Tancredo Augusto Feitosa de Souza

Arbuscular mycorrhizal fungi in Mimosa tenuiflora (Willd.) Poir from Brazilian semi-arid

Many plant species from Brazilian semi-arid present arbuscular mycorrhizal fungi (AMF) in their rhizosphere. These microorganisms play a key role in the establishment, growth, survival of plants and protection against drought, pathogenic fungi and nematodes. This study presents a quantitative analysis of the AMF species associated with Mimosa tenuiflora, an important native plant of the Caatinga flora. AMF diversity, spore abundance and root colonization were estimated in seven sampling locations in the Ceará and Paraíba States, during September of 2012. There were significant differences in soil properties, spore abundance, percentage of root colonization, and AMF diversity among sites. Altogether, 18 AMF species were identified, and spores of the genera Acaulospora, Claroideoglomus, Dentiscutata, Entrophospora, Funneliformis, Gigaspora, Glomus, Racocetra, Rhizoglomus and Scutellospora were observed. AMF species diversity and their spore abundance found in M. tenuiflora rhizosphere shown that this native plant species is an important host plant to AMF communities from Brazilian semi-arid region. We concluded that: (a) during the dry period and in semi-arid conditions, there is a high spore production in M. tenuiflora root zone; and (b) soil properties, as soil pH and available phosphorous, affect AMF species diversity, thus constituting key factors for the similarity/dissimilarity of AMF communities in the M. tenuiflora root zone among sites.

Long-term effects of alternative and conventional fertilization I: Effects on arbuscular mycorrhizal fungi community composition

The influence of long-term fertilization on arbuscular mycorrhizal fungi community composition was investigated. Soil samples were taken from a long-term field experiment which was conducted for 5 years to explore the effect of three treatments: control (non-fertilization), conventional (mineral fertilizers—NPK), and alternative (organic fertilizers—farmyard manure). The highest values of AMF community composition were found in the alternative fertilization system after the thirty year of its utilization. After the thirty year the conventional fertilization system showed lower AMF diversity compared to alternative fertilization system. In conclusion the alternative fertilization system enhanced mycorrhizal effectiveness that contributes to increase wheat growth after a long-term experiment. Our findings also suggest that inputs of organic matter source can change positively the AMF community composition, and these results highlight the importance of considering the long-term effect of mineral and organic fertilizers on the AMF community diversity. Thus, the long-term utilization of an alternative fertilization system with continuous input of organic matter may exploit positive situations of jointly beneficial biotic and abiotic conditions.

Agronomic Evaluation of Legume Cover Crops for Sustainable Agriculture

The agronomic characteristics of different legume cover crops and their effects on soil chemical properties were investigated in a short-term field study. We compared weed biomass, nitrogen equivalence, growth rate, leaf chlorophyll content, cover crop biomass, soil total organic carbon, and soil total nitrogen under eight different legume cover crops in a short-term field experiment. We found the highest growth rate, cover crop dry biomass, N plant content, and N contribution with C. ochroleuca plants, whereas for leaf chlorophyll content, soil organic carbon, and total nitrogen the highest values were found with M. pruriens. We did not find any significant difference among C. ochroleuca and M. pruriens for cover crop dry biomass. Our findings suggest that the incorporation of cover crops into the soil can change positively the soil chemical properties, such as soil organic carbon and total nitrogen. Our results also highlight the importance of considering the short-term effect of cover crops on the tropical soil fertility maintenance, in this case, Regosol.

Long-Term Effects of Fertilization on Soil Organism Diversity

Fertilization applied in long-term farming systems exerts a crucial influence on soil organism diversity and soil properties. This chapter reviews the use of fertilizers for conventional and alternative farming systems in field experiments in order to improve our understanding of the temporal changes on soil organic carbon, soil total nitrogen, arbuscular mycorrhizal fungi diversity and soil macroarthropods during their long-term utilization. We introduce what are the main effects of long-term fertilization systems on several agricultural farming systems around the world. We also present our experimental data about long-term utilization of mineral and organic fertilization from wheat and rapeseed field experiments. Published field studies show that the continuous use of mineral fertilizers might affect negatively soil organic carbon and total nitrogen, which in turn modifies the community composition of macroarthropods, and arbuscular mycorrhizal fungi, whereas organic fertilizers might affect positively these soil properties and soil organism diversity. Our review shows that inputs of organic matter sources can change positively soil properties and annual crop development and yield. Our review also highlights the importance of considering the long-term effect of organic fertilization combined with agricultural management practices, such as stubble retention, fertilization with micronutrient, and inoculation with arbuscular mycorrhizal fungi and N-fixing bacteria on the maintenance of soil fertility and to improve the diversity of soil organisms.

Biological Invasion Influences the Outcome of Plant-Soil Feedback in the Invasive Plant Species from the Brazilian Semi-arid

Plant-soil feedback is recognized as the mutual interaction between plants and soil microorganisms, but its role on the biological invasion of the Brazilian tropical seasonal dry forest by invasive plants still remains unclear. Here, we analyzed and compared the arbuscular mycorrhizal fungi (AMF) communities and soil characteristics from the root zone of invasive and native plants, and tested how these AMF communities affect the development of four invasive plant species (Cryptostegia madagascariensis, Parkinsonia aculeata, Prosopis juliflora, and Sesbania virgata). Our field sampling revealed that AMF diversity and frequency of the Order Diversisporales were positively correlated with the root zone of the native plants, whereas AMF dominance and frequency of the Order Glomerales were positively correlated with the root zone of invasive plants. We grew the invasive plants in soil inoculated with AMF species from the root zone of invasive (Ichanged) and native (Iunaltered) plant species. We also performed a third treatment with sterilized soil inoculum (control). We examined the effects of these three AMF inoculums on plant dry biomass, root colonization, plant phosphorous concentration, and plant responsiveness to mycorrhizas. We found that Iunaltered and Ichanged promoted the growth of all invasive plants and led to a higher plant dry biomass, mycorrhizal colonization, and P uptake than control, but Ichanged showed better results on these variables than Iunaltered. For plant responsiveness to mycorrhizas and fungal inoculum effect on plant P concentration, we found positive feedback between changed-AMF community (Ichanged) and three of the studied invasive plants: C. madagascariensis, P. aculeata, and S. virgata.

Long-term effects of alternative and conventional fertilization II: Effects on Triticum aestivum L. development and soil properties from a Brazilian ferralsols

The influence of long-term fertilization on plant development and soil properties was investigated. Soil samples were taken from a long-term field experiment which was conducted for 5 years to explore the effect of three treatments: control (non-fertilization), conventional (mineral fertilizers—NPK), and alternative (organic fertilizers—farmyard manure). The highest values of plant yield and soil properties were found in the alternative fertilization system after the thirty year of its utilization. Conventional fertilization showed positive effects until the second year of its utilization where enhanced soil fertility (total nitrogen and available phosphorous content) and plant development (plant yield, plant dry biomass, plant phosphorous concentration, and plant nitrogen concentration). After the thirty year the conventional fertilization system showed lower values for these studied variables compared to alternative fertilization system. Our findings suggest that inputs of organic matter source can change positively the wheat growth and soil fertility, and these results highlight the importance of considering the long-term effect of mineral and organic fertilizers on these variables.The influence of long-term fertilization on plant development and soil properties was investigated. Soil samples were taken from a long-term field experiment which was conducted for 5 years to explore the effect of three treatments: control (non-fertilization), conventional (mineral fertilizers—NPK), and alternative (organic fertilizers—farmyard manure). The highest values of plant yield and soil properties were found in the alternative fertilization system after the thirty year of its utilization. Conventional fertilization showed positive effects until the second year of its utilization where enhanced soil fertility (total nitrogen and available phosphorous content) and plant development (plant yield, plant dry biomass, plant phosphorous concentration, and plant nitrogen concentration). After the thirty year the conventional fertilization system showed lower values for these studied variables compared to alternative fertilization system. Our findings suggest that inputs of organic matter source can change positively the wheat growth and soil fertility, and these results highlight the importance of considering the long-term effect of mineral and organic fertilizers on these variables.

An Old Relationship

In this chapter I discuss about the history of AMF. So, to explain the evolutionary history of AMF and the several proposed AMF classifications between 1800 and the present day, I divided this long period in six phases. Phase I (1800–1900)—Characterized for the first AMF taxonomy classification, and the first description of genus Glomus, Rhizophagus and Sclerocystis. Phase II (1901–1975)—this phase was characterized for two important events: Genus Geosiphon was proposed, and important keys to identify Endogonaceae species were proposed. Phase III (1976–1990)—This phase was characterized: the standardized terminology about concepts of spore wall characteristics and murographs, and the new classification proposed by Morton and Benny in 1990. Phase IV (1991–2000)—In this phase, the first PCR primer (VANS1) to perform molecular analysis was developed. Phase V (2001–2010)—The most important event of this phase was the study done Schusler and co-workers in 2001, where they proposed a new monophyletic phylum for AMF. They transferred all AMF species from Zygomycota to Glomeromycota, and their study was base for other studies until 2009. Phase VI (2011–present day)—This phase is characterized by two important works: (1) the new phylogenetic data for systematics and phylotaxonomy of AMF proposed by Kruger and co-workers in 2012, and the new classification of Glomeromycota proposed by Redecker and co-workers in 2013.

AMF’s Main Structures

In this chapter I discuss about the AMF main structures. So, I introduce you the main structures of arbuscular mycorrhizal fungi, like: hyphae, arbuscules, vesicles, and auxiliary cells, as well as, the development of the symbiosis, how does it work, and the main abiotic and biotic factors that can mediate the development of the mycorrhiza. The development of the symbioses begins with the spore germination (Asymbiotic phase) because spore germination does not depend of the host plant. It depends of biotic and abiotic favorable conditions to occur like: moisture, temperature, pH, mineral nutrients level, organic matter, soil microorganisms, and pollutants action. Pre-symbiotic phase starts even before physical contact between symbionts, where both AMF species and host plants start to exchange chemical and molecular signals, and its success is very dependent of soil properties (e.g., pH, moisture and temperature), and the host plant (e.g., root exudates, like flavonoids, CO2, and unknown ramification factors). After to establish physical contact with root surface, extraradical hyphae differentiate in appressorium, and here starts the Symbiotic phase. Once into root, AMF are able to develop extra- and intraradical hyphae, arbuscules, vesicles, auxiliary cells, and spores.

Spores: A Special Tool to Survive

I discuss in this chapter all spore characteristics, structures and functions. AMF spores are composed by several walls, and each wall has its own function and characteristics to help AMF to survive. Each spore produces one outer wall, which is originated from the fertile hypha on which the spore is borne. Within it a number of layers between one and three layers (although rarely more than three) are synthesized. Usually, these layers are numbered from outermost to innermost (L1, L2, L3, etc.). Spores also produce an inner wall that is described as a flexible germinal wall composed by two bilayered walls groups (Gw1 and Gw2). Sometimes, AMF spores produces different structures, such as subtending hypha, sporiferous saccule, sporogenous cell, pre-germination structures, peridium, cicatrix, or pedicel. These structures are unique, and just occur in same AMF genus, such as Acaulospora, Ambispora, Claroideoglomus, Diversispora, Funneliformis, Glomus, Paraglomus, Rhizophagus, Sclerocystis, and Septoglomus.