Effects of fire on soil nitrogen dynamics and microbial biomass in savannas of Central Brazil

O objetivo deste trabalho foi estudar o efeito do fogo sobre as taxas de mineralização líquida de N e biomassa microbiana do solo em áreas de cerrado stricto sensu. O estudo foi realizado entre abril de 1998 e abril de 2000. O pH foi maior na área queimada enquanto o teor de umidade do solo foi maior na área sem queima (P < 0,05). A razão C/N do solo foi de 22/1. A concentração de N nítrico disponível ficou entre 1,5 e 2,8 mg kg-1 de matéria seca enquanto a de N amoniacal variou entre 3 e 34 mg kg-1 de matéria seca na área queimada e entre 3 e 22 mg kg-1 de matéria seca na área sem queima. A concentração de N amoniacal aumentou significativamente após o fogo (P < 0,05). Pequenos acúmulos de N nítrico no solo ocorreram somente durante curto período na estação chuvosa. A biomassa microbiana teve seu pico máximo em novembro de 1998, chegando a 850 mg kg-1 de C no solo da área queimada. Os dados indicam que o pico da atividade microbiana ocorreu no início das chuvas, com um período inicial de imobilização seguido de mineralização líquida. Ambas as áreas apresentaram um mesmo padrão de mineralização/imobilização, mas com menor produção anual de N mineral na área queimada (14,7 kg ha-1 por ano na área sem queima e 3,8 kg ha-1 por ano na área queimada), um ano após a queima.The objective of this work was to study the effects of fire on net N mineralization and soil microbial biomass in burned and unburned cerrado stricto sensu sites. The study was carried out from April 1998 to April 2000. The pH values were significantly higher in the burned site while soil moisture content was significantly higher in the unburned site (P < 0.05). The soil C/N ratio was 22/1 and the available NO3-N ranged between 1.5 and 2.8 mg kg-1 dry weight. However, the NH4-N concentration ranged between 3 and 34 mg kg-1 dry weight in the burned site and between 3 and 22 mg kg-1 dry weight in the unburned site. The NH4-N increased after fire, but no significant changes were observed for NO3-N (P < 0.05). The NO3-N accumulation occurred in short periods during the rainy season. The rates of net N mineralization increased during the rainy season while reductions in soil microbial biomass were observed at both sites. This suggested that the peak in microbial activities occurred with the first rain events, with an initial net immobilization followed by net mineralization. Both sites presented the same pattern for mineralization/immobilization, however, the amount of inorganic-N cycled annually in unburned site was 14.7 kg ha-1 per year while the burned site presented only 3.8 kg ha-1 of inorganic-N, one year after the burning

Efeitos do fogo na dinâmica do nitrogênio no solo e biomassa microbiana em área de Cerrado

O objetivo deste trabalho foi estudar o efeito do fogo sobre as taxas de mineralização líquida de N e biomassa microbiana do solo em áreas de cerrado stricto sensu. O estudo foi realizado entre abril de 1998 e abril de 2000. O pH foi maior na área queimada enquanto o teor de umidade do solo foi maior na área sem queima (P<0,05). A razão C/N do solo foi de 22/1. A concentração de N nítrico disponível ficou entre 1,5 e 2,8 mg kg-1 de matéria seca enquanto a de N amoniacal variou entre 3 e 34 mg kg-1 de matéria seca na área queimada e entre 3 e 22 mg kg-1 de matéria seca na área sem queima. A concentração de N amoniacal aumentou significativamente após o fogo (P<0,05). Pequenos acúmulos de N nítrico no solo ocorreram somente durante curto período na estação chuvosa. A biomassa microbiana teve seu pico máximo em novembro de 1998, chegando a 850 mg kg-1 de C no solo da área queimada. Os dados indicam que o pico da atividade microbiana ocorreu no início das chuvas, com um período inicial de imobilização seguido de mineralização líquida. Ambas as áreas apresentaram um mesmo padrão de mineralização/imobilização, mas com menor produção anual de N mineral na área queimada (14,7 kg ha-1 por ano na área sem queima e 3,8 kg ha-1 por ano na área queimada), um ano após a queima.The objective of this work was to study the effects of fire on net N mineralization and soil microbial biomass in burned and unburned cerrado stricto sensu sites. The study was carried out from April 1998 to April 2000. The pH values were significantly higher in the burned site while soil moisture content was significantly higher in the unburned site (P<0.05). The soil C/N ratio was 22/1 and the available NO3-N ranged between 1.5 and 2.8 mg kg-¹ dry weight. However, the NH4-N concentration ranged between 3 and 34 mg kg-1 dry weight in the burned site and between 3 and 22 mg kg-1 dry weight in the unburned site. The NH4-N increased after fire, but no significant changes were observed for NO3-N (P<0.05). The NO3-N accumulation occurred in short periods during the rainy season. The rates of net N mineralization increased during the rainy season while reductions in soil microbial biomass were observed at both sites. This suggested that the peak in microbial activities occurred with the first rain events, with an initial net immobilization followed by net mineralization. Both sites presented the same pattern for mineralization/immobilization, however, the amount of inorganic-N cycled annually in unburned site was 14.7 kg ha-1 per year while the burned site presented only 3.8 kg ha-¹ of inorganic-N, one year after the burning

Nutrient enrichment changes water transport structures of savanna woody plants

Brazilian savanna is a seasonally dry biome, highly diverse and distributed mainly on nutrient-limited soils. Interactions between water stress and nutrient availability are important evolutionary filters in these environments. Previous evidence indicated that reducing the nutritional limitation increases growth rate, optimizes water transport and decreases stomatal conductance in woody plants. However, the anatomical mechanisms that explain such responses are not well-understood. We studied the effects of long-term (20 years) nutrient addition (N, NP and P) on soil chemistry and hydraulic morphological and anatomical traits in six dominant woody savanna species. Nutrient addition and decrease in soil moisture, probably related to changes in grass cover, influenced the plant hydraulic traits at the anatomical level, namely increasing the xylem vessels’ diameter. Consequently, the specific theoretical xylem conductivity (Ktx) increased in five species under NP and P addition. Additionally, the stomatal pore index (SPI) decreased with species-specific responses regarding the intrinsic water use efficiency (iWUE). Four species had higher vulnerability to cavitation (lvul) under NP and P addition. Using community-weighted mean and structural equation modeling approaches, we observed that nutrient enrichment at the community level did not affect iWUE, while the vulnerability to cavitation (lvul) strongly increased. The Ktx and SPI were positively and negatively affected by nutrient addition, respectively, but the effects were not as strong as expected due to contrasting species responses. These changes optimized water transport with a hydraulic safety cost and reduced water loss. In comparison with responses to N addition, the greater P-limitation in Cerrado vegetation explains the inter-specific convergence in the responses of P-fertilized individuals. We showed that long-term responses to increased nutrient availability in dystrophic soils include anatomical changes in savanna woody vegetation with relevant interactions with soil-plant–atmosphere water relations.Fil: Silva Costa, Lucas. Universidade do Brasília; BrasilFil: De Moura, Clapton Olimpio. Universidade do Brasília; BrasilFil: Bucci, Sandra Janet. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; ArgentinaFil: Sonsin-Oliveira, Julia. Universidade do Brasília; BrasilFil: Gomes, Sueli Maria. Universidade do Brasília; BrasilFil: Da Cunha Bustamante, Mercedes Maria. Universidade do Brasília; Brasi

PROTECTED AREAS IN BRAZIL: EVOLUTION, LAND USE AND COVER, AND IMPACT ON EMISSIONS INVENTORY

Faced with population growth and intensification of the use of natural resources, Protected Areas (PA) and Indigenous Lands (IL) play a fundamental role in environmental conservation. The carbon increment of preserved vegetation within these areas is accounted for as CO2 removal in the Land Use, Land-Use Change, and Forestry (LULUCF) sector of the National Emissions Inventory. A topological evaluation of overlaps was made of the databases of PAs (full protection and sustainable use) and ILs, showing that they represent 6% of the protected areas. Of the total of PAs and ILs areas, 43% were established by 1994, 26% by 2002, 26% by 2010, and 4% between 2011 and 2016. This evaluation showed that 30% of the territory is within PAs and ILs. In terms of area, 84% is distributed in the Amazon, 9% in the Cerrado, 4% in the Atlantic Forest, 3% in the Caatinga, 0,2% in the Pantanal, and 0,3% in the Pampa. In assessing the use and cover of 2010 of the PAs and ILs created up to this year, it was possible to notice that 68% of the areas within the PAs have preserved vegetation, whereas in ILs, this percentage increases to 89%. Under the Third Emissions Inventory, the removal of vegetation protected in PAs and ILs decreased by 16% of the national net emissions of the LULUCF sector between 2002 and 2010, showing the importance of preserving forests and grasslands

Fertilidade do solo, estoques de carbono e nitrogênio sob plantas de cobertura e sistemas de manejo

O objetivo deste trabalho foi avaliar o efeito de diferentes plantas de cobertura sobre a fertilidade do solo, particularmente sobre os estoques de carbono e nitrogênio de um Latossolo Vermelho sob preparo convencional e Sistema Plantio Direto. Considerou-se a hipótese de que o Sistema Plantio Direto associado à utilização de plantas de cobertura promove uma manutenção ou incremento nos estoques de carbono e nitrogênio e melhora a fertilidade do solo. Não houve diferença significativa entre os estoques de carbono e nitrogênio entre os sistemas de preparo do solo, porém, o Sistema Plantio Direto apresentou maiores concentrações de bases trocáveis, maiores valores de CTC e saturação por bases na camada superficial do solo, principalmente na presença de Canavalia brasiliensis em sucessão ao milho. Os estoques de carbono e nitrogênio na camada de 0-40 cm diferiram significativamente na comparação entre plantas de cobertura e as espécies Mucuna pruriens e Canavalia brasiliensis foram as que apresentaram maiores valores de estoques de carbono e nitrogênio entre as espécies avaliadas. O uso do Sistema Plantio Direto resultou em acúmulo de matéria orgânica na camada 0-5 cm e promoveu melhoria na fertilidade do solo. A utilização das plantas de cobertura Canavalia brasiliensis ou Mucuna pruriens no Sistema Plantio Direto em sucessão ao milho é uma alternativa para o sequestro de carbono e melhoria da qualidade do solo no Cerrado.The aim of the present study was to evaluate the effects of cover crops on the soil's chemical fertility, in particular its carbon and nitrogen content, in a Typic Acrustox under conventional and no-tillage corn systems. We hypothesized that the no-tillage system associates with cover crops maintains or increases soil carbon and nitrogen stocks and enhance soil fertility. The no-tillage system did not present higher carbon and nitrogen stocks than conventional tillage, but resulted in higher concentrations of exchangeable bases, higher CEC, and higher base saturation in the surface soil layer, mainly under use of Canavalia brasiliensis. Carbon and nitrogen stocks (up to 40 cm depth) differ significantly between the different cover crop species. The use of Mucuna pruriens and Canavalia brasiliensis allows maintain or increase soil C and N stocks. The no-tillage system results in higher accumulation of soil organic matter (0-5 cm), and appears very likely to enhance soil fertility. The use of Canavalia brasiliensis and Mucuna pruriens in succession to corn promotes carbon sequestration and can be used to enhance soil quality in Cerrado agroecosystems

Structure and composition of bacterial and fungal community in soil under soybean monoculture in the Brazilian Cerrado

Soybean is the most important oilseed cultivated in the world and Brazil is the second major producer. Expansion of soybean cultivation has direct and indirect impacts on natural habitats of high conservation value, such as the Brazilian savannas (Cerrado). In addition to deforestation, land conversion includes the use of fertilizers and pesticides and can lead to changes in the soil microbial communities. This study evaluated the soil bacterial and fungal communities and the microbial biomass C in a native Cerrado and in a similar no-tillage soybean monoculture area using PCR-DGGE and sequencing of bands. Compared to the native area, microbial biomass C was lower in the soybean area and cluster analysis indicated that the structure of soil microbial communities differed. 16S and 18S rDNA dendrograms analysis did not show differences between row and inter-row samples, but microbial biomass C values were higher in inter-rows during soybean fructification and harvest. The study pointed to different responses and alterations in bacterial and fungal communities due to soil cover changes (fallow x growth period) and crop development. These changes might be related to differences in the pattern of root exudates affecting the soil microbial community. Among the bands chosen for sequencing there was a predominance of actinobacteria, y-proteobacteria and ascomycetous divisions. Even under no-tillage management methods, the soil microbial community was affected due to changes in the soil cover and crop development, hence warning of the impacts caused by changes in land use

Utilização do classificador Spectral Correlation Mapper em imagens TM-Landsat

Neste trabalho é proposta uma metodologia para a análise de mistura espectral a partir de dados TM-Landsat. A área selecionada na imagem abrange áreas de reserva e de agricultura, em Brasília, DF. O procedimento adotado para a detecção dos membros finais (pixels puros) na imagem TM-Landsat foi o mesmo utilizado para o tratamento de dados hiperespectrais, com adaptações específicas. Inicialmente foi feita a conversão dos Números Digitais para valores de reflectância e então foi feita a identificação dos membros finais na área selecionada. A conversão dos Números Digitais em valores de reflectância permitiu a comparação dos espectros obtidos com os de bibliotecas espectrais, os quais auxiliaram na identificação. Para essa área, os membros puros identificados foram: vegetação verde, vegetação não fotossinteticamente ativa, solo e queimada. Foi utilizado o classificador espectral SCM (Spectral Correlation Mapper) para mostrar a disposição dos membros puros na imagem. O uso do procedimento dedetecção dos membros finais antes da classificação revelou-se interessante porquea juda da determinação de amostras para a classificação. Com o uso da análise de mistura espectral, a classificação torna-se mais fiel à concepção do pixel, que pode conter mais de uma classe. _______________________________________________________________________________ ABSTRACTIn this work a methodology is proposed for the analysis of spectral mixture from TM-Landsat data. The selected area in the image embraced preserved and agricultural areas in Brasília, DF. The adopted procedure for endmembers’s (pure pixels) detection was the same used for the hyperespectrals data treatment, with the specific adaptations. Initially was made a conversion of the Digital Numbers for reflectance values and after, the identification of the endmembers of the selected area. The Digital Numbers conversion in reflectance values allowed the comparison of the spectra obtained with the spectral libraries, which could help in the identification. For that area, the identified pure members were: green vegetation, non-photosynthetically active vegetation, soil and burned. It was used the spectral classifier SCM (Spectral Correlation Mapper) to show the pure members disposition in the image. The use of the endmembers detection procedure before the classification revealed quite interesting because it helped in the samples determination for the classification. Using the analysis of spectral mixture the classification becomes more trustworthy to the pixel conception that can contain more than one class

Seasonal variations in leaf pigments and nutrients in "cerrado" species with different phenological patterns

Vários estudos têm procurado estabelecer relações entre as condições ambientais e as propriedades foliares. Neste trabalho foram medidas as concentrações de pigmentos (clorofilas a, b, carotenóides e antocianinas), N e P e área foliar específica (AFE) em folhas de seis espécies de cerrado (sendo três decíduas e três sempre-verdes) em dois sítios de cerrado stricto sensu com diferenças de cobertura arbustiva-arbórea e em diferentes períodos: início do período seco (junho), fim da seca (setembro) e início das chuvas (novembro). As concentrações de nutrientes variaram mais em função da fenologia e da sazonalidade do que em relação às diferenças estruturais nos sítios, ao contrário do que foi observado para os pigmentos foliares. Os maiores valores de concentração de clorofilas a e b foram encontrados no início (junho) em relação ao final da seca (setembro) nas duas áreas. Em junho, as concentrações de clorofilas a e b foram maiores na área mais densa enquanto a razão clorofila a/b foi menor. A razão clorofila total/carotenóides também foi significativamente maior no cerrado fechado em relação ao aberto nesse período devido às maiores concentrações de clorofilas no primeiro sítio. Espécies decíduas apresentaram maiores médias de AFE em relação às sempre-verdes, tanto na estação seca como na chuvosa, mas concentrações mais elevadas de N e P foram encontradas em espécies sempre-verdes em relação às decíduas. Nos dois grupos fenológicos, as concentrações foliares de N e P e a razão N:P foram maiores na estação chuvosa (novembro) em relação à estação seca (junho).Several studies have been trying to establish relationships between environmental conditions and leaf traits. In the present study, concentrations of pigments (chlorophylls a, b, carotenoids and anthocyanins), N and P and specific leaf area (SLA) were measured in leaves of six "cerrado" species (three deciduous and three evergreen species) in two cerrado stricto sensu sites with differences in canopy cover and in different periods: at the beginning of the dry season (June), end of dry season (September) and beginning of the rainy season (November). Nutrient concentrations differed significantly as a function of phenology and seasonality while pigments were more sensitive to changes in vegetation structure. The highest chlorophyll a and b concentrations were measured at the beginning of the dry season (June) in comparison to the end of the dry season (September) in both sites. In June, chlorophyll a and b concentrations were higher in the denser cerrado while the chlorophyll a/b ratio was lower. Total chlorophyll/carotenoids ratio was also significantly higher in the denser cerrado at the beginning of the dry season due to the higher chlorophyll concentration. Deciduous species showed higher SLA mean values than evergreen species, in dry and wet season but higher N and P concentrations were found in the evergreen species. In both phenological groups, N and P concentrations and the N:P ratios were higher in the wet season (November) than in the dry season (June)

Seasonal effects in a lake sediment archaeal community of the brazilian savanna

The Cerrado is a biome that corresponds to 24% of Brazil’s territory. Only recently microbial communities of this biome have been investigated. Here we describe for the first time the diversity of archaeal communities from freshwater lake sediments of the Cerrado in the dry season and in the transition period between the dry and rainy seasons, when the first rains occur. Gene libraries were constructed, using Archaea-specific primers for the 16S rRNA and amoA genes. Analysis revealed marked differences between the archaeal communities found in the two seasons. I.1a and I.1c Thaumarchaeota were found in greater numbers in the transition period, while MCG Archaea was dominant on the dry season. Methanogens were only found in the dry season. Analysis of 16S rRNA sequences revealed lower diversity on the transition period. We detected archaeal amoA sequences in both seasons, but there were more OTUs during the dry season. These sequences were within the same cluster as Nitrosotalea devanaterra’s amoA gene. The principal coordinate analysis (PCoA) test revealed significant differences between samples from different seasons. These results provide information on archaeal diversity in freshwater lake sediments of the Cerrado and indicates that rain is likely a factor that impacts these communities

Óxidos de nitrogênio e CO2 de Latossolo cultivado com milho em sucessão a plantas de cobertura

O objetivo deste trabalho foi avaliar o efeito de duas leguminosas (Crotalaria juncea e Mucuna pruriens), usadas como plantas de cobertura, e de vegetação espontânea, como tratamento-controle, sobre as emissões de NOx, N2O e CO2 de um Latossolo Vermelho cultivado com milho, em sistemas convencional e de plantio direto, na região do Cerrado, no Brasil Central. As variações dos fluxos de CO2 no solo foram explicadas principalmente pela umidade do solo e, nas leguminosas, sob sistema convencional, pela concentração de N-NH4+. Parcelas com leguminosas em sistema plantio direto mostraram maiores emissões anuais de CO2, NOx e N2O do que a vegetação espontânea. Os resultados mostram que o uso de leguminosas como plantas de cobertura favorece as emissões de N-NOx + N-N2O e C-CO2. Entretanto, ao se considerar o potencial de mitigação de emissões de CO2 e de óxidos de nitrogênio oriundas do solo, é importante avaliar as variações nos estoques de carbono e nitrogênio no solo.The objective of this work was to evaluate the effect of two legumes (Crotalaria juncea and Mucuna pruriens), as cover crops, and of natural fallow, as a control treatment, on the emissions of NOx, N2O, and CO2 from an Oxisol cultivated with corn, under conventional and no-tillage systems, in the Cerrado region, in Central Brazil. Variations of CO2 fluxes in the soil were explained mainly by soil humidity and, in the legumes, under conventional system, by soil NH4+-N concentration. Plots with legumes under no-tillage system had higher annual emissions of CO2, NOx, and N2O than natural fallow. Results show that the use of legumes as cover crops favors the emissions of NOx-N + N2O-N and CO2-C. However, when considering the potential for mitigation of CO2 and nitrogen oxide emissions from the soil, it is important to evaluate changes in soil carbon and nitrogen stocks