Mycorrhizas in Agroecosystems

Abstract

This review was done to explore the current information on the benefit of arbuscular mycorrhizal symbioses in agricultural systems, drawing on results of research on agroecosystems in Argentina and Brazil. The increasing recognition that agricultural intensification and use of agrochemicals can adversely affect soil quality, modifying the number, diversity and activity of the soil microbiota, including symbiotic fungal populations, have improved the research aimed at crop yield improvement and sustainability. Thus, microbial-based approaches have been proposed and quantitative relationships between soil or plant phosphorus (P) levels and arbuscular mycorrhizas (AM) are being investigated in order to adjust the fertilizer dose to obtain acceptable yield production without depressing the symbiosis. Biodiversity of AM is high in agricultural soils from Argentina both under tillage or non-tillage management. Soils cultivated with wheat, one of the most important crops in Argentina, contain indigenous AM that colonize this crop; however the selection of effective fungus, as well as the study of the mycorrhizal populations in soils supplied with P may allow the attainment of acceptable yield levels with low fertilizer inputs, while also reducing costs and environmental pollution risk. Fertilization with synthetic P sources as superphosphate decreases both mycorrhizal potential and indigenous arbuscular mycorrhizal colonization (AMC) of grain and grasses crops. However, fertilization with rock phosphate doesn't negatively affect both mycorrhizal potential and indigenous AMC. Additionally, the positive effects of mycorrhizal inoculation are shown with the rock phosphate fertilization, while when the fertilizer was superphosphate mycorrhizal benefit was only evident at moderate/low doses of P. Alternatively, fertilizer placement also affects indigenous AMC. Applications with banded superphosphate depress the AM formation of wheat roots as compared with broadcasted applications both under no-tillage and under conventional tillage. In Brazil, reports for maize, peanut, soybean and sorghum as well as for green manure species have pointed their mycotrophy and AM dependency. However, more research is needed in relation to germplasm banks of AM for increase the production of agricultural plants as well as to optimize the use of renewable P sources, which is essential to the Brazilian agribusiness. This chapter discusses the AM parameters, such as root colonization and spore number in agricultural systems and the relationship with some soil characteristics, such as organic matter and glomalin contents. Relevant findings are emphasized, such as inoculation and management benefits for farmers by increasing soil fertility without loss of yield or added costs. Research directions that are needed to increase understanding of mycorrhizal associations in agriculture are indicated. © 2011 Nova Science Publishers, Inc. All rights reserved.