New Phytologist 141 (1999), 99–108

In the January 1999 issue of New Phytologist , we published the research paper entitled 'The effect of light on the growth and reproduction of Floerkea proserpinacoides ' by Margaret F. McKenna and Gilles Houle ( New Phytol . (1999) 141 , 99–108). Since its publication, the authors have identified two important errors in the text. First, values given for leaf area ratio (LAR) and specific leaf area (SLA) have been given erroneously in units of cm² g⁻¹; the correct units are cm² mg⁻¹. Second, the values for unit leaf rate (ULR) have been given incorrectly as tenfold lower than they should be; these should be multiplied by ten to give the correct values in mg m⁻² d⁻¹.
We apologise to our readers for these mistakes.     

Evidence that differences in phosphate metabolism in mycorrhizas formed by species of Glomus and Gigaspora might be related to their life-cycle strategies

A glasshouse experiment was done to assess the development and phosphate metabolism of mycorrhizas formed by species of arbuscular mycorrhizal fungi (AMF) from two different genera, Gigaspora and Glomus on Desmodium ovalifolium plants at three concentrations of a phosphate source. The addition of phosphate (0–100 mg P kg⁻¹) had no effect on the alkaline phosphatase activity, stained histochemically, in the intra-radical mycelium of Gigaspora rosea (BEG111), but decreased that of Glomus manihotis (BEG112) over a 10-wk period. The alkaline phosphatase activity of the extra-radical mycelium was unaffected by increasing phosphate addition (0–100 mg P kg⁻¹) in both species of AMF over a 10-wk period. The extra-radical mycelium of Gi. rosea (BEG111) accumulated polyphosphate, determined by staining with 4',6-diamidino-2-phenylindole, whereas polyphosphate was not detected in the extra-radical mycelium of G. manihotis (BEG112). This work indicates differences in the mechanisms of phosphate metabolism in the mycelium of AMF from different genera on a tropical host. This might be determined by the life-cycle strategies of these fungi, in particular the formation of auxiliary cells in Gigaspora . The possibility of a negative-feedback mechanism between alkaline phosphatase and polyphosphate in the extra-radical mycelium of Gi. rosea (BEG111) and the role of polyphosphate in the symbiosis are discussed.     

New Phytologist 140 (1998), 709–714

In the December 1998 issue of New Phytologist , we published the research paper entitled 'Natural occurrence of Ampelomyces intracellular mycoparasites in mycelia of powdery mildew fungi' by Levente Kiss ( New Phytol. (1998) 140 , 709–714). Since its publication, an error in the published title has been brought to our attention: this refers to the ampelomyces , but the name should be Ampelomyces , meaning the genus.
We apologise to the author and to our readers for this mistake.     

Comparison of phosphatase localization in the intraradical hyphae of arbuscular mycorrhizal fungi,Glomus spp. and Gigaspora spp.

The localization of acid and alkaline phosphatases in the intraradical hyphae of the arbuscular mycorrhizal fungi, Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (Gm), Gl. etunicatum Becker and Gerd. (Ge) and Gigaspora rosea Nicol. and Schenck (Gir) were compared. Marigold (Tagetes patula L.) and leek (Allium porrum L.) were inoculated with each of the three fungi. The mycorrhizal roots were harvested at 3, 4, 5 and 6 weeks after sowing (WAS), treated with a digestion solution containing cellulase and pectinase, and then stained for phosphatase activities at pH 5.0 and pH 8.5. The development of fungal structures in the host root was also examined. Gm formed fine-branched (mature) arbuscules only at the early phase of infection (3 to 4 WAS). Mature arbuscules of Ge and Gir were observed from the early phase (4 WAS) up to the end of experiment. At pH 5.0, the localization of the phosphatase activities of the three fungi were similar irrespective to host plant species. The activity appeared in mature arbuscules and intercellular hyphae, whereas the collapsed arbuscules were inactive. Ten millimolar NaF, an acid phosphatase inhibitor, inhibited the phosphatase activities of Gm and Ge but did not affect that of Gir. At pH 8.5, a difference among the fungal species was found in the localization of phosphatase activity while that between host species was not. The mature arbuscules were also the active sites in all three species. Only Gir showed the activity in the intercellular hyphae while the two Glomus spp. did not. Five millimolar EDTA inhibited the activity of Gir at pH 8.5 while the activities of Ge and Gm were not affected by either 5 mM EDTA or 10 mM KCN (both are alkaline phosphatase inhibitors).     

The role of different arbuscular mycorrhizal fungi in the growth of Calamagrostis villosa and Deschampsia flexuosa, in experiments with simulated acid rain

A series of microcosm experiments was established to investigate the effects of simulated acid rain on the capacity of three arbuscular mycorrhizal fungi (AMF) to germinate and colonize two grasses, Calamagrostis villosa and Deschampsia flexuosa. These two grasses are normally found in degraded Norway spruce forests in the Northern Czech Republic where acid rain pollution exists and C. villosa initially outcompetes D. flexuosa for the same niche. An AM fungus isolated from acid soils (Acaulospora tuberculata BEG41) was more tolerant of acidification than two species of Glomus (isolated from agricultural soils of neutral pH) in microcosm studies. Different effects of simulated acid rain (SAR) were found at all stages of the development of three AMF studied in model systems, including spore germination, colonization of host roots, and alkaline phosphatase (ALP) and NADH diaphorase activity of the extraradical mycelium. No ALP activity was found in hyphae germinating from the spores without plants whereas it was detected in all hyphae linked to a functioning intraradical mycelium.Simulated acid rain also affected the mycorrhizal growth response and belowground competition of the two grasses. Disturbance of the ERM between the two plant species significantly reduced the growth of C. villosa but not D. flexuosa. Disturbance also decreased root colonization by AMF of both plants, the total length of ERM and the total length of extraradical hyphae with ALP and NADH diaphorase activity adjacent to both plants. D. flexuosa appeared less dependent on the mycorrhizal state, for shoot and root growth, than C. villosa under the experimental conditions. The ability, therefore, of C. villosa to thrive in forest stands suffering from acid rain pollution may be related to this dependence on its mycorrhizal hyphal links to D. flexuosa under the environmental conditions produced by the pollution including higher light levels.     

Molecular analysis of Gigaspora (Glomales, Gigasporaceae)

This work presents a cooperative effort to integrate new molecular (isozyme and SSU analyses) characters into the morphological taxonomy of the genus Gigaspora (Glomales). Previous analyses of published Gigaspora SSU sequences indicated the presence of a few polymorphic nucleotides in the region delimited by primers NS71-SSU 1492'. In our study, the SSU of 24 isolates of arbuscular mycorrhizal (AM) fungi from the Gigasporaceae were amplified and the NS71-SSU 1492' region was directly sequenced. The corresponding sequences of four more isolates of AM fungi from Gigasporaceae, already published, were also included in our analyses. Three Gigaspora groups were identified on the basis of a 6 nucleotide-long 'molecular signature': Gigaspora rosea group ( G. rosea + G. albida ), Gigaspora margarita group ( G. margarita + G. decipiens ) and Gigaspora gigantea , which constituted a group by itself. The isozyme profiles (malate dehydrogenase, MDH) of 12 of these 28 isolates, and seven other isolates not sequenced, were compared. The results obtained further supported the grouping of isolates provided by the SSU analysis. Both SSU and MDH analysis indicated that two out of the 35 isolates had been misidentified, which was confirmed when their morphology was reassessed. The use of the Gigaspora intrageneric molecular signature as a quick, unambiguous and objective method to recognize Gigaspora isolates under any (field or laboratory) experimental conditions is suggested.     

Cadmium for all meals – plants with an unusual appetite

Since the beginning of the Bronze Age the acquisition of metals and the mastering of metal processing has been a driving force in human civilisation. It is difficult to imagine, however, how a plant could possibly profit from accumulating excessive amounts of a metal for which there is no metabolic need. Leaving behind an environmentally degraded wasteland, human mining and smeltering activities contributed to providing the niches for such plants, sometimes even accomplishing seed dispersal – through seeds attached to the boots of migrating miners. A stunning example of this is found in the healthy populations of Thlaspi caerulescens in the Cevennes (southern France), the leaves of which have been found to contain the toxic and non-essential metal cadmium (Cd) at concentrations between 1000 and 3000 mg kg⁻¹ dry biomass (R. D. Reeves, unpublished). In this issue, experiments under controlled experimental and glasshouse conditions are reported, confirming an extraordinary level of Cd accumulation and tolerance in these populations (Lombi et al ., pp. 11–20).     

Interactions between Tamarix ramosissima (Saltcedar), Populus fremontii (Cottonwood), and Mycorrhizal Fungi: Effects on Seedling Growth and Plant Species Coexistence

Little is known about the composition and function of the mycorrhizal fungal community in riparian areas, or its importance in competitive interactions between Populus fremontii, a dominant tree in southwestern United States riparian forests which forms arbuscular and ectomycorrhizas, and Tamarix ramosissima, an introduced tree species that has spread into riparian areas. The objectives of this study were to determine the mycorrhizal status of Tamarixand to evaluate the effect of mycorrhizal fungal inoculation on Tamarix growth and on the coexistence between Tamarix and Populus.Arbuscular mycorrhizal fungal colonization of Tamarix was very low in both field and greenhouse grown roots, but levels of colonization by dark septate endophytes were high. Fungal inoculation had little effect on Tamarix seedling growth in monoculture. When Populus and Tamarix were grown together in a greenhouse pot experiment, fungal inoculation reduced the height and biomass of Tamarix but had no effect on Populus. Fungal inoculation shifted coexistence ratios. When Tamarix and Populuswere grown together, Tamarixplants averaged 20 of pot biomass in the uninoculated control but only 5 of pot biomass in the inoculated treatment. These results indicate that Tamarix is non-mycotrophic and that in this greenhouse experiment inoculation altered patterns of coexistence between Populus and Tamarix.     

Influence of colonisation by an arbuscular mycorrhizal fungus on the growth of seedlings of<Emphasis Type="Italic"> Banksia ericifolia</Emphasis> (Proteaceae)

Tap and primary lateral roots of seedlings of the putatively non-mycorrhizal Banksia ericifolia became marginally colonised when grown in an established mycelium of an arbuscular mycorrhizal (AM) fungus in the laboratory. A similar degree of colonisation was found in seedlings from an open woodland. All colonies lacked arbuscules. Two factors influencing colonisation and associated growth of host plants were examined experimentally: concentration of P in the soil and organic energy associated with the fungus. While some inoculated seedlings were slightly smaller when colonised by AM fungi, the results were inconsistent and never statistically significant. Seedlings take up insignificant quantities of soil P during early growth, even in the presence of abundant added P. Though colonisation was minor in all cases, an existing mycelium, whether or not connected to a companion plant, slightly increased the amount of root of B. ericifolia colonised by an AM fungus. All seedlings grew slowly. Shoots were significantly larger than roots, until the initiation of proteoid roots which commenced at about 40 days after germination, with both relatively high and low P supply.