Intertwined Existence: The Life of Plant Symbiotic Fungi in Agricultural Soils

Abstract

Arbuscular mycorrhizal (AM) fungi are root endophytes that have evolved with land plants for over 400 million years (Pirozinsky and Dalpe 1992). Through time, fungal endophytes and plants have become interdependent. Plants rely largely on fungi for soil nutrient uptake and some fungi even became obligate biotrophs unable to exist without a living host plant. Plants and fungi have coevolved within relatively stable ecosystems, in very successful symbiosis at times, as illustrated by the widespread occurrence of AM mycorrhizae. Cropping systems are typically highly disturbed systems in which cropping practices often harm symbiotic fungi or their host plants. We know that the full potential of the AM symbiosis is rarely realized in cultivated fields, leading to inefficiencies in the function of these ecosystems. Other fungal endophytes of crop roots were overlooked and their role in plant fitness remains largely obscure, although they may be important in ecosystem function. Disruption in the proper function of plant symbioses may lead to inefficiencies in the function of cultivated soils. With the impoverishment of cultivated soils in poor countries and environmental quality degradation due to the loss of residual fertilizer to the environment in economically favored countries, it becomes urgent to improve the nutrient use efficiency of crop production. Improving the effectiveness of the AM symbiosis in cultivated fields would certainly be an important step toward this goal. Improving plant symbiosis effectiveness requires a good understanding of the conditions specific to cultivated soils that are influencing beneficial plant symbiosis. Therefore, the goal of this chapter is to consider the factors influencing the symbioses formed between plants roots and soil fungi, most importantly AM fungi.