Arbuscular Mycorrhizal Fungi Colonization Levels Research Articles

Impact of elevated carbon dioxide on the rhizosphere communities of Carex arenaria and Festuca rubra

AbstractThe increase in atmospheric carbon dioxide (CO2) levels is predicted to stimulate plant carbon (C) fixation, potentially influencing the size, structure and function of micro‐ and mesofaunal communities inhabiting the rhizosphere. To assess the effects of increased atmospheric CO2 on bacterial, fungal and nematode communities in the rhizosphere, Carex arenaria (a nonmycorrhizal plant species) and Festuca rubra (a mycorrhizal plant species) were grown in three dune soils under controlled soil temperature and moisture conditions, while subjecting the aboveground compartment to defined atmospheric conditions differing in CO2 concentrations (350 and 700 μL L−1). Real‐time polymerase chain reaction (PCR) and PCR‐denaturing gradient gel electrophoresis methods were used to examine effects on the size and structure of rhizosphere communities. Multivariate analysis of community profiles showed that bacteria were most affected by elevated CO2, and fungi and nematodes to a lesser extent. The influence of elevated CO2 was plant dependent, with the mycorrhizal plant (F. rubra) exerting a greater influence on bacterial and fungal communities. Biomarker data indicated that arbuscular mycorrhizal fungi (AMF) may play an important role in the observed soil community responses. Effects of elevated CO2 were also soil dependent, with greater influence observed in the more organic‐rich soils, which also supported higher levels of AMF colonization. These results indicate that responses of soil‐borne communities to elevated CO2 are different for bacteria, fungi and nematodes and dependent on the plant type and soil nutrient availability.

Arbuscular mycorrhizal fungi species associated with rhizosphere of Phoenix dactylifera L. in Morocco

A survey of arbuscular mycorrhizal fungi (AMF) diversity and date palm ( Phoenix dactylifera L.) tree root colonization in arid areas was undertaken in ten palm groves located along the Ziz valley (Tafilalet, south-west Morocco). The frequency and the mean intensity of root colonization reached 72 and 43% respectively and the spore population varied from 238 to 1840 spores/10g of soil. The AMF colonization levels of field date palm roots were found to be negatively correlated with soil phosphorus content (r2 =-0,64). A total of ten AMF species were trapped from the 10 studied sites with a population of 4 to 7 species per sites. The isolated species included: Glomus mosseae, G. fasciculatum, G. constrictum, G. aggregatum, G. macrocarpum , 3 undescribed species of Acaulospora and two of Scutellospora genera . The latter two species were trapped only at the second trapping cycle. Keywords: AMF, diversity, Morocco, palm grove, Phoenix dactylifer ,.

Starter Phosphorus and Broadcast Nutrients on Corn with Contrasting Colonization by Mycorrhizae

Early P nutrition in corn (Zea mays L.) is important for early growth and arbuscular mycorrhizal fungi (AMF) may help juvenile corn plants access soil P. The role of AMF colonization in manured soils and the impact of AMF on the need for starter P is not well known. This study was designed to assess the response of corn with contrasting levels of AMF colonization to low rates of starter P under inputs of broadcast liquid dairy manure or N and P fertilizer. The study was conducted on a high‐P‐testing soil in south‐coastal British Columbia. Contrasting AMF colonization was achieved by growing corn either after corn or after fallow. Both AMF colonization and starter P improve early growth and, to a lesser extent, final harvest even on a relatively high P soil receiving a heavy application of P as broadcast liquid dairy manure or fertilizer. The effects of AMF colonization and starter P were additive, so both contribute to maximum yield. Our study suggests that practices favoring AMF colonization will help juvenile corn plants take up P. While strategically placed low rates of starter P were beneficial for juvenile plants, these treatments were less effective than conventional sidebanding at 30 kg P ha−1 because the effect did not carry forward to final harvest, even in corn that was well colonized by AMF. Therefore, better nutrient strategies and AMF colonization are needed to ensure that corn crops will gain sufficient P with minimum starter mineral fertilizer on manured soils.

Soil Inoculum Potential And Arbuscular Ycorrhizal Colonization Of Acer Rubrum In Forested And Developed Landscapes

Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with numerous landscape tree species and can improve tree growth and environmental stress tolerance. Construction-related soil disturbance is thought to diminish AMF colonization of transplanted trees in newly developed landscapes. We gathered root, soil, and foliar data from red maples (Acer rubrum) growing in newly developed landscape sites and adjacent native forest sites to test two independent hypotheses: (1) landscape trees show lower levels of AMF colonization than forest trees, and (2) the AMF inoculum potential of landscape soils is lower than that of forest soils. Fine roots sampled from landscape maples had significantly lower AMF colonization than maples from adjacent forest sites (3% versus 22%). However, soil­sand mixtures made from landscape soils possessed greater AMF inoculum potential than those made from forest soils (10% versus 4%). Forest soils were more acidic and possessed less extractable P than landscape soils, and differences in AMF colonization between field and landscape maples appeared to reflect differences in soil chemical properties rather than in inoculum potential. The results of this study suggest that not all disturbed landscape soils are deficient in AMF propagules.

Arbuscular mycorrhizal fungi in the tree seedlings of two Australian rain forests: occurrence, colonization, and relationships with plant performance

The roots of rain forest plants are frequently colonized by arbuscular mycorrhizal fungi (AMF) that can promote plant growth in the nutrient poor soils characteristic of these forests. However, recent studies suggest that both the occurrence of AMF on rain forest plants and the dependence of rain forest plants on AMF can be highly variable. We examined the occurrence and levels of AMF colonization of some common seedling species in a tropical and a subtropical rain forest site in Queensland, Australia. We also used a long-term database to compare the growth and mortality rates of seedling species that rarely formed AMF with those that regularly formed AMF. In both forests, more than one-third of the seedling species rarely formed AMF associations, while 40% of species consistently formed AMF in the tropical site compared to 27% in the subtropical site. Consistent patterns of AMF occurrence were observed among plant families at the two sites. Variation among seedling species in AMF occurrence or colonization was not associated with differences in seed mass among species, variation in seedling size and putative age within a species, or lack of AMF inoculum in the soil. Comparisons of four seedling species growing both in the shaded understory and in small canopy gaps revealed an increase in AMF colonization in two of the four species in gaps, suggesting that light limitation partially explains the low occurrence of AMF. Seedling survival was significantly positively associated with seed biomass but not with AMF colonization. Furthermore, seedling species that regularly formed AMF and those that did not had similar rates of growth and survival, suggesting that mycorrhizal and nonmycorrhizal strategies were equivalent in these forests. Furthermore, the high numbers of seedlings that lacked AMF and the overall low rate of seedling growth (the average seedling required 6 years to double its height) suggest that most seedlings did not receive significant indirect benefits from AMF through connection to canopy trees via a common mycorrhizal network.

(115) Soil Inoculum Potential and Mycorrhizal Colonization of Acer rubrum in Forested and Developed Landscapes

Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with numerous landscape tree species and can improve tree growth and environmental stress tolerance. Construction-related soil disturbance is thought to diminish AMF colonization of transplanted trees in newly developed landscapes. We gathered root, soil, and foliar data from red maples (Acer rubrum) growing in newly developed landscape sites and adjacent native forest sites to test the hypotheses that: 1) landscape trees show lower levels of AMF colonization than forest trees; and 2) the AMF inoculum potential of landscape soils is lower than that of forest soils. Fine roots sampled from landscape maples had significantly lower AMF colonization than maples from adjacent forest sites (3% vs. 22%; P= 0.0002). However, soil-sand mixtures made from landscape soils possessed greater AMF inoculum potential than those made from forest soils (10% vs. 4%; P= 0.0081). Forest soils were more acidic and possessed less extractable P than landscape soils, and differences in AMF colonization between forest and landscape maples appeared to reflect differences in soil chemical properties rather than in soil inoculum potential.

Associação micorrízica e teores de nutrientes nas folhas de cupuaçuzeiro (Theobroma grandiflorum) e guaranazeiro (Paullinia cupana) de um sistema agroflorestal em Manaus, Amazonas

As micorrizas arbusculares podem ser importantes na nutrição das plantas em solos ácidos e de baixa fertilidade, como são os da Amazônia de modo geral. Avaliaram-se a colonização radicular por fungos micorrízicos arbusculares (FMAs) nativos e os teores de nutrientes em cupuaçuzeiro e guaranazeiro em um sistema agroflorestal no município de Manaus, Amazonas. Dez plantas de cada espécie foram selecionadas, das quais foram coletadas amostras de raiz, folha e solo durante o período seco e chuvoso da região de Manaus. Os guaranazeiros e os cupuaçuzeiros apresentaram maior colonização radicular por FMAs na época chuvosa. Os teores foliares de Ca, Mg, K, P, Zn, Cu e Mn nas duas espécies não foram influenciados pelas épocas de amostragem. O teor de Fe nas folhas dos cupuaçuzeiros foi maior na época chuvosa, enquanto o dos guaranazeiros, na época seca. A colonização micorrízica correlacionou-se com a concentração foliar de Ca, Mg, P e Cu nos cupuaçuzeiros e com a de Ca, Fe, Zn e Cu nos guaranazeiros.

The influence of Rhizobium and arbuscular mycorrhizal fungi on nitrogen and phosphorus accumulation by Vicia faba.

The aim of this study was to investigate the effects of the interactions between the microbial symbionts, Rhizobium and arbuscular mycorrhizal fungi (AMF) on N and P accumulation by broad bean (Vicia faba) and how increased N and P content influence biomass production, leaf area and net photosynthetic rate. A multi-factorial experiment consisting of four different legume-microbial symbiotic associations and two nitrogen treatments was used to investigate the influence of the different microbial symbiotic associations on P accumulation, total N accumulation, biomass, leaf area and net photosynthesis in broad bean grown under low P conditions. AMF promoted biomass production and photosynthetic rates by increasing the ratio of P to N accumulation. An increase in P was consistently associated with an increase in N accumulation and N productivity, expressed in terms of biomass and leaf area. Photosynthetic N use efficiency, irrespective of the inorganic source of N (e.g. NO3- or N2), was enhanced by increased P supply due to AMF. The presence of Rhizobium resulted in a significant decline in AMF colonization levels irrespective of N supply. Without Rhizobium, AMF colonization levels were higher in low N treatments. Presence or absence of AMF did not have a significant effect on nodule mass but high N with or without AMF led to a significant decline in nodule biomass. Plants with the Rhizobium and AMF symbiotic associations had higher photosynthetic rates per unit leaf area. The results indicated that the synergistic or additive interactions among the components of the tripartite symbiotic association (Rhizobium-AMF-broad bean) increased plant productivity.

Growth response of lentil and wheat to Glomus clarum NT4 over a range of P levels in a Saskatchewan soil containing indigenous AM fungi

The growth responses of lentil (Lens esculenta L. cv. Laird) and two wheat cultivars (Triticum aestivum L. cv. Laura and Neepawa) to Glomus clarum NT4 in soil containing indigenous arbuscular mycorrhizal fungi (AMF) and fertilized with phosphorus at different (0, 5, 10, 20 ppm) levels was studied in a growth chamber. Soil was inoculated with a monospecific culture of G. clarum NT4 to provide an inoculant:indigenous AMF ratio of ca. 1 : 100. The shoot and root growth, and AMF colonization levels of NT4-inoculated lentil were significantly (P≤0.05) greater than the appropriate control plants in the unfertilized soil at 48 days after planting (DAP). At 95 DAP, NT4 inoculation had significantly increased the shoot dry weight (P≤0.08) and AMF colonization (P≤0.05) of lentil plants receiving 5 mg P kg–1 soil, whereas 20 mg P kg–1 soil reduced the shoot growth of NT4-inoculated plants. The NT4 inoculant had no effect (P≤0.05) on shoot P content, but increased (P≤0.08) the P-use efficiency of lentil plants receiving 5 mg P kg–1 soil. In contrast to the inoculant's effect on lentil, NT4 generally had no positive effect on any of the parameters assessed for wheat cv. Laura at any P level at 48 or 95 DAP. Similarly, there was no positive effect of NT4 on shoot or root growth, or AMF colonization of wheat cv. Neepawa plants at any P level at 48 DAP. However, NT4 inoculation increased the grain yield of Neepawa by 20% (P≤0.05) when fertilized with 20 mg P kg–1 soil. This yield increase was associated with a significant (P≤0.05) reduction in root biomass and a significant (P≤0.05) increase in the grain P content of inoculated plants. Thus, NT4 appears to have a preference for the Neepawa cultivar. Our results show that lentil was more dependent on mycorrhizae than wheat and responded to an AMF inoculant even in soil containing high levels of indigenous AMF. It might, therefore, be possible to develop mixed inoculants containing rhizobia and AMF for field production of legumes.