Impact of historical soil management on the interaction of plant-growth-promoting bacteria with maize (Zea mays L.)

Edaphic factors can modulate the effects of microbial inoculants on crop yield promotion. Given the potential complexity of microbial inoculant responses to diverse soil management practices, we hypothesize that sustainable management of soil and water irrigation may improve soil quality and enhance the effects of plant growth-promoting bacteria (PGPB). Consequently, the primary objective was to assess the effectiveness of microbial inoculants formulated with Herbaspirillum seropedicae (Hs) and Azospirillum brasilense (Ab) on maize growth in soils impacted by different historical conservation management systems. We evaluated two soil management systems, two irrigation conditions, and four treatments: T0 - without bioinoculant and 100% doses of NPK fertilization; T1 - Hs + humic substances and 40% of NPK fertilization; T2 - Ab and 40% of NPK fertilization; T3 - co-inoculation (Hs + Ab) and 40% of NPK fertilization. Using a reduced fertilization dose (40% NPK) associated with microbial inoculants proved efficient in increasing maize shoot dry mass : on average, there was a 16% reduction compared to the treatment with 100% fertilization. In co-inoculation (Hs + Ab), the microbial inoculants showed a mutualistic effect on plant response, higher than isolate ones, especially increasing the nitrogen content in no-tillage systems irrigated by swine wastewater. Under lower nutrient availability and higher biological soil quality, the microbial bioinputs positively influenced root development, instantaneous water use efficiency, stomatal conductance, and nitrogen contents.

Nitrogen fertilization regulates crosstalk between marandu palisadegrass and Herbaspirillum seropedicae: An investigation based on 15N isotopic analysis and root morphology

Strategies seeking to increase the use efficiency of nitrogen (N) fertilizers and that benefit plant growth through multiple mechanisms can reduce production costs and contribute to more sustainable agriculture free of polluting residues. Under controlled conditions, we investigated the compatibility between foliar inoculation with an endophytic diazotrophic bacterium (Herbaspirillum seropedicae HRC54) at control and low, medium and high N fertilization levels (0, 25, 50 and 100 mg of N kg-1 as urea, respectively) in Marandu palisadegrass. Common procedures in our research field (biometric and nutritional assessments) were combined with isotopic techniques (natural abundance - δ15N‰ and 15N isotope dilution) and root scanning to determine the contribution of fixed N and recovery of N fertilizer by the grass. Overall, the combined use of 15N isotopic techniques revealed that inoculation not only improved the recovery of applied N-urea from the soil but also provided fixed nitrogen to Marandu palisade grass, resulting in an increase in the total accumulated N. When inoculated plants grew at control and low levels of N, a positive cascade effect encompassing root growth stimulation (nodes of smaller diameter roots), better soil and fertilizer resource exploitation and increased forage production was observed. In contrast, increasing N reduced the contributions of N fixed by H. seropedicae from 21.5% at the control level to 8.6% at the high N level. Given the minimal to no observed growth promotion, this condition was deemed inhibitory to the positive effects of H. seropedicae. We discuss how to make better use of H. seropedicae inoculation in Marandu palisadegrass, albeit on a small scale, thus contributing to a more rational and efficient use of N fertilizers. Finally, we pose questions for future investigations based on 15N isotopic techniques under field conditions, which have great applicability potential.

Geochemical soil dynamics on a bimodal post-collisional intrusive complex

The importance of environmental quality for global social and ecological development, including soil degradation, cannot be overstated. Trace elements dispersed in the environment due to anthropogenic or geogenic activities can result in ecotoxicological impacts, negatively influencing environmental quality. The reference values for soil quality concerning trace elements are primarily based on geological, geomorphological, and pedological patterns. However, intrinsic geological factors may diverge some concentration levels from established norms. Therefore, conducting comprehensive surveys of environmental quality reference values becomes imperative, incorporating geological, geomorphological, and pedological patterns. A deeper understanding of the distribution of these elements is also required. Multivariate analysis proves crucial in compartmentalizing the most relevant factors, particularly in regions marked by bimodal magmatism arising from post-collisional distensional processes, such as the Santa Angélica intrusive suite in southeast Brazil. This study collected soil samples from pastures and natural grasslands with minimal anthropogenic intervention at two depths. These samples underwent various chemical and physical analyses. Statistical techniques such as correlation analysis, principal component analysis, hierarchical clustering, and geostatistics were utilized to interpret the data. The analysis revealed a correlation between the clay fraction and trace elements, demonstrating that clustering is an effective methodology for ascertaining landscape distribution patterns of these components. When compared to quality reference values, it was observed that most soil content levels exceeded both global and local standards. This study suggests that the presence of barium (Ba) in the soil might be due to the isomorphic replacement of feldspathic minerals in acidic and intermediate rocks, whereas molybdenum (Mo) seems to be associated with soils in the domain of porphyritic allanite granite. However, additional research is warranted to determine the concentration factor of Mo in this scenario accurately.

Trace metals in Rio Doce sediments before and after the collapse of the Fundão iron ore tailing dam, Southeastern Brazil

The collapse of the Fundão Dam, in Southeastern Brazil, caused about 50 million m³ of iron ore tailings to sluice down the mountain to Rio Doce, in what is considered the greatest environmental disaster in Brazilian history. The fluvial system received an intense and sudden mudflow that was transported for more than 650 km, before reaching the Atlantic Ocean. Because the area was already impacted by the mineral activities in the region, it becomes essential to evaluate the environmental conditions before the disaster to correctly assess the disaster real damage. This study compares the concentration of trace metals in the sediments of the Rio Doce alluvial plain, before and after the dam collapse, as well as the newly deposited iron ore tailings that became part of the sedimentary framework. The data indicate that the fine particles deposited have since been incorporated into the sandy river sediments. The cadmium and arsenic contents in the sediments increased to levels above the National Environment Council thresholds. The comparison between the levels of trace metals in the situations before and after disaster shows that the mining mud is the source of cadmium while the arsenic was present before the environmental disaster, and its concentration increased due to sediment remobilization. The iron ore tailings deposited on the alluvial sediments also affected the physical parameters since the formed ferruginous crusts waterproofed the ground surface and may, gradually, release toxic metals when exposed to weathering and river reworking.