The carbon and water cycles for a southwestern Amazonian forest site were investigated using the longest time series of fluxes of CO2 and water vapor ever reported for this site. The period from 2004 ...to 2010 included two severe droughts (2005 and 2010) and a flooding year (2009). The effects of such climate extremes were detected in annual sums of fluxes as well as in other components of the carbon and water cycles, such as gross primary production and water use efficiency. Gap-filling and flux-partitioning were applied in order to fill gaps due to missing data, and errors analysis made it possible to infer the uncertainty on the carbon balance. Overall, the site was found to have a net carbon uptake of approximately 5 t C ha-1 year-1, but the effects of the drought of 2005 were still noticed in 2006, when the climate disturbance caused the site to become a net source of carbon to the atmosphere. Different regions of the Amazon forest might respond differently to climate extremes due to differences in dry season length, annual precipitation, species compositions, albedo and soil type. Longer time series of fluxes measured over several locations are required to better characterize the effects of climate anomalies on the carbon and water balances for the whole Amazon region. Such valuable datasets can also be used to calibrate biogeochemical models and infer on future scenarios of the Amazon forest carbon balance under the influence of climate change.
Soil respiration plays a significant role in the carbon cycle of Amazonian rainforests. Measurements of soil respiration have only been carried out in few places in the Amazon. This study ...investigated the effects of the method of ring insertion in the soil as well as of rainfall and spatial distribution on CO2 emission in the central Amazon region. The ring insertion effect increased the soil emission about 13-20% for sandy and loamy soils during the firsts 4-7 hours, respectively. After rainfall events below 2 mm, the soil respiration did not change, but for rainfall greater than 3 mm, after 2 hours there was a decrease in soil temperature and respiration of about 10-34% for the loamy and sand soils, with emissions returning to normal after around 15-18 hours. The size of the measurement areas and the spatial distribution of soil respiration were better estimated using the Shuttle Radar Topographic Mission (SRTM) data. The Campina reserve is a mosaic of bare soil, stunted heath forest-SHF and tall heath forest-THF. The estimated total average CO2 emissions from the area was 3.08±0.8 µmol CO2 m-2 s-1. The Cuieiras reserve is another mosaic of plateau, slope, Campinarana and riparian forests and the total average emission from the area was 3.82±0.76 µmol CO2 m-2 s-1. We also found that the main control factor of the soil respiration was soil temperature, with 90% explained by regression analysis. Automated soil respiration datasets are a good tool to improve the technique and increase the reliability of measurements to allow a better understanding of all possible factors driven by soil respiration processes.
Respiração do solo possui um importante papel no ciclo do carbono em florestas tropicais Amazônicas. Entretanto poucas medidas de respiração do solo foram feitas. Neste estudo são apontados os efeitos na metodologia de instalação dos anéis no solo, bem como os efeitos da precipitação e a distribuição espacial da emissão de CO2 na Amazônia central. Os efeitos da inserção de anéis no solo aumentaram de 13 a 20% para o solo arenoso e argiloso, o efeito durou de 4 a 7 horas, respectivamente. Já os efeitos na precipitação, notamos que os eventos abaixo de 2 mm a respiração do solo permaneceu indiferente, mas para precipitação acima de 3 mm, 2 horas depois, houve uma diminuição da temperatura e respiração em 10 a 34% para o solo argilosos e arenosos, retornando a emissão normal após 15 a 18 horas. Para estimar a distribuição espacial da respiração do solo e o tamanho correto das áreas medidas, foram utilizadas as imagens do Shuttle Radar Topographic Mission (SRTM). Considerando que a Reserva de Campina é um mosaico de solo desnudo, floresta alagável de baixa e alta estatura (SHF e THF). A emissão total média de CO2 para a área foi de 3.08±0.8 µmol CO2 m-2 s-1. Já a Reserva do Cuieiras possui outro mosaico de florestas de platôs, encostas, Campinaranas e riparias, sendo a emissão média total desta área foram de 3.82±0.76 µmol CO2 m-2 s-1. Encontramos também que a respiração do solo foi controlada pela temperatura do solo, sendo uma correlação de 90% encontrada pela análise de regressão. Dados obtidos com sistema automático de respiração do solo é uma grande oportunidade de melhoramento da técnica e o aumento da confiança nas medidas em relação aos possíveis fatores que controlam os processos de emissão de CO2 do solo.
Soil respiration plays a significant role in the carbon cycle of Amazonian rainforests. Measurements of soil respiration have only been carried out in few places in the Amazon. This study ...investigated the effects of the method of ring insertion in the soil as well as of rainfall and spatial distribution on CO2 emission in the central Amazon region. The ring insertion effect increased the soil emission about 13-20% for sandy and loamy soils during the firsts 4-7 hours, respectively. After rainfall events below 2 mm, the soil respiration did not change, but for rainfall greater than 3 mm, after 2 hours there was a decrease in soil temperature and respiration of about 10-34% for the loamy and sand soils, with emissions returning to normal after around 15-18 hours. The size of the measurement areas and the spatial distribution of soil respiration were better estimated using the Shuttle Radar Topographic Mission (SRTM) data. The Campina reserve is a mosaic of bare soil, stunted heath forest-SHF and tall heath forest-THF. The estimated total average CO2 emissions from the area was 3.08±0.8 µmol CO2 m-2 s-1. The Cuieiras reserve is another mosaic of plateau, slope, Campinarana and riparian forests and the total average emission from the area was 3.82±0.76 µmol CO2 m-2 s-1. We also found that the main control factor of the soil respiration was soil temperature, with 90% explained by regression analysis. Automated soil respiration datasets are a good tool to improve the technique and increase the reliability of measurements to allow a better understanding of all possible factors driven by soil respiration processes.Respiração do solo possui um importante papel no ciclo do carbono em florestas tropicais Amazônicas. Entretanto poucas medidas de respiração do solo foram feitas. Neste estudo são apontados os efeitos na metodologia de instalação dos anéis no solo, bem como os efeitos da precipitação e a distribuição espacial da emissão de CO2 na Amazônia central. Os efeitos da inserção de anéis no solo aumentaram de 13 a 20% para o solo arenoso e argiloso, o efeito durou de 4 a 7 horas, respectivamente. Já os efeitos na precipitação, notamos que os eventos abaixo de 2 mm a respiração do solo permaneceu indiferente, mas para precipitação acima de 3 mm, 2 horas depois, houve uma diminuição da temperatura e respiração em 10 a 34% para o solo argilosos e arenosos, retornando a emissão normal após 15 a 18 horas. Para estimar a distribuição espacial da respiração do solo e o tamanho correto das áreas medidas, foram utilizadas as imagens do Shuttle Radar Topographic Mission (SRTM). Considerando que a Reserva de Campina é um mosaico de solo desnudo, floresta alagável de baixa e alta estatura (SHF e THF). A emissão total média de CO2 para a área foi de 3.08±0.8 µmol CO2 m-2 s-1. Já a Reserva do Cuieiras possui outro mosaico de florestas de platôs, encostas, Campinaranas e riparias, sendo a emissão média total desta área foram de 3.82±0.76 µmol CO2 m-2 s-1. Encontramos também que a respiração do solo foi controlada pela temperatura do solo, sendo uma correlação de 90% encontrada pela análise de regressão. Dados obtidos com sistema automático de respiração do solo é uma grande oportunidade de melhoramento da técnica e o aumento da confiança nas medidas em relação aos possíveis fatores que controlam os processos de emissão de CO2 do solo.
The productivity of rainforests growing on highly weathered tropical soils is expected to be limited by phosphorus availability1. Yet, controlled fertilization experiments have been unable to ...demonstrate a dominant role for phosphorus in controlling tropical forest net primary productivity. Recent syntheses have demonstrated that responses to nitrogen addition are as large as to phosphorus2, and adaptations to low phosphorus availability appear to enable net primary productivity to be maintained across major soil phosphorus gradients3. Thus, the extent to which phosphorus availability limits tropical forest productivity is highly uncertain. The majority of the Amazonia, however, is characterized by soils that are more depleted in phosphorus than those in which most tropical fertilization experiments have taken place2. Thus, we established a phosphorus, nitrogen and base cation addition experiment in an old growth Amazon rainforest, with a low soil phosphorus content that is representative of approximately 60% ofthe Amazon basin. Here we show that net primary productivity increased exclusively with phosphorus addition. After 2 years, strong responses were observed in fine root (+29%) and canopy productivity (+19%), but not stem growth. The direct evidence of phosphorus limitation of net primary productivity suggests that phosphorus availability may restrict Amazon forest responses to CO2 fertilization4, with major implications for future carbon sequestration and forest resilience to climate change.
During the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign, size-resolved cloud condensation nuclei (CCN) spectra were characterized at a research site (T3) 60 km ...downwind of the city of Manaus, Brazil, in central Amazonia for 1 year (12 March 2014 to 3 March 2015). Particle hygroscopicity (κCCN) and mixing state were derived from the size-resolved CCN spectra, and the hygroscopicity of the organic component of the aerosol (κorg) was then calculated from κCCN and concurrent chemical composition measurements. The annual average κCCN increased from 0.13 at 75 nm to 0.17 at 171 nm, and the increase was largely due to an increase in sulfate volume fraction. During both wet and dry seasons, κCCN, κorg, and particle composition under background conditions exhibited essentially no diel variations. The constant κorg of ∼ 0. 15 is consistent with the largely uniform and high O : C value (∼ 0. 8), indicating that the aerosols under background conditions are dominated by the aged regional aerosol particles consisting of highly oxygenated organic compounds. For air masses strongly influenced by urban pollution and/or local biomass burning, lower values of κorg and organic O : C atomic ratio were observed during night, due to accumulation of freshly emitted particles, dominated by primary organic aerosol (POA) with low hygroscopicity, within a shallow nocturnal boundary layer. The O : C, κorg, and κCCN increased from the early morning hours and peaked around noon, driven by the formation and aging of secondary organic aerosol (SOA) and dilution of POA emissions into a deeper boundary layer, while the development of the boundary layer, which leads to mixing with aged particles from the residual layer aloft, likely also contributed to the increases. The hygroscopicities associated with individual organic factors, derived from PMF (positive matrix factorization) analysis of AMS (aerosol mass spectrometry) spectra, were estimated through multivariable linear regression. For the SOA factors, the variation of the κ value with O : C agrees well with the linear relationship reported from earlier laboratory studies of SOA hygroscopicity. On the other hand, the variation in O : C of ambient aerosol organics is largely driven by the variation in the volume fractions of POA and SOA factors, which have very different O : C values. As POA factors have hygroscopicity values well below the linear relationship between SOA hygroscopicity and O : C, mixtures with different POA and SOA fractions exhibit a steeper slope for the increase in κorg with O : C, as observed during this and earlier field studies. This finding helps better understand and reconcile the differences in the relationships between κorg and O : C observed in laboratory and field studies, therefore providing a basis for improved parameterization in global models, especially in a tropical context.
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