation of microbial activity, which enhanced absorption of P, rather than N, by microbes. This may eventually reduce P availability for plant uptake

We determined concentrations of major nutrients in the vegetation of six habitat types (hummock, scrub, lawn, fen meadow, hollow and marginal stream), spanning a broad range of environmental conditions as regards water-table depth and water chemistry, in five mires on the southern Alps of Italy. Our study was based on chemical analyses of living tissues of plant species, grouped into growth-form based plant functional types (PFTs). We aimed at assessing to what extent the observed differences in tissue nutrient content were accounted for by community composition (both in terms of species and PFTs) and by habitat. Nutrient concentrations were overall lowest in Sphagnum mosses and highest in forbs, although the latter showed large variations presumably due to heterogeneity in mechanisms and adaptations for acquiring nutrients among species within this PFT. Nutrient content patterns in the other three PFTs varied greatly in relation to individual nutrients, with evergreen shrubs showing low nitrogen (N) concentrations, graminoids showing high N concentrations but low potassium (K) and magnesium (Mg) concentrations and deciduous shrubs showing rather high phosphorus (P) concentrations. Habitat accounted for a modest fraction of variation in tissue concentration of all nutrients except P. We concluded that the nutrient status of mire vegetation is primarily controlled by community composition and structure although habitat does exert a direct control on P concentration in the vegetation, presumably through P availability for plant uptake

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We determined aboveground net primary production (ANPP) in five mires in the South-eastern Alps of Italy. The mires differed considerably from each other with regard to pore-water chemistry, ranging from bog to rich fen. In different habitat types (hummock, scrub, lawn, fen meadow, hollow and marginal stream) within each mire type we assessed nutrient status based on measurements of nutrient concentrations and nutrient ratios in the plant biomass in order to test whether ANPP patterns along the poor-rich gradient could be related to the limiting effects of one or several nutrients for biomass production. Vegetation composition varied considerably both among mire sites and among habitat types in terms of individual species and plant functional types (PFTs). Nonetheless, mean ANPP was similar in the five mires. However, ANPP showed a positive correlation with total P concentration and negative correlations with the N:P ratio and with the K:P ratio of the vegetation. We conclude that plant biomass production is limited by P, rather than by other nutrients, across a broad range of mire types in this region.Produzione primaria e status nutritizio nella vegetazione di torbiera nelle Alpi sud-orientali italiane Riassunto In questo lavoro viene analizzata la produzione primaria netta in cinque torbiere delle Alpi sudorientali.Queste torbiere presentano notevoli differenze nel chimismo dell'acqua di falda e la loro tipologia varia da torbiere alte ombrotrofiche a torbiere basse fortemente minerotrofiche. La vegetazione di queste torbiere differisce inoltre considerevolmente sia in termini di composizione specifica che di frequenza dei tipi funzionali. Nonostante tali differenze, la produzione primaria nelle cinque torbiere non presenta differenze significative tra le cinque torbiere. La produzione primaria risulta invece positivamente correlata con la concentrazione totale di fosforo nella vegetazione e negativamente correlata con il rapporto N:P e con il rapporto K:P nella vegetazione. In conclusione, la produzione primaria nei siti esaminati è principalmente limitata da carenze di fosforo. Tale limitazione si esercita in un ampio ambito di tipi di torbiera.