Editorial: Molecular characterization of humic substances and regulatory processes activated in plants, volume II

The excessive use of synthetic fertilizers in agriculture over recent decades has had detrimental effects on soil properties, particularly in terms of reducing organic matter content and diminishing the soil microbial activity and biodiversity. Overuse of fertilizers has also increased the risk of nutrient losses through leaching into the soil, groundwater drainage, or surface runoff, thereby posing a threat to the environment. In addition, high fertilizer input can cause an imbalance in nutrient availability in the soil, leading to low nutrient use efficiency (NUE) and metabolic alterations, as plants may not be able to adequately absorb ad manage all the supplied nutrients. These adverse effects can be further intensified by ongoing climate changes, creating a scenario that requires the adoption of sustainable agricultural practices aimed at reducing the input of nutrients through fertilizers by optimizing the use of nutrients by plants and reducing their dependence on chemical fertilizers. In this context, biostimulants have attained growing interest in the last few decades, and their market has raised remarkably on a global scale. Among biostimulants, humic substances (HS) have a longer history. Their capacity to stimulate plant growth and nutrition through diverse mechanisms, both acting in the soil and within the plant, has been thoroughly ascertained. However, part of the mechanisms explaining their action and their effects still needs to be completely elucidated in small- scale and in field trials. Recent studies focusing on both these topics are included in the second volume of this Research Topic.