Changes in soil properties during iron mining and in rehabilitating minelands in the Eastern Amazon

Assessing differential land use impacts on soil quality: A method based on log-response ratios and polygonal projections

Soil quality indices (SQI) used for assessing soil degradation are often developed using additive scoring functions. However, these SQI may lack reference values for interpreting their outputs and the capacity to differentiate changes in specific variables. To overcome these limitations, this study introduces SQI using Log Response Ratios (LRR) as measures of size effects caused by land use in physical, chemical, and microbiological soil quality indicators. LRR vectors projected 2D polygons with condensed change measures along their perimeters. This method was tested in andosols within the southeastern region of Antioquia, Colombia. These soils were subjected to contrasting stages of degradation determined by the extent of A-horizon removal due to land use practices. This study shows that mining and agriculture have detrimental effects on soil organic carbon and water contents, and that size effects vary significantly between land uses (p < 0.05). Microbiological features also exhibit distinct size effects, such as populations of culturable mesophilic bacteria and fungi, microbial basal respiration, spore density of arbuscular mycorrhizal fungi (AMF), their diversity, and total glomalin-related soil proteins (p < 0.05). The SQI proposed exhibited a negative correlation with SQI computed from scoring additive functions either considering the entire dataset (R2 = 0.87) or a minimum dataset (R2 = 0.90). This approach underscores the utility of using LRR geometrical analysis to assess global soil quality differences among land uses (p < 0.01), offering a visual, quantifiable representation of the effects of each land use over specific soil quality indicators.

Pioneer Tree Bellucia imperialis (Melastomataceae) from Central Amazon with Seedlings Highly Dependent on Arbuscular Mycorrhizal Fungi

Bellucia imperialis is one of the most abundant pioneer tree species in anthropized areas of the Central Amazon, and has ecological importance for the environmental resilience of phosphorus (P)-depleted areas. Thus, we investigated whether B. imperialis depends on symbiosis with arbuscular mycorrhizal fungi (AMF) to grow and establish under the edaphic stresses of low nutrient content and low surface moisture retention capacity of the substrate. We tried three AMF inoculation treatments: (1) CON-no mycorrhizae; (2) MIX-with AMF from pure collection cultures, and (3) NAT-with native AMF, combined with five doses of P via a nutrient solution. All CON treatment seedlings died without AMF, showing the high mycorrhizal dependence of B. imperialis. Increasing P doses significantly decreased the leaf area and shoot and root biomass growth for both the NAT and MIX treatments. Increasing P doses did not affect spore number or mycorrhizal colonization, but decreased the diversity of AMF communities. Some species of the AMF community showed plasticity, enabling them to withstand shortages of and excess P. B. imperialis was shown to be sensitive to excess P, promiscuous, dependent on AMF, and tolerant of scarce nutritional resources, highlighting the need to inoculate seedlings to reforest impacted areas.

Molecular Mechanisms Underlying Mimosa acutistipula Success in Amazonian Rehabilitating Minelands

Mimosa acutistipula is endemic to Brazil and grows in ferruginous outcrops (canga) in Serra dos Carajás, eastern Amazon, where one of the largest iron ore deposits in the world is located. Plants that develop in these ecosystems are subject to severe environmental conditions and must have adaptive mechanisms to grow and thrive in cangas. Mimosa acutistipula is a native species used to restore biodiversity in post-mining areas in canga. Understanding the molecular mechanisms involved in the adaptation of M. acutistipula in canga is essential to deduce the ability of native species to adapt to possible stressors in rehabilitating minelands over time. In this study, the root proteomic profiles of M. acutistipula grown in a native canga ecosystem and rehabilitating minelands were compared to identify essential proteins involved in the adaptation of this species in its native environment and that should enable its establishment in rehabilitating minelands. The results showed differentially abundant proteins, where 436 proteins with significant values (p < 0.05) and fold change ≥ 2 were more abundant in canga and 145 in roots from the rehabilitating minelands. Among them, a representative amount and diversity of proteins were related to responses to water deficit, heat, and responses to metal ions. Other identified proteins are involved in biocontrol activity against phytopathogens and symbiosis. This research provides insights into proteins involved in M. acutistipula responses to environmental stimuli, suggesting critical mechanisms to support the establishment of native canga plants in rehabilitating minelands over time.