Effects of dry-deposited sulphur dioxide on fungal decomposition of angiosperm tree leaf litter I. Changes in communities of fungal saprotrophs

Warming, shading and a moth outbreak reduce tundra carbon sink strength dramatically by changing plant cover and soil microbial activity

Future increases in temperature and cloud cover will alter plant growth and decomposition of the large carbon pools stored in Arctic soils. A better understanding of interactions between above- and belowground processes and communities of plants and microorganisms is essential for predicting Arctic ecosystem responses to climate change. We measured ecosystem CO2 fluxes during the growing season for seven years in a dwarf-shrub tundra in West Greenland manipulated with warming and shading and experiencing a natural larvae outbreak. Vegetation composition, soil fungal community composition, microbial activity, and nutrient availability were analyzed after six years of treatment. Warming and shading altered the plant community, reduced plant CO2 uptake, and changed fungal community composition. Ecosystem carbon accumulation decreased during the growing season by 61% in shaded plots and 51% in warmed plots. Also, plant recovery was reduced in both manipulations following the larvae outbreak during the fifth treatment year. The reduced plant recovery in manipulated plots following the larvae outbreak suggests that climate change may increase tundra ecosystem sensitivity to disturbances. Also, plant community changes mediated via reduced light and reduced water availability due to increased temperature can strongly lower the carbon sink strength of tundra ecosystems.

Nutrient cycling in different terrestrial ecosystems in relation to fungi

Comparisons are made between nutrient cycling systems of arctic tundra, temperate forest, tropical forest, grassland, arable, and desert ecosystems. Detailed nutrient budgets are not given, but general differences between ecosystems are discussed primarily in relation to the role of soil fungi. General discussion reviews the impact of anthropogenic factors, including land management, pollution, and climate change on the role of fungi in nutrient cycling. Areas where further research is needed to complete our understanding of the functional aspects of fungi and nutrient cycling are highlighted and some of the techniques that may be employed are discussed. Key words: nutrient cycling, ecosystems, fungi.

Effects of dry-deposited sulphur dioxide on fungal decomposition of angiosperm tree leaf litter III. Decomposition rates and fungal respiration

Ash (Fraxinus excelsior L.), birch (Betula spp.), hazel (Corylus avellana L.), sessile oak [Quercus petraea (Mattuschka) Liebl.] and sycamore (Acer pseudoplatanus L.) leaf litters from a virtually non-polluted and a heavily sulphur dioxide (SO₂ )-polluted woodland were fumigated with environmentally-realistic concentrations (0.010-0.030μl l^-1 ) of SO₂ for 16-68 wk in an open-air field-fumigation experiment. Fumigation inhibited the respiration (CO₂ evolution) and decomposition rates of the leaf litters. However, there were few differences in the responses between leaf litters from the two woodlands. In addition, pure cultures of four saprotrophic fungi were grown individually on irradiated hazel litter and exposed to c. 0.030μl l^-1 of gaseous SO² , for 28 d in the laboratory. The gas inhibited the respiration of Phoma exigua Desm. and Phoma macrostoma Mont, but not the respiration of Cladosporium cladosporioides (Fres.) de Vries or Coniothyrium quercinum Sacc. var. glandicola Grove. These results in part substantiated findings of previous experiments examining the effects of SO₂ on the structures of saprotrophic fungal communities. The effects of SO₂ on fungal decomposition of angiosperm tree leaf litter as possible causes of forest decline are discussed.

Effects of dry-deposited sulphur dioxide on fungal decomposition of angiosperm tree leaf litter II. Chemical content of leaf litters

Ash (Fraxinus excelsior L.), birch (Betula spp.), hazel (Corylus avellana L.), sessile oak [Quercus petraea (Mattuschka) Liebl.] and sycamore (Acer pseudoplatanus L.) leaf litters from a non-polluted and a heavily sulphur dioxide (SO₂ )-polluted woodland were fumigated with environmentally-realistic concentrations (0.010-0.030 μl l^-1 ) of SO₂ for 16-68 wk in an open-air field-fumigation experiment. Fumigation markedly increased sulphate and protons in leachates from the litters and decreased calcium and magnesium contents of the leaves. However, there were few differences in the responses between leaf litters from the two woodlands. This was attributed to rapid sulphate wash-out from the litters from the heavily polluted woodland, so that the litters from the two sites quickly reached the same sulphate status.