Phosphate transport by hyphae of field communities of arbuscular mycorrhizal fungi at two levels of P fertilization

This study was conducted to elucidate the effect of P fertilisation on the function of field communities of arbuscular mycorrhizal fungi (AMF) measured as P transport to flax. Two methods were applied to soil from a long-term field experiment with NaHCO₃-extractable soil P levels of 24 and 50 mg kg^-1in an experiment under controlled conditions: i) Measurement of plant growth and P uptake in the presence or absence of the fungicide benomyl and ii) measurement of hyphal P transport from a root-free compartment labelled with ³²P. Benomyl successfully prevented mycorrhizal function. The absolute contribution of AMF to plant P uptake was of the same magnitude with or without P fertilisation at 27 days after sowing. Therefore, even though plants grown at the higher soil P level had greater P uptake, the relative contribution of AMF to P uptake was greater at the lower P level than at the higher P level (77 and 49% of total P uptake, respectively). The AMF in P-fertilized soil transported less P³² from the root-free compartment to the plant after 23 days than the AMF in unfertilized soil, but this difference disappeared in plants harvested after 27 and 32 days. The production of hyphae was largely similar in both fertilization treatments, indicating that the capacity for P uptake and transport by hyphae of the two AMF communities was similar. This revised version was published online in June 2006 with corrections to the Cover Date.     

Mycorrhizal‐mediated nitrogen acquisition in switchgrass under elevated temperatures and N enrichment

Arbuscular mycorrhizal fungi (AMF) can perform key roles in ecosystem functioning through improving host nutrient acquisition. Nitrogen (N) is an essential nutrient for plant growth, however, anthropogenic N loading (e.g. crop fertilization and deposition from combustion sources) is increasing so that N now threatens ecosystem sustainability around the world by causing terrestrial and aquatic eutrophication and acidification. It is important to better understand the capacity of AMF to directly uptake N from soils and transfer it to host plants because this process may increase N recycling and retention within ecosystems. In addition to understanding the role of AMF in the N cycle in the present day it is important to understand how AMF function may change as global change proceeds. Currently the net effects of N enrichment and elevated temperature predicted with global change on AMF are unknown. In this study, we examined the effects of N enrichment by simulated N‐deposition loading, elevated temperatures expected by future global changes and their interactions on growth and AMF‐mediated N acquisition of switchgrass (Panicum virgatum var. Alamo), an important species for biofuel production. Switchgrass plants were grown in microcosm units that divided mycorrhizal roots from AMF hyphae and organic residues enriched with ¹⁵N by compartments separated by an air gap to reduce N diffusion. While AMF did not enhance switchgrass biomass, mycorrhizas significantly increased ¹⁵N in shoots and total shoot N. Neither N enrichment nor elevated temperatures influenced this mycorrhizal‐mediated N uptake and transfer. Results from this study can aid in developing sustainable bioethanol and switchgrass production practices that are less reliant on synthetic fertilizers and more dependent on internal N recycling from AMF.     

Acquisition of Cu, Zn, Mn and Fe by mycorrhizal maize (Zea mays L.) grown in soil at different P and micronutrient levels

Sustainability of soil-plant systems requires, among other things, good development and function of mycorrhizal symbioses. The effects of P and micronutrient levels on development of an arbuscular mycorrhizal fungus (AMF) and uptake of Zn, Cu, Mn and Fe by maize (Zea mays L.) were studied. A pot experiment with maize either inoculated or not with Glomus intraradices was conducted in a sand:soil (3 :1) mix (pH 6.5) in a greenhouse. Our goal was to evaluate the contribution of mycorrhizae to uptake of Cu, Zn, Mn and Fe by maize as influenced by soil P and micronutrient levels. Two levels of P (10 and 40 mg kg⁻¹ soil) and three levels of a micronutrient mixture: 0, 1X and 2X (1X contained, in mg kg⁻¹ soil, 4.2 Fe, 1.2 Mn, 0.24 Zn, 0.06 Cu, 0.78 B and 0.036 Mo), were applied to pots. There were more extraradical hyphae at the low P level than at the high P level when no micronutrients were added to the soil. Root inoculation with mycorrhiza and application of micronutrients increased shoot biomass. Total Zn content in shoots was higher in mycorrhizal than non-mycorrhizal plants grown in soils with low P and low or no micronutrient addition. Total Cu content in shoots was increased by mycorrhizal colonization when no micronutrients were added. Mycorrhizal plants had lower Mn contents than non-mycorrhizal plants only at the highest soil micronutrient level. AMF increased total shoot Fe content when no micronutrients were added, but decreased shoot Fe when plants were grown at the high level of micronutrient addition. The effects of G. intraradices on Zn, Cu, Mn, and Fe uptake varied with micronutrient and P levels added to soil. Accepted: 27 December 1999     

Interaction of <i>Acaena elongata</i> L. with Arbuscular Mycorrhizal Fungi under Phosphorus Limitation Conditions in a Temperate Forest

The aim of this study was to analyze the performance of Acaena elongata colonized by arbuscular mycorrhizal fungi (AMF) to different phosphorus (P) concentrations, as a measure of AMF dependency. A. elongata, is a species from soils where P availability is limited, such as temperate forests. Our research questions were: 1) How do different P concentrations affect the AMF association in Acaena elongata, and 2) How does the AMF association influence A. elongata’s growth under different P concentrations? A. elongata’s growth, P content in plant tissue, AMF colonization and dependency were measured under four P concentrations: control (0 g P kg⁻¹ ), low (0.05 g P kg⁻¹ ), intermediate (0.2 g P kg⁻¹ ) and high (2 g P kg⁻¹ ) in different harvests. A complete randomized block design was applied. A. elongata’s growth was higher under -AMF in intermediate and high P concentrations, and the lowest growth corresponded to +AMF in the low and intermediate P concentration. We observed a negative effect on the root biomass under +AMF in intermediate P concentration, while the P concentration had a positive effect on the leaf area ratio. The AMF colonization in A. elongata decreased in the highest P concentration and it was favored under intermediate P concentration; while the low and the high concentrations generated a cost-benefit imbalance. Our results suggest that the performance of some plant species in soils with low P availability may not be favored by their association with AMF, but a synergy between AMF and intermediate P concentrations might drive A. elongata’s growth.     

Functional diversity in arbuscular mycorrhizas: exploitation of soil patches with different phosphate enrichment differs among fungal species

Most terrestrial plant species form associations with arbuscular mycorrhizal fungi (AMF) that transfer soil P to the plant via their external hyphae. The distribution of nutrients in soils is typically patchy (heterogeneous) but little is known about the ability of AMF to exploit P patches in soil. This was studied by growing symbioses of Linum usitatissimum and three AMF (Glomus intraradices, G. mosseae and Gigaspora margarita) in pots with two side-arms, which were accessible to hyphae, but not to roots. Soil in one side-arm was either unamended (P0) or enriched with P; simultaneous labelling of this soil with ³²P revealed that G. intraradices responded to P enrichment both in terms of hyphal proliferation and P uptake, whereas the other AMF did not. Labelling with ³³P of P0 soil in the other side arm revealed that the increased P uptake by G. intraradices from the P-enriched patch was paralleled by decreased P uptake by other parts of the mycelium. This is the first demonstration of variation in growth and nutrient uptake by an AMF as influenced by a localized P enrichment of the soil. The results are discussed in the context of functional diversity of AMF.     

Short-term response of arbuscular mycorrhizal association to spider mite herbivory

We examined effects of aboveground herbivory by spider mites (Tetranychus urticae) on colonization and activity of arbuscular mycorrhizal fungi (AMF; Gigaspora margarita) using potted plants (Lotus japonicus). We evaluated changes in arbuscular mycorrhizal (AM) association two ways: (1) conventional trypan blue staining of mycorrhizal hyphae to examine AMF biomass in roots (mycorrhizal colonization) and (2) vital staining for a mycorrhizal enzyme (succinate dehydrogenase, SDH) to examine mycorrhizal activity (SDH activity). Mycorrhizal colonization and SDH activity started to increase 4 days after aboveground herbivory, and returned to the initial levels in the absence of mite herbivory in 7 and 12 days, respectively. These results suggest that the change in AM association in response to mite herbivory is a short-term response.     

Combined application of arbuscular mycorrhizal fungi and steel slag improves plant growth and reduces Cd,Pb accumulation in Zea mays

Abstract

Little attention has been paid to the combined use of arbuscular mycorrhizal fungus (AMF) and steel slag (SS) for ameliorating heavy metal polluted soils. A greenhouse pot experiment was conducted to study the effects of SS and AMF?Funneliformis mosseae (Fm), Glomus versiforme (Gv) and Rhizophagus intraradices (Ri) on plant growth and Cd, Pb uptake by maize grown in soils added with 5?mg Cd kg^?1 and 300?mg Pb kg^?1 soil. The combined usage of AMF and SS (AMF?+?SS) promoted maize growth, and Gv?+?SS had the most obvious effect. Meanwhile, single SS addition and AMF?+?SS decreased Cd, Pb concentrations in maize, and the greater reductions were found in combined utilization, and the lowest Cd, Pb concentrations of maize appeared in Gv?+?SS. Single SS amendment and AMF?+?SS enhanced soil pH and decreased soil diethylenetriaminepentaacetic acid (DTPA)-extractable Cd, Pb concentrations. Furthermore, alone and combined usage of AMF and SS increased contents of soil total glomalin. Our research indicated a synergistic effect between AMF and SS on enhancing plant growth and reducing Cd, Pb accumulation in maize, and Gv?+?SS exerted the most pronounced effect. This work suggests that AMF inoculation in combination with SS addition may be a potential method for not only phytostabilization of Pb-Cd-contaminated soil but maize safety production.     

Zn uptake by maize under the influence of AM-fungi and Collembola Folsomia candida

Zn uptake by maize plants may be affected by the presence of arbuscular mycorrhizal fungi (AMF). Collembola often play an important controlling role in the inter-relationship between AMF and host plants. The objective of this experiment was to examine whether the presence of Collembola at different densities (0.4 and 1 individuals g⁻¹ dry soil) and their activity have any effect on Zn uptake by maize through the plant–AMF system. The presence of the AMF (Glomus intraradices) and of the Collembola species Folsomia candida was studied in a laboratory microcosm experiment, applying a Zn exposure level of 250 mg kg⁻¹ dry soil. Biomass and water content of the plants were no different when only AMF or when both AMF and Collembola were present. In the presence of AMF the Zn content of the plant shoots and roots was significantly higher than without AMF. This effect was reduced by Collembola at both low and high density. High densities of Collembola reduced the extent of AMF colonization of the plant roots and hyphal length in the soil, but low densities had no effect on either. The results of this experiment reveal that the F. candida–G. intraradices interaction affects Zn uptake by maize, but the mechanisms are still unknown.     

Influence of arbuscular mycorrhizal fungi on growth and selenium uptake by garlic plants

The aim of this study is to investigate the effects of arbuscular mycorrhizal fungi (AMF) on garlic plants growth and the uptake of selenium (Se). Garlic plants were grown in the pots inoculated with Glomus fasciculatum and G. mosseae and maintained in a greenhouse. Three weeks after planting, the pots had received different concentrations of Se (5, 10, 15, 20, 25 mg kg^?1 of soil) in the form of selenium dioxide (SeO₂) at 3 weeks intervals up to 12 weeks. For physiological and biochemical analysis, the samples were randomly collected from five plants of each experiment. Maximum AM infection, spore population and plant biomass were observed in the roots of mycorrhizal-mediated plants without Se, and they were gradually declined in both mycorrhizal and non-mycorrhizal (NM) plants with increasing concentrations of Se. Among the two Glomus species tested, G. fasciculatum-mediated plants showed higher AM infection, spore population and plant biomass than G. mosseae. No differences were observed for the uptake of Se in mycorrhizal plants and NM plants. However, NM plants uptake more Se than mycorrhizal plants. Higher contents of total chlorophyll and sugars were observed in plants inoculated with G. fasciculatum without Se and they were decreased in the presence of Se. In contrast, increased amount of glutathione peroxidase was observed at increasing concentrations of Se up to 20 mg kg^?1. High-performance liquid chromatography data revealed that SeO₂ converted to organic form of Se as γ-glutamyl-Se-methylselenocysteine. These results are basis for further investigations on the role of AMF on plant growth and uptake of Se in crop plants.     

Transport of nitrogen and zinc to rhodes grass by arbuscular mycorrhiza and roots as affected by different nitrogen sources (NH<Subscript>4</Subscript><Superscript>+</Superscript>-N and NO<Subscript>3</Subscript><Superscript>−</Superscript>-N)

We investigated the effect of mineral nitrogen forms on transfer of nitrogen (N) and zinc (Zn) from attached compartments to rhodes grass (Chloris gayana) colonised with arbuscular mycorrhizal fungi (AMF). After being pre-cultivated in substrates with adequate nutrient supply and either AMF inoculated (+AM) or left non-inoculated (?AM), rhodes grass was positioned adjacent to an outer compartment holding a similar substrate but applied with labelled nitrogen (¹⁵N) either as ammonium (NH₄ ⁺) or nitrate (NO₃ ^?), and a high supply of Zn (150 mg kg^?1 DS). Plant roots together with fungal mycelium were either allowed to explore the outer compartment (with root access) or only mycorrhizal hyphae were allowed (without root access). Within each access treatment, biomasses of rhodes grass were not significantly affected by AMF inoculation or N form. AMF contribution to plant ¹⁵N uptake was about double in NH₄ ⁺ compared with NO₃ ^?-supplied treatments while the mycorrhizal influence on plant Zn uptake was insignificant. Without root access, the shoot ¹⁵N/Zn concentration ratio was up to ten-fold higher in +AM than –AM treatments and this ratio increase was clearly more pronounced in NH₄ ⁺ than NO₃ ^?-supplied treatments. In conclusion, rhodes grass in symbiosis with the tested AMF acquired more N when supplied with ammonium. Moreover, there is clear indication that although the AMF have transported both nutrients (N and Zn), N was preferentially transferred as compared to Zn. We confirmed that, while rhodes grass is not able to prevent excessive Zn uptake via roots under conditions of high Zn, mycorrhiza is able to avoid excessive Zn supply to the host plant when the fungus alone has access to contaminated patches.     

Arbuscular Mycorrhizal Fungi and Arsenate Uptake by Brachiaria Grass (Brachiaria decumbens)

ABSTRACT Using a compartmentalized treatment technique, the role of arbuscular mycorrhizal fungi (AMF; Acaulospora scrobiculata) on arsenic (As) uptake and translocation in Brachiaria decumbens. Treatments consisted of a factorial arrangement of three As doses (0, 50, and 100 mg kg^?1) and the presence/absence of AMF inoculates. In the absence of AMF, B. decumbens did not show As accumulation, indicating the probable presence of tolerance mechanism via As exclusion by the roots. B. decumbens plants showed high AMF colonization levels, especially in the arsenic treatments, with AMF improving shoot and root growth independent of As concentrations. Arsenic accumulation occurred only with AMF inoculation. Phosphorous uptake was reduced in B. decumbens roots in the presence of arsenic with and without inoculation of AMF. Results suggest that B. decumbens can be used in phytoremediation procedures when inoculated with A. scrobiculata, although pasture formation should be strictly avoided in contaminated sites.     

The phytoprotective effects of arbuscular mycorrhizal fungi on Enterolobium contorstisiliquum (Vell.) Morong in soil containing coal-mine tailings

The purpose of this study was to evaluate the effects of arbuscular mycorrhizal fungi (AMF) on pacara earpod tree (Enterolobium contorstisiliquum) growth and phytoprotection in soil containing coal-mining waste. A greenhouse experiment was carried out with three inoculation treatment groups (non-inoculated, inoculated with Rhizophagus clarus, and inoculated with Acaulospora colombiana) in two substrates (0 or 30% tailings). After 90 days the seedlings were collected to quantify growth parameters, quality, mycorrhizal root colonization rate, and leaf content of chlorophylls and carotenoids. Macronutrients were quantified in the shoots; Cu, Zn, and Mn levels were measured in the shoots and roots; and glomalin content was measured in the rhizosphere. Colonization by A. colombiana (40%) promoted phytoprotection and better growth in seedlings planted in partial tailing substrate, due to the lower Cu (1.04 mg kg^?1) and Zn (13.4 mg kg^?1) levels in shoot dry mass and reduced translocation of these elements to the shoots. A. colombiana increased soil glomalin concentrations (2.98 mg kg^?1) and the accumulation of nutrients necessary for synthesizing chlorophylls and carotenoids in the leaves. Colonization by R. clarus (81%) produced no phytoprotective effects.     

Effect of Different Amendments on Growing of Canna indica L. Inoculated with AMF on Mining Substrate

Canna indica L. (CiL) was used here in phytoremediation of mining soils. Our work evaluated the effect of AMF (i) on the growth and (ii) on the uptake of heavy metals (HM). The tests were conducted in the greenhouse on mining substrates collected from the Kettara mine (Morocco). The mine soil was amended by different proportions of agricultural soil and compost and then inoculated with two isolates of AMF (IN1) and (IN2) of different origins. After six months of culture, the results show that on mining soils (100%) only AMF (IN2) was able to colonize the roots of CiL with a frequency of 40 ± 7% and an intensity of 6.5 ± 1.5%. Also, the lowest values of shoot and root dry biomass are obtained on these mining soils with respectively 0.30 g and 0.27 g. In contrast, the accumulation of HM was higher and reached more than 50% of that contained in the mining soils, the highest values with 138 mg kg^?1 Cu²⁺, Zn²⁺ 270 mg kg^?1 and 1.38 mg kg^?1 Cd was recorded. These results indicate that the colonization of CiL roots by AMF (IN2) could significantly improve its potential to be used in phytoremediation of polluted soil.     

Mycorrhizal symbiosis and phosphorus fertilization effects on Zea mays growth and heavy metals uptake

Arbuscular mycorrhizal fungi (AMF) can promote plant growth and reduce plant uptake of heavy metals. Phosphorus (P) fertilization can affect this relationship. We investigated maize (Zea mays L.) uptake of heavy metals after soil AMF inoculation and P fertilization. Maize biomass, glomaline and chlorophyll contents and uptake of Fe, Mn, Zn, Cu, Cd and Pb have been determined in a soil inoculated with AMF (Glomus aggregatum, or Glomus intraradices) and treated with 30 or 60 µg P-K₂HPO₄ g^?1 soil. Consistent variations were found between the two mycorrhizal species with respect to the colonization and glomalin content. Shoot dry weight and chlorophyll content were higher with G. intraradices than with G. aggregatum inoculation. The biomass was highest with 30 µg P g^?1 soil. Shoot concentrations of Cd, Pb and Zn decreased with G. aggregatum inoculation, but that of Cd and Pb increased with G. intraradices inoculation. Addition of P fertilizers decreased Cd and Zn concentrations in the shoot. AMF with P fertilization greatly reduced maize content of heavy metals. The results provide that native AMF with a moderate application rate of P fertilizers can be exploited in polluted soils to minimize the heavy metals uptake and to increase maize growth.     

Contribution of the VA mycorrhizal hyphae in acquisition of phosphorus and zinc by maize grown in a calcareous soil

An investigation was carried out to test whether the mechanism of increased zinc (Zn) uptake by mycorrhizal plants is similar to that of increased phosphorus (P) acquisition. Maize (Zea mays L.) was grown in pots containing sterilised calcareous soil either inoculated with a mycorrhizal fungus Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe or with a mixture of mycorrhizal fungi, or remaining non-inoculated as non-mycorrhizal control. The pots had three compartments, a central one for root growth and two outer ones for hyphal growth. The compartmentalization was done using a 30-m nylon net. The root compartment received low or high levels of P (50 or 100 mg kg^–1 soil) in combination with low or high levels of P and micronutrients (2 or 10 mg kg^–1 Fe, Zn and Cu) in the hyphal compartments.Mycorrhizal fungus inoculation did not influence shoot dry weight, but reduced root dry weight when low P levels were supplied to the root compartment. Irrespective of the P levels in the root compartment, shoots and roots of mycorrhizal plants had on average 95 and 115% higher P concentrations, and 164 and 22% higher Zn concentrations, respectively, compared to non-mycorrhizal plants. These higher concentrations could be attributed to a substantial translocation of P and Zn from hyphal compartments to the plant via the mycorrhizal hyphae. Mycorrhizal inoculation also enhanced copper concentration in roots (135%) but not in shoots. In contrast, manganese (Mn) concentrations in shoots and roots of mycorrhizal plants were distinctly lower, especially in plants inoculated with the mixture of mycorrhizal fungi.The results demonstrate that VA mycorrhizal hyphae uptake and translocation to the host is an important component of increased acquisition of P and Zn by mycorrhizal plants. The minimal hyphae contribution (delivery by the hyphae from the outer compartments) to the total plant acquisition ranged from 13 to 20% for P and from 16 to 25% for Zn.     

Carbon allocation mediated by arbuscular mycorrhizal fungi alters the soil microbial community under various phosphorus levels

Studies have shown that arbuscular mycorrhizal fungi (AMF) can shape the rhizosphere microbial community of the host plant, but the underlying mechanisms are unclear. Here, we tested the hypotheses that AMF may affect the rhizosphere microbial community by mediating carbon (C) allocation of the host plant, and that this mediation may be modulated by the soil phosphorus (P) level. Using a split-root system, we conducted a microcosm experiment with three main effects (soil P level: 5 or 25 mg kg⁻¹; AMF: with or without inoculation; and spatial niche (i.e., rhizosphere, hyphosphere, and mycorrhizosphere). Host plant growth benefited from AMF under low soil-P conditions. ¹³CO₂ isotope labeling showed that AMF increased C allocation to the colonized root and AMF mycelia under low-P conditions, which promoted AMF growth. ¹³C-DNA-SIP and 16S rRNA sequencing further indicated that the enhanced C allocation from the host altered the soil microbial community. Our results suggest that AMF enhances the C allocation of the host plant below ground, which can shape microbial community composition. These AMF effects were greater with a low than with a high level of soil P.     

Moderating mycorrhizas: arbuscular mycorrhizas modify rhizosphere chemistry and maintain plant phosphorus status within narrow boundaries

Pastures often experience a pulse of phosphorus (P) when fertilized. We examined the role of arbuscular mycorrhizal fungi (AMF) in the uptake of P from a pulse. Five legumes (Kennedia prostrata, Cullen australasicum, Bituminaria bituminosa, Medicago sativa and Trifolium subterraneum) were grown in a moderate P, sterilized field soil, either with (+AMF) or without (?AMF) addition of unsterilized field soil. After 9–10 weeks, half the pots received 15 mg P kg^?1 of soil. One week later, we measured: shoot and root dry weights; percentage of root length colonized by AMF; plant P, nitrogen and manganese (Mn) concentrations; and rhizosphere carboxylates, pH and plant‐available P. The P pulse raised root P concentration by a similar amount in uncolonized and colonized plants, but shoot P concentration increased by 143% in uncolonized plants and 53% in colonized plants. Inoculation with AMF decreased the amount of rhizosphere carboxylates by 52%, raised rhizosphere pH by ～0.2–0.7 pH units and lowered shoot Mn concentration by 38%. We conclude that AMF are not simply a means for plants to enhance P uptake when P is limiting, but also act to maintain shoot P within narrow boundaries and can affect nutrient uptake through their influence on rhizosphere chemistry.     

Enrichment of nosZ-type denitrifiers by arbuscular mycorrhizal fungi mitigates N2O emissions from soybean stubbles

Hotspots of N₂O emissions are generated from legume residues during decomposition. Arbuscular mycorrhizal fungi (AMF) from co-cultivated intercropped plants may proliferate into the microsites and interact with soil microbes to reduce N₂O emissions. Yet, the mechanisms by which or how mycorrhizal hyphae affect nitrifiers and denitrifiers in the legume residues remain ambiguous. Here, a split-microcosm experiment was conducted to assess hyphae of Rhizophagus aggregatus from neighbouring maize on overall N₂O emissions from stubbles of nodulated or non-nodulated soybean. Soil microbes from fields intercropped with maize/soybean amended with fertilizer nitrogen (SS-N1) or unamended (SS-N0) were added to the soybean chamber only. AMF hyphae consistently reduced N₂O emissions by 20.8%–61.5%. Generally, AMF hyphae promoted the abundance of N₂O-consuming (nosZ-type) denitrifiers and altered their community composition. The effects were partly associated with increasing MBC and DOC. By contrast, AMF reduced the abundance of nirK-type denitrifiers in the nodulated SS-N0 treatment only and that of AOB in the non-nodulated SS-N1 treatment. Taken together, our results show that AMF reduced N₂O emissions from soybean stubbles, mainly through the promotion of N₂O-consuming denitrifiers. This holds promise for mitigating N₂O emissions by manipulating the efficacious AMF and their associated microbes in cereal/legume intercropping systems.     

P uptake by arbuscular mycorrhizal hyphae: effect of soil temperature and atmospheric CO2 enrichment

Mycorrhizas are ubiquitous symbioses that may have an important role in the movement of C from air to soil. Studies on the effects of climate change factors on mycorrhizas have been concentrated on the effects of atmospheric [CO₂] whereas temperature effects have been neglected. Based on previous results showing no effect of varying atmospheric [CO₂] on the development and P uptake of the arbuscular mycorrhizal fungi (AMF) colonizing plants growing in controlled conditions, we hypothesized that soil temperature would have a higher impact on AMF development and nutrient uptake than the effects of [CO₂] on the host plant. Pea plants were grown in association with either a single isolate of Glomus caledonium or AMF from field soil in factorial combination with the corresponding current (10 °C) or elevated (15 °C) soil temperatures at current (350 p.p.m) or elevated (700 p.p.m) atmospheric [CO₂]. ³³P uptake by extraradical AMF hyphae was measured independently from root P uptake in a root exclusion compartment. Intraradical colonization developed well at both soil temperatures and almost duplicated from 10 to 15 °C. Extraradical mycelium developed only at 15 °C in the root exclusion compartment and hyphal P uptake could therefore be studied at 15 °C only. Hyphal P uptake differed markedly between inoculum types, but was not altered by growing the host plants at two atmospheric [CO₂] levels. No significant [CO₂] × soil temperature interactions were observed. The results suggested that, in the system tested, AMF development and function is likely more influenced by the temperature component of climate change than by its [CO₂] component. We suggest that much more attention should be paid to temperature effects in future studies.