# The Quirky Rot Fungi: Underexploited Potential for Soil Remediation and Rehabilitation
## 1 Soil Ecology, Health, and Erosion Control  
It is important to highlight the primary functions of rot fungi in soils because these functions are fundamental to soil maintenance. They are also known as saprotrophic and decaying fungi. Rot fungi are ubiquitous, occupying a prominent position in nature. Although they often go unnoticed, they play a fundamental role in the decomposition of materials, such as cellulose and lignin [1]. Cellulose and lignin are recalcitrant carbon (C) compounds; that is, forms of C that are resistant to decomposition and are therefore not readily available for use by other soil organisms, such as other microorganisms or plants. Without the action of fungi, plant matter remains in the environment for an indefinite period. The ability to degrade recalcitrant C forms is due to the set of enzymes present in the secretome that act on these sources of organic matter and allow its degradation into more easily decomposable (labile) C forms, which can serve as sources of nutrients for others. Rot fungi largely contribute to the nutrient cycle in the soil; namely, phosphorus (P) and nitrogen (N) [2,3]. By promoting the degradation of organic matter, this group of fungi also contributes to the formation of soil, particularly the upper part called humus [4], improving the physical structure of the soil, its water retention capacity, and, generally, soil productivity (Figure 1). It is also worth highlighting that the growth of these fungi can result in hyphal extensions of hundreds of meters, which constitute up to 70% of soil biomass. This network can function as an expansion route for other decomposer microorganisms with less mobility capacity (e.g., bacteria; [5]) and a communication route between other organisms, such as trees, but it also allows the maximization of soil resources (Figure 1). Soil habitat modification by fungal hyphae dictates the establishment and resilience of bacteria, whereas fungi are unaffected by modifications introduced by bacteria [6]. Soils are spatially heterogeneous, and the hyphal network of these fungi allows the translocation of nutrients from more nutritious places to places of greater scarcity [4], thus indirectly fostering soil-related ecosystem services. These characteristics are highlighted below in the context of environmental rehabilitation, focusing on scenarios of agriculture, forest fires, and land reclamation in mining areas, and are perfectly harmonized with the current political agendas of the European Union [7,8]. Agricultural Sustainability, Post-Fire Forest Management, and Ore-Affected Soils: Shared Challenges with Common Goals  
Why address and explore the characteristics of rot fungi in scenarios of agricultural sustainability, forest management after fires, and soil affected by mining activities? Although each has its own intrinsic characteristics, they have common challenges that revolve around the need to balance the use of resources in relation to soil degradation and converge towards the same objectives of environmental protection and soil rehabilitation, which can be met by the natural activity of these fungi. Soils that are affected by mineral activities, are devoid of nutrients, and are loaded with heavy metals are unsuitable for agriculture or forestry in their raw state. Mining disrupts land and ecosystems and alters soil quality, water resources, and vegetation cover [9, 10, 11]. Areas affected by fires generally face the same challenges as those affected by mines, with soils being devoid of nutrients or lacking structures, prone to erosion by water or wind [12], and agricultural soils being increasingly pressured by the entry of various synthetic products [13]. All three scenarios, each with different weights, contribute negatively to various ecosystem services. Contamination  
Figure 1: Overview of the main characteristics of rot fungi that can be harnessed and fostered to restore and reclaim anthropogenically stressed or climate change-stressed soils.