First assessment of soil mesofauna, microbiota, and humic substances associations in a minesoil revegetated with four grasses in Brazil: An 18-year field study

Abstract

Moving away from coal protects our environment and soil. However, coal use in 2022 exceeded all previous years, systematically generating minesoils. The reestablishment of vegetation and organisms in minesoils is jeopardized by excessive soil compaction, eventual acidity, and depletion of soil organic matter (SOM), fauna, and microbial communities. Therefore, monitoring the recovery of soil attributes and functions as influenced by revegetation species is crucial to understanding the processes and time of ecological restoration. We aimed to verify if 18 years of revegetation with perennial grasses (Hemarthria altissima, Paspalum notatum, Cynodon dactylon, Urochloa brizantha) transformed the minesoil a habitat for mites, springtails and other invertebrates as well as for soil microorganisms. Moreover, we investigated associations between these biological indicators with soil humic substances (HS) content. The minesoil is located in Candiota (Brazil), and was constructed in 2003, when revegetation with the grasses started. In 2021, soil samples (0.10 m depth) were collected to determine mites and springtails abundance, microbial respiration, carbon and metabolic quotient, soil, HS content, pH, bases, and aluminum saturation. In order to monitor the soil attributes recovery by the perennial grasses, the means of treatments were compared to the control using percentage differences (positive or negative), as the control was not part of the experimental design. The relationship between the biological variables and the soil variables was assessed using Spearman correlation, and the Canonical Correspondence Analysis was used to identify the performance of each grass in relation to the dataset. The associations observed confirm that the minesoil recovery process is still in its initial, mainly between soil biological functions with SOM humification. Positive associations occurred between mites and microbial respiration and accumulation of humin, especially with Urochloa brizantha revegetation.