Non-mycorrhizal Fungi Research Articles

Simulating C cycles in forest soils: Including the active role of micro-organisms in the ANAFORE forest model

A soil module was developed to improve on the ecosystem-scale simulations of forest models. The module includes simulations of bacteria, mycorrhizal and non-mycorrhizal fungi. The inclusion of these soil organisms allows for the simulation of several soil biological processes in a more mechanistic way. In this paper the soil module is used in combination with the forest model ANAFORE (ANAlysing Forest Ecosystems) a stand-scale forest model that simulates wood tissue development, carbon (C) and water (H 2O) fluxes dynamically from physiological principles. Although the main purpose of this paper is the model description, a showcase run of the new soil model was performed using a Bayesian parameterization procedure for 16 forest sites (pedunculate oak, beech, Scots pine and poplar) on different soils in Belgium. Emphasis was on the soil organic horizons formation. The results show that one single parameter set could be used for the different forests in the study, and yielded reasonably close fits for most sites concerning pH and formation of the humus layer. Although running the Bayesian procedure to obtain good input parameter distributions was time-consuming (several months), runs using the developed parameter set are reasonably fast (days). These results are promising. However, the high uncertainty of both the input and the output of the model indicates that it is mainly useful as an experimental tool, rather than a predictive instrument.

Phyto‐bioconversion of hard coal in the Cynodon dactylon/coal rhizosphere

Fundamental processes involved in the microbial degradation of coal and its derivatives have been well documented. A mutualistic interaction between plant roots and certain microorganisms to aid growth of plants such as Cynodon dactylon (Bermuda grass) on hard coal dumps has recently been suggested. In the present study coal bioconversion activity of nonmycorrhizal fungi was investigated in the C. dactylon/coal rhizosphere. Fungal growth on 2% Duff-agar, gutation formation on nitric acid treated coal and submerged culture activity in nitrogen-rich and -deficient broth formed part of the screening and selection of the fungi. The selected fungal isolates were confirmed to be found in pristine C. dactylon/coal rhizosphere. To simulate bioconversion, a fungal aliquot of this rhizosphere was used as inoculum for a Perfusate fixed bed bioreactor, packed with coal. The results demonstrate an enhanced coal bioconversion facilitated by low molecular weight organics and the bioconversion of coal may be initiated by an introduction of nitrogen moieties to the coal substrate. These findings suggest a phyto-bioconversion of hard coal involving plant and microbes occurring in the rhizosphere to promote the growth of C. dactylon. An understanding of this relationship can serve as a benchmark for coal dumps rehabilitation as well as for the industrial scale bioprocessing of hard coal.

A molecular survey of ectomycorrhizal hyphae in a California Quercus–Pinus woodland

Ectomycorrhizal (ECM) hyphal communities have not been well characterized. Furthermore, there have been few studies where the ECM hyphal community is compared to fungi detected as sporocarps or ECM-colonized root tips. We investigated fungi present as hyphae in a well-studied California Quercus-Pinus woodland. Hyphal species present were compared to those found as sporocarps and ECM root tips at the same site. Hyphae were extracted from root-restrictive nylon mesh in-growth bags buried in the soil near mature Quercus douglasii, Quercus wislizeni, and Pinus sabiniana. Taxa were identified using PCR, cloning, and DNA sequencing of internal transcribed spacer and 28s rDNA. Among the 33 species detected, rhizomorph-forming ECM fungi dominated the hyphal community, especially species of Thelephoraceae and Boletales. Most fungi in soils near Quercus spp. and P. sabiniana were ECM basidiomycetes, but we detected two ECM ascomycetes and three non-mycorrhizal fungi. Many ECM species present as hyphae were also previously detected at this site as sporocarps (18%) or on ECM root tips (58%). However, the hyphal community was mostly dominated by different taxa than either the sporocarp or ECM root communities.

Elevated CO2and nitrogen influence exudation of soluble organic compounds by ectomycorrhizal root systems

Root and mycelial exudation contributes significantly to soil carbon (C) fluxes, and is likely to be altered by an elevated atmospheric carbon dioxide (CO(2)) concentration and nitrogen (N) deposition. We quantified soluble, low-molecular-weight (LMW) organic compounds exuded by ectomycorrhizal plants grown under ambient (360 p.p.m.) or elevated (710 p.p.m.) CO(2) concentrations and with different N sources. Scots pine seedlings, colonized by one of five different ectomycorrhizal or nonmycorrhizal fungi, received 70 muM N, either as NH(4)Cl or as alanine, in a liquid growth medium. Exudation of LMW organic acids (LMWOAs), dissolved monosaccharides and total dissolved organic carbon were determined. Both N and CO(2) had a significant impact on exudation, especially of LMWOAs. Exudation of LMWOAs was negatively affected by inorganic N and decreased by 30-85% compared with the organic N treatment, irrespective of the CO(2) treatment. Elevated CO(2) had a clear impact on the production of individual LMWOAs, although with very contrasting effects depending on which N source was supplied.

Two differentially regulated phosphate transporters from the symbiotic fungus Hebeloma cylindrosporum and phosphorus acquisition by ectomycorrhizal Pinus pinaster

Ectomycorrhizal symbiosis markedly improves plant phosphate uptake, but the molecular mechanisms underlying this benefit are still poorly understood. We identified two ESTs in a cDNA library prepared from the ectomycorrhizal basidiomycete Hebeloma cylindrosporum with significant similarities to phosphate transporters from the endomycorrhizal fungus Glomus versiforme and from non-mycorrhizal fungi. The full-length cDNAs corresponding to these two ESTs complemented a yeast phosphate transport mutant (Deltapho84). Measurements of (33)P-phosphate influx into yeast expressing either cDNA demonstrated that the encoded proteins, named HcPT1 and HcPT2, were able to mediate Pi:H(+) symport with different affinities for Pi (K(m) values of 55 and 4 mum, respectively). Real-time RT-PCR showed that Pi starvation increased the levels of HcPT1 transcripts in H. cylindrosporum hyphae grown in pure culture. Transcript levels of HcPT2 were less dependent on Pi availability. The two transporters were expressed in H. cylindrosporum associated with its natural host plant, Pinus pinaster, grown under low or high P conditions. The presence of ectomycorrhizae increased net Pi uptake rates into intact Pinus pinaster roots at low or high soil P levels. The expression patterns of HcPT1 and HcPT2 indicate that the two fungal phosphate transporters may be involved in uptake of phosphate from the soil solution under the two soil P availability conditions used.

Effects of Fertilization and Microbial Inoculants Applied at Transplanting on the Growth of Mexican Fan Palm and Queen Palm

Container-grown mexican fan palm (Washingtonia robusta) and queen palm (Syagrus romanzoffiana) transplanted into a field nursery having phosphorus (P)-sufficient and P-deficient soils were treated at the time of planting with four commercial microbial inoculants (each containing arbuscular mycorrhizal fungi, alone or with other microbial components or fertilizers), two fertilizers, or nothing (control). All but the control palms received applications of an 8N–0.9P–10K palm fertilizer every 3 months for 2 years. None of the treatments improved growth over the control in the P-deficient soil. In the P-sufficient soil, none of the microbial inoculants improved growth over that of similarly fertilized noninoculated palms. Discrepancies were observed regarding nonmycorrhizal fungi and bacteria present in the microbial inoculant products. The type and quantity of these microbes listed on the labels of the microbial inoculant products did not necessarily match the type and quantity actually detected in the products.

Effects of Fertilization and Microbial Inoculants Applied at Transplanting on the Growth of Mexican Fan Palm and Queen Palm

Container-grown mexican fan palm (Washingtonia robusta) and queen palm (Syagrus romanzoffiana) transplanted into a field nursery having phosphorus (P)-sufficient and P-deficient soils were treated at the time of planting with four commercial microbial inoculants (each containing arbuscular mycorrhizal fungi, alone or with other microbial components or fertilizers), two fertilizers, or nothing (control). All but the control palms received applications of an 8N–0.9P–10K palm fertilizer every 3 months for 2 years. None of the treatments improved growth over the control in the P-deficient soil. In the P-sufficient soil, none of the microbial inoculants improved growth over that of similarly fertilized noninoculated palms. Discrepancies were observed regarding nonmycorrhizal fungi and bacteria present in the microbial inoculant products. The type and quantity of these microbes listed on the labels of the microbial inoculant products did not necessarily match the type and quantity actually detected in the products.

Early events in the life of apple roots: variation in root growth rate is linked to mycorrhizal and nonmycorrhizal fungal colonization

Early events of mycorrhizal and nonmycorrhizal fungal colonization in newly-emerging roots of mature apple (Malus domestica Borkh) trees were characterized to determine the relationship of these events to fine root growth rate and development. New roots were traced on root windows to measure growth and then collected and stained to quantify microscopically the presence of mycorrhizal and nonmycorrhizal fungal structures. Most new roots were colonized by either mycorrhizal or nonmycorrhizal fungi but none less 25 days old were ever internally colonized by both. Compared to nonmycorrhizal colonization, mycorrhizal colonization was associated with faster growing roots and roots that grew for a longer duration, leading to longer roots. While either type of fungi was observed in roots as soon as 3 days after root emergence, intraradical colonization by mycorrhizal fungi was generally faster (peaking at 7 to 15 days) than that by nonmycorrhizal fungi and often occurred more frequently in younger roots. Only 15 to 35% of the roots had no fungal colonization by 30 days after emergence. This study provides the first detailed examination of the early daily events of mycorrhizal and nonmycorrhizal fungal colonization in newly emerging roots under field conditions. We observed marked discrimination of roots between mycorrhizal and nonmycorrhizal fungi and provide evidence that mycorrhizal fungi may select for faster growing roots and possibly influence the duration of root growth by non-nutritional means.

Arbuscular Mycorrhizal Assemblages in Native Plant Roots Change in the Presence of Invasive Exotic Grasses

Plant invasions have the potential to significantly alter soil microbial communities, given their often considerable aboveground effects. We examined how plant invasions altered the arbuscular mycorrhizal fungi of native plant roots in a grassland site in California and one in Utah. In the California site, we used experimentally created plant communities composed of exotic (Avena barbata, Bromus hordeaceus) and native (Nassella pulchra, Lupinus bicolor) monocultures and mixtures. In the Utah semi-arid grassland, we took advantage of invasion by Bromus tectorum into long-term plots dominated by either of two native grasses, Hilaria jamesii or Stipa hymenoides. Arbuscular mycorrhizal fungi colonizing roots were characterized with PCR amplification of the ITS region, cloning, and sequencing. We saw a significant effect of the presence of exotic grasses on the diversity of mycorrhizal fungi colonizing native plant roots. In the three native grasses, richness of mycorrhizal fungi decreased; in the native forb at the California site, the number of fungal RFLP patterns increased in the presence of exotics. The exotic grasses also caused the composition of the mycorrhizal community in native roots to shift dramatically both in California, with turnover of Glomus spp., and Utah, with replacement of Glomus spp. by apparently non-mycorrhizal fungi. Invading plants may be able to influence the network of mycorrhizal fungi in soil that is available to natives through either earlier root activity or differential carbon provision compared to natives. Alteration of the soil microbial community by plant invasion can provide a mechanism for both successful invasion and the resulting effects of invaders on the ecosystem.

Interactions between arbuscular mycorrhizal fungi and intraspecific competition affect size, and size inequality, of Plantago lanceolata L.

Summary 1 Intraspecific competition causes decreases in plant size and increases in size inequality. Arbuscular mycorrhizas usually increase the size and inequality of non-competing plants, but mycorrhizal effects often disappear when plants begin competing. We hypothesized that mycorrhizal effects on size inequality would be determined by the experimental conditions, and conducted simultaneous field and glasshouse experiments to investigate how AM fungi and intraspecific competition determine size inequality in Plantago lanceolata . 2 As predicted, plant size was reduced when plants were competing, in both field and controlled conditions. However, size inequality was unexpectedly reduced by competition. Plants may have competed in a symmetric fashion, probably for nutrients, rather than the more common situation, in which plant competition is strongly asymmetric. 3 Mycorrhizas had no effect on plant size or size inequality in competing plants in either field or controlled conditions, possibly because competition for nutrients was intense and negated any benefit the fungi could provide. 4 The effects of mycorrhizas on non-competing plants were also unexpected. In field-grown plants, AM fungi increased plant size, but decreased size inequality: mycorrhizal plants were more even in size, with few very small individuals. In glasshouse conditions, mycorrhizal colonization was extremely high, and was generally antagonistic, causing a reduction in plant size. Here, however, mycorrhizas caused an increase in size inequality, supporting our original hypothesis. This was because most plants were heavily colonized and small, but a few had low levels of colonization and grew relatively large. 5 This study has important implications for understanding the forces that structure plant communities. AM fungi can have a variety of effects on size inequality and thus potentially important influences on long-term plant population dynamics, by affecting the genetic contribution of individuals to the next generation. However, these effects differ, depending on whether plants are competing or not, the degree of mycorrhizal colonization and the responsiveness of the plant to different colonization densities.

Soil microorganisms of a native shrub and exotic grasses along a nitrogen deposition gradient in southern California

Both anthropogenic nitrogen deposition and exotic annual grass invasion are occurring in the coastal sage scrub vegetation (CSS) of southern California. A study was carried out to determine the effects of these changes on soil microbial communities. Soils were sampled under exotic grasses and the native shrub Artemisia californica along an urban-to-rural N deposition gradient, and in N-fertilized plots in a rural site with low deposition. Arbuscular mycorrhizal (AM) colonization of A. californica was highest in low-N soils, but annual grasses (mainly Bromus madritensis) were colonized primarily by a fine endophyte that showed no pattern of response to soil N level. In addition, annual grasses generally had higher colonization by nonmycorrhizal, primarily septate, fungi in high N soils, while nonmycorrhizal colonization of A. californica was low in all soils. Spore density declined in the rhizosphere of A. californica with elevated N, but not of B. madritensis. Fatty acid methyl esters (FAME) were extracted from soil and their profiles were used to describe the soil microbial communities. Principal components analysis of FAME profiles showed a significant but weak relationship with levels of soil N. At the low N-deposition site that received N fertilizer, host plant was more important than soil N in determining FAME profiles. The most abundant fatty acids were the biomarkers for AM fungi. The different microbial communities of the two species, especially the predominance of fine endophyte and nonmycorrhizal fungi in roots of B. madritensis, warrant further research on functional responses to understand how these microorganisms may be involved in the invasion of native shrubland by exotic grasses.

Fungi associated with hair roots of Rhododendron lochiae (Ericaceae) in an Australian tropical cloud forest revealed by culturing and culture‐independent molecular methods

The culturable fungal assemblage associated with hair roots of Rhododendron lochiae (Ericaceae) from a tropical cloud forest in Queensland, Australia was investigated using rDNA internal transcribed spacer (ITS) restriction fragment length polymorphisms (RFLPs) and sequence analysis, and the abilities of the fungi to form ericoid mycorrhizas were tested. DNA was further extracted directly from hair roots and partial fungal ITS products compared with those from the cultured isolate assemblage using denaturing gradient gel electrophoresis (DGGE). A range of ericoid mycorrhizal and non-mycorrhizal fungi was identified using both approaches, with ericoid mycorrhizal fungi found to be taxonomically similar to those associated with Ericaceae in temperate habitats worldwide. Both approaches identified several unique fungi and, although most of the abundant RFLP types identified in the cultured fungal assemblage were also present in DGGE profiles of DNA extracted directly from roots, one the most commonly isolated RFLP types, a putative Xylariaceae taxon, was absent. The data suggest that a combination of culturing and culture-independent approaches may be more efficacious than either method individually.

Metal hyperaccumulation in plants - Biodiversity prospecting for phytoremediation technology

The importance of biodiversity (below and above ground) is increasingly considered for the cleanup of the metal contaminated and polluted ecosystems. This subject is emerging as a cutting edge area of research gaining commercial significance in the contemporary field of environmental biotechnology. Several microbes, including mycorrhizal and non-mycorrhizal fungi, agricultural and vegetable crops, ornamentals, and wild metal hyperaccumulating plants are being tested both in lab and field conditions for decontaminating the metalliferous substrates in the environment. As on todate about 400 plants that hyperaccumulate metals are reported. The families dominating these members are Asteraceae, Brassicaceae, Caryophyllaceae, Cyperaceae, Cunouniaceae, Fabaceae, Flacourtiaceae, Lamiaceae, Poaceae, Violaceae, and Euphobiaceae. Brassicaceae had the largest number of taxa viz. 11 genera and 87 species. Different genera of Brassicaceae are known to accumulate metals. Ni hyperaccumulation is reported in 7 genera and 72 species and Zn in 3 genera and 20 species. Thlaspi species are known to hyperaccumulate more than one metal i.e . T. caerulescence = Cd, Ni. Pb, and Zn; T. goesingense = Ni and Zn and T. ochroleucum = Ni and Zn and T. rotundifolium = Ni, Pb and Zn. Plants that hyperaccumulate metals have tremendous potential for application in remediation of metals in the environment. Significant progress in phytoremediation has been made with metals and radionuclides. This process involves rising of plants hydroponically and transplanting them into metal-polluted waters where plants absorb and concentrate the metals in their roots and shoots. As they become saturated with the metal contaminants, roots or whole plants are harvested for disposal. Most researchers believe that plants for phytoremediation should accumulate metals only in the roots. Several aquatic species have the ability to remove heavy metals from water, viz., water hyacinth ( Eichhornia crassipes (Mart.) Solms); pennywort ( Hydrocotyle umbellata L.) and duckweed ( Lemna minor L.). The roots of Indian mustard are effective in the removal of Cd, Cr, Cu, Ni, Pb, and Zn and sunflower removes Pb, U, 137 Cs, and 90 Sr from hydroponic solutions. Aquatic plants in freshwater, marine and estuarine systems act as receptacle for several metals. Hyperaccumulators accumulate appreciable quantities of metal in their tissue regardless of the concentration of metal in the soil, as long as the metal in question is present. The phytoextraction process involves the use of plants to facilitate the removal of metal contaminants from a soil matrix. In practice, metal-accumulating plants are seeded or transplanted into metal-polluted soil and are cultivated using established agricultural practices. If metal availability in the soil is not adequate for sufficient plant uptake, chelates or acidifying agents would be applied to liberate them into the soil solution. Use of soil amendments such as synthetics (ammonium thiocyanate) and natural zeolites have yielded promising results. Synthetic cross-linked polyacrylates, hydrogels have protected plant roots from heavy metals toxicity and prevented the entry of toxic metals into roots. After sufficient plant growth and metal accumulation, the above-ground portions of the plant are harvested and removed, resulting the permanent removal of metals from the site. Soil metals should also be bioavailable, or subject to absorption by plant roots. Chemicals that are suggested for this purpose include various acidifying agents, fertilizer salts and chelating materials. The retention of metals to soil organic matter is also weaker at low pH, resulting in more available metal in the soil solution for root absorption. It is suggested that the phytoextraction process is enhanced when metal availability to plant roots is facilitated through the addition of acidifying agents to the soil. Chelates are used to enhance the phytoextraction of a number of metal contaminants including Cd, Cu, Ni, Pb, and Zn Researchers initially applied hyperaccumulators to clean metal polluted soils. Several researchers have screened fast-growing, high-biomass-accumulating plants, including agronomic crops, for their ability to tolerate and accumulate metals in their shoots. Genes responsible for metal hyperaccumulation in plant tissues have been identified and cloned. Glutathione and organic acids metabolism plays a key role in metal tolerance in plants. Glutathione is ubiquitous component cells from bacteria to plants and animals. In phytoremediation of metals in the environment, organic acids play a major role in metal tolerance. Organic acids acids form complexes with metals, a process of metal detoxification. Genetic strategies and transgenic plant and microbe production and field trials will fetch phytoremediaition field applications.The importance of biodiversity and biotechnology to remediate potentially toxic metals are discussed in this paper. Brassicaceae amenable to biotechnological improvement and phytoremediation hype are highlighted.

Diversity of fungi in organic soils under a moorland – Scots pine (Pinus sylvestris L.) gradient

The conservation and regeneration of native Scots pine (Pinus sylvestris L.) woodlands is being actively encouraged by conservation agencies in the UK because of their high biodiversity value. In the present study, the consequences of regeneration on terrestrial fungal communities was determined in three parallel transects running from open moorland, through an intermediate zone showing seedling colonization, into a mature Scots pine forest at Abernethy Forest, Cairngorm, Scotland. Soil cores were taken at 18 m intervals along each 180 m transect, and the diversity of the soil fungal community was investigated by DGGE and sequence analysis of ITS fragments PCR-amplified from DNA extracted from soil. Analysis of DGGE profiles generated for two of the three transects indicates a clear shift in the community from the moorland region of the transects to the forest region. Whereas a few bands were present at all sampling points across the transects, the majority of bands were unique to either the moorland or forest samples. FASTA database searches of ITS sequence data generated from excised DGGE bands revealed the closest species match for each band. In some cases, the similarity of ITS sequences to database sequences was poor, but the remaining sequences were most closely related to ITS sequences of both mycorrhizal and non-mycorrhizal fungi. The data are discussed in relation to the effect of native pine woodland expansion on the soil fungal community.

Arbuscular mycorrhizas in cycads of southern India.

Root and soil samples of three potted or ground-grown cycads ( Cycas circinalis, C. revoluta, Zamiasp.) were collected between November 1999 and June 2000 and surveyed for arbuscular mycorrhizal (AM) colonization and spore populations. AM fungi were associated with all root systems and rhizosphere samples examined. Root colonization was of a typical Arum type and AM colonization levels differed significantly between species and between potted and ground-grown cycads. Mycorrhizal colonization levels were inversely related to root hair number and length. Spores of nine morphotypes belonging to three genera ( Acaulospora, Glomus, Scutellospora) were extracted from soil. The percentage root length colonized by AM fungi was not related to soil factors, but total AM fungal spore numbers in the rhizosphere soil were inversely related to soil nitrogen and phosphorus levels. AM fungal spore numbers in the soil were linearly related to root length colonized. The co-occurrence of septate non-mycorrhizal fungi was recorded for the first time in cycads. These observations and the relationship between plant mycorrhizal status and soil nutrients are discussed.

Tillage Intensity, Mycorrhizal and Nonmycorrhizal Fungi, and Nutrient Concentrations in Maize, Wheat, and Canola

Reduced tillage can change numerous physico‐chemical properties of soil and the activity of various microorganisms including mycorrhizal and pathogenic soil fungi, and thus influence nutrient uptake by plant roots. We studied the colonization of roots by mycorrhizal and nonmycorrhizal fungi and nutrient concentrations in plant tops grown during a 3‐yr rotation of maize (Zea mays L.), winter wheat (Triticum aestivum L.), and canola (Brassica napus L.) in two sites in Switzerland where fields have been under three tillage treatments (conventional, CT; chisel plow, CP; and no‐tillage, NT) since 1987. Maize roots were colonized to a greater extent by mycorrhizal fungi with NT than with CP or CT treatments. Wheat roots were equally and weakly colonized by mycorrhizal fungi in all treatments but were relatively heavily (up to 35% of the root length) colonized by several nonmycorrhizal fungi such as Olpidium, Polymyxa, and Gaeumannomyces–Phialophora complex. Canola roots, as expected, were not colonized by any mycorrhizal fungi but were colonized by O. brassicae Reduced tillage intensity altered the concentration of some nutrients in the leaves of mycorrhizal host plants (maize and wheat) but did not change those in nonhost canola. Changes in nutrient concentrations in maize and wheat leaves were likely due to the combined effects of colonization of their roots by various mycorrhizal and nonmycorrhizal fungi and not to some changes in the physical or chemical properties of soils. Cluster analysis showed that Mn concentration in wheat leaves was closely related to the Gaeumannomyces–Phialophora complex and concentrations of Ca, K, and Zn were related to tillage intensity and to the Polymyxa colonization of roots. We conclude that the colonization of roots by nonmycorrhizal root parasites, and especially by nonfilamentous obligate fungi, need to be taken into account in mycorrhizal studies conducted under field conditions.

Arbuscular mycorrhizae of Gutierrezia sarothrae and elevated carbon dioxide: evidence for shifts in C allocation to and within the mycobiont

In a complete 2×2 factorial greenhouse experiment we examined the responses of arbuscular mycorrhizal (AM) and non-mycorrhizal fungi to Gutierrezia sarothrae shrubs grown in elevated atmospheric carbon dioxide (750 μl l −1) and fertilized with N. AM percent infection did not change significantly with elevated CO 2, but arbuscular infection increased 14-fold in the low-N treatment. Extraradical hyphal length increased on an absolute basis in elevated CO 2, and also per infected root length. In the high-N treatments, increasing CO 2 caused a decrease in hyphal length per infected root length, and an increase in vesicular infection. There was a significant positive response of AM infection intensity to increasing CO 2 for the high N treatment, and a similar trend in the low N treatment. Infection intensity was positively correlated with arbuscular infection and with vesicular infection. Non-mycorrhizal fungi did not respond to any of the treatment combinations, as measured by percent root infection and external hyphal length. Our results indicate that C allocation to the AM fungi was increased in elevated CO 2, and that the mycobiont in turn increased C allocation to external hyphae.

Plant species-specific changes in root-inhabiting fungi in a California annual grassland: responses to elevated CO2 and nutrients.

Five co-occurring plant species from an annual mediterranean grassland were grown in monoculture for 4 months in pots inside open-top chambers at the Jasper Ridge Biological Preserve (San Mateo County, California). The plants were exposed to elevated atmospheric CO2 and soil nutrient enrichment in a complete factorial experiment. The response of root-inhabiting non-mycorrhizal and arbuscular mycorrhizal fungi to the altered resource base depended strongly on the plant species. Elevated CO2 and fertilization altered the ratio of non-mycorrhizal to mycorrhizal fungal colonization for some plant species, but not for others. Percent root infection by non-mycorrhizal fungi increased by over 500% for Linanthus parviflorus in elevated CO2, but decreased by over 80% for Bromus hordeaceus. By contrast, the mean percent infection by mycorrhizal fungi increased in response to elevated CO2 for all species, but significantly only for Avena barbata and B. hordeaceus. Percent infection by mycorrhizal fungi increased, decreased, or remained unchanged for different plant hosts in response to fertilization. There was evidence of a strong interaction between the two treatments for some plant species and non-mycorrhizal and mycorrhizal fungi. This study demonstrated plant species- and soil fertility-dependent shifts in below-ground plant resource allocation to different morpho-groups of fungal symbionts. This may have consequences for plant community responses to elevated CO2 in this California grassland ecosystem.

Below-Ground Microbial and Microfaunal Responses to Artemisia tridentata Grown Under Elevated Atmospheric Co 2

1. Soil microbes are fed primarily by root-derived substrates, fulfil functions such as mineralization, immobilization, decomposition, pathogeneity and improvement of plant nutrition, and form the basis of the below-ground food web. Hitherto, below-ground processes have generally been monitored using a 'black-box' approach, thereby ignoring effects of global change at a finer level of resolution. We describe shifts in the activity between microbial functional groups associated with roots of Artemisia tridentata, and the influence of this change on higher trophic levels. 2. We tested the hypothesis that elevated atmospheric CO 2 causes the soil community to change qualitatively. We measured the responses of several soil microbe and soil microfaunal parameters to a double-ambient CO 2 concentration and nutrient additions. The soil community, as measured by those parameters, showed great changes in response to the treatments. There was a very strong interaction between elevated CO 2 and the nutrient addition. 3. Under low nutrient conditions, total microbial biomass did not change under elevated atmospheric CO 2 , but doubled under conditions of elevated CO 2 and added nutrients. As we increased the resolution of our analysis, however, results shifted. Under low nutrient conditions, mycorrhizal fungi responded positively to elevated CO 2 , whereas with added soil nutrients they responded negatively to the same elevated CO 2 concentration. Bacteria and non-mycorrhizal fungi did not respond under the former conditions but more than doubled in biomass under conditions of elevated CO 2 and added nutrients. Soil fauna was also affected by the treatments. Overall, elevated CO 2 shifted carbon flow in the plant-soil system to a more mutualistic-closed, mycorrhizal-dominated system, whereas the combination of elevated CO 2 and nutrient addition shifted carbon flow to a more opportunistic-open, saprobe/pathogen-dominated one. 4. This indicates that elevated atmospheric CO 2 may lead to far less predictable feedback patterns than previously thought and that qualitative shifts in the soil community may be far more important than mere changes in total C sink strength.

Development of fungi below ground in association with plants growing in disturbed and undisturbed soils

It is well established that young maize plants take-up more P when they are sown in soil that has been left undisturbed after the removal of the shoots of previously grown maize plants. In a growth chamber experiment we eliminated arbuscular mycorrhizal (AM) fungi by pasteurization of soil and thus prevented any such stimulation of P uptake for plants growing in undisturbed soil. Arbuscules were absent from roots growing in the pasteurized soil. Arbuscular colonization (the % root length colonized by arbuscules) of roots growing in non-pasteurized soil that had been disturbed by breaking-up and mixing by hand was 32%, compared to arbuscular colonization of 51% in the corresponding undisturbed treatment. Following soil disturbance, non-mycorrhizal fungi showed a response that was similar to that of AM fungi. Colonization of roots in the pasteurized soil by parasitic hyphae in the disturbed treatment was one-third of that in the corresponding undisturbed treatment. At the end of the experiment, the total lengths of hyphae stained with trypan-blue (TB) in the non-pasteurized bulk soil around the roots were 42.5 and 28.7 m g −1 o.d. soil for the undisturbed and disturbed treatments, respectively; corresponding values in the pasteurized soil were almost identical, at 40.1 and 25.0 m g −1. These results show that the extent of production of both AM and parasitic fungi inside roots, and the net production of TB-staining hyphae in the bulk soil around those roots, are all lower during the period of growth following soil disturbance, as compared to the undisturbed situation. Caution should be taken in the interpretation of the functional status of TB-stained hyphae collected from bulk soil in the root zone.