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The diversity of arbuscular mycorrhizal fungi (AMF) was studied in the Atlantic Forest in Serra do Mar Park (SE Brazil), based on seven host plants in relationship to their soil environment, altitude and seasonality. The studied plots along an elevation gradient are located at 80, 600, and 1,000 m. Soil samples (0–20 cm) were collected in four seasons from SE Brazilian winter 2012 to autumn 2013. AMF spores in rhizosperic soils were morphologically classified and chemical, physical and microbiological soil caracteristics were determined. AMF diversity in roots was evaluated using the NS31/AM1 primer pair, with subsequent cloning and sequencing. In the rhizosphere, 58 AMF species were identified. The genera Acaulospora and Glomus were predominant. However, in the roots, only 14 AMF sequencing groups were found and all had high similarity to Glomeraceae. AMF species identities varied between altitudes and seasons. There were species that contributed the most to this variation. Some soil characteristics (pH, organic matter, microbial activity and microbial biomass carbon) showed a strong relationship with the occurrence of certain species. The highest AMF species diversity, based on Shannon’s diversity index, was found for the highest altitude. Seasonality did not affect the diversity. Our results show a high AMF diversity, higher than commonly found in the Atlantic Forest. The AMF detected in roots were not identical to those detected in rhizosperic soil and differences in AMF communities were found in different altitudes even in geographically close-lying sites.

Our knowledge of the rhizosphere bacterial communities in deep soils and the role of Eucalyptus and Acacia on the structure of these communities remains very limited. In this study, we targeted the bacterial community along a depth profile (0 to 800 cm) and compared community structure in monospecific or mixed plantations of Acacia mangium and Eucalyptus grandis. We applied quantitative PCR (qPCR) and sequence the V6 region of the 16S rRNA gene to characterize composition of bacterial communities. We identified a decrease in bacterial abundance with soil depth, and differences in community patterns between monospecific and mixed cultivations. Sequence analysis indicated a prevalent effect of soil depth on bacterial communities in the mixed plant cultivation system, and a remarkable differentiation of bacterial communities in areas solely cultivated with Eucalyptus. The groups most influenced by soil depth were Proteobacteria and Acidobacteria (more frequent in samples between 0 and 300 cm). The predominant bacterial groups differentially displayed in the monospecific stands of Eucalyptus were Firmicutes and Proteobacteria. Our results suggest that the addition of an N2-fixing tree in a monospecific cultivation system modulates bacterial community composition even at a great depth. We conclude that co-cultivation systems may represent a key strategy to improve soil resources and to establish more sustainable cultivation of Eucalyptus in Brazil.

Despite the strong ecological importance of ectomycorrhizal (ECM) fungi, their vertical distribution remains poorly understood. To our knowledge, ECM structures associated with trees have never been reported in depths below 2 meters. In this study, fine roots and ECM root tips were sampled down to 4-m depth during the digging of two independent pits differing by their water availability. A meta-barcoding approach based on Illumina sequencing of internal transcribed spacers (ITS1 and ITS2) was carried out on DNA extracted from root samples (fine roots and ECM root tips separately). ECM fungi dominated the root-associated fungal community, with more than 90% of sequences assigned to the genus Pisolithus. The morphological and barcoding results demonstrated, for the first time, the presence of ECM symbiosis down to 4-m. The molecular diversity of Pisolithus spp. was strongly dependent on depth, with soil pH and soil water content as primary drivers of the Pisolithus spp. structure. Altogether, our results highlight the importance to consider the ECM symbiosis in deep soil layers to improve our understanding of fine roots functioning in tropical soils.

The cattle production in Brazil has increased considerably in the last years, mainly due to the control of parasite infestation of the animals, which cause loss of productivity to the sector. Fluazuron is an active ingredient (a.i.) of the benzoylurea class used to control ticks in cattle. As this a.i. has been found unchanged in animal feces, which may present a risk to edaphic organisms, this study aimed to assess the effects of fluazuron on survival, reproduction, and behavior of the soil invertebrates Folsomia candida and Eisenia andrei , through ecotoxicological assays. We carried out bioassays in a tropical artificial soil (TAS) spiked with increasing doses of the insecticide. Earthworm mortality was found only at the highest tested fluazuron concentration (LOEC = 160 mg a.i. kg −1 dry soil and NOEC = 80 mg kg −1 ), while the reproduction of F. candida and E. andrei was reduced at lower fluazuron concentrations (EC 50  = 4.48 mg kg −1 and EC 50  = 20.8 mg kg −1 , respectively). Avoidance behavior was detected for both species at lower concentrations than those that caused impacts on reproduction, indicating that the substance may affect the soil habitat function. Since the possible adverse effects of fluazuron on edaphic fauna are still unknown or neglected, this study also warns about the possible harmful effect of veterinary pharmaceutical products on edaphic fauna.

This study explored how different sugarcane vinasses influence the structure and composition of soil bacterial communities in two tropical Oxisols with contrasting textures. In a controlled microcosm experiment with sugarcane seedlings, two concentrations of three vinasse types were applied, and bacterial communities were monitored over 10, 30, and 60 days using T-RFLP and 16S rRNA gene sequencing. Across all treatments, vinasse application led to clear changes in bacterial community structure in both soils, regardless of the time point. Certain bacterial groups, such as Sphingobacteriia, Alphaproteobacteria, and Gammaproteobacteria, became more abundant—likely responding to increased carbon availability, higher pH, and greater soil moisture. At the same time, other groups declined, possibly due to excess nutrients like potassium and sulfur. Notably, these shifts occurred even when standard biochemical indicators suggested no major impact, highlighting the sensitivity of microbial community-level responses. These findings point to the importance of looking beyond traditional soil quality metrics when assessing the environmental effects of organic residue applications. Incorporating microbial indicators can offer a more nuanced understanding of how practices like vinasse reuse affect soil functioning in tropical agroecosystems.

Arbuscular mycorrhizal fungi (AMF) play a crucial role in plant health due to their ability to improve tolerance to biotic and abiotic stresses. Our aim was to evaluate the effectiveness of a pool of native AMF from a harsh environment on plant performance and changes in soil attributes under different levels of drought. An experiment using maize was established, varying the soil water content to simulate severe drought (30% of the water-holding capacity [WHC]), moderate (50% of the WHC) and no drought (80% of the WHC, control treatment). Soil and plant attributes were measured (enzyme activity, microbial biomass, AMF root colonisation and plant biomass and nutrient uptake). There was a two-fold increase in plant biomass under moderate drought when compared to no drought treatment, but there was no difference in nutrient uptake. Under severe drought, there were the highest enzyme activities related to phosphorus (P) cycling and P microbial biomass, indicating higher P microbial immobilization. The increase in AMF root colonisation was observed in plants under moderate and no drought. Our findings demonstrated that the better use of the AMF inoculum varied according to drought levels, with better performance under moderate drought due to the increase in plant biomass.

Sugarcane vinasse is a liquid waste derived from ethanol production. In Brazil, large amounts of this waste are applied to soil as fertigation. In general, this management seems to be beneficial for soil fertility and for some biological parameters, though the published information about the effects of sugarcane vinasse on the soil biota is controversial and the results may vary according to the vinasses’ composition. In this study, we assessed the effects of different sugarcane vinasses on microbial growth and activity indicators to verify their influence on soil microbial metabolism. For this purpose, we used two vinasses from different distillery plants (VA and VB) and a vinasse from a laboratory production (VC). Increasing concentrations of these vinasses were amended on two tropical Oxisols, with 33.6% (RL) and 17.6% (RYL) of clay, in a microcosm experiment with sugarcane plants. Ten, 30 and 60 days after application, we assessed the effects of the vinasses on soil microbial biomass carbon (MBC), basal soil respiration (C–CO 2 ), the metabolic quotient ( q CO2) and dehydrogenase activity of the soils. We found an increase in MBC, C–CO 2 , q CO2, as well as in dehydrogenase activity with increasing vinasse concentrations in both soils, when compared to the control. These changes were attributed mainly to the addition of carbon sources (C) of the vinasses to the soils, which improves the general biological activity.

Araucaria forests in Brazil today correspond to only 0.7 % of the original 200 km² of natural forest that covered a great part of the southern and southeastern area of the Atlantic Forest and, although Araucaria angustifolia is an endangered species, illegal exploitation is still going on. As an alternative to the use of hardwoods, Pinus elliottii presents rapid growth and high tolerance to climatic stress and low soil fertility or degraded areas. Thus, the objective of this study was to evaluate the effect of IAA-producing bacteria on the development of A. angustifolia and P. elliottii. We used five bacterial strains previously isolated from the rhizosphere of A. angustifolia, which produce quantities of IAA ranging from 3 to 126 μg mL⁻¹. Microbiolized seeds were sown in a new gnotobiotic system developed for this work, that allowed the quantification of the plant hormone IAA produced by bacteria, and the evaluation of its effect on seedling development. Also, it was shown that P. elliottii roots were almost as satisfactory as hosts for these IAA producers as A. angustifolia, while different magnitudes of mass increases were found for each species. Thus, we suggest that these microbial groups can be helpful for the development and reestablishment of already degraded forests and that PGPR isolated from Araucaria rhizosphere have the potential to be beneficial in seedling production of P. elliottii. Another finding is that our newly developed gnotobiotic system is highly satisfactory for the evaluation of this effect.

The relationship between sugarcane genotype and symbiosis with arbuscular mycorrhizal fungi (AMF) remains poorly understood, especially regarding different soil moisture levels. Our objective was to evaluate the effect of soil moisture on the AMF community structure, spore abundance and colonization ratio in a plantation with eight sugarcane genotypes (CTC15, CTC17, RB867515, RB92579, RB931011, RB966928, IAC5000 and NCo376). The study was carried out in Piracicaba, São Paulo and Brazil in an experimental plot setup in a randomized block design, with three replicates (blocks). We collected soil and root samples in a greenhouse experiment under two water replenishment levels: 100 and 50% of soil moisture at field capacity ( θ FC ). We extracted spores and assessed the AMF root colonization ratio by using specific dyes and determining the percentage of root length colonized in the different sugarcane genotypes. In addition, we evaluated the AMF community structure by PCR and denaturing gradient gel electrophoresis. In general, the spore abundance and root colonization ratio were higher in all varieties at 100% θ FC . However, the IAC5000 and RB966928 genotypes showed higher colonization levels even at 50% θ FC . The AMF community structure was also influenced by soil water levels with group separations across 100 and 50% θ FC . Sugarcane productivity as measured by stalk plus root dry mass was positively correlated with AMF colonization rates in 100% θ FC . Thus, the water replenishment levels used in sugarcane cultivation can influence spore abundance, colonization ratios and AMF community structure in the soil. The selection of a sugarcane genotype with greater AMF association under low water replenishment levels may be a primary factor in growing sugarcane in areas with low water availability.

Soil bacterial and fungal communities are suitable soil ecosystem health indicators due to their sensitivity to management practices and their role in soil ecosystem processes. Here, information on composition and functions of bacterial and fungal communities were evaluated at two phenological stages of sugarcane (six and twelve months, equivalent to the most intensive vegetative stage and to final maturation, respectively) when organomineral fertilizer, combined with phosphate-solubilizing bacteria (PSB), was added into the soil. Organic compost enriched with apatite (C + A) or phosphorite (C + P) and compost without phosphate enrichment (C) were used in the presence or absence of PSB. In addition, we used a control fertilized with soluble triple superphosphate. The differences were more related to the sampling period than to the type of organomineral fertilizer, being observed higher available phosphorus at six months than at twelve months. Only in the C treatment we observed the presence of Bacillaceae and Planococcaceae, while Pseudomonadaceae were only prevalent in inoculated C + A. As for fungi, the genera Chaetomium and Achroiostachys were only present in inoculated C + P, while the genus Naganishia was most evident in inoculated C + A and in uninoculated C + P. Soliccocozyma represented 75% of the total fungal abundance in uninoculated C while in inoculated C, it represented 45%. The bacterial community was more related to the degradation of easily decomposable organic compounds, while the fungal community was more related to degradation of complex organic compounds. Although the microbial community showed a resilient trait, subtle changes were detected in microbial community composition and function, and this may be related to the increase in yield observed.