Ectomycorrhizal Biomass Research Articles

Zinc Phosphate Transformations by the Paxillus involutus/Pine Ectomycorrhizal Association

In this research, we investigate zinc phosphate transformations by Paxillus involutus/pine ectomycorrhizas using zinc-resistant and zinc-sensitive strains of the ectomycorrhizal fungus under high- and low-phosphorus conditions to further understand fungal roles in the transformation of toxic metal minerals in the mycorrhizosphere. Mesocosm experiments with ectomycorrhizas were performed under sterile conditions with zinc phosphate localized in cellophane bags: zinc and phosphorus mobilization and uptake by the ectomycorrhizal biomass were analyzed. In the presence of a phosphorus source, an ectomycorrhizal association with a zinc-resistant strain accumulated the least zinc compared to a zinc-sensitive ectomycorrhizal association and non-mycorrhizal plants. Under low-phosphorus conditions, mycorrhizal seedlings infected with the zinc-resistant strain increased the dissolution of zinc phosphate and zinc accumulation by the plant. Extended X-ray absorption fine structure analysis of both mycorrhizal and nonmycorrhizal roots showed octahedral coordination of zinc by oxygen-containing ligands such as carboxylates or phosphate. We conclude that zinc phosphate solubilization and zinc and phosphorus uptake by the association depend on ectomycorrhizal infection, strain of the mycobiont, and the phosphorus status of the matrix.

Drought effects on fine-root and ectomycorrhizal-root biomass in managed Pinus oaxacana Mirov stands in Oaxaca, Mexico

The effects of a severe drought on fine-root and ectomycorrhizal biomass were investigated in a forest ecosystem dominated by Pinus oaxacana located in Oaxaca, Mexico. Root cores were collected during both the wet and dry seasons of 1998 and 1999 from three sites subjected to different forest management treatments in 1990 and assessed for total fine-root biomass and ectomycorrhizal-root biomass. Additionally, a bioassay experiment with P. oaxacana seedlings was conducted to assess the ectomycorrhizal inoculum potential of the soil for each of the three stands. Results indicated that biomasses of both fine roots and ectomycorrhizal roots were reduced by almost 60% in the drought year compared to the nondrought year. There were no significant differences in ectomycorrhizal and fine-root biomass between the wet and dry seasons. Further, the proportion of total root biomass consisting of ectomycorrhizal roots did not vary between years or seasons. These results suggest that both total fine-root biomass and ectomycorrhizal-root biomass are strongly affected by severe drought in these high-elevation tropical pine forests, and that these responses outweigh seasonal effects. Forest management practices in these tropical pine forests should consider the effects of drought on the capacity of P. oaxacana to maintain sufficient levels of ectomycorrhizae especially when there is a potential for synergistic interactions between multiple disturbances that may lead to more severe stress in the host plant and subsequent reductions in ectomycorrhizal colonization.

An ecosystem-scale radiocarbon tracer to test use of litter carbon by ectomycorrhizal fungi

The degree to which ectomycorrhizal fungi rely on decomposing litter as a carbon source in natural ecosystems is unknown. We used a radiocarbon ( 14C) tracer to test for uptake of litter carbon by ectomycorrhizal fungi as part of the Enriched Background Isotope Study (EBIS) in Oak Ridge Reservation, Tennessee. In EBIS, leaf litter from a highly 14C-labeled Quercus alba (white oak) forest was reciprocally transplanted with litter from a nearby low-labeled forest that had not been as strongly exposed to 14C. These litter transplants were conducted yearly. We measured Δ 14C signatures of ectomycorrhizal fungi collected from each forest four months and 2.25 years after the first litter transplant. The ectomycorrhizas were associated with white oak trees. We found no significant differences in 14C signatures of ectomycorrhizal fungi exposed to low-labeled versus high-labeled litter, indicating that less than 2% of the carbon in ectomycorrhizal biomass originated from transplanted litter. In contrast, ectomycorrhizal Δ 14C signatures from the high-labeled forest were 117–140‰ higher than those from the low-labeled forest. This pattern suggests that ectomycorrhizal fungi acquired most (or all) of their carbon from their host plants, probably via direct transfer of photosynthate through the roots.

Ectomycorrhizas associated with a relict population of Dryas octopetala in the Burren, western Ireland II. Composition, structure and temporal variation in the ectomycorrhizal community

The composition, structure and temporal variation of ectomycorrhizal (EM) communities associated with mountain avens (Dryas octopetala) in grass heaths of the Burren, western Ireland were assessed by using soil core sampling in two permanent plots and 30 other sites (196 cores in total). Of the 34 different EM types observed, 11 were common and constituted over 80% of the EM biomass. Four EM types, Craterellus lutescens, Tomentella sp., Dryadirhiza fulgens and Cenococcum geophilum were the most abundant as measured by EM length and frequency of occurrence in cores. The species profile and relative abundances were very similar in cores from the permanent plots and different sites in the Burren, indicating that they were all representative of the same EM community. The below-ground EM community in both plots was compared with production of basidiomes, and the latter was found to be an unreliable indicator of EM community structure. Temporal variation in the EM community was assessed by repeated core sampling of the two permanent plots over a 14-month period (between March 1998 and May 1999). No statistically significant shifts in EM abundance were found between sampling dates, probably as a consequence of the large variation in EM abundance between core samples over the sampling period. No significant relationship was found between rainfall, soil moisture or soil temperature and fluctuations in EM abundance. Patterns of total EM abundance and fluctuations in EM diversity were strongly correlated between the two permanent plots over the sampling period. Temporal fluctuations in the dominant EM type, Craterellus lutescens, were similar in both plots with respect to mycorrhizal length, biomass and relative abundance, and the patterns between both plots were positively correlated. EM diversity was negatively correlated with biomass of ectomycorrhizas of Craterellus lutescens in both plots, but it was significant only in plot 1.

Can the extent of degradation of soil fungal mycelium during soil incubation be used to estimate ectomycorrhizal biomass in soil?

The extent of degradation of the fungal biomass in forest soil during laboratory incubation was investigated as a measure of ectomycorrhizal (EM) biomass. The method simulates the disappearance of fungal mycelium after root trenching, where the EM fungi, deprived of its energy source (the tree), will start to die off. Incubating a forest humus soil at 25 °C resulted in a decrease in the relative proportion (mol%) of the phospholipid fatty acid 18:2ω6,9 (a fungal marker molecule) within 3–6 months, indicating that fungal biomass was disappearing. Incubation at 5 °C resulted in essentially no change in the amount of 18:2ω6,9. The measurement of ergosterol, another fungal marker molecule, gave similar results. Incubation of different forest soils (pine, spruce and spruce/oak), and assuming that the disappearance of fungal biomass during this period of time was entirely due to EM fungi, resulted in an estimation of EM biomass of between 47 and 84% of the total fungal biomass in these soils. The humus layer had more EM biomass than deeper mineral layers.

Production, standing biomass and natural abundance of 15N and 13C in ectomycorrhizal mycelia collected at different soil depths in two forest types.

Nutrient uptake by forest trees is dependent on ectomycorrhizal (EM) mycelia that grow out into the soil from the mycorrhizal root tips. We estimated the production of EM mycelia in root free samples of pure spruce and mixed spruce-oak stands in southern Sweden as mycelia grown into sand-filled mesh bags placed at three different soil depths (0-10, 10-20 and 20-30 cm). The mesh bags were collected after 12 months and we found that 590+/-70 kg ha(-1) year(-1) of pure mycelia was produced in spruce stands and 420+/-160 kg ha(-1) year(-1) in mixed stands. The production of EM mycelia in the mesh bags decreased with soil depth in both stand types but tended to be more concentrated in the top soil in the mixed stands compared to the spruce stands. The fungal biomass was also determined in soil samples taken from different depths by using phospholipid fatty acids as markers for fungal biomass. Subsamples were incubated at 20 degrees C for 5 months and the amount of fungal biomass that degraded during the incubation period was used as an estimate of EM fungal biomass. The EM biomass in the soil profile decreased with soil depth and did not differ significantly between the two stand types. The total EM biomass in the pure spruce stands was estimated to be 4.8+/-0.9 x 10(3) kg ha(-1) and in the mixed stands 5.8+/-1.1 x 10(3) kg ha(-1) down to 70 cm depth. The biomass and production estimates of EM mycelia suggest a very long turnover time or that necromass has been included in the biomass estimates. The amount of N present in EM mycelia was estimated to be 121 kg N ha(-1) in spruce stands and 187 kg N ha(-1) in mixed stands. The delta13C value for mycelia in mesh bags was not influenced by soil depth, indicating that the fungi obtained all their carbon from the tree roots. The delta13C values in mycelia collected from mixed stands were intermediate to values from pure spruce and pure oak stands suggesting that the EM mycelia received carbon from both spruce and oak trees in the mixed stands. The delta15N value for the EM mycelia and the surrounding soil increased with soil depth suggesting that they obtained their entire N from the surrounding soil.

Do nutrient additions alter carbon sink strength of ectomycorrhizal fungi?

Summary • Carbon sink strength differences are examined here between ectomycorrhizal fungi in interaction with additions of ammonium and apatite (a phosphorus- and calcium-containing mineral). • Pinus muricata associated with Paxillus involutus and four suilloid isolates ( Suillus pungens and members of three Rhizopogon section Amylopogon species groups) were used in microcosm nutrient addition experiments. • The associations differed in ectomycorrhizal biomass, mycelial growth rate, biomass and respiration. P. involutus produced the lowest biomass of ectomycorrhizal connections to P. muricata , but it consumed proportionally more carbon per connection and transferred more than twice as much ammonium to the host per unit mycorrhizal biomass. Paxillus also colonized the soil more rapidly and intensely than the other fungi, but its mycelial respiration was lowest. Ammonium and apatite addition resulted in a marked increase in respiration and mycelial biomass, respectively, by the suilloid fungi. • The high carbon cost of ammonium uptake is suggested as one explanation for reduced sporocarp production and mycelial growth by ectomycorrhizal fungi commonly found after high levels of nitrogen addition.

Early effects of prescribed fire on the structure of the ectomycorrhizal fungus community in a Sierra Nevada ponderosa pine forest

The eects of a prescribed fire on the presence of ectomycorrhizal fungi on the root tips of ponderosa pine were investigated one year after a prescribed ground fire. Ectomycorrhizas were sampled within 1 m# plots before and one year after the fire, and in nearby control plots that were not burned. The cores were divided into litter}organic, upper mineral, and lower mineral layers. The total ectomycorrhizal biomass in the control plots did not dier between year one and year two samples for any core layer, while in the fire plots the destruction of the litter}organic layer resulted in an eight-fold reduction in total ectomycorrhizal biomass. Mycorrhizal biomass in the two mineral layers was not significantly reduced by the fire. We used molecular tools to identify fungi directly from the ectomycorrhizas. In unburned plots members of the Russulaceae and Thelephoraceae were among the most frequent and abundant ectomycorrhizal types; species of most other taxa were rare. In the control plots these two families were among the dominant species in both years, but patchiness on a fine spatio-temporal scale caused some major changes in ranking of individual species between sample years. Rhizopogon subcaerulescens was the most pronounced example; its biomass in the control plot samples was seven times greater in year two than in year one because of an exceptionally large cluster of mycorrhizas encountered in a single core. The eect of fire on individual species was dicult to assess because of this patchiness and because all species were low in abundance after the fire. The most abundant pre-fire species were reduced to undetectable post-fire levels, while several less abundant species, including R. subcaerulescens, Cenococcum geophilum, and several unknown types were not substantially reduced by the fire. We speculate that the more abundant species, Martellia sp., thelephoroid 1, and Tomentella sublilacina, were dierentially aected because their dominance was most prominent at the litter and organic layers. In any case, a short-term eect of this fire appears to be increased species evenness.

Ectomycorrhizal fungi associated with Arctostaphylos contribute to Pseudotsuga menziesii establishment

Chaparral on the central coast of California can occur as relatively stable patches of ectomycorrhizal Arctostaphylos directly adjacent to arbuscular mycorrhizal Adenostoma. Vegetation surveys and seedling survival assays show that Pseudotsuga establishes only in Arctostaphylos. We found no significant differences between Arctostaphylos and Adenostoma in allelopathy; light; temperature; or soil NH4+, NO3-, or K. Arctostaphylos soils tended to be higher in phosphate and were lower in pH, Ca, Mg, Ni, and Cr than those from Adenostoma. After 1 year of growth of Pseudotsuga seedlings in an Arctostaphylos patch, 17 species of fungi colonized both Pseudotsuga and Arctostaphylos. Fifty-six of 66 seedlings were colonized by fungi that also colonized Arctostaphylos within the same soil core. Forty-nine percent of the Pseudotsuga ectomycorrhizal biomass was colonized by fungi that were also associated with Arctostaphylos within the same core. Another 12% was colonized by fungi known to associate with Arctostaphylos from different cores. After 4 months of growth, Pseudotsuga seedlings in four of five Arctostaphylos plots were ectomycorrhizal and colonized by fungi in Russulaceae, Thelephoraceae, and Amanitaceae. Pseudotsuga seedlings in two of five Adenostoma plots were ectomycorrhizal but colonized by only two species of fungi in Thelephoraceae. These results provide compelling evidence that ectomycorrhizal fungi associated with Arctostaphylos contribute to Pseudotsuga seedling establishment.Key words: arbutoid, Douglas-fir, ectomycorrhizae, manzanita, RFLP, PCR.

Quantification of dead ectomycorrhizae from forest soils using computerized image analysis

A first-generation regression model is presented, describing a linear relationship between dead ectomycorrhizal biomass (mg dry weight) and mycorrhizal area in the xy-plane (mm 2) ( r 2=0.996). This model enables reliable estimates of dead ectomycorrhizal biomass in soils through area measurements of mycorrhizae using computerized image analysis.

Accumulation patterns of heavy metals in soil profiles as affected by forest clear-cutting

Vertical distribution of Zn, Pb, Cu and Cd was studied in podzol soil profiles of adjacent forested and clear-cut areas in a region contaminated with Zn, Pb and Cd from long-range atmospheric transport. This was in order to investigate possible effects of deforestation on accumulation and distribution patterns of these metals in surface soil profiles. Lower Zn and Cd contents were observed in the H horizon of clear-cut area soils than in forest area soils. However, this was not sufficient to entail a significantly lower total Zn and Cd pool in the humus layer of clear-cut area soils compared to forest area soils. The total content of Pb in the L + F + H horizons was significantly lower in clear-cut than in forested areas, attributable to distinctly lower Pb contents in the H horizon of clear-cut area soils. This fact combined with significantly thinner humus layers in clear-cut areas compared to forested areas, presents evidence for increased losses of Pb from the humus layer after clear-cutting. Higher Pb contents in the Ae and B horizons of clear-cut area soils than in forest area soils, show that at least parts of the Pb lost from the H horizon in clear-cut areas were re-adsorbed or re-precipitated in the Ae and B horizon. As in the case of Pb, Cu concentrations were higher in the Ae and B horizons of clear-cut area soils compared to forest area soils. In the case of Cu, however, this cannot be explained by increased inputs from the humus layer following forest clear-cutting, but rather by increased weathering in the Ae and B horizons. The high retention of Zn, Cu and Cd in the humus layer of clear-cut areas, compared to that of Pb, is most probably due to a stronger accumulation of these metals in ectomycorrhizal biomass.