Methane fluxes in permafrost habitats of the Lena Delta: effects of microbial community structure and organic matter quality

For the understanding and assessment of recent and future carbon dynamics of arctic permafrost soils the processes of CH4 production and oxidation, the community structure and the quality of DOM were studied in two soils of a polygonal tundra. Activities of methanogens and methanotrophs differed significantly in their rates and distribution patterns among the two investigated profiles. Community structure analysis showed similarities between both soils for esterlinked PLFAs and differences in the fraction of unsaponifiable PLFAs and PLELs. Furthermore, a shift of the overall composition of the microbiota with depth at both sites was indicated by an increasing portion of iso- and anteiso-branched fatty acids related to the amount of straight chain fatty acids. Although permafrost soils represent a large carbon pool, it was shown, that the reduced quality of organic matter leads to a substrate limitation of the microbial metabolism. It can be concluded from our and previous findings firstly that microbial communities in the active layer of an Arctic polygon tundra are composed by members of all three domains of life, with a total biomass comparable to temperate soil ecosystems. And secondly that these microorganisms are well adapted to the extreme temperature gradient of their environment

Water type and irrigation time effects on microbial metabolism of a soil cultivated with Bermuda-grass Tifton 85

This study investigated the microbial metabolism in Bermuda-grass Tifton 85 areas after potable-water and effluent irrigation treatments. The experiment was carried out in Lins/SP with samples taken in the rainy and dry seasons (2006) after one year and three years of irrigation management, and set up on an entirely randomized block design with four treatments: C (control, without irrigation or fertilization), PW (potable water + 520 kg of N ha-1 year-1); TE3 and TE0 (treated effluent + 520 kg of N ha-1 year-1) for three years and one year, respectively. The parameters determined were: microbial biomass carbon, microbial activity, and metabolic quotient. Irrigation with wastewater after three years indicated no alteration in soil quality for C and ET3; for PW, a negative impact on soil quality (microbial biomass decrease) suggested that water-potable irrigation in Lins is not an adequate option. Microbial activity alterations observed in TE0 characterize a priming effect

Nitrous oxide and methane fluxes in south Brazilian gleysol as affected by nitrogen fertilizers Fluxos de óxido nitroso e de metano em gleissolo influenciados pela aplicação de fertilizantes nitrogenados no sul do Brasil

Nitrogen fertilizers increase the nitrous oxide (N2O) emission and can reduce the methane (CH4) oxidation from agricultural soils. However, the magnitude of this effect is unknown in Southern Brazilian edaphoclimatic conditions, as well as the potential of different sources of mineral N fertilizers in such an effect. The aim of this study was to investigate the effects of different mineral N sources (urea, ammonium sulphate, calcium nitrate, ammonium nitrate, Uran, controlled- release N fertilizer, and urea with urease inhibitor) on N2O and CH4 fluxes from Gleysol in the South of Brazil (Porto Alegre, RS), in comparison to a control treatment without a N application. The experiment was arranged in a randomized block with three replications, and the N fertilizer was applied to corn at the V5 growth stage. Air samples were collected from a static chambers for 15 days after the N application and the N2O and CH4 concentration were determined by gas chromatography. The topmost emissions occurred three days after the N fertilizer application and ranged from 187.8 to 8587.4 µg m-2 h-1 N. The greatest emissions were observed for N-nitric based fertilizers, while N sources with a urease inhibitor and controlled release N presented the smallest values and the N-ammonium and amidic were intermediate. This peak of N2O emissions was related to soil NO3--N (R² = 0.56, p < 0.08) when the soil water-filled pore space was up to 70 % and it indicated that N2O was predominantly produced by a denitrification process in the soil. Soil CH4 fluxes ranged from -30.1 µg m-2 h-1 C (absorption) to +32.5 µg m-2 h-1 C (emission), and the accumulated emission in the period was related to the soil NH4+-N concentration (R² = 0.82, p < 0.001), probably due to enzymatic competition between nitrification and metanotrophy processes. Despite both of the gas fluxes being affected by N fertilizers, in the average of the treatments, the impact on CH4 emission (0.2 kg ha-1 equivalent CO2-C ) was a hundredfold minor than for N2O (132.8 kg ha-1 equivalent CO2-C). Accounting for the N2O and CH4 emissions plus energetic costs of N fertilizers of 1.3 kg CO2-C kg-1 N regarding the manufacture, transport and application, we estimated an environmental impact of N sources ranging from 220.4 to 664.5 kg ha-1 CO2 -C , which can only be partially offset by C sequestration in the soil, as no study in South Brazil reported an annual net soil C accumulation rate larger than 160 kg ha-1 C due to N fertilization. The N2O mitigation can be obtained by the replacement of N-nitric sources by ammonium and amidic fertilizers. Controlled release N fertilizers and urea with urease inhibitor are also potential alternatives to N2O emission mitigation to atmospheric and systematic studies are necessary to quantify their potential in Brazilian agroecosystems.<br>Fertilizantes nitrogenados incrementam os fluxos de óxido nitroso (N2O) e podem deprimir a oxidação de metano (CH4) em solos agrícolas. Entretanto, não existem resultados da magnitude desses efeitos nas condições edafoclimáticas do Sul do Brasil, tampouco do potencial de algumas fontes de N em mitigar esses efeitos. O presente estudo objetivou avaliar o impacto da aplicação de fertilizantes nitrogenados (ureia, sulfato de amônio, nitrato de cálcio, nitrato de amônio, Uran, N de liberação lenta e ureia com inibidor de urease) nos fluxos de N2O e CH4 em um Gleissolo no Sul do Brasil (Porto Alegre, RS), em comparação a um tratamento controle sem aplicação de N. O experimento seguiu um delineamento de blocos ao acaso, com três repetições, e os fertilizantes foram aplicados, em cobertura, numa dose única de 150 kg ha-1 N, no estádio V5 da cultura do milho. A avaliação dos gases foi feita utilizando-se o método da câmara estática, nos 15 dias que sucederam a aplicação de N, e a análise das concentrações de N2O e CH4 nas amostras de ar foi realizada por meio de cromatografia gasosa. O pico de emissão de N2O ocorreu no terceiro dia após a aplicação dos fertilizantes nitrogenados e a sua intensidade variou de 187,8 a 8.587,4 µg m-2 h-1 N, destacando-se as fontes nítricas com as maiores emissões, as fontes amoniacais e amídicas com emissões intermediárias e os fertilizantes de liberação lenta e com inibidor de urease com as menores emissões. As emissões no terceiro dia tiveram relação direta com os teores de N-NO3- do solo (R² = 0,56, p < 0,08) e ocorreram quando este apresentava valores de porosidade preenchida por água (PPA) maiores que 70 %, o que indica que a desnitrificação foi o processo predominante na produção de N2O. Os fluxos de CH4 do solo variaram de -30,1 µg m-2 h-1 C (absorção) a +32,5 µg m-2 h-1 C (emissão), e a emissão acumulada desse gás teve relação direta com os teores de NH4+ no solo (R² = 0,82, p < 0,001), possivelmente pela competição enzimática entre os processos de nitrificação e de metanotrofia. Apesar de os fluxos de ambos os gases terem sido alterados pela aplicação dos fertilizantes nitrogenados, na média dos tratamentos, o impacto das emissões de CH4 (0,2 kg ha-1C-CO2 equivalente) foi centenas de vezes menor que o verificado para as emissões de N2O (132,8 kg ha-1 C-CO2 equivalente). Considerando as emissões desses gases no solo fertilizado e o custo médio de 1,3 kg C-CO2 kg-1 N referente à produção, transporte e aplicação do fertilizante, o impacto ambiental dos fertilizantes nitrogenados variou de 220,4 a 664,5 kg ha-1 C-CO2, o qual pode ser apenas parcialmente contrabalanceado pelo acúmulo de C na matéria orgânica do solo, pois nenhum estudo realizado no Sul do Brasil evidenciou taxa anual de acúmulo de C no solo, decorrente da adubação nitrogenada, maior que 160 kg ha-1 C. A redução das emissões de N2O do solo e, portanto, do impacto ambiental pode ser obtida pelo uso de fontes amoniacais e amídicas em detrimento de fontes nítricas. Os fertilizantes de liberação lenta e com inibidores de urease também são alternativas potenciais visando à mitigação das emissões de N2O para atmosfera, e esforços deverão ser empreendidos numa avaliação sistemática desse potencial em agroecossistemas brasileiros