The effects of multiple metal contamination on ectomycorrhizal Scots pine (Pinus sylvestris) seedlings

Experiments were conducted to investigate the effects of single and multiple metal contamination (Cd, Pb, Zn, Sb, Cu) on Scots pine seedlings colonised by ectomycorrhizal (ECM) fungi from natural soil inoculum. Seedlings were grown in either contaminated field soil from the site of a chemical accident, soils amended with five metals contaminating the site, or in soil from an uncontaminated control site. Although contaminated and metal-amended soil significantly inhibited root and shoot growth of the Scots pine seedlings, total root tip density was not affected. Of the five metals tested in amended soils, Cd was the most toxic to ECM Scots pine. Field-contaminated soil had a toxic effect on ECM fungi associated with Scots pine seedlings and caused shifts in ECM species composition on ECM seedlings. When compared to soils amended with only one metal, soils amended with a combination of all five metals tested had lower relative toxicity and less accumulation of Pb, Zn and Sb into seedlings. This would indicate that the toxicity of multiple metal contamination cannot be predicted from the individual toxicity of the metals investigated.     

Effects of mycorrhizae and other soil microbes on revegetation of heavy metal contaminated mine spoil

The effects of mycorrhizal fungi and other soil microorganisms on growth of two grasses, Andropogon gerardii Vitm. and Festuca arundinacea Schreb., in heavy metal-contaminated soil and mine tailings were investigated. A. gerardii is highly dependent on mycorrhizal fungi in native prairie, while F. arundinacea is a facultative mycotroph and relies on mycorrhizal symbiosis only in extremely infertile soils. Regardless of microbial amendments, neither plant species was able to establish and grow in the mine tailings. Both plant species grew in the moderately contaminated or non-contaminated soils, although A. gerardii grew in these soils only when mycorrhizal. Other soil microbes significantly improved growth of A. gerardii only in uncontaminated soil, but to a lesser extent than mycorrhizae. Although F. arundinacea was more highly colonized by mycorrhizal fungi than A. gerardii, neither microbial amendment affected growth of fescue in any soil. In several treatments mycorrhizal fungi adapted to uncontaminated soil stimulated plant growth more than mycorrhizae adapted to the moderately contaminated soil. However, mycorrhizal fungi adapted to contaminated soil did not increase the productivity of plant growth in contaminated soil more than fungi adapted to uncontaminated soil. A. gerardii plants inoculated with mycorrhizal fungi retained more Zn in roots than in shoots, confirming earlier reports that mycorrhizal fungi alter the translocation pattern of heavy metals in host plants. In contrast, mycorrhizae did not affect translocation patterns in F. arundinaceae, suggesting that the mycorrhizal dependence of a plant species is correlated with the retention of metals in roots. The correlation between mycorrhizal dependence of a plant species and mycorrhizal alteration of translocation pattern may also explain the inconsistent reports of mycorrhizal effects on translocation of heavy metals in plants. Plant response to mycorrhizal symbiosis may therefore provide a useful criterion for the selection of the plant species to be used in revegetation of contaminated sites.     

Effects of ozone and simulated acid rain on birch seedling growth and formation of ectomycorrhizae

Four-week-old paper birch (Betula papyrifera Marsh.) seedlings, inoculated or non-inoculated with the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker & Couch and grown in steamed or non-steamed soil, were exposed to ozone (O(3)) and/or simulated acid rain (SAR). Plants were exposed to O(3) for 7 h per day on 5 days per week for 12 weeks. O(3) concentrations were maintained between 0.06 and 0.08 ppm. SAR was applied 10 min per day on 2 days per week. O(3), SAR, soil regime and mycorrhizal treatment did not significantly affect any of the measured variables. Interactions between O(3) and SAR, SAR and mycorrhizal treatment, soil regime and mycorrhizal treatment and ozone and soil regime had significant effects. Treatment of seedlings with pH 3.5 SAR caused increases in growth which were more apparent in birch exposed to O(3). Mucorrhizal treatment caused increased growth in non-steamed soil, while growth appeared to decrease in steamed soil. Birch seedlings grew much better in steamed soil. The implications of increased growth in steamed soil may demonstrate the importance of looking at the secondary effects of pollutants on soil-borne organisms.     

Urban polluted forest soils induce elevated root peroxidase activity in Scots pine (Pinus sylvestris L.) seedlings.

Plant biomass. mycorrhizal status and root peroxidase activity were measured in ectomycorrhizal Scots pine (Pinus sylvestris L.) seedlings grown in urban polluted and native, non-polluted forest soils with added ammonium or potassium sulphates simulating N and S deposition of urban areas. Peroxidase activity in the fine roots of seedlings planted in polluted forest soils was higher than in those planted in non-polluted soils and correlated positively with the activities measured in an earlier study in the roots of mature Scots pines growing at the sites from where the soils were collected. Growth of seedlings and mycorrhizal status were not affected by the origin of soil. Exposing the seedlings to winter acclimation conditions for 6 weeks elevated peroxidase activity in the roots. The addition of ammonium or potassium sulphate to non-polluted soils did not induce elevated root peroxidase activity, although at the levels of 0.5 and 1.0 g of ammonium sulphate a slight increasing trend was observed. We suggest, that indirect biotic factors, i.e. changes in the community structure of soil fungi, early stages of recognition, and defence reactions of pine roots against saprophytic and pathogenic fungi may be participating in the elicitation of peroxidase (POD) activity, although the possible role of heavy metals cannot be excluded.     

The effect of mycorrhiza on the growth and elemental composition of Ni-hyperaccumulating plant Berkheya coddii Roessler

The effect of arbuscular mycorrhizal fungi (AMF) on growth and element uptake by Ni-hyperaccumulating plant, Berkheya coddii, was studied. Plants were grown under laboratory conditions on ultramafic soil without or with the AM fungi of different origin. The AM colonization, especially with the indigenous strain, significantly enhanced plants growth and their survival. AMF affected also the elemental concentrations that were studied with Particle-induced X-ray emission (PIXE). AMF (i) increased K and Fe in shoots, Zn and Mn in roots, P and Ca both, in roots and shoots; (ii) decreased Mn in shoots, Co and Ni both, in shoots and roots. Due to higher biomass of mycorrhizal plants, total Ni content was up to 20 times higher in mycorrhizal plants compared to the non-mycorrhizal ones. The AMF enhancement of Ni uptake may therefore provide an improvement of a presently used technique of nickel phytomining.     

Effects of mycorrhizae and fertilizer amendments on zinc tolerance of plants

In soils containing elevated levels of zinc, plant growth may be impaired because of Zn interference with P uptake by plants and because of detrimental effects of Zn toxicity itself. Because mycorrhizal fungi are known to improve uptake of plant P, the beneficial effects of mycorrhizal symbiosis on Zn tolerance of Andropogon gerardii Vitm. were assessed in soil amended with various levels of Zn and P. In the absence of P amendment, mycorrhizal fungi stimulated plant growth, but the degree of benefit depended on the inoculum source and the soil Zn level. Mycorrhizal fungi from a Zn contaminated site were more effective in increasing plant biomass at higher levels of Zn in the soil, whereas plant growth at lower levels of soil Zn was greater with mycorrhizal fungi from a non-contaminated site. Mycorrhizal fungus inoculation had no effect on shoot Zn concentration; however, inoculation significantly improved the plant P nutrition and therefore resulted in a high shoot P/Zn concentration ratio at all the soil Zn levels. To a certain extent, addition of P to the soil alleviated the Zn toxicity that had inhibited plant growth, but plant biomass tended to decrease with increasing soil Zn levels. Although P amendment improved P uptake, it also resulted in increased shoot Zn uptake.     

The arbuscular mycorrhizal fungus Glomus mosseae induces growth and metal accumulation changes in Cannabis sativa L

The effect of arbuscular mycorrhiza on heavy metal uptake and translocation was investigated in Cannabis sativa. Hemp was grown in the presence and absence of 100 microg g-1 Cd and Ni and 300 microg g-1 Cr(VI), and inoculated or not with the arbuscular mycorrhizal fungus Glomus mosseae. In our experimental condition, hemp growth was reduced in inoculated plants and the reduction was related to the degree of mycorrhization. The percentage of mycorrhizal colonisation was 42% and 9% in plants grown in non-contaminated and contaminated soil, suggesting a significant negative effect of high metal concentrations on plant infection by G. mosseae. Soil pH, metal bioavailability and plant metal uptake were not influenced by mycorrhization. The organ metal concentrations were not statistically different between inoculated and non-inoculated plants, apart from Ni which concentration was significantly higher in stem and leaf of inoculated plants grown in contaminated soil. The distribution of absorbed metals inside plant was related to the soil heavy metal concentrations: in plant grown in non-contaminated soil the greater part of absorbed Cr and Ni was found in shoots and no significant difference was determined between inoculated and non-inoculated plants. On the contrary, plants grown in artificially contaminated soil accumulated most metal in root organ. In this soil, mycorrhization significantly enhanced the translocation of all the three metals from root to shoot. The possibility to increase metal accumulation in shoot is very interesting for phytoextraction purpose, since most high producing biomass plants, such as non-mycorrhized hemp, retain most heavy metals in roots, limiting their application.     

Effects of simulated rain acidity on ectomycorrhizae of red spruce seedlings potted in natural soil

Formation of ectomycorrhizae of red spruce (Picea rubens) grown in natural soil was measured after seedlings were exposed to 25 or 50 applications of simulated rain of pH 5.5, 3.5 or 2.5. Ectomycorrhizae were quantified as the total number of ectomycorrhizal tips per centimeter, and as the number of ectomycorrhizal tips for each morphotype and for Cenococcum geophilum. Rain solutions were applied to the soil alone, to foliage and stem alone, or to entire potted seedlings. Final soil pH was linearly related to rain solution acidity. Lower base saturation, calcium and zinc content, and higher exchangeable acidity were observed after pH 2.5 treatments if the soil was exposed. Rain solutions and the subsequent changes in soil characteristics did not affect the total numbers of ectomycorrhizal tips. Four morphotypes of ectomycorrhizae observed for these seedlings were unaffected by simulated rain. However, the numbers of ectomycorrhizal tips formed by C. geophilum tended to increase with rain solution acidity after 50 applications. Method of rain deposition did not affect ectomycorrhizae, suggesting both plant and soil mediated responses may favor certain mycobionts. The results of this study indicate that short-term acidic deposition does not induce significant changes in the frequency of ectomycorrhizae, but higher numbers of C. geophilum tips suggest there may be changes in the relative occurrence of specific morphotypes of fungus species.     

Biodegradation of aromatic compounds by white rot and ectomycorrhizal fungal species and the accumulation of chlorinated benzoic acid in ectomycorrhizal pine seedlings

The capability of different white rot (WR, Heterobasidion annosum, Phanerochaete chrysosporium, Trametes versicolor) and ectomycorrhizal (ECM, Paxillus involutus, Suillus bovinus) fungal species to degrade different aromatic compounds and the absorption of 3-chlorobenzoic acid (3-CBA) by ECM pine seedlings was examined. The effect of aromatic compounds on the fungal biomass development varied considerably and depended on (a) the compound, (b) the external concentration, and (c) the fungal species. The highest effect on the fungal biomass development was observed for 3-CBA. Generally the tolerance of WR fungi against aromatic compounds was higher than that of the biotrophic fungal species. The capability of different fungi to degrade aromatic substances varied between the species but not generally between biotrophic and saprotrophic fungi. The highest degradation capability for aromatic compounds was detected for T. versicolor and H. annosum, whereas for Phanerochaete chrysosporium and the ECM fungi lower degradation rates were found. However, Paxillus involutus and S. bovinus showed comparable degradation rates at low concentrations of benzoic acid and 4-hydroxybenzoic acid. In contrast to liquid cultures, where no biodegradation of 3-CBA by S. bovinus was observed, mycorrhizal pines inoculated with S. bovinus showed a low capability to remove 3-CBA from soil substrates. Additional X-ray microanalytical investigations showed, that 3-CBA supplied to mycorrhizal plants was accumulated in the root cell cytoplasm and is translocated across the endodermis to the shoot of mycorrhizal pine seedlings.     

The Influence of Mycorrhiza on Uranium and Phosphorus Uptake by Barley Plants from a Field-contaminated Soil (7 pp)

Background Recent studies indicated that arbuscular mycorrhizal fungi (AMF) play important roles in plant accumulation of uranium (U) from contaminated environments, but the impacts of fertilization practices on functioning of the symbiotic associations, which are crucial factors influencing plant nutrition and growth responses to mycorrhiza, have rarely been considered. Materials and Methods In a greenhouse experiment, a bald root barley mutant (brb) together with the wild type (wt) were used to test the role of root hairs and AMF in uranium (U) uptake by host plants from a U contaminated soil. Nil, 20 and 60 mg KH2PO4-P kg–1 soil were included to investigate the influences of phosphorus (P) fertilization on plant growth and accumulation of U. Results Dry matter yield of barley plants increased with increasing P additions and wt produced significantly higher dry weight than brb. Mycorrhiza markedly improved dry matter yield of both genotypes grown at nil P, whereas only brb responded positively to mycorrhiza at 20 mg P kg-1. At the highest P level, mycorrhiza resulted in growth depressions in both genotypes, except for the roots of wt. In general, plant P concentrations increased markedly with increasing P additions and in response to mycorrhiza. Mycorrhiza and P additions had no significant effects on shoot U concentrations. However, root U concentrations in both genotypes were significantly increased by mycorrhiza. On the other hand, shoot U contents increased with increasing P levels, while 20 mg P kg-1 stimulated, but 60 mg P kg-1 marginally affected the U accumulation in roots. Root length specific U uptake was moderately enhanced both by root hairs and strongly enhanced by mycorrhiza. Moreover, non-inoculated plants generally had higher shoot-root ratios of U content than the corresponding inoculated controls. Conclusion Our study shows that AMF and root hairs improves not only P acquisition but also the root uptake of U, and mycorrhiza generally decreases U translocation from plant root to shoot. Hence, mycorrhiza is of potential use in the phytostabilization of U contaminated environments. Perspectives The complex impacts of P on U accumulation by barley plants suggested that U behavior in mycorrhizosphere and translocation along the soil-fungi-plant continuum as affected by fertilization practices deserve extensive studies for optimizing the function of mycorrhizal associations for phytoremediation purposes.     

Plant accumulation of potentially toxic elements in sewage sludge as affected by soil organic matter level and mycorrhizal fungi.

Leek (Allium ameloprasum) was grown in pot trials in two clay loams of contrasting organic contents, with and without indigenous mycorrhizal propagules. Sewage sludges containing varying levels of Cd, Cu and Zn were added. Extractable soil metals, plant growth, major nutrient content and accumulation of metals, and soil microbial indices were investigated. The aim was to establish whether soil organic content and mycorrhizal status affected plant and microbial exposure to these metals. Extractable metals were higher and responses to inputs more pronounced in the arable, lower organic matter soil, although only Cd showed a soil difference in the CaCl2 fraction. There were no metal toxic effects on plants and some evidence to suggest that they promoted growth. Uptake of each metal was higher in the larger plants of the grassland, higher organic matter soil. Inoculation with arbuscular mycorrhizal fungi increased root Cd and Zn concentrations. With the exception of Cd (roots) and Zn (shoots), higher inputs of sludge metals did not increase plant metals. Zn and Cu, but not Cd, concentrations were higher in roots than in shoots.     

Response of mycorrhizal Norway spruce seedlings to various nitrogen loads and sources

Norway spruce seedlings were grown under greenhouse conditions in Rootrainers with a vermiculite-peat moss mixture under various N-regimes for 6 months. Either ammonium or nitrate was applied in loads of 100 or 800 kg N ha(-1) year(-1) to seedlings which were either non-mycorrhizal or inoculated with the mycorrhizal fungi Hebeloma crustuliniforme or Laccaria bicolor. The use of increasing N loads enhanced shoot and total biomass, whereas root/shoot ratio, number of short roots and mycorrhization decreased. A significant enhancement of the concentration and content was obvious for the element N, whereas a significant decrease was obvious for P and Zn concentrations. The use of ammonium, as opposed to nitrate, significantly enhanced the biomass and the numbers of short roots, and reduced the root/shoot ratios, but did not influence the mycorrhization. It further significantly enhanced the N concentrations in roots and shoots. Fungal inoculation with H. crustuliniforme or L. bicolor compared to non-inoculated controls significantly enhanced shoot and total biomass, but reduced root/shoot ratios. The mycorrhization further significantly enhanced N and P concentrations and contents, but reduced Mn. Overall, the mycorrhization improved the P nutrition of the seedlings independently on the applied N loads or N sources. Dose response curves using ammonium nitrate as N source with a maximum load of 1600 kg N ha(-1) year(-1) applied on seedlings associated with H. crustuliniforme revealed that the maximum growth was reached at a load of 800 kg N ha(-1) year(-1) with a simultaneous decrease of the mycorrhization. In both shoots and roots, N concentrations increased constantly with increasing N loads, while P, Ca, and Zn concentrations decreased constantly.     

Container-grown tree seedling responses to sodium chloride applications in different substrates

Seedlings of Norway maple (Acer platanoides), silver birch (Betula pendula), Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) were grown in selected sodium chloride (NaCl) concentrations, soil types and under different watering regimes. Plants were raised from seeds, except for Scots pine plants which were obtained from a commercial source. Among the plant species tested, Scots pine was the most tolerant to soil salinity, while Norway spruce was the most susceptible. For both Norway maple and Norway spruce some half-sib families were more tolerant than others. No significant correlation was found between the tolerance of different half-sib families and the tolerance of mother trees observed in the field. The extent of leaf necrosis correlated significantly with the leaf concentrations of sodium (Na) and chloride (Cl). Among half-sib families within the species no such correlation was found. On the other hand, the least injured progeny of Norway maples had the highest concentrations of NaCl. The extent of salt-induced leaf necrosis varied with soil type, and a significant interaction between species and soil type was observed. Seedlings of Norway spruce grown in sand showed more severe necrosis and significantly higher concentrations of Na and Cl than seedlings grown in loam, silt loam, and peat. The severity of salt-induced leaf injury varied with the watering regime. Silver birch was the most affected species by drought and autumn watering treatments. Plants of silver birch subjected to drought showed increased leaf necrosis compared to the non-treated plants, and autumn watering treatment reduced the severity of leaf necrosis.     

Effect of crude oil contamination on the chlorophyll content and morpho-anatomy of Cyperus brevifolius (Rottb.) Hassk

Chlorophyll plays a pivotal role in the plant physiology and its productivity. Cultivation of plants in crude oil contaminated soil has a great impact on the synthesis of chlorophyll pigment. Morpho-anatomy of the experimental plant also shows structural deformation in higher concentrations. Keeping this in mind, a laboratory investigation has been carried out to study the effect of crude oil on chlorophyll content and morpho-anatomy of Cyperus brevifolius plant. Fifteen-day-old seedling of the plant was planted in different concentrations of the crude oil mixed soil (i.e., 10,000, 20,000, 30,000, 40,000, and 50,000 ppm). A control setup was also maintained without adding crude oil. Results were recorded after 6 months of plantation. Investigation revealed that there is a great impact of crude oil contamination on chlorophyll content of the leaves of the experimental plant. It also showed that chlorophyll a, chlorophyll b, and total chlorophyll content of leaves grown in different concentrations of crude oil were found to be lower than those of the control plant. Further, results also demonstrated that chlorophyll content was lowest in the treatment that received maximum dose of crude oil. It also showed that chlorophyll content was decreased with increased concentration of crude oil. Results also demonstrated that there was a reduction in plant shoot and root biomass with the increase of crude oil concentration. Results also revealed that the shoot biomass is higher than root biomass. Morphology and anatomy of the experimental plant also show structural deformation in higher concentrations. Accumulation of crude oil on the cuticle of the transverse section of the leaves and shoot forms a thick dark layer. Estimation of the level of pollution in an environment due to oil spill is possible by the in-depth study of the harmful effects of oil on the morphology and anatomy and chlorophyll content of the plants grown in that particular environment.     

90Sr uptake by Pinus ponderosa and Pinus radiata seedlings inoculated with ectomycorrhizal fungi

Strontium-90 ((90)Sr) is a radionuclide characteristic of fallout from nuclear reactor accidents and nuclear weapons testing. Prior studies have shown that Pinus ponderosa and P. radiata seedlings can remove appreciable quantities of (90)Sr from soil and store it in plant tissue. In this study, we inoculated P. ponderosa and P. radiata seedlings with one of five isolates of ectomycorrhizal fungi. Inoculated and noninoculated (control) seedlings were compared for their ability to remove (90)Sr from an organic growth medium. Seedlings were grown in a growth chamber in glass tubes containing 165 cm(3) of sphagnum peat moss and perlite (1 : 1 (v/v)) and, except in the controls, the fungal inoculum. After 3 months, 5978 Bq of (90)Sr in 1 ml of sterile, distilled, deionized water was added. Seedlings were grown for an additional month and then harvested. P. ponderosa seedlings with ectomycorrhizae accumulated 3.0-6.0% of the (90)Sr; bioconcentration ratios (Bq (90)Sr cm(-3) plant tissue/Bq (90)Sr cm(-3) growth medium) ranged from 98-162. Ectomycorrhizal P. radiata seedlings accumulated 6.0-6.9% of the (90)Sr; bioconcentration ratios ranged from 88-133. Nonmycorrhizal P. ponderosa and P. radiata seedlings accumulated only 0.6 and 0.7% of the (90)Sr and had bioconcentration ratios of 28 and 27, respectively. Ectomycorrhizal P. ponderosa and P. radiata seedlings are able to remove 3-5 times more (90)Sr from contaminated soil than seedlings without ectomycorrhizae.     

Phytoremediation in the tropics--influence of heavy crude oil on root morphological characteristics of graminoids

When studying species for phytoremediation of petroleum-contaminated soils, one of the main traits is the root zone where enhanced petroleum degradation takes place. Root morphological characteristics of three tropical graminoids were studied. Specific root length (SRL), surface area, volume and average root diameter (ARD) of plants grown in crude oil-contaminated and uncontaminated soil were compared. Brachiaria brizantha and Cyperus aggregatus showed coarser roots in polluted soil compared to the control as expressed in an increased ARD. B. brizantha had a significantly larger specific root surface area in contaminated soil. Additionally, a shift of SRL and surface area per diameter class towards higher diameters was found. Oil contamination also caused a significantly smaller SRL and surface area in the finest diameter class of C. aggregatus. The root structure of Eleusine indica was not significantly affected by crude oil. Higher specific root surface area was related to higher degradation of petroleum hydrocarbons found in previous studies.     

Influence of arbuscular mycorrhizal fungi on the growth and nutrient status of bermudagrass grown in alkaline bauxite processing residue

A nursery experiment was conducted to evaluate the potential role of arbuscular mycorrhizal (AM) fungi in encouraging the vegetation cover on bauxite residue (red mud) sites. An alkali tolerant bermudagrass (Cynodon dactylon) adapted to local conditions were grown in red mud with different amendments with and without AM fungi to assess mycorrhizal effects on plant growth, mineral nutrition, metal uptake and neutralization of bauxite residue. Inoculation of AM fungi significantly increased the plant growth, nutrient uptake and reduced Fe, Al accumulation in plant tissue and also improved the soil physico-chemical and biochemical properties. Gypsum and sludge amended treatments inoculated with AM fungi had maximum biomass, nutrient uptake and reduced accumulation of metals. The neutralization of red mud was significant in presence of AM fungi than control. The experiment provided evidence for the potential use of bermudagrass in combination with AM fungi for ecological restoration of bauxite residue sites.     

Biodegradation of aliphatic and aromatic hydrocarbons by natural soil microflora and pure cultures of imperfect and lignolitic fungi

The biodegradation of aliphatic and aromatic hydrocarbons by natural soil microflora and seven fungi species, including imperfect strains and higher level lignolitic species, is compared in a 90-day laboratory experiment using a natural, not-fertilized soil contaminated with 10% crude oil. The natural microbial soil assemblage isolated from an urban forest area was unable to significantly degrade crude oil, whereas pure fungi cultures effectively reduced the residues by 26-35% in 90 days. Normal alkanes were almost completely degraded in the first 15 days, whereas aromatic compounds (phenanthrene and methylphenanthrenes) exhibited slower kinetics. Aspergillus terreus and Fusarium solani, isolated from oil-polluted areas, produced the more efficient attack of aliphatic and aromatic hydrocarbons, respectively. Overall, imperfect fungi isolated from polluted soils showed a somewhat higher efficiency, but the performance of unadapted, indigenous, lignolitic fungi was comparable, and all three species, Pleurotus ostreatus, Trametes villosus and Coriolopsis rigida, effectively degraded aliphatic and aromatic components. The simultaneous, multivariate analysis of 22 parameters allowed the elucidation of a clear reactivity trend of the oil components during biodegradation: lower molecular weight n-alkanes > phenanthrene > 3-2-methylphenanthrenes > intermediate chain length n-alkanes > longer chain length n-alkanes > isoprenoids approximately 9-1-methylphenanthrenes. Irrespective of the individual degrading capacities, all fungi species tested seem to follow this decomposition sequence.     

Ectomycorrhizal colonization of loblolly pine seedlings during three growing seasons in response to ozone, acidic precipitation, and soil Mg status

A three-year study was initiated in 1987 to evaluate the impact of O3, acidic precipitation, and soil Mg on ectomycorrhizal colonization of loblolly pine (Pinus taeda L.) seedlings. Thirty-six open-top chambers equipped with a rainfall exclusion/addition system were utilized to administer three levels of O3 (subambient, ambient, or twice ambient) and two precipitation acidity levels (pH 3.8 or 5.2) to seedlings growing in 24-liter plastic pots containing soil having either 35 or 15 mg kg(-1) of exchangeable Mg. Seedlings exposed to the twice ambient O3 treatment exhibited smaller percentages of total ectomycorrhizal short roots at the end of each year of the study, but trends were statistically significant in 1989 only. Changes in number of specific ectomycorrhizal morphotypes in response to O3 were not consistent from year to year. Acidic precipitation treatments had no effect on number or percent of mycorrhizal short roots, and responses of two morphotypes to soil Mg treatments were probably due to differences in the soil environment rather than a result of changes in aboveground processes. Temporal shifts in morphotype frequencies were observed for seedlings in all treatments and indicate that mycorrhizal succession occurred during the study period.