Intertwined existence: The life of plant symbiotic fungi in agricultural soils

Abstract

The impoverishment of cultivated soils in some countries and nutrient seepage from cultivated lands in others, coupled to the ever increasing demand for food, fiber and fuel, makes it urgent to improve the nutrient use efficiency of crops. Recognition of the intertwined existence of plants and symbiotic fungi would open the possibility of a more sustainable future. Crop management can have a large impact on the effectiveness of the arbuscular mycorrhizal (AM) symbiosis. Soil nutrient imbalance and excessive or too low soil fertility limit AM development. Soil fertility problems can be addressed by the careful selection of fertilizer materials, rates, and modes of application. Soil tillage disrupts AM hyphal networks with impact on crop nutrient uptake, but also on the biodiversity of the AM fungal community. Different growth habits found in the Glomeromycota makes certain groups more vulnerable to the negative effect of tillage. Pesticide use may also impact the AM fungi associated to crop plants through their effect on target organisms interacting with them, or through modification in the physiology of the host plant. The effect of herbicides, fungicides and insecticides are not always negative, indicating that pest control does not necessarily inhibit AM fungi contribution to crop production. The choice of crop sequence including host and non-host plants affects the development, activity and diversity of AM fungi. Forage plants are typically low input, perennial crops that maintain important relationships with AM fungi and dark septate endophytes (DSE). These fungi can improve plant capture of nitrogen and phosphorus, among other effects. These adaptive transient symbioses increase the fitness of host plants in particular times and soil depths. During their co-evolution plants, and AM fungi have developed a chemical language allowing mutual recognition. Signal molecules and AM inoculants are additional options for the management of the AM symbiosis and to improve the nutrient use efficiency of host crops.