Phosphate influx into ectomycorrhizal and saprotrophic fungal hyphae in relation to phosphate supply; a potential method for selection of efficient mycorrhizal species

Phosphorus source alters host plant response to ectomycorrhizal diversity

We examined the influence of phosphorus source and availability on host plant (Pinus rigida) response to ectomycorrhizal diversity under contrasting P conditions. An ectomycorrhizal richness gradient was established with equimolar P supplied as either inorganic phosphate or organic inositol hexaphosphate. We measured growth and N and P uptake of individual P. rigida seedlings inoculated with one, two, or four species of ectomycorrhizal fungi simultaneously and without mycorrhizas in axenic culture. Whereas colonization of P. rigida by individual species of ectomycorrhizal fungi decreased with increasing fungal richness, colonization of all species combined increased. Plant biomass and N content increased across the ectomycorrhizal richness gradient in the organic but not the inorganic P treatment. Plants grown under organic P conditions had higher N concentration than those grown under inorganic P conditions, but there was no effect of richness. Phosphorus content of plants grown in the organic P treatment increased with increasing ectomycorrhizal richness, but there was no response in the inorganic P treatment. Phosphorus concentration was higher in plants grown at the four-species richness level in the organic P treatment, but there was no effect of diversity under inorganic P conditions. Overall, few ectomycorrhizal composition effects were found on plant growth or nutrient status. Phosphatase activities of individual ectomycorrhizal fungi differed under organic P conditions, but there was no difference in total root system phosphatase expression between the inorganic or organic P treatments or across richness levels. Our results provide evidence that plant response to ectomycorrhizal diversity is dependent on the source and availability of P.

Ectomycorrhizal community effects on hybrid spruce seedling growth and nutrition in clearcuts

A diverse community of ectomycorrhizal (ECM) fungi is generally considered beneficial to forest ecosystems, but the function of ECM communities should be considered within an ecological context. The growth of hybrid spruce (Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carrière) seedlings was compared after transplanting into recent clearcuts, where soil moisture and nitrogen are typically readily available. The seedlings had either a "forest" ECM community (taken from forest gap edges) or a "pioneer" ECM community (taken from disturbed road edges) and were planted at wide and close spacing. After 3 years, morphotype distribution and abundance (64% community similarity between "forest" and "pioneer" seedlings) overlapped considerably, but height growth was 25% greater for the "pioneer" seedlings. There was a reduction in diameter at close spacing, with little difference in competition effects between ECM communities. There were no differences detected in foliar nitrogen concentrations and no evidence of nitrogen or phosphorus deficiencies. The advantage of fungi such as Amphinema byssoides, Thelephora terrestris, and Laccaria laccata might be the proliferation of fine roots that allows for the fullest utilization of abundant soil resources. The results suggest that the ECM communities arising after clearcut disturbances are well adapted to these initial soil conditions.Key words: ectomycorrhiza, disturbance, diversity, productivity, competition, Picea glauca.

Ectomycorrhizal diversity alters growth and nutrient acquisition of grey birch (Betula populifolia) seedlings in host-symbiont culture conditions

•  The influence of ectomycorrhizal fungal diversity on plant performance was investigated by establishing a gradient of ectomycorrhizal diversity on Betula populifolia (grey birch) seedlings. •  We measured growth, as well as N and P uptake, of individual B. populifolia seedlings inoculated with replicate one, two and four species 'communities' of ectomycorrhizal fungi simultaneously and without mycorrhizas in axenic culture. •  Colonization of B. populifolia by individual species of ectomycorrhizal fungi decreased with increasing fungal diversity although total colonization increased. Shoot biomass decreased with increasing ectomycorrhizal diversity and mycorrhizal root biomass increased. Plant biomass did not differ with individual mycorrhizal species or composition. Shoot N concentration showed a small increase with increasing ectomycorrhizal diversity. Whole plant P content and concentration increased across the ectomycorrhizal diversity gradient. Despite higher mycorrhizal colonization rates with increasing fungal diversity, plant growth and nutrient responses were best explained by changes in ectomycorrhizal diversity. •  Greater ectomycorrhizal diversity per se, rather than colonization or composition, increased mycorrhizal root biomass at the expense of shoot biomass and increased P uptake of B. populifolia seedlings.

Ectomycorrhizal diversity and community structure in oak forest stands exposed to contrasting anthropogenic impacts

We compared the ectomycorrhizal community structure of oak forest stands located in either an urban or a rural area. Urban stands had higher N deposition rates, soil heavy metal levels, and earthworm counts than rural stands. Ectomycorrhizal types were quantified on roots of mature oak (Quercus) in soil cores and on Quercus rubra L. seedlings grown in soil cores in the glasshouse. Twenty-six ectomycorrhizal types were distinguished on mature oak in rural soils versus 16 in urban soils. Nine ectomycorrhizal types were distinguished on Q. rubra seedlings grown in rural soils versus seven in urban soils. Despite fewer ectomycorrhizal types in urban soils, richness of ectomycorrhizal types per centimetre fine root of mature oak or Q. rubra seedlings did not differ between urban and rural soils. Ectomycorrhizal colonization (ectomycorrhizal tips/m fine root) was lower in urban than rural soil cores but higher on Q. rubra seedlings grown in urban versus rural soils. Fine root length per unit soil volume was higher in urban than rural stands. No difference in fine root length was observed between Q. rubra seedlings grown in urban and rural soils. These differences in ectomycorrhizal community structure between the urban and rural stands are likely due to anthropogenic impacts.Key words: air pollution, anthropogenic impacts, community structure, diversity, ectomycorrhiza, Quercus rubra.