Roots Of Native Plants Research Articles

Influence of Potentially Toxic Elements and Physio-Chemical Parameters of Industrially Contaminated Soil on Arbuscular Mycorrhizal Fungal Diversity in BBN Corridor, Himachal Pradesh, India

ABSTRACT Arbuscular mycorrhizal fungi (AMF) play an essential role in plant growth and have great potential to enhance plant tolerance under polluted and toxic conditions. This study deals with a survey of five contaminated sites of the Baddi Barotiwala Nalagarh (BBN) industrial corridor/hub to investigate the morpho-diversity of endotrophic AM fungi associated with native plants. The high contamination factor of Cd and Fe in different study sites revealed a high intensity of contamination, indicating that the sites were significantly polluted with Cd and Fe. Results showed that AM symbioses were successfully established in the roots of native plants, highlighting their role in mitigating the harmful effects of potentially toxic elements (PTEs) through bioremediation. A total of 50 AMF morphotypes across 9 genera (Acaulospora, Entrophospora, Ambispora, Diversispora, Gigaspora, Scutellospora, Glomus, Rhizophagus, and Sclerocystis) were identified, with Glomeraceae being the most abundant (46%), followed by Acaulosporaceae (39%) and others contributing less (15%). The study also indicated that the hyphal and vesicular infections were prominent than arbuscular infections in roots. This is the first report on the diversity of native and putative AMF species associated with plants in the BBN industrial corridor, suggesting that these fungi could be cultured for further use as a sustainable organic approach in agriculture and rehabilitation practices in polluted areas.

Investigating the effects of plant growth-promoting rhizobacteria isolates on germination and physiology status of durum wheat under salt stress

The aim of this work is to evaluate the seedling growth and physiology status of wheat seeds inoculated with a suspension of eight plant growth-promoting rhizobacteria (PGPR) isolates. For this purpose, rhizobacteria strains were isolated from the roots of native plants growing in the Algerian steppe, then evaluated for their plant growth promotion (PGP) features, and finally applied on wheat seeds. The obtained results showed that the majority of the tested strains displayed pertinent PGP features. In in vitro experiments, results showed that salinity affected negatively seed germination and impaired plant growth while the inoculation with BC3, BC6 and BC7 strains induced a good germination rate and improved significantly the root length. In greenhouse experience, data demonstrated that non-inoculated plants accumulated a significant amount of osmoregulators (proline and glycine betaine), and recorded a decrease of their chlorophyll content, compared to inoculated plants, where the salinity tolerance of this latter has been much better with a high seedling growth as well as high chlorophyll and low osmolyte contents. The results may be a useful extension of our knowledge of the interaction between plant and PGPR, in view of their possible applications as a biofertilizer to improve plant growth in salinity-impacted regions.

Dry-Season Soil and Co-Cultivated Host Plants Enhanced Propagation of Arbuscular Mycorrhizal Fungal Spores from Sand Dune Vegetation in Trap Culture.

The use of arbuscular mycorrhizal fungi (AMF) as biofertilizer in agriculture is a sustainable approach to fertilization. The first step in the production of AMF biofertilizer is inoculation of mycotrophic plants with a composite of soil and native plant roots, containing potentially viable AMF spores from natural habitats, to a trap culture. A single host plant or a consortium of host plants can be used to propagate AMF spores. However, the difference in the comparative efficiency of mono- and co-cultivated host plants used for the production of AMF spores and the maintenance of original AMF community composition has not been well elucidated. Here, we prepared trap culture with nutrient-poor soil from coastal sand dune vegetation collected during the dry season when the AMF spore density and relative abundance of Glomeromycota ITS2 sequences were significantly higher (p = <0.05) than in the wet season. The AMF communities in the soil were mainly composed of Glomus spp. Maize (Zea mays L.) and/or Sorghum (Sorghum bicolor (L.). Moench) were grown in trap cultures in the greenhouse. Our results demonstrated that co-cultivation of the host plants increased the production of AMF spores but, compared to mono-cultivation of host plants, did not better sustain the native AMF community compositions in the coastal sand dune soil. We propose that the co-cultivation of host plants in a trap culture broadens AMF-host plant compatibilities and thus sustains the symbiotic association of the natively diverse AMF. Therefore, the results of this study suggest that further research is needed to confirm whether the co-culturing of more than one host plant is as efficient a strategy as using a monoculture of a single host plant.

Plant invasion alters community structure and decreases diversity of arbuscular mycorrhizal fungal communities

Invasive plants often pose serious threats to the natural biodiversity of invaded ecosystems and in this way are likely to alter ecosystem services. This applies to arbuscular mycorrhizal (AM) fungi, in which the invaders have been reported to modify community structure, which facilitates their further intrusion. Information as to the impact of such invasion on AM fungal communities is insufficient and therefore needed. In particular, little is known about how AM fungal communities shift in response to individual invasive species. To ascertain whether invasion changes the structure of indigenous AM fungal communities, we examined changes in AM fungal community composition and diversity in soil and in roots of native neighboring plants in response to incursion of five invasive plant species from the family Asteraceae: Conyza canadensis, Erigeron annuus, Echinops sphaerocephalus, Solidago canadensis, and Symphyotrichum novi-belgii. We found that invasions of tested invasive plant species altered composition of the AM fungal community and reduced the diversity of AM fungi in soil and in the roots of some native plants. Statistical significance of the invasions' effects depended on composition of AM fungal communities in roots of the native plant species and/or site and was not connected with changes in soil parameters. Our results confirm the notable influence of plant invasion on indigenous AM fungal biodiversity and the need for further study in various environmental conditions.

Decreased mycorrhizal colonization of Conyza canadensis (L.) Cronquist in invaded range does not affect fungal abundance in native plants

If we are to fight against plant invasions, we need to know the invasion mechanisms of particular neophytes. Conyza canadensis is a successful invader that is native to North America and expanding to human-made as well as natural habitats. Arbuscular mycorrhizal fungi (AMF) are obligate symbionts of a large majority of land plants, and they seem to play significant roles in a number of plant invasions. Although C. canadensis hosts AMF, their role in its invasion remains to be addressed. This survey’s aim was to test the interactions of C. canadensis with AMF in its native (North America) and invaded (Europe) range and the effect of its invasion on the AMF in roots of native plants within the invaded range. We compared AMF colonization of C. canadensis in both ranges, as well as AMF colonization of three native plant species of not yet invaded and invaded sites within the invaded range. Although this survey proved the colonization of C. canadensis with arbuscules and decreased AMF colonization of C. canadensis in the invaded versus its native range, AMF colonization of native plants was not affected by the invasion of C. canadensis. We presume there to be decreased dependence of C. canadensis on mycorrhiza in the invaded range and that another mechanism supports the successful invasions of this plant species. Nevertheless, this is the first time that the impact of C. canadensis on the abundance of AMF in roots of native plants has been assessed.

Nocardiopsis dassonvillei strain MB22 from the Algerian Sahara promotes wheat seedlings growth and potentially controls the common root rot pathogen Bipolaris sorokiniana

The biocontrol potential and plant-growth-promotion activities of seventeen actinobacteria, isolated from roots of native plants and soils harvested in the Algerian Sahara, were investigated. All strains were tested in vitro against five soil-borne phytopathogenic fungi. Six out of seventeen strains were tested in vivo for their biocontrol potential against Bipolaris sorokiniana strain LB12 as well as for their growth-promotion activities of durum wheat (cv. Vitron) seedlings via seed treatments in sterilized and non-sterilized soils. The root rot disease severity index (DSI) of wheat plants derived from seeds treated with actinobacteria (biological seed treatment) was significantly lower (p < 0.05) compared with those obtained from non-treated wheat seeds sown in inoculated pots (positive control). The strain Nocardiopsis dassonvillei MB22 showed the highest biocontrol activity with the DSI much lower than that of the positive control (27.7% versus 90.8% when non-treated seeds were sown in infested soil). No significant difference was observed between the DSI of plants obtained from biological seed treatments with the strain MB22 and those derived from seeds treated with the chemical fungicide Difeconazole®. Biological seed treatment with the spores of the strain MB22 resulted in greatest increases in the dry weight, the root and shoot length of seedlings. In in vitro tests, the strain MB22 was positive for the production of indole-3-acetic acid, siderophores, hydrogen cyanide, showed chitinolytic activity and solubilized inorganic phosphates which are commonly known features for the plant-growth-promotion and biocontrol activities of a given strain.

Common mycorrhizal networks influence the distribution of mineral nutrients between an invasive plant, Solidago canadensis, and a native plant, Kummerowa striata.

Invasive species often reduce ecosystem services and lead to a serious threat to native biodiversity. Roots of invasive plants are often linked to roots of native plants by common mycorrhizal networks (CMNs) of arbuscular mycorrhizal (AM) fungi, but whether and how CMNs mediate interactions between invasive and native plant species remains largely uninvestigated. We conducted two microcosm experiments, one in which we amended the soil with mineral N and another in which we amended the soil with mineral P. In each experiment, we grew a pair of test plants consisting of Kummerowia striata (native to our research site) and Solidago canadensis (an invasive species). CMNs were established between the plants, and these were either left intact or severed. Intact CMNs increased growth and nutrient acquisition by S. canadensis while they decreased nutrient acquisition by K. striata in comparison with severed CMNs. 15N and P analyses indicated that compared to severed CMNs, intact CMNs preferentially transferred mineral nutrients to S. canadensis. CMNs produced by different species of AM fungi had slightly different effects on the interaction between these two plant species. These results highlight the role of CMNs in the understanding of interactions between the invasive species S. canadensis and its native neighbor.

Arbuscular Mycorrhizal Fungal Community Composition in Carludovica palmata, Costus scaber and Euterpe precatoria from Weathered Oil Ponds in the Ecuadorian Amazon.

Arbuscular mycorrhizal fungi (AMF) are ubiquitous to most natural and anthropized ecosystems, and are often found in polluted environments. However, their occurrence and community composition in highly weathered petroleum-polluted soils has been infrequently reported. In the present study, two ponds of weathered crude oil and their surrounding soil from the Charapa field in the Amazon region of Ecuador were selected and root colonization by AMF of their native plants investigated. The AMF community was further analyzed in three selected plant species (i.e., Carludovica palmata, Costus scaber and Euterpe precatoria) present in the two ponds and the surrounding soil. A fragment covering partial SSU, the whole ITS and partial LSU rDNA region was amplified (i.e., 1.5 kb), cloned and sequenced from the roots of each host species. AMF root colonization exceeded 56% in all plant species examined and no significant difference was observed between sites or plants. For AMF community analysis, a total of 138 AMF sequences were obtained and sorted into 32 OTUs based on clustering (threshold ≥97%) by OPTSIL. The found OTUs belonged to the genera Rhizophagus (22%), Glomus (31%), Acaulospora (25%) and Archaeospora (22%). Glomus and Archaeospora were always present regardless of the plant species or the site. Acaulospora was found in the three plant species and in the two ponds while Rhizophagus was revealed only in the surrounding soil in one plant species (Euterpe precatoria). Our study contributed to the molecular community composition of AMF and revealed an unexpected high presence of four AMF genera which have established a symbiosis with roots of native plants from the Amazon forest under high polluted soil conditions.

Potential of endophytic Streptomyces spp. for biocontrol of Fusarium root rot disease and growth promotion of tomato seedlings

ABSTRACTSixteen endophytic actinobacteria isolated from roots of native plants were evaluated for their antagonistic potential against soil-borne phytopathogenic fungi. Among them, three strong antagonistic isolates were selected and characterised for in vitro plant-growth-promoting and biocontrol traits, including production of hydrogen cyanide, indole-3-acetic acid and siderophores, chitinase and β-1,3-glucanase activities, and inorganic phosphate solubilisation. In all trials, the strain Streptomyces sp. SNL2 revealed promising features. The selected actinobacteria were investigated for the biocontrol of Fusarium oxysporum f. sp. radicis lycopersici and for growth promotion of tomato (Solanum lycopersicum L. cv. Aïcha) seedlings in autoclaved and non-autoclaved soils. All seed-bacterisation treatments significantly reduced the root rot incidence compared to a positive control (with infested soil), and the isolate SNL2 exhibiting the highest protective activity. It reduced the disease incidence from 88.5% to 13.2%, whereas chemical seed treatment with Thiram® provided 14.6% disease incidence. Furthermore, isolate SNL2 resulted in significant increases in the dry weight, shoot and root length of seedlings. 16S rDNA sequence analysis showed that isolate SNL2 was related to Streptomyces asterosporus NRRL B-24328T (99.52% of similarity). Its interesting biocontrol potential and growth enhancement of tomato seedlings open up attractive uses of the strain SNL2 in crop improvement.

Could biological invasion by Cryptostegia madagascariensis alter the composition of the arbuscular mycorrhizal fungal community in semi-arid Brazil?

Biological invasions pose a serious threat to native semi-arid areas of Brazil, especially in areas of the state of Ceara that are typically invaded byCryptostegia madagascariensis, an exotic plant species from Madagascar. However, how this biological invasion influences the composition of the arbuscular mycorrhizal fungal (AMF) community and how this affects further invasion by C. madagascariensis is not well known. Here we tested how inoculation with species of AMF affects the development of this invasive plant. We analyzed and compared the AMF community composition of four different stages of biological invasion by C. madagascariensis, and examined the effects of inoculation with these four AMF communities, plus a dominant AMF species (Rhizoglomus intraradices) on plant dry biomass, root colonization, plant phosphorous concentration, and plant responsiveness to mycorrhizas of plants of C. madagascariensis. We found that all studied treatments (except the inoculum from the native plant root zone) promoted the growth of C. madagascariensis and lead to a higher P concentration. Our results demonstrate that the invader might be altering the composition of the AMF community in field conditions, because inoculation with this community enhanced invader growth, root colonization, and P uptake.

Experimental Study on Native Plant Root Tensile Strength for Slope Stabilization

The use of plants for protection of slopes or river embankments against water and wind erosion is spreading in civil and environmental engineering. Naturalistic approach for slope stabilization has been more and more studied and experimented, and a genuine discipline, that integrates traditional geotechnical engineering methods, has been created: Bioengineering. To evaluate plants roots effect on soil shear strength and slope stability, theoretical and experimental studies about biotechnical and mechanical characteristics are needed, to better understand soil-root interaction mechanism. This work provides indications on mechanical strength parameters of some species of native plant roots. Tensile strength of two Mediterranean species have been analyzed caring out a series of experimental tests. Results indicate that tensile strength of roots is influenced by many factors, among which, the most important are root diameter, its moisture and the location where plants had grown up.

Effects of warming and nitrogen on above- and below-ground herbivory of an exotic invasive plant and its native congener

Warming and atmospheric nitrogen deposition could impact plant community composition by altering competitive interactions, however, the effects of these environmental changes on plant invasions via above- and below-ground herbivory are unknown. Here we report the effects of warming and nitrogen addition on aboveground insect defoliation and belowground root-knot nematode infection of a native plant and an introduced invasive congener. Warming increased belowground nematode infection only, while nitrogen addition increased both nematodes and defoliation. Defoliation rates were similar for the exotic invasive and native species and the increases with nitrogen addition were large (almost doubled) but comparable. However, roots of native plant were more intensively infected (i.e., knot density) than roots of the exotic invasive plant (~4-fold in ambient conditions) and this difference increased under elevated temperature (~30-fold higher) in which total nematode infection were nearly tenfold higher. Compared to the exotic invasive plant, the native plant had a higher proportion of fine roots and specific leaf area, but lower photosynthesis ability irrespective of warming and nitrogen deposition treatments. The nematode preferred fine roots to coarse roots for both plant species. Our study indicates that above- and below-ground herbivory of plants differ in their sensitivity to varying drivers of environmental change, which may alter plant interactions and makes it difficult to predict future community structure. Together with the dramatic response of belowground nematodes to warming, this suggests that future modeling or experimental studies on species’ responses to environmental change should simultaneously consider above- and below-ground communities.

Plastic responses of native plant root systems to the presence of an invasive annual grass.

• The ability to respond to environmental change via phenotypic plasticity may be important for plants experiencing disturbances such as climate change and plant invasion. Responding to belowground competition through root plasticity may allow native plants to persist in highly invaded systems such as the cold deserts of the Intermountain West, USA.• We investigated whether Poa secunda, a native bunchgrass, could alter root morphology in response to nutrient availability and the presence of a competitive annual grass. Seeds from 20 families were grown with high and low nutrients and harvested after 50 d, and seeds from 48 families, grown with and without Bromus tectorum, were harvested after ∼2 or 6 mo. We measured total biomass, root mass fraction, specific root length (SRL), root tips, allocation to roots of varying diameter, and plasticity in allocation.• Plants had many parallel responses to low nutrients and competition, including increased root tip production, a trait associated with tolerance to reduced resources, though families differed in almost every trait and correlations among trait changes varied among experiments, indicating flexibility in plant responses. Seedlings actively increased SRL and fine root allocation under competition, while older seedlings also increased coarse root allocation, a trait associated with increased tolerance, and increased root mass fraction.• The high degree of genetic variation for root plasticity within natural populations could aid in the long-term persistence of P. secunda because phenotypic plasticity may allow native species to persist in invaded and fluctuating resource environments.

Biocontrol of Rhizoctonia solani damping-off and promotion of tomato plant growth by endophytic actinomycetes isolated from native plants of Algerian Sahara

Thirty-four endophytic actinomycetes were isolated from the roots of native plants of the Algerian Sahara. Morphological and chemical studies showed that twenty-nine isolates belonged to the Streptomyces genus and five were non-Streptomyces. All isolates were screened for their in vitro antifungal activity against Rhizoctonia solani. The six that had the greatest pathogen inhibitory capacities were subsequently tested for their in vivo biocontrol potential on R. solani damping-off in sterilized and non-sterilized soils, and for their plant-growth promoting activities on tomato seedlings. In both soils, coating tomato seeds with antagonistic isolates significantly reduced (P<0.05) the severity of damping-off of tomato seedlings. Among the isolates tested, the strains CA-2 and AA-2 exhibited the same disease incidence reduction as thioperoxydicarbonic diamide, tetramethylthiram (TMTD) and no significant differences (P<0.05) were observed. Furthermore, they resulted in a significant increase in the seedling fresh weight, the seedling length and the root length of the seed-treated seedlings compared to the control. The taxonomic position based on 16S rDNA sequence analysis and phylogenetic studies indicated that the strains CA-2 and AA-2 were related to Streptomyces mutabilis NBRC 12800T (100% of similarity) and Streptomyces cyaneofuscatus JCM 4364T (100% of similarity), respectively.

Investigation of fungal root colonizers of the invasive plant Vincetoxicum rossicum and co-occurring local native plants in a field and woodland area in Southern Ontario

Fungal communities forming associations with plant roots have generally been described as ranging from symbiotic to parasitic. Disruptions to these associations consequently can have significant impacts on native plant communities. We examined how invasion by Vincetoxicum rossicum, a plant native to Europe, can alter both the arbuscular mycorrhizal fungi, as well as the general fungal communities associating with native plant roots in both field and woodland sites in Southern Ontario. In two different sites in the Greater Toronto Area, we took advantage of invasion by V. rossicum and neighbouring uninvaded sites to investigate the fungal communities associating with local plant roots, including goldenrod (Solidago spp.), wild red raspberry (Rubus idaeus), Canada anemone (Anemone canadensis), meadow rue (Thalictrum dioicum), and wild ginger (Asarum canadense). Fungi colonizing roots were characterized with terminal restriction fragment length polymorphism (T-RFLP) analysis of amplified total fungal (TF) and arbuscular mycorrhizal fungal (AMF) ribosomal fragments. We saw a significant effect of the presence of this invader on the diversity of TF phylotypes colonizing native plant roots, and a composition shift of both the TF and AMF community in native roots in both sites. In native communities invaded by V. rossicum, a significant increase in richness and colonization density of TF suggests that invaders such as V. rossicum may be able to influence the composition of soil fungi available to natives, possibly via mechanisms such as increased carbon provision or antibiosis attributable to unique root exudates. Nature Conservation 4: 55–75 (2013) doi: 10.3897/natureconservation.4.3578 http://www.pensoft.net/natureconservation Copyright Cindy L. Bongard et al. This is an open access article distributed under the terms of the Creative Commons Attribution License 3.0 (CC-BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. ReSeARCh ARtICle Launched to accelerate biodiversity conservation A peer-reviewed open-access journal

NATIVE MICHIGAN PLANTS STIMULATE SOIL MICROBIAL SPECIES CHANGES AND PAH REMEDIATION AT A LEGACY STEEL MILL

A 1.3-acre phytoremediation site was constructed to mitigate polyaromatic hydrocarbon (PAH) contamination from a former steel mill in Michigan. Soil was amended with 10% (v/v) compost and 5% (v/v) poultry litter. The site was divided into twelve 11.89 m X 27.13 m plots, planted with approximately 35,000 native Michigan perennials, and soils sampled for three seasons. Soil microbial density generally increased in subplots of Eupatorium perfoliatum (boneset), Aster novae-angliae (New England aster), Andropogon gerardii (big bluestem), and Scirpus atrovirens (green bulrush) versus unplanted subplots. Using enumeration assays with root exudates, PAH degrading bacteria were greatest in soils beneath plants. Initially predominant, Arthrobacter were found capable of degrading a PAH cocktail in vitro, especially upon the addition of root exudate. Growth of some Arthrobacter isolates was stimulated by root exudate. The frequency of Arthrobacter declined in planted subplots with a concurrent increase in other species, including secondary PAH degraders Bacillus and Nocardioides. In subplots supporting only weeds, an increase in Pseudomonas density and little PAH removal were observed. This study supports the notion that a dynamic interplay between the soil, bacteria, and native plant root secretions likely contributes to in situ PAH phytoremediation.

Low allelochemical concentrations detected in garlic mustard-invaded forest soils inhibit fungal growth and AMF spore germination

Garlic mustard’s (Alliaria petiolata, Brassicaceae) invasive success is attributed in part to its release of allyl isothiocyanate (AITC) into the soil. AITC can disrupt beneficial arbuscular mycorrhizal fungi (AMF) associated with native plant roots, which limits their soil resource uptake. However, AITC and its precursor, sinigrin, have never been detected in garlic mustard-invaded forest soils. Here, we use high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC–MS) to assess the concentration and bioactivity of these putative allelochemicals in paired forest plots uninvaded or invaded by garlic mustard. Our methods detected AITC and sinigrin only where garlic mustard was present and our recovery of AITC/sinigrin coincided with adult senescence. A bioassay of in situ fungal hyphae abundance revealed significantly reduced hyphal abundance in the presence of garlic mustard relative to uninvaded soils. Finally, the lowest concentration of AITC measured in the field (~0.001 mM) is highly inhibitory to the spore germination of a forest AMF species, Glomus clarum. Together, our data provide the first direct evidence of garlic mustard-produced sinigrin and AITC in forest soils and demonstrate that even low levels of these chemicals have the potential to significantly suppress AMF growth and spore germination, strengthening their status as allelopathic novel weapons.

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.

Growth improvement of Ethiopian acacias by addition of vesicular-arbuscular mycorrhizal fungi or roots of native plants to non-sterile nursery soil

The effect of applying vesicular-arbuscular mycorrhizal (VAM) fungi or chopped roots of native plants to a standard, non-sterile nursery soil was investigated in a tree nursery in Ethiopia. Acacia abyssinica and Acacia sieberiana were grown for 3 and 4 months, respectively, in five different soils: standard nursery soil, soil inoculated with a tropical or with a temperate isolate of the VAM fungus Glomus mosseae, and soil inoculated with chopped roots of native forest plants or of grasses. Inoculation with both kinds of native roots and with the tropical G. mosseae isolate increased the shoot dry weight of A. sieberiana significantly, by 48, 33 and 36%, respectively, compared with seedlings in the standard soil. Inoculation with native forest roots and the tropical G. mosseae increased the shoot dry weight of A. abyssinica by 23 and 38%. The temperate isolate of G. mosseae did not improve the growth of either acacia species significantly. Growth stimulation was accompanied by a significantly higher mycorrhizal colonization in all cases except one, whereas shoot phosphorus and magnesium uptakes were generally not significantly affected. The survival of the A. abyssinica seedlings 6 months after their transfer from the nursery to the field was enhanced by all inoculations, although significantly so only with the tropical VAM isolate. The root dry weight after 18 months in the field was also improved in this treatment. The results demonstrate that application of a simple inoculum consisting of chopped roots of native plants with naturally occuring VAM fungi can be equally effective in enhancing seedling growth in tree nurseries in the tropical region as the more elaborate use of pure cultures of VAM fungi, both when seedlings are amply watered and when they are drought-stressed.

Campbellenchinae (Nematoda: Tylodoridae), a new subfamily from campbell Island, with a description of two new species

The first paragraph of the Introduction serves as an Abstract. Specimens of an undescribed subfamily of Tylodoridae Paramonov, 1967 were found in each of 50 soil samples collected since 1951 from around the roots of native plants on Campbell Island, New Zealand. This taxon, Campbellenchinae n.subfam., its type‐genus, Campbellenchus n.gen., and 2 new species, C. poae and C. filicauda, are described. The diagnostic characters of the new subfamily include a lip region without a labial disc, a stylet of moderate length, a characteristic zone of cuticular annulation anterior to the stylet knobs, a slit‐like amphidial opening, a single ovary, and a filiform tail.