Scots pine responses to CO2 enrichment--I. Ectomycorrhizal fungi and soil fauna

Ectomycorrhizal Scots pine seedlings were grown in unfertilized forest soil at ambient and double (ca 700 ppm) atmospheric concentrations of CO2. The biomass of seedlings and fungal biomass both in the roots and in the soil and the numbers of certain groups of soil animals were measured under summer conditions and after an artificial winter acclimation period. No biomass parameter showed any significant change due to CO2 elevation. Increases were found during the winter acclimation period in total and fine root biomasses, fungal biomass in the soil and total fungal biomass both in the roots and in the soil, while the ratio of needle biomass: fungal biomass and the shoot: root ratio decreased. The N concentration in previous-year needles was lower in the double CO2 environment than with ambient CO2. Enchytraeids almost disappeared in the double CO2 environment during winter acclimation, while the numbers of nematodes increased at the same time in both treatments.     

Shift in ectomycorrhizal community composition in Scots pine (Pinus sylvestris L.) seedling roots as a response to nickel deposition and removal of lichen cover

Scots pine seedlings were exposed to wet-deposited nickel (Ni) and removal of lichen cover in a dry heath Scots pine forest. Ni deposition affected the colonization of roots by indigenous ectomycorrhizal fungi in contrasting ways in intact and skimmed quadrats. Highest frequencies of tubercle morphotypes of ectomycorrhiza were found in quadrats exposed to 100 mg m⁻² year⁻¹ Ni in lichen covered treatment, while in skimmed quadrats these peaked after the treatment with 10 mg Ni m⁻² year⁻¹. Removal of the lichen layer increased the value of diversity index (H′) of ectomycorrhizal fungal community, probably due to the increase in the evenness of the morphotype distribution. Lichen removal seemed also to improve the condition of the short roots, as the frequencies of poor and senescent short roots were decreased by the removal.     

Shift in ectomycorrhizal community composition in Scots pine (Pinus sylvestris L.) seedling roots as a response to nickel deposition and removal of lichen cover

Scots pine seedlings were exposed to wet-deposited nickel (Ni) and removal of lichen cover in a dry heath Scots pine forest. Ni deposition affected the colonization of roots by indigenous ectomycorrhizal fungi in contrasting ways in intact and skimmed quadrats. Highest frequencies of tubercle morphotypes of ectomycorrhiza were found in quadrats exposed to 100 mg m(-2) year(-1) Ni in lichen covered treatment, while in skimmed quadrats these peaked after the treatment with 10 mg Ni m(-2) year(-1). Removal of the lichen layer increased the value of diversity index (H') of ectomycorrhizal fungal community, probably due to the increase in the evenness of the morphotype distribution. Lichen removal seemed also to improve the condition of the short roots, as the frequencies of poor and senescent short roots were decreased by the removal.     

Mycorrhizal colonisation of mountain birch (Betula pubescens ssp. czerepanovii) along three environmental gradients: does life in harsh environments alter plant-fungal relationships?

Environmental stress affects ectomycorrhizal communities (ECM), but it is not known how general the detected ECM responses are. We investigated ECM fungi on roots of mountain birch, Betula pubescens subsp. czerepanovii (Orlova) H?met-Ahti, along three environmental gradients, two natural (altitude, seashore) and one human-induced (pollution), within the Kola Peninsula, NW Russia. Chlorophyll fluorescence of birch leaves indicated no environmental stress even in the conditions that were presumed most stressful in terms of abiotic environment, where the biomass and population density of birches were strongly reduced. Although neither overall ECM colonisation nor root fungal biomass showed stress-related patterns, colonisation by Cenococcum geophilum tended to decrease with abiotic stress. ECM morphotype diversity declined with abiotic stress, and along altitudinal gradient this decline was related to an increase in proportion of morphotypes with high fungal biomass. Polycormic birches had higher ECM colonisation than monocormic birches at high stress sites only. ECM morphotype diversity increased with foliar nitrogen concentration at low stress sites, but not at high stress sites. Birches with higher chlorophyll fluorescence had lower chitin concentration in their roots (indicating lower proportion of fungal structures) at high stress sites only. Our results suggest that at high stress sites (1) mechanical shelter created by polycormic trees may favour ECM fungi and (2) mountain birches maintain lower ECM diversity than at low stress sites.     

Root fungal colonisation in Deschampsia flexuosa: effects of pollution and neighbouring trees

In industrial barrens adjacent to a nickel-copper smelter at Monchegorsk, the Kola Peninsula, root colonisation in Deschampsia flexuosa by arbuscular mycorrhizal (AM)-type of hyphae was lower than in unpolluted forests (60.9 vs. 80.4%), while Olpidium-colonisation showed a marginally significant decline, and dark septate endophytic (DSE) hyphal colonisation was not affected. We detected an interactive effect of pollution and a neighbouring tree on DSE hyphal colonisation: at the highly polluted sites, colonisation was lower in D. flexuosa growing near trees, whereas at sites with low pollution the presence of the neighbouring tree had no effect on colonisation. High numbers of intracellular DSE sclerotia in the industrial barrens (13.3 vs. 3.4%) may indicate a survial strategy in an unfavourable environment and a dispersal strategy into a more favourable environment. While lower root colonisation by AM fungi has been also earlier reported in graminoids for heavy metal contamination, the results on other ubiquitous fungi colonising D. flexuosa roots are more novel.