SUMMARY (3) In deciduous shrubs, up to 14%. of the total plant capital of nitrogen and phosphorus was translocated from stems and large roots into leaves during the 3 weeks following snow-melt. The amount in stems and roots was not fully replaced by uptake until late autumn. At this time, 50-60%0 of the nitrogen and phosphorus which had been in leaves was removed. In contrast, the evergreen shrub translocated nitrogen and phosphorus to leaves gradually throughout the growing season, and showed no evidence of large stores of nutrients in stems or roots. By late August 46% of the total nitrogen of evergreen shrubs was present in leaves. (4) Potassium was not effectively back-translocated to stems of the deciduous species sampled. (5) In the graminoid Eriophorum vaginatum, spring production of roots as well as leaves depleted nitrogen reserves in the rhizome. Similar dependence of root production upon stored nutrient reserves is suggested in deciduous shrubs. (6) The differences in nutrient allocation between the mosses Aulacomnium spp. and Polytrichum spp. were just as pronounced as those between evergreen and deciduous vascular species, and may relate to the source of nutrients. Lichens had a uniformly low content of the major nutrients. (7) Some implications of seasonal nutrient patterns for herbivores are discussed.

Seasonal movement of nutrients in plants of differing growth form in an Alaskan tundra ecosystem: implications for herbivory.

Les resultats obtenus dans un marais domine par Puccinellia phryganodes et Carex subspathacea a La Perouse Bay (Canada) suggerent que le pâturage stimule la production primaire en accelerant le cycle de l'azote

The Effects of Grazing by Lesser Snow Geese on the Vegetation of a Sub- Arctic Salt Marsh

Summary
•Altitudinal gradients strongly affect the diversity of plants and animals, yet little is known about the altitudinal effects on the distribution of microorganisms, including ectomycorrhizal fungi.
•By combining morphological and molecular identification methods, we addressed the relative effects of altitude, temperature, precipitation, host community and soil nutrient concentrations on species richness and community composition of ectomycorrhizal fungi in one of the last remaining temperate old-growth forests in Eurasia.
•Molecular analyses revealed 367 species of ectomycorrhizal fungi along three altitudinal transects. Species richness declined monotonically with increasing altitude. Host species and altitude were the main drivers of the ectomycorrhizal fungal community composition at both the local and regional scales. The mean annual temperature and precipitation were strongly correlated with altitude and accounted for the observed patterns of richness and community.
•The decline of ectomycorrhizal fungal richness with increasing altitude is consistent with the general altitudinal richness patterns of macroorganisms. Low environmental energy reduces the competitive ability of rare species and thus has a negative effect on the richness of ectomycorrhizal fungi. Because of multicollinearity with altitude, the direct effects of climatic variables and their seasonality warrant further investigation at the regional and continental scales.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.2011.03927.x

Regional and local patterns of ectomycorrhizal fungal diversity and community structure along an altitudinal gradient in the Hyrcanian forests of northern Iran.

Boreal forests harbour diverse fungal communities with decisive roles in decomposition and plant nutrition. Although changes in boreal plant communities along gradients in soil acidity and nitrogen (N) availability are well described, less is known about how fungal taxonomic and functional groups respond to soil fertility factors. We analysed fungal communities in humus and litter from 25 Swedish old-growth forests, ranging from N-rich Picea abies stands to acidic and N-poor Pinus sylvestris stands. 454-pyrosequencing of ITS2 amplicons was used to analyse community composition, and biomass was estimated by ergosterol analysis. Fungal community composition was significantly related to soil fertility at the levels of species, genera/orders and functional groups. Ascomycetes dominated in less fertile forests, whereas basidiomycetes increased in abundance in more fertile forests, both in litter and humus. The relative abundance of mycorrhizal fungi in the humus layer remained high even in the most fertile soils. Tolerance to acidity and nitrogen deficiency seems to be of greater importance than plant carbon (C) allocation patterns in determining responses of fungal communities to soil fertility, in old-growth boreal forests.

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/nph.13426

Changes in fungal communities along a boreal forest soil fertility gradient

Summary
Small open-top chambers (OTC) are used widely in ecosystem warming experiments. The efficacy of the open-top chamber as an analogue of climatic warming is examined. Twenty-four small OTCs were used to passively warm canopy temperatures in wet meadow tundra at Barrow, Alaska, during two consecutive summers with contrasting surface air-temperatures. Fortuitously, the seasonal average temperature regime within chambers in the colder year (1995) was similar to the controls of the warmer year (1996); this allowed a comparison of natural vs. chamber warming. All measured plant responses behaved similarly to both year and treatment 68% of the time. A comparison of the populations of the warmer summer's control with the cooler summer's OTC found no statistical difference in 80% of the response variables measured. A meta-analysis also found no significant difference between the responses of the two populations. These results give empirical biotic validation for the use of the OTC as an analogue of regional climate warming.

P. Widden

Papers

Arctic Tundra Ecosystems