Microbiota recovery in a chronosquences of impoverished Cerrado soils with biosolids applications.

Mining activities put the Brazilian savannas, a global biodiversity hotspot, in danger of species and soil carbon losses. Experiments employing biosolids have been applied to rejuvenate this degraded ecosystem, but a lingering question yet to be answered is whether the microbiota that inhabits these impoverished soils can be recovered towards its initial steady state after vegetation recovery. Here, we selected an 18-year-old restoration chronosequence of biosolids-treated, untreated mining and native soils to investigate the soil microbiota recovery based on composition, phylogeny, and diversity, as well as the potential factors responsible for ecosystem recovery. Our results revealed that the soil microbiota holds a considerable recovery potential in the degraded Cerrado biome. Biosolids application not only improved soil health, but also led to 41.7 % recovery of the whole microbial community, featuring significantly higher microbiota diversity and enriched groups (e.g., Firmicutes) that benefit carbon storage compared to untreated mining and native soils. The recovered community showed significant compositional distinctions from the untreated mining or native soils, rather than phylogenetic differences, with physiochemical properties explaining 55 % of the overall community changes. This study advances our understanding of soil microbiota dynamics in response to disturbance and restoration by shedding light on its recovery associated with biosolid application in a degraded biodiverse ecosystem.

Efeitos do uso de lodo de estações de tratamento de esgoto sobre a disponibilidade de água em um substrato minerado no Cerrado / Effects of the use of wastewater sludge on water availability of a mine substrate in the Brazilian Savanna

RESUMO A mineração expõe à superfície material genericamente denominado de substrato, que possui atributos físicos, químicos e biológicos diferentes do solo natural. O lodo de estações de tratamento de esgoto (ETE) é a principal fonte de matéria orgânica utilizada na recuperação de áreas mineradas no Distrito Federal. Apesar de as tecnologias de recuperação afetarem positivamente o substrato minerado, seus efeitos sobre a disponibilidade de água para a vegetação foram pouco estudados. Diante disso, este estudo objetivou verificar se a disponibilidade de água em um substrato de mineração de cascalho foi alterada pela aplicação de lodo de ETE. Três materiais foram investigados: substrato minerado sem aplicação de lodo, substrato minerado com aplicação de lodo e solo sob Cerrado original. Esses materiais foram caracterizados por meio da granulometria, densidade aparente, porosidade total, microporosidade, macroporosidade, condutividade hidráulica saturada, teor volumétrico de água à capacidade de campo e ponto de murcha permanente. Posteriormente, monitorou-se, nesses materiais, o teor volumétrico de água e de ar durante 22 semanas. Os resultados indicaram que o substrato minerado armazenou água acima da capacidade de campo durante 86% do período investigado e o teor de ar permaneceu em níveis críticos durante 55% do mesmo período. A incorporação de lodo de ETE e a colonização de plantas aumentaram os valores de condutividade hidráulica na saturação (Ksat) e reduziu o período em que a água se manteve armazenada à capacidade de campo. Todavia, o regime de umidade do substrato tratado com lodo de ETE se manteve dissimilar ao do solo original usado como referência.

ABSTRACT Mining exposes to surface a material generically called substrate, which has different physical, chemical and biological attributes compared to natural soils. The wastewater sludge (WWS) is the main source of organic matter used in reclamation works of mines in the Federal District of Brazil. Reclamation works positively affect mine substrate but their effects on water availability (AW) have been little studied. This work aimed to evaluate the effects of WWS into a mine substrate on its hydraulic conductivity (Ksat) and AW. Samples of a mine substrate exposed to surface, the same material treated with wastewater sludge and soil under natural Savanna vegetation were collected and analyzed for bulk density, granulometry, total porosity, microporosity, macroporosity, saturated Ksat, volumetric water content at field capacity (FC) and at permanent wilt point (PWP). Subsequently, volumetric water and air content were monitored on the field for 22 weeks. Results showed that the substrate exposed by mining presented water content above FC during 86% of the investigation period and air content at critic levels during 55% of the same period. The incorporation of WWS and subsequent plant colonization increased Ksat values and shortened the period in which water was store at FC. However, the moisture regime in the substrate treaded with WWS remained dissimilar to that of the original soil used as reference.

A new hypothesis for the origin of Amazonian Dark Earths.

Amazonian Dark Earths (ADEs) are unusually fertile soils characterised by elevated concentrations of microscopic charcoal particles, which confer their distinctive colouration. Frequent occurrences of pre-Columbian artefacts at ADE sites led to their ubiquitous classification as Anthrosols (soils of anthropic origin). However, it remains unclear how indigenous peoples created areas of high fertility in one of the most nutrient-impoverished environments on Earth. Here, we report new data from a well-studied ADE site in the Brazilian Amazon, which compel us to reconsider its anthropic origin. The amounts of phosphorus and calcium-two of the least abundant macronutrients in the region-are orders of magnitude higher in ADE profiles than in the surrounding soil. The elevated levels of phosphorus and calcium, which are often interpreted as evidence of human activity at other sites, correlate spatially with trace elements that indicate exogenous mineral sources rather than in situ deposition. Stable isotope ratios of neodymium, strontium, and radiocarbon activity of microcharcoal particles also indicate exogenous inputs from alluvial deposition of carbon and mineral elements to ADE profiles,  beginning several thousands of years before the earliest evidence of soil management for plant cultivation in the region. Our data suggest that indigenous peoples harnessed natural processes of landscape formation, which led to the unique properties of ADEs, but were not responsible for their genesis. If corroborated elsewhere, this hypothesis would transform our understanding of human influence in Amazonia, opening new frontiers for the sustainable use of tropical landscapes going forward.

Floristic woody composition of revegetated mining sites in the Brazilian Federal District / Composição florística lenhosa de jazidas revegetadas no Distrito Federal

The extension degraded by mining in the Brazilian Federal District - BFD is proportionately five times larger than country's average. The restoration of plant communities at these sites is ecologically necessary and legally compulsory. Native woody species are commonly used for ecosystem restoration and this study aimed to identify the floristic composition of woody species introduced in BDF mining sites and discuss its outcomes. The floristic survey was conducted by sampling groups of one hundred individuals until sampling sufficiency was achieved. In total 4,500 plants were sampled in ten sites, which housed 92 autochthonous and 21 allochthonous woody species. Plant communities in the sites assembled between 13 and 62 species, planted at low density - 467 ± 222 plants ha-1. The preferential use of autochthonous species in the revegetation projects resembles the standards recommended by successional restoration models, but the floristic diversity and plant density in initial communities fall below the values deemed as ideal. The 92 autochthonous species include representatives of various habitats, ecological groups and dispersal syndromes. These 92 species currently in use may be regrouped in initial plant communities denser and more diverse than those found in the revegetated sites. The surveyed plant communities were massively composed of arboreal species and such pattern may drive succession towards the formation of forest ecosystems where previously inhabited savanna formations.

A extensão minerada no Distrito Federal - DF é proporcionalmente cinco vezes superior à média nacional. A restauração das comunidades vegetais nesses locais é necessária e obrigatória, e o plantio de espécies lenhosas é prática comum de restauração. Dessa forma, este trabalho visou identificar e avaliar a composição florística lenhosa introduzida em jazidas mineradas no DF como meio de restaurar o ecossistema natural. O levantamento florístico nas áreas selecionadas foi realizado por meio da amostragem de grupos de cem indivíduos, até se obter suficiência amostral. Foram amostradas 4.500 plantas em dez jazidas, que abrigavam 92 espécies lenhosas autóctones e 21 alóctones. As comunidades vegetais levantadas eram formadas por 13 a 62 espécies, plantadas a uma baixa densidade - 467 ± 222 plantas ha-1. O uso preferencial de espécies autóctones nos projetos de revegetação os assemelham aos padrões recomendados pelos modelos sucessionais de restauração, mas a diversidade florística e densidade de plantas nas comunidades iniciais estão abaixo dos valores considerados ideais. Entre as 92 espécies identificadas há representantes de variados habitats, grupos ecológicos e síndromes de dispersão. Portanto, essas 92 espécies podem ser reagrupadas em comunidades iniciais mais densas e diversas do que as verificadas nos projetos executados. As comunidades vegetais nos locais investigados eram predominantemente compostas por espécies arbóreas e tal padrão pode levar à formação de ecossistemas florestais onde antes havia formações savanânicas.

Effect of compost treatment of sewage sludge on nitrogen behavior in two soils.

This work aims to evaluate the effects of compost treatment of digested sewage sludge on nitrogen behavior in two soils, a Spodosol and an Oxisol soil. Digested sewage sludge was composted with sawdust and woodchips, diluting the total nitrogen to one-fourth (dry mass basis) of its original value. Then, sludge and compost were added to the two soils on an equivalent dry weight basis to consider the risk of NO3- -N leaching. Compost treatment of sewage sludge has slowed down the release of mineral-N to half in the Spodosol and to one-third in Oxisol soil. As a result, NO3- -N concentrations in soils incubated with compost were less than half of the amounts found from soils incubated with digested sludge. Estimates were made of the maximum monthly nitrate to leach from the four combinations of soil and sludge treatment. Application of digested sludge, at a higher nitrogen application rate, resulted in a higher nitrate leaching potential than application of the compost product. Soil type also played an important role, with the Oxisol having slightly higher estimated leaching potential than the Spodosol. The higher nitrate release rate in the Oxisol is counterbalanced by its higher field capacity to lessen the expected difference between the two soils.