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Summary1 A 3-year experiment involving nutrient addition and removal of one of two coexisting dwarf shrub species was conducted in two community types in a subalpine heathland on the northern Apennines (Italy). Vaccinium uliginosum occurred at all sites but was associated with the deciduous Vaccinium myrtillus at more sheltered nutrient-rich sites (HV community), and with the evergreen Empetrum hermaphroditum where the habitat was poorer and more exposed (EV community). Length of current-year shoots and fruit production of each species were determined in each of the 3 years, and standing crop at the beginning and end of the experiment.2 The length of current-year shoots of both deciduous species, but not of the evergreen, varied considerably between years, presumably due to varying temperatures at the beginning of the three growing seasons. Fruit production also varied. 3 Fertilization promoted an increase in the length of V. uliginosum shoots at the HV community but not at the EV community. The removal of V. uliginosum enhanced shoot elongation in V. myrtillus (HV community) but reduced shoot elongation in E. hermaphroditum (EV community). Neighbour removal did not aect shoot length of V. uliginosum at either community. There were few treatment eects on fruiting of these clonal species. 4 The standing crop in untreated stands did not change during the experimental period. Changes in shoot length resulting from environmental manipulations were not accompanied by consistent variation in the standing crop of any species. Standing crop increased only for V. myrtillus after removing V. uliginosum at the HV community (same direction as shoot length). The standing crop of E. hermaphroditum did not change after removing V. uliginosum at the EV community, although shoot length was signi®cantly reduced. The standing crop of V. uliginosum was unaected by neighbour removal and was decreased by nutrient addition at both communities. 5 None of the shrubs appeared able to utilize more abundant resources to increase above-ground biomass. However, increased shoot length in nutrient-rich habitats gave V. uliginosum a superior ability to capture light compared with V. myrtillus, the latter being more successful when the coexisting competitively superior species was removed. This would support Grime's theory, indicating that competition becomes more important as soil resource levels increase. Positive interactions appeared to play a role in the more extreme habitat, where E. hermaphroditum normally bene®ted from the shelter of the V. uliginosum canopy but was able to adapt its architecture when exposed.

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Two subalpine dwarf-shrub heath communities with differing levels of soil nutrient availability were subjected to a 3-year experimental manipulation, including nutrient addition or removal of one of the two co-dominant species from each community. The main objective of our study was to assess the relative importance of interspecific competition versus nutrient limitation in relation to soil fertility. We also aimed to investigate if and to what extent current-year shoot size, leaf-based rates of net photosynthesis and foliar nutrient status accounted for the observed changes in the aboveground biomass of the shrubs. At the end of the experiment, neighbour removal increased the aboveground biomass of all shrubs, especially in the more fertile community, while fertilization did not. We concluded that: (1) competition is more effective than nutrient limitation in structuring the vegetation of subalpine heathlands; and (2) competition intensity is stronger in the more fertile community. The observed patterns of variations in aboveground biomass were not consistently related to net photosynthetic rates, size of individual shoots and foliar nutrient status. Hence, we also concluded that the growth response of dwarf shrubs to altered environmental conditions is primarily determined by developmental plasticity.

Periodic measurements of gas‐exchange rates and determinations of foliar N and P concentrations were used for evaluating instantaneous water‐use efficiency and photosynthetic nutrient‐use efficiency in two co‐existing dwarf shrubs of different growth form (V. myrtillus, deciduous, and V. vitis‐idaea, evergreen) in a subalpine heath in the southern Alps of Italy. Those data were compared with cumulative assessments of water‐use efficiency and photosynthetic nutrient‐use efficiency obtained by measuring leaf carbon isotope discrimination in leaf tissues and by estimating nutrient resorption from senescing leaves. V. myrtillus presented higher dry‐weight based rates of net photosynthesis (Aweight) compared to V. vitis‐idaea. Aweight was positively correlated with foliar‐nutrient status and intercellular‐to‐ambient gradient in CO2 concentrations. Aweight was, furthermore, negatively correlated with leaf specific mass. Instantaneous photosynthetic nutrient‐use efficiency did not differ between the two species but the percentages of N and P pools resorbed from senescing leaves were somewhat higher in the deciduous species. The evergreen species showed lower P concentrations in senescing leaves which indicated a higher proficiency in resorbing phosphorus compared to the deciduous species. In addition, the evergreen species achieved a higher carbon gain per unit foliar N and P, due to a longer mean residence time of both nutrients. The two species did not differ from each other with respect to both instantaneous and long‐term water‐use efficiency. This was consistent with the climatic pattern, showing no sign of water deficiency through the growing season. Current‐year V. vitis‐idaea leaves had a significantly higher Δ13C compared to previous‐year leaves, possibly mirroring a long term acclimation of evergreen leaves, as far as they age, to the habitat conditions in the understory where evergreen species are usually confined within mixed dwarf‐shrub communities.

AimsAltitude is often used as a proxy for ascertaining how warming affects plant growth and leaf level properties. However, we have a poor understanding of how the effects of altitude-related warming varies across geology. therefore, this study examined the independent and interactive effects of altitude and geology and species on plant growth and foliar nutrient status. MethodsWe determined leaf growth rates and concentrations of major nutrients (nitrogen, N and phosphorus, P) in leaves of five species across two altitudinal gradients (1200-2200 m) in the Dolomites (south-eastern Alps, Italy). the two transects were located on carbonate bedrock and silicate bedrock, respectively. We also determined concentrations of inorganic and organic N and P forms in soils, and δ 15 N signature in leaves and soils. Important FindingsFoliar N concentrations were unrelated to bedrock geology. the negative foliar δ 15 N signature suggested that organic N was the primary source of N supply across the gradients. Foliar P concentrations were strongly affected by bedrock geology and their altitudinal patterns depended on the concentrations of organic and inorganic P forms in the soil. Phosphates and organic P appeared to be the main sources of P supply. Leaf growth rates increased with higher altitude on silicate bedrock and decreased with higher altitude on carbonate bedrock and presented a significant positive correlation with foliar N:P. In conclusion, bedrock geology interacted with altitude in controlling the foliar nutrient status mainly owing to availability of soil P and its effect on foliar nutrient stoichiometry.