Integration of Multidimensional Challenges by Roots in the Life of a Plant.

Roots of vascular plants continuously explore the soil environment and optimize their growth behavior by stimulating or suppressing local growth depending on the spatially diverse environmental conditions of the rooting substrate. The developmental toolbox of roots comprises activity control of apical meristems, initiation and growth of root hairs, lateral and adventitious root formation and cambial growth and, cum grano salis, is well understood. The underlying molecular mechanisms have been described in some detail, in particular with respect to single environmental variables. In a converse manner, we have insufficient knowledge on root responses to heterogeneous and multifactorial soil environments in time and space although parameter gradients (temperature, water potentials, nutrients etc.), local accumulation of relevant beneficial or adverse compounds (nitrogen, phosphorous, other nutrients, heavy metals) and multifactorial challenges of synergistic, antagonistic or neutral interaction of the parameters are the rule rather than the exception. Taking into account that global climate change and pollution by anthropogenic sources add further components to this multifactorial environment, the understanding of the interaction between stressors has particular importance. Improved understanding of root growth and physiology in heterogeneous substrates and multifactorial stress environments is urgently needed to bridge the knowledge gap between controlled laboratory experiments and plant performance under real-life environmental conditions. The Special Issue on the topic "Root responses to multifactorial environmental constraints" aims at contributing innovative insight to narrow the knowledge gap with a focus on roots that are often neglected in current approaches. It should be noted that this editorial deals with the roots of vascular plants and that knowledge from model thallophytes is not included.