“…In many cases, they result in an increase in growth and crop yield, especially when the soil conditions (for example, nutrient-deficient degraded habitats, or polluted soil) are suboptimal for the plant or during stress periods (see, e.g., Varma 1995Varma , 1998Varma and Schuepp 1996;Biro et al 2006). They are therefore a main parameter in ecosystem functions and highly advantageous in sustainable agriculture.…”