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Purpose: The objective of this study is to improve our understanding of soil organic matter (SOM) stability in Brazilian Cerrado, by interpreting soil properties at the ecosystem scale and elaborating on the interactions of biotic, climatic and edaphic controls. Methods: Three 2 m soil profiles with significantly different total organic carbon TOC content but located on the same geomorphological unit were studied for δ13C isotopic composition to connect tree-grass patterns to TOC content. To gain insight into soil carbon stability, C/N, δ13C and δ15N were analysed for functional organic matter (OM) pools: free particulate OM (POM), occluded POM, base-extractable OM, and mineral-associated OM. Results: Small but abrupt shifts of δ13C with depth reflected simultaneous changes in tree-grass vegetation patterns over the past 10,000 years in all three profiles. These temporal changes were superimposed on spatial differences as indicated by consistent differences in δ13C values between the profiles, reflecting that site-specific differences in tree-grass patterns persisted over the past 10,000 years. Profiles with a historically larger contribution from trees (as evidenced by lower δ13C) had increased charcoal contents. Downward movement of charcoal by intense bioturbation occurred faster in the OM-rich soils as suggested by 14C dating. Conclusion: We found that long-term carbon storage in Brazilian Cerrado soils was a conjunction of wildfires, bioturbation, and local edaphic controls on tree-grass composition. Soils with an OM-rich thick A-horizon had more trees, more charcoal, and a higher activity of soil macrofauna, which was related to local differences in soil water availability.

Complexation of dissolved organic matter (DOM) with cations and minerals contributes to the stabilization of carbon in soils, and can enable the transport of metals in the environment. Hence, a proper understanding of mechanisms that control DOM binding properties in the soil is important for major environmental challenges, such as climate change and stream pollution. However, the role of DOM source in those mechanisms remains understudied. Here, we consider poorly drained tropical Podzols as a model environment to isolate effects of aluminium and DOM on sorption and desorption processes in podzolisation. We collected E- and Bh-horizons from a Brazilian coastal Podzol under tropical rainforest to conduct a column experiment, and percolated the columns with DOM collected from a stream (Stream), peat water (Peat), litter (Litter) and charred litter (Char). To quantify sorption and desorption from the columns, leachates were analysed for DOC content, aluminium content, pH, and the amount of fulvic acid relative to humic acid. The results showed large differences in DOC retention between DOM-types, which were consistent over all columns. Retention of DOC in the column varied between 25 % and 92 % for DOM-type Stream, between 33 % and 63 % for DOM-type Peat, between 22 % and 47 % for DOM-type Litter, and between 8 % and 49 % for DOM-type Char. Similarly, desorption from columns with B-horizon material highly differed between DOM-types. Percolation with DOM-types Stream and Peat caused a release of native DOC from B columns that was higher than in those percolated with water only. On the other hand, percolation of B columns with DOM-types Litter and Char caused a net DOC retention. These differences reflect that certain DOM-types hindered desorption, while other DOM-types caused active desorption. The large differences in sorption/desorption between DOM-types implies that changes in environmental conditions may highly influence the fate of soil carbon in Podzols.

The aim of this work was to carry out a paleoenvironmental study of Holocene sedimentary deposits in the southern sector of Pernambuco's coast (northeastern Brazil). This work addresses an important aspect of Quaternary research that has implications for current climate debates, for instance, how does vegetation react to changing climate and rising sea levels. Thus, we provide a combined approach using sedimentological, palynological, geochemical analyses (stable isotopes i.e., δ13C, δ15N and C:N), in addition to AMS 14C dating from two surficial sediment cores i.e. T4 (up to 150 cm depth) and T5 (up to 136 cm depth) collected from the Formoso River estuarine system. Climatic oscillations show variation in precipitation and atmosphere humidity, marked by areas of expansion and/or retraction of herbaceous plain and forest vegetation. Variations in vegetation composition over the last 7168–7260 cal yr BP in the Formoso River estuary reflects the strong influence of sea-level variations, which were responsible for changes in coastal paleogeography and paleogeomorphology. Changes in vegetation composition indicate its close relationship with transgressive and regressive marine events and corresponding variation of the depositional environment like lakes to coastal lagoons, tidal channels, sandy strand-plain, and the modern estuary of the Formoso River.

By analyzing 6,480 tree leaf samples from 57 sites within Brazilian biomes, we considered whether vegetation types in terrestrial ecosystems reflect biogeochemical diversity and whether they fit into a leaf economics spectrum (LES). To achieve this, we investigated the relations among leaf carbon (C) and nitrogen (N) concentrations, their isotope natural abundance and C:N ratio. In addition, we tested their correlations with mean annual temperature (MAT) and precipitation (MAP), as climatic factors. We found consistent differences in the C and N concentrations and their isotopic composition among the vegetation types. MAP is the main climatic driver of changes in N, C:N ratio, δ15N, and δ13C, correlating negatively with N and positively with C:N ratio. These relations show that these biomes follow an LES. The Caatinga had the highest δ15N values, suggesting that N residence time in soil is longer due to low leaching and plant uptake. We observed that MAP is not the only factor influencing δ13C values in different biomes; instead canopy effect probably explains the highest values observed in the Cerrado. Our results reinforce earlier findings that life diversity in the tropics reflects biogeochemistry diversity and leaf δ15N opens the possibility for investigating plant trade-offs dictated by the LES. Finally, we expect our findings to contribute to a better understanding of the tropics in global climate models.

Background: Deforestation threatens the integrity of the Amazon biome and the ecosystem services it provides. Most of this deforested land is converted to pastures for cattle raising. Early studies revealed that forest-to-pasture conversion alters the flux of methane gas (CH4) in Amazonian soils, driving a switch from acting as a sink to a source of atmospheric CH4. We sought to better understand this phenomenon by investigating the soil microbial metagenomes, focusing on the taxonomic and functional structure of methane-cycling communities. Results: Metagenomic data were combined with in situ measurements of CH4 fluxes, and measurements of soil edaphic factors. We found a significantly higher abundance of methanogens and reduced methanotrophs in pasture soils. As inferred by co-occurrence networks, these microorganisms seem to be less interconnected within the soil microbiota in pasture soils. Metabolic traits were also different between land uses, with increased hydrogenotrophic and methylotrophic pathways of methanogenesis in pasture soils. Similarly, methanotrophs harboring the soluble form of methane monooxygenase enzyme (sMMO) were depleted in pasture soils. Redundancy analysis and multimodel inference revealed that the shift in methane-cycling communities in pasture soils was associated with higher soil compaction, pH, organic matter, and micronutrients. Conclusions: These results provide new knowledge about the effect of forest-to-pasture conversion on the community traits of methane-cycling microorganisms in the Amazon region, resulting in increased abundance and functional potential of methanogens in pastures, and thus increasing the emission of CH4 in deforested soils. Keywords: land-use change, methanogens, methanotrophs, soil properties, multimodel inference

Acknowledgements This work was supported by Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)/Brazil (grant to I.H.T. – regular doctoral scholarship FAPESP 2010/51637‐0 and research internships abroad BEPE/FAPESP 2012/00676‐1), Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)/Brazil (Universal 14/2011−482815/2001‐6), Ministerio de Economia y Competitividad (CGL2010‐20662) and Xunta de Galicia (10PXIB200182PR, ED431D2917/08 and ED431B2018/20). We are grateful to Noemi Silva Sanchez and Luis Rodriguez Lado (Univesidad de Santiago de Compostela), and Fabricio da Silva Terra (Universidade Federal dos Vales do Jequitinhonha e Mucuri) for their collaboration and assistance during different stages of the research.

A análise isotópica tem se tornado uma ferramenta muito útil para os ecólogos e pesquisadores que estudam o ciclo da matéria. Os isótopos de C e N foram utilizados para demonstrar características ecológicas da espécie Podocnemis unifilis na região do Baixo Xingu, apresentando a análise isotópica como um método complementar em estudos ecológicos. Foram coletados amostras de tecidos de 63 indivíduos de P. unifilis, sendo 34 machos e 29 fêmeas em quatro áreas. Através da análise isotópica verificamos possíveis variações intraespecíficas (relacionadas ao sexo e massa corporal) nos níveis tróficos e fontes primárias de carbono de suas dietas. Não foram apresentadas diferenças significativas ou padrões de absorção de C e N em relação ao tamanho do corpo e sexo. Porém foram encontradas diferenças no valor isotópico entre áreas com diferentes fisionomias.

O estudo do solo e importante devido a sua relacao direta com a oferta de alimentos e a manutencao e melhoria das condicoes ambientais. Neste trabalho, um metodo analitico foi desenvolvido com base na espectroscopia no infravermelho proximo (NIR) e analise de componentes principais (PCA) para estudar um Latossolo submetido a diferentes usos da terra (floresta primaria; floresta secundaria; fruticultura; horticultura; pastagem degradada; pastagem melhorada e agricultura anual) na Amazonia Oriental brasileira. Os resultados da PCA usando espectros de refletância difusa, apresentaram 97% da variância total explicada em PC1 e PC2, indicando a formacao de quatro grupos de amostras relacionados a diferentes usos e atributos fisico-quimicos (quantidade de carbono, nitrogenio, potassio e densidade) do solo. O metodo analitico desenvolvido, baseado em espectros NIR e PCA, e uma forma promissora para identificar solos submetidos a diferentes usos.

Made available in DSpace on 2022-04-28T19:50:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-03-01 Brazil has become the world leader in soy production, leading to an increase in the conversion of the Amazon rainforest into cropland. These actions had consequences for Forest's biodiversity, including the soil. In this sense, a better understanding of how long-term land use affects soil microbial communities, and their functions is urgent. This study aimed to evaluate the long-term land-use effects over bacterial and archaeal communities in soil and soybean rhizosphere in the Amazon region. For this, mesocosms experiments were carried out with Amazon soils with a history of 2-, 8-, and 20-years of agricultural use. We then assessed the bacterial and archaeal communities based on the 16S rRNA sequencing and real-time PCR. Our results showed a distinct bacterial community structure in soils with 20-years of land use. For both, bulk soil and soybean rhizosphere with 20-years of use, there was an increase in the abundance of Gemmatimonadetes, Chloroflexi, Firmicutes, and Planctomycetes. Interestingly, the niche occupancy analysis revealed an increase of specialist microbes in these soils. Also, these soils with 20-years of use showed a more complex network for both bulk and rhizosphere samples, highlighting the importance of Actinobacteria and Chloroflexi phyla to soil network structure. Our analysis also revealed an increased abundance of total bacteria, N-fixers, and ammonia-oxidizers bacteria in rhizosphere soil with 20-years of use. In addition, based on the potential functional analysis, nitrification processes increased in those soils. However, we noticed a homogenization in the abundance of the genes between rhizosphere and bulk soil with 20-years of use. In general, the differences were associated with changes in soil chemical characteristics such as pH, Ca2+, Mg2+, and organic matter, which are a consequence of liming and no-till practices over time. Our findings demonstrate that long-term agriculture in Amazon soils affects microbial community composition and functions, bringing new insights to better understand anthropogenic actions over the soil microbiome. Netherlands Institute of Ecology NIOO-KNAW Department of Terrestrial Ecology Luiz de Queiroz College of Agriculture (ESALQ) University of São Paulo (USP) Center for Nuclear Energy in Agriculture (CENA) University of São Paulo (USP) Cell and Molecular Biology Laboratory College of Agricultural Sciences São Paulo State University (UNESP) Department of Crop Science College of Agricultural Sciences São Paulo State University (UNESP) Department of Crop Science

The Atlantic Forest is an important biome formed by different phytophysionomy and is considered a hot spot of biodiversity. Some parts of the biome has received more attention in recent studies but few articles has stood out in the physiognomy of nebular forest, especially in peri-urban forests. The objective of this study was to evaluate soil fertility and litterfall production and decomposition in a peri-urban forest of São Paulo city, Brazil. The studied area is located at the Curucutu nucleus, at the State Park of Serra do Mar, southern of São Paulo city. The phytofisignomy is characterized by dense broadleaf vegetation in a nebular forest. Five different points were selected in 1 ha plot to collect soil samples at 0-10, 10-20, 20-30 cm depths to analyze physicochemical properties and fertility. For analysing litterfall production 20 litter traps were randomly distributed in the plot. After collected, the material was dried and weighted. For decomposition, sixty litter bags were randomly placed on the soil and 12 of them were monthly collected to assess the biomass loss. The results indicated low nutrient availability and high values of aluminum in the soil due to extremely acidic conditions. The soil C:N, C:P and P:N ratios showed an inefficiency in nutrient cycling probably due to the slow decomposition rate, which probably contributed to low availability of nutrients. Litterfall production reached the amount of 6.4 Mg ha-1 year-1 with the highest production during the spring and summer. The litter bags methodology confirmed the lower decomposition rates and the time to decompose 50% and 95% of the material was higher than the expected for fragments of the Atlantic forests. The low values of macro and micronutrients verified, associated with the acidity and the presence of toxic element, affect the fertility of the soil at the Curucutu, resulting in nutritional deficiencies to the existing vegetation.

Purpose Large parts of the Amazon rainforest grow on weathered soils depleted in phosphorus and rock-derived cations. We tested the hypothesis that in this ecosystem, fine roots stimulate decomposition and nutrient release from leaf litter biochemically by releasing enzymes, and by exuding labile carbon stimulating microbial decomposers. Methods We monitored leaf litter decomposition in a Central Amazon tropical rainforest, where fine roots were either present or excluded, over 188 days and added labile carbon substrates (glucose and citric acid) in a fully factorial design. We tracked litter mass loss, remaining carbon, nitrogen, phosphorus and cation concentrations, extracellular enzyme activity and microbial carbon and nutrient concentrations. Results Fine root presence did not affect litter mass loss but significantly increased the loss of phosphorus and cations from leaf litter. In the presence of fine roots, acid phosphatase activity was 43.2% higher, while neither microbial stoichiometry, nor extracellular enzyme activities targeting carbon- and nitrogen-containing compounds changed. Glucose additions increased phosphorus loss from litter when fine roots were present, and enhanced phosphatase activity in root exclusions. Citric acid additions reduced litter mass loss, microbial biomass nitrogen and phosphorus, regardless of fine root presence or exclusion. Conclusions We conclude that plant roots release significant amounts of acid phosphatases into the litter layer and mobilize phosphorus without affecting litter mass loss. Our results further indicate that added labile carbon inputs (i.e. glucose) can stimulate acid phosphatase production by microbial decomposers, highlighting the potential importance of plant-microbial feedbacks in tropical forest ecosystems.

Rainfall is generally partitioned into throughfall, stemflow, and interception in ecosystems. Stemflow variability can affect the hydrology, ecology, and soil chemistry patterns. However, the influence of canopy structure and rainfall characteristics on stemflow production in sugarcane plantations which are important for renewable energy production remain poorly understood. By using funnels attached to the sugarcane stems, the present study determined the stemflow amount during the period of sugarcane growth and its relationship with plant development. Approximately, 14% of gross rainfall reached the soil as stemflow, and the funneling ratios was 60. In general, it was observed a positive relationship between stemflow rates with both leaf area index and plant height. This was attributed to an increasing number of acute branching angles of the sugarcane leaves as well as high stem tillering and density. However, at the end of growth cycle, stemflow rate was lower than in previous periods which can be attributed to changes in sugarcane canopy such as stems inclination and lodging, reducing the effectiveness of water conveyance along the stem. Our study showed the need to include stemflow to better understand the hydrology of sugarcane plantations.

We investigated the fluvial geochemistry of two catchments at different stages in the forest recovery process which have been a focus of an Environmental Services Payment (ESP) program in Brazil. The Posses (PS) and Salto de Cima (SC) catchments (1200 ha and 1500 ha, respectively) are situated in the municipality of Extrema, Minas Gerais state. Their streams flow into the Jaguari River that supplies part of the water demand of the São Paulo metropolitan area. Samples were collected for chemical analysis and physical-chemical field measures every 2 weeks from January to December 2017. An important pollution point source was discovered in the PS stream related to bovine urine and feces, as well another unidentified source that can be related to a small food processing industry and/or a small fish farm. At the SC stream, on the other hand, there was clear evidence of domestic sewage input. This preliminary study confirmed a limited improvement of the stream water quality in response to recovery of the forest vegetation. Therefore, we recommend that in addition to enhanced monitoring to help distinguish biogeochemical sources and the benefits of land conservation practices, the ESP program should consider controlling point source pollution to accomplish its purpose. Made available in DSpace on 2020-12-12T09:02:19Z (GMT). No. of bitstreams: 1 Figueiredo-Hydrobiogeochemistry-Catchments-2020.pdf: 1803241 bytes, checksum: 739bf4b8390c0a9ec968700725c9b2c1 (MD5) Previous issue date: 2021

The Neotropics harbor some of the most diversified woody species in the world, and to understand the nutrient dynamics in these ecosystems, it is crucial to understand the role of plant taxonomy. In addition, biological nitrogen (N) fixation (BNF) in the tropics is one of the key processes affecting the global N cycle. Our objective was to (i) investigate the role of taxonomy and sampling site as predictors of foliar carbon (C) and N concentration and its stable isotopes (i.e., δ13C and δ15N); (ii) assess differences in foliar N, C:N ratio, and δ15N among three functional groups: species of N2-fixers and non-fixers of the Fabaceae family, as well as non-Fabaceae species; and (iii) examine the effect of wood density on tree foliar properties. We hypothesized that Fabaceae specimens in symbiosis with N2-fixers would possess a higher foliar N than non-fixing plants, including those of the Fabaceae family, as well as high-density trees would have higher foliar C and C:N ratio relative to low-density trees, where the latter invest in nutrients instead of structural C. We used a data set composed of 3,668 specimens sampled in three main biomes of Brazil: Amazon, Atlantic Forest, and Cerrado. The partitioning of variance had a higher influence of taxonomy on leaf C, N, and C:N ratio. Conversely, foliar δ13C and δ15N were environmentally constrained. While family was the most important taxonomy level for C, N, and C:N ratio, species played a major role for δ13C and δ15N. Foliar N followed the pattern fixers > non-fixers > non-Fabaceae, while C:N ratio had an opposite trend. In addition, foliar C was correlated with wood density, where high-density > medium-density and low-density woods. The large variability of δ15N was observed among Fabaceae species, demonstrates the complexity of using δ15N as an indicator of BNF. The higher foliar N of Fabaceae non-fixers than non-Fabaceae specimens support the hypothesis that an N-demanding lifestyle is an inherent pattern in this family. Lastly, although observed in some studies, the prediction of foliar properties using wood density is challenging, and future research on this topic is needed.

Deforestation and land use change (LUC) to expand the agricultural frontier in the Brazilian Amazon deplete soil carbon (C) stocks, and negatively impact climate regulation. The variety of soil types, land-transition options, and management practices present in the Amazon region require detailed inventories to reduce the uncertainties associated with estimates of soil C change. Therefore, we conducted a study covering ca. 1 million hectares to estimate the soil C stock changes due to LUC in Paragominas and Santarem, Para state, eastern Brazilian Amazon, for the period of 1990–2010. Soil C stocks for 1990 were modeled based on land cover at the time. In 2010, we carried out a field work taking soil samples to measure soil C stock changes in 356 transects across contrasting land uses (logged and burnt forest, young secondary forest, intermediate secondary forest, old secondary forest, pasture, and cropland). The response ratios for the conversion from undisturbed forest to new land uses were calculated considering the differences in soil C stocks, with the undisturbed forest as reference. Between 1990 and 2010, LUC induced a total loss of 1.51 Tg C year-1 (over an area of 7350 km2). For this period, the uncertainty of estimates was ± 23.2%. The land transitions to pasture and cropland were the main drivers of soil C losses. Thus, deforestation contributes to climate change not only through losses of forest biomass but also subsequently soil C losses. These results can inform national and international climate change initiatives associated with LUC in the eastern Brazilian Amazon.

The Ecosystem Demography model version 2.2 (ED-2.2) is a terrestrial biosphere model that simulates the biophysical, ecological, and biogeochemical dynamics of vertically and horizontally heterogeneous terrestrial ecosystems. In a companion paper (Longo et al., 2019a), we described how the model solves the energy, water, and carbon cycles, and verified the high degree of conservation of these properties in long-term simulations that include long-term (multi-decadal) vegetation dynamics. Here, we present a detailed assessment of the model's ability to represent multiple processes associated with the biophysical and biogeochemical cycles in Amazon forests. We use multiple measurements from eddy covariance towers, forest inventory plots, and regional remote-sensing products to assess the model's ability to represent biophysical, physiological, and ecological processes at multiple timescales, ranging from subdaily to century long. The ED-2.2 model accurately describes the vertical distribution of light, water fluxes, and the storage of water, energy, and carbon in the canopy air space, the regional distribution of biomass in tropical South America, and the variability of biomass as a function of environmental drivers. In addition, ED-2.2 qualitatively captures several emergent properties of the ecosystem found in observations, specifically observed relationships between aboveground biomass, mortality rates, and wood density; however, the slopes of these relationships were not accurately captured. We also identified several limitations, including the model's tendency to overestimate the magnitude and seasonality of heterotrophic respiration and to overestimate growth rates in a nutrient-poor tropical site. The evaluation presented here highlights the potential of incorporating structural and functional heterogeneity within biomes in Earth system models (ESMs) and to realistically represent their impacts on energy, water, and carbon cycles. We also identify several priorities for further model development.

Global warming can intensify the soil organic matter (SOM) turnover, damaging soil health. Crop residues left on the soil are important to maintain a positive SOM budget and nutrient cycling. But, sugarcane (Saccharum officinarum) straw has been removed from the field for bioenergy purposes. We hypothesize that global warming, together with straw removal, will negatively impact Brazil’s ethanol carbon footprint. Thus, we conducted an experiment under controlled conditions to evaluate the impacts of warming and straw removal on greenhouse gas (GHG) emissions, soil carbon and nitrogen storage, and nutrient cycling. Two soils (Rhodic Acrisol and Eutric Nitisol) were tested with three rates of sugarcane straw removal (no removal (NR): equivalent to 12 Mg ha−1; medium removal (MR): 6 Mg ha−1; and total removal (TR): bare soil) and submitted to two temperatures (24 °C and 30 °C) and soil moistures (30% and 50%). Straw decomposition was stimulated by lower rates of straw removal, resulting in increases on carbon dioxide (CO2) emissions between 5 to 14 times, and N2O between 25 and 40%. There were no significant methane (CH4) fluxes. Soil carbon and nitrogen did not change due to straw removal, yet labile carbon fractions (living and non-living) were highly impacted, causing reductions of 15 to 40% on the carbon management index (CMI). Furthermore, straw removal reduced nutrient cycling between 10 and 30%. Overall, in a scenario of warming, our findings point to an intensification of SOM dynamic, resulting in increases of 35% on the GHG emissions and a CMI reduction by 20%. In practical terms, at least 6 Mg ha−1 of straw should be left in the field, guaranteeing raw-material for bioenergy, without causing major impacts on the GHG emission and soil attributes.

Productivity of grassland ecosystems is highly dependent on the availability of nitrogen (N) from the soil and/or biological fixation (BNF) from the atmosphere. However, the high cost of N-fertilizers and the increasing awareness of the need for sustainable nutrient alternative sources have increased the strategic importance of the BNF. Defoliation interferes with plant growth and also with BNF in legumes, since it modifies the leaf area and the availability of energy to plants. In spite of the potential advantages of forage legumes to pastures, current knowledge regarding the effects of grazing management on BNF is scarce. In order to evaluate the effect of grazing management on aerial and root mass, nodulation and BNF in forage peanut (Arachis pintoi cv. Belmonte), two experimental protocols based on the continuous and intermittent (rotational grazing) stocking methods were used. In the continuous stocking protocol, treatments corresponded to four grazing intensities represented by four management heights - 5, 10, 15 and 20 cm. In the intermittent stocking protocol, treatments corresponded to combinations between two pre- (95% and maximum canopy light interception during regrowth – LI95% and LIMax, respectively) and two post-grazing (post-grazing heights equivalent to 40 and 60% of the pre-grazing height) conditions. It was hypothesized that hard grazing, represented by low management heights under continuous stocking or low post-grazing heights under intermittent stocking, causes reduction in root mass and nodulation interfering with the balance between root and aerial, with negative impacts on BNF. Under continuous stocking, greater number of nodules was associated with lower nodule mass and vice-versa throughout the year. Swards managed at 5 and 10 cm had greater root and nodule mass than those managed at 15 and 20 cm. However, greater BNF (%Ndfa and BNF) was recorded on swards managed at 15 and 20 cm relative to those managed at 5 and 10 cm. Under intermittent stocking, the combinations between frequencies and severities of grazing did not affect root mass or nodule number at both pre- and post-grazing conditions. Overall, swards managed with the LIMax target showed greater BNF than those managed with the LI95% target. For swards managed with the same LI target (LI95% or LIMax), hard grazing (40% of the pre-grazing height) resulted in lower %Ndfa and BNF during early and late spring and summer II. For both grazing methods, the range of management targets used did not result in negative impacts on root mass or nodulation. Regardless of grazing method, BNF was determined by aerial biomass, indicating that moderate intensities of grazing would be adequate for optimizing BNF.

The Amazon rainforest is a biodiversity hotspot and large terrestrial carbon sink threatened by agricultural conversion. Rainforest-to-pasture conversion stimulates the release of methane, a potent greenhouse gas. The biotic methane cycle is driven by microorganisms; therefore, this study focused on active methane-cycling microorganisms and their functions across land-use types. We collected intact soil cores from three land use types (primary rainforest, pasture, and secondary rainforest) of two geographically distinct areas of the Brazilian Amazon (Santarém, Pará and Ariquemes, Rondônia) and performed DNA stable-isotope probing coupled with metagenomics to identify the active methanotrophs and methanogens. At both locations, we observed a significant change in the composition of the isotope-labeled methane-cycling microbial community across land use types, specifically an increase in the abundance and diversity of active methanogens in pastures. We conclude that a significant increase in the abundance and activity of methanogens in pasture soils could drive increased soil methane emissions. Furthermore, we found that secondary rainforests had decreased methanogenic activity similar to primary rainforests, and thus a potential to recover as methane sinks, making it conceivable for forest restoration to offset greenhouse gas emissions in the tropics. These findings are critical for informing land management practices and global tropical rainforest conservation.

The focus of this study was to investigate the wide use of Eucalyptus spp., an exotic plant with high allelopathic ability, in the reforestation programs of urban parks in São Paulo City, Brazil, over the last century. To understand the implications of using Eucalyptus spp. in the city’s parks, this study aimed to compare nutrient cycling and litter decomposition between a mixed composition of litter (i.e., native and exotic species) and the litter of a single species (i.e., Eucalyptus). To accomplish this, newly deciduous leaves were collected from two native and two exotic species that are commonly used in the afforestation of São Paulo as well as from Eucalyptus spp. The mixed composition of litter yielded a higher dry mass loss and return of macro- and micronutrients to the forest floor. The decomposition constant (k) values were 0.00322 and 0.00207 g g−1 day−1 for the mixed composition and Eucalyptus spp., respectively. The time required for decomposition of 50 and 95% of deciduous material was 215 and 931 days, respectively, and for the mixed litterfall 334 and 1449 days, respectively, for Eucalyptus spp. Therefore, the mixed litter exhibited greater dry mass loss and nutrient cycling in an urban forest of São Paulo City, since dry mass losses as well as speed and amount of nutrients returned to the forest floor were relatively higher compared to Eucalyptus spp. Nutrient cycling via Eucalyptus spp. litter was less efficient than mixed composition of litter, demonstrating that reforestation programs carried out in the twentieth century using only one species may have had little success. The results of this work emphasize the fact that in urban reforestation programs the City of São Paulo must consider the environmental and biogeographic characteristics of the species employed and use high levels of biodiversity, since the city lies in a megadiverse biome.

Extreme climatic events may be translated into a higher frequency of both dry and wet years. Frequent droughts pose a challenge to water supply in terms of both quantity and quality. In order to cope with this, there has to be a documentation on the concentration of chemicals in water during such events. The southeast region of Brazil experienced a major drought event in 2014 leading to number of social, economic, and environmental impacts. The objective of the present paper is to understand the effect of an extreme drought on dissolved organic and inorganic carbon concentrations of the Piracicabal river, which is under high human pressure. Concentrations of both dissolved organic (DOC) and inorganic carbon (DIC) were monitored daily, for 30 days, during a dry month in 2014. DOC values found here were at least twice those observed in the river in non-extreme conditions. Rain events within this drought led to significant differences in discharge, DOC, and DIC. We built a dilution-concentration model which described an exponential relationship between discharge and both carbon forms. This indicated that drastic changes in concentrations of DOC and DIC are expected during such events. Our results may also apply to a number of regions in the world especially those of the developing countries where rivers are highly subjected to sewage impact.