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Question In cold regions, snow cover duration is expected to decrease, especially in spring, as a consequence of climate warming. We investigated effects of changes in timing of snowmelt in relation to weather conditions on Vaccinium myrtillus, a dominant shrub in heath vegetation. We tested the hypothesis that advanced snowmelt will enhance shrub growth in years with few frosts, but will reduce shrub growth in years with frequent frosts. Location A sub‐alpine heath in the Northern Apennines (Italy). Methods We carried out two experiments. In the main experiment, snow was added to (+S) or removed from (−S) experimental plots in spring of three growing seasons (2004–2006), with a mean delay in snowmelt timing of about 2 wk from −S to +S. In a companion experiment, we simulated a freezing event in late spring 2004. Results During the snowmelt period, the −S plants experienced 6–10 more frost events, compared with +S and unmanipulated controls (C) in 2004 and 2005, but not in 2006. In the first 2 yr leaf production, leaf expansion and flowering were all significantly reduced in the −S plants, while shoot elongation was unaffected. In the companion experiment with artificial frost V. myrtillus presented similar responses. Conversely, the manipulations of snow did not affect either the hydric or nutrient status of plants and soils. Conclusions The results overall support our hypothesis, as shown by the differing effects of snow depth and timing of melt on V. myrtillus in the 3 yr. Spring frost was the cause of reduced growth and reduced flower production in 2004 and 2005. However, advanced snowmelt will not decrease the cover of this dominant species. Therefore, the structure and species dominance patterns in sub‐alpine heath are not expected to change significantly in response to reduced snow cover. Support for this conclusion is provided by the capacity of V. myrtillus to recover vegetatively from frost injury through stimulated shoot elongation, and by the low importance of sexual reproduction for propagating dominant ericaceous shrubs in closed heath communities.

In this study, we describe the seasonal variation in 15 N abundance in the litter of two Sphagnum species and four vascular plant species during 3 years of field decomposition in an Italian Alpine bog. Litter bags were periodically retrieved at the end of summer and winter periods, and the δ 15 N in residual litter was related to mass loss, litter chemistry, and climatic conditions. In Sphagnum litter, higher rates of decomposition during summer months were associated with an increase of δ 15 N probably due to the incorporation of microbial organic compounds rich in 15 N. The litter of Eriophorum vaginatum and Carex rostrata was characterized by a decrease of δ 15 N, so that the final signature was significantly lower than in initial litter. On the other hand, the residual litter of Potentilla erecta and Calluna vulgaris was characterized by a final δ 15 N higher than in initial litter. Our data reported a seasonality of 15 N abundance in the residual litter of Sphagnum species, but not in that of vascular plant species, thus highlighting the role of differences in litter chemistry.

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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