Marcela C. Pagano

Dual inoculation of a woody legume (Centrolobium tomentosum) with rhizobia and mycorrhizal fungi in south-eastern Brazil

The integration of N2 fixing trees into stable agroforestry systems in the tropics is being tested due to their ability to produce high biomass N and P yields, when symbiotically associated with rhizobia and mycorrhizal fungi. The growth of Centrolobium tomentosum Guill. ex Benth, a native leguminous tree from the Brazilian Atlantic Forest, was assessed with dual inoculation of Rhizobium spp and mycorrhizal fungi under field conditions. Complete fertilization was compared to treatments of inoculation with selected rhizobia strains BHICB-Ab1 or BHICB-Ab3, associated or not to arbuscular mycorrhizal (AM) fungi. The dual inoculation increased the height and growth in relation to the plants treated with rhizobia alone. Plants inoculated with strain BHICB-Ab1 and arbuscular mycorrhizal fungi (AMF) exhibited an increase of 56% dry matter over uninoculated control and nitrogen accumulation was greater than with BHICB-Ab3 inoculated plants. Strain BHICB-Ab1 presented a synergetic relationship with mycorrhizal fungi since the combined inoculation with BHICB-Ab1 enhanced plant height and dry weight more than single inoculation while the growth of BHICB-Ab3 plants was not modified by AMF inoculation. Arbuscular mycorrhizal fungi enhanced plants survival and seemed to favour the nodule occupation by rhizobia strains as compared to the non-mycorrhizal plants. Inoculation with selected rhizobia and AMF improved the growth of C. tomentosum under field conditions.

Septoglomus fuscum and S. furcatum, two new species of arbuscular mycorrhizal fungi (Glomeromycota)

Two new arbuscular mycorrhizal fungal species, (Glomeromycota) Septoglomus fuscum and S. furcatum, are described and illustrated. Spores of S. fuscum usually occur in loose hypogeous clusters, rarely singly in soil or inside roots, and S. furcatum forms only single spores in soil. Spores of S. fuscum are brownish orange to dark brown, globose to subglobose, (20–)47(–90) μm diam, rarely ovoid, 21–50 × 23–60 μm. Their spore wall consists of a semi-persistent, semi-flexible, orange white to golden yellow, rarely hyaline, outer layer, easily separating from a laminate, smooth, brownish orange to dark brown inner layer. Spores of S. furcatum are reddish brown to dark brown, globose to subglobose, (106–) 138(–167) μm diam, rarely ovoid, 108–127 × 135–160 μm, usually with one subtending hypha that is frequently branched below the spore base, or occasionally with two subtending hyphae located close together. Spore walls consists of a semipermanent, hyaline to light orange outermost layer, a semipermanent, hyaline to golden yellow middle layer, and a laminate, smooth, reddish brown to dark brown innermost layer. None of the spore-wall layers of S. fuscum and S. furcatum stain in Melzer’s reagent. In the field, S. fuscum was associated with roots of Arctotheca populifolia colonizing maritime dunes located near Strand in South Africa and S. furcatum was associated with Cordia oncocalyx growing in a dry forest in the Ceará State, Brazil. In single-species cultures with Plantago lanceolata as host plant, S. fuscum and S. furcatum formed arbuscular mycorrhizae. Phylogenetic analyses of the SSU, ITS and LSU nrDNA sequences placed the two new species in genus Septoglomus and both new taxa were separated from described Septoglomus species.

Effect of the inoculation and distribution of mycorrhizae in Plathymenia reticulata Benth under monoculture and mixed plantation in Brazil

This paper investigates the distribution of arbuscular mycorrhizal fungi (AMF) spores and AMF colonization in a field study in southeastern Brazil. Response to AMF and rhizobial inoculation was studied in monocultures of Plathymenia reticulata and mixed plantations with both Tabebuia heptaphylla and Eucalyptus camaldulensis in a sandy soil during two consecutive years. P. reticulata height and diameter and mycorrhizal colonization and AMF diversity were measured in dry and rainy periods. The inoculated treatment of E. camaldulensis, T. heptaphylla and P. reticulata mixed plants showed higher height and diameter growth of P. reticulata used as well as increased root colonization and AMF spore numbers. Spore populations were found to belong to five genera: Acaulospora, Entrophospora, Glomus, Gigaspora and Scutellospora, with Glomus dominating. Agroforestry practices including use of leguminous tree P. reticulata effectively maintained AMF spore numbers in soils and high AMF colonization levels compared with monocultures, proving an efficient system for productivity and sustainability.

Advances in Arbuscular Mycorrhizal Taxonomy

Arbuscular mycorrhizal fungi (AMF) are commonly sustained by root plants. Current classification systems of AMF involve both morphological and molecular methods and their accelerated progress shows a natural organization and relationships among species. Different research groups discuss the taxonomy, systematics, and evolution of AMF. However, more robust systems of AMF classification will facilitate the research of specialists and nonspecialists. This chapter discusses current classification systems of AMF and changes in AMF species identification drawing on results of research worldwide. The increase in new AMF species is also mentioned. We aim at providing an overview of recent AMF taxonomic studies and the importance of recognizing new AMF species. Some new AM spore morphotypes are illustrated, and relevant findings are emphasized.

Drought Stress and Mycorrhizal Plant

It is recognized that mycorrhizas permit the plant to perform more efficiently under stressful and unfavorable conditions. Recent reports on plant growth under drought stress and mycorrhizas account for 3.7 % of the published papers on mycorrhizas. Stress affects soil physical and chemical properties, as well as plant performance, which affect soil microbes, including symbiotic populations. This chapter was done to explore the current information on the mycorrhizas symbioses with respect to the research results on plant growth as affected by drought. The increasing appreciation that in arid and semiarid regions, most plants are mycorrhizal showed that underground processes are essential for understanding of ecosystem function. Accordingly, important findings related to the benefits of mycorrhizal management by increasing drought tolerance are highlighted. Therefore, research paths that are necessary for the increased understating of mycorrhizal benefits and soil amendments under drought stress are discussed.

Mycorrhizal Interactions for Reforestation: Constraints to Dryland Agroforest in Brazil

Reforestation provides restoration of forest ecosystem services including improved soil fertility, which leads to increased productivity and/or sustainability of the system. Trees also increase the average carbon stocks providing wood supply for local communities; however, C sequestration strategies highlight tree plantations without considering their full environmental consequences, such as losses in stream flow. The productivity of a site is a consequence of their physical, chemical, and biological properties, resulting in natural fertile soils or adequate managed soils for improved quality. Thus, it is required to know the variations in the properties of land-use systems for adoptability of agroforestry innovations. The choice of agroforestry tree species (highly mycorrhizal dependent plants should be selected) would have great implications for the manipulation of arbuscular mycorrhizass species. In dry forest, the inevitable consequence of cutting has been the loss of vegetation cover and insufficient scientific information on the capacity to optimize forest recuperation affects agroforestry adoption. To study the biological properties of soils is now of interest; therefore, this paper reviews the literature that has hitherto been published on mycorrhizal interactions for reforestation and points out the use of mycorrhizal technology as one of the alternatives to improve forest products and environmental quality.

Aboveground nutrient components of Eucalyptus camaldulensis and E. grandis in semiarid Brazil under the nature and the mycorrhizal inoculation conditions

A study was conducted to evaluate the aboveground biomass, nutrient content and the percentages of mycorrhizal colonization in Eucalyptus camaldulensis and Eucalyptus grandis plantations in the semiarid region (15° 09′ S 43° 49′ W) in the north of the State of Minas Gerais in Brazil. Results show that the total above-ground biomass (dry matter) was 33.6 Mg·ha−1 for E. camaldulensis and 53.1 Mg·ha−1 for E. grandis. The biomass of the stem wood, leaves, branches, and stem bark for E. camaldulensis accounted for 64.4%, 19.6%, 15.4%, and 0.6% of the total biomass, respectively (Table 2); meanwhile a similar partition of the total above-ground biomass was also found for E. grandis. The dry matter of leaves and branches of E. camaldulensis accounted for 35% of total biomass, and the contents of N, P, K, Ca, Mg, and S in leaves and branches accounted for 15.5%, 0.7%, 12.3%, 22.6%, 1.9%, and 1.4% of those in total above-ground biomass, respectively. In the trunk (bark and wood), nutrient accumulation in general was lower. Nutrient content of E. grandis presented little variation compared with that of E. camaldulensis. Wood localized in superior parts of trunk presented a higher concentration of P and bark contained significant amounts of nutrients, especially in E. grandis. This indicated that leaving vegetal waste is of importance on the site in reducing the loss of tree productivity in this semi-arid region. The two species showed mycotrophy.

Effect of plant species and mycorrhizal inoculation on soil phosphate-solubilizing microorganisms in semi-arid Brazil: Growth promotion effect of rhizospheric phosphate-solubilizing microorganisms on Eucalyptus camaldulensis

The Jaiba Project is an irrigation enterprise in the north of the state of Minas Gerais and its native vegetation is a dry deciduous forest called woody Caatinga. Two experimental areas (1.5 ha/site) were established in a degraded area using native species intercropped with Eucalyptus camaldulensis in three blocks at random. In each experimental area six plots, randomly distributed in each of the three blocks were cultivated as follows: In area A: (1) Platymenia reticulata Benth (2) P. reticulata inoculated with Rhizobia and spores of Arbuscular Mycorrhizal Fungi (AMF) (3) Eucalyptus camaldulensis Dehnh, (4) Eucalyptus camaldulensis + AMF (5) P. reticulata + Eucalyptus camaldulensis + Tabebuia sp. (6) P. reticulata. (Rhizobia + AMF) + Eucalyptus camaldulensis (AMF) + Tabebuia sp. In the other area plots were cultivated as follows: (1) Schinopsis brasiliensis Engl (2) Schinopis brasiliensis + AMF (3) Eucalyptus camaldulensis (4) Eucalyptus camaldulensis + AMF (5) Schinopis brasiliensis + Myracrodruon urundeuva Fr. Allen + Eucalyptus camaldulensis (6) Schinopis brasiliensis (AMF) + Eucalyptus camaldulensis (AMF) + Myracroduon urundeuva. Soil samples were taken in the root zone of each cultivated plant and analyzed in relation to the number of phosphate solubilizing microorganisms (PSM) and AMF spores. The results showed that the number of PSM and MF spores was significantly higher in the inoculated Eucalyptus rhizosphere, when compared to the native species and also to the non-inoculated Eucalyptus plants. The treatment where PSM and AMF populations were increased the plants also showed greatest height and diameter growth and it was not related to soil phosphatase activity. The growth promotion effect of PSM and AMF was confirmed under greenhouse conditions where the double inoculation improved the dry matter production and phosphorus content. Double inoculation of PSM and MF was recommended to Eucalyptus plants cultivated in semiarid land.

The importance of soybean production worldwide

Abstract Interest in the impact of agriculture on soil structure or changing soil species makeup has increased. Due to its major position as one of the more important crops, more research into soybean (Glycine max L. (Merr)) management can contribute to better understanding of its production. With respect to the importance of soybean production worldwide, its production must be evaluated from different perspectives including its symbiosis with soil microbes. Soybean is an important source of food, protein, and oil, and hence more research is essential to increase its yield under different conditions, including stress. The most important countries of the world with the highest rate of soybean production include the USA, Brazil, Argentina, China, and India. Many crop species including soybean are found associated with arbuscular mycorrhizal fungi and rhizobia. However, other beneficial rhizospheric microorganisms have also been tested, applied, and used as biofertilizers. Microbial interactions may have important functions in soybean production and health. It is also important to evaluate the abiotic factors which interact with the growth and yield of this crop. This chapter explores the current available information relevant to the benefits of soybean production worldwide. Among the major factors affecting the production of soybean is the appropriate use of inocula. Better knowledge of the wide variation in abiotic/biotic parameters is important for understanding the ecology of the soybean system and for management purposes. Evaluation of soybean production, worldwide, can improve our understanding relative to the effects of different factors affecting the growth and yield of soybean globally.

Incidence and diversity of arbuscular mycorrhizal fungi and successor herbaceous plants in an agro-system irrigated with produced water

The purpose of this study was to evaluate the diversity of herbaceous plants and arbuscular mycorrhizal fungi following the cultivation of sunflower (Helianthus annuus L., cv. BRS 321) irrigated with produced water. The sunflower plants were irrigated during three successive cycles with different types of water: produced water obtained through simple filtration (PWSF), and secondly, produced water treated by reverse osmosis (PWRO), and the control with groundwater from the aquifer Açu (WCA). In June 2014, five months after the final harvest, the treatments were evaluated in terms of the diversity of successor plants and their roots colonized by arbuscular mycorrhiza (AM); and samples of soil, in which the following were measured: the spore abundance of AM fungi, the levels of glomalin in easily extracted glomalin and total glomalin. Of a total of eighteen species of herbaceous plants which were identified in the experimental field, Dactyloctenium aegyptium was related with the use of PWSF, Panicum sp. and Diodella apiculata with the use of PWRO, and Trianthema portulacastrum and Eragrostis tenella with the control WCA. The diversity of AM fungi was affected by irrigation with PWSF, in which two species of Acaulospora, one species of Gigaspora and species of Paraglomus were absent, compared to the treatment with PWRO. Acaulospora sp.1 was related with the WCA control as an indicator species. The use of produced water which had undergone reverse osmosis had a short-term effect on the content of glomalin which is easily extractable from the soil but did not change the mycorrhization rates of plants. These results enable us to infer that irrigation with produced water leads to a reduction in the diversity of herbaceous plants and of arbuscular mycorrhizal fungi in the soil, confirming the importance of monitoring agro-systems irrigated with residual water.