Seasonal nitrogen fixation in the sediment of an Amazonian lake impacted by bauxite tailings (Batata Lake-Pará)

Batata Lake is an Amazonian clear water lake that undergoes large seasonal fluctuations in water level. For a period of 10 years (1979-1989), the northern end of the lake received a total of 50,000 m³d^1 of bauxite tailings. As a consequence spelling aproximately 30 % of its sediments are covered by tailings. The principal goal of this research was to estimate rates of nitrogen fixation in the impacted and non-impacted sediment in the different hydroperiods that occur in this ecosystem (drawdown, drying, fìlling and flooding). Nitrogen fìxation was estimated using the acetylene reduction method. The highest rates of nitrogen fixation were observed to occur during the drying period and appear to be directly related to an increase in primary production by phytoplankton. Decreased rates of nitrogen fixation occurred during the hydroperiods of filling, flooding and drawdown with the greatest reductions occuring in the impacted area of the lake. In the impacted area of the lake, bauxite tailings have reduced primary production in the water column, decreased labile authoctonous carbon availability to heterotrophic bacteria in the sediments, and decreased nitrogen fixing activity of organisms present the sediments

Latin America's Nitrogen Challenge

Latin America (LA) has many social indicators similar to those of highly developed economies but most frequently falls midway between least developed countries and industrialized regions. To move forward, LA must address uncontrolled urbanization, agricultural production, social inequity, and destruction of natural resources. We discuss these interrelated challenges in terms of human impact on the nitrogen (N) cycle. Human activity has caused unprecedented changes to the global N cycle; in the past century; total global fixation of reactive N (Nr) has at least doubled (1). Excess Nr leaked into the environment negatively affects soils, atmosphere, and water resources in temperate zones (1). In addition to N excess from human impact, mining of natural soil N creates N deficits in some regions (2, 3).Fil: Austin, Amy Theresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Bustamante, M. M. C.. Universidade Do Brasilia; BrasilFil: Nardoto, G. B.. Universidade Do Brasilia; BrasilFil: Mitre, S. K.. Universidade Do Brasilia; BrasilFil: Pérez, T.. Instituto Venezolano de Investigaciones Cientificas; VenezuelaFil: Ometto, J. P. H. B.. Centro de Previsao de Tempo e Estudos Climaticos. Instituto Nacional de Pesquisas Espaciais; BrasilFil: Ascarrunz, N. L.. Instituto Boliviano de Investigación Forestal; BoliviaFil: Forti, M. C.. Centro de Previsao de Tempo e Estudos Climaticos. Instituto Nacional de Pesquisas Espaciais; BrasilFil: Longo, K.. Centro de Previsao de Tempo e Estudos Climaticos. Instituto Nacional de Pesquisas Espaciais; BrasilFil: Gavito, M. E.. Universidad Nacional Autónoma de México; MéxicoFil: Enrich Prast, A.. Universidade Federal do Rio de Janeiro; BrasilFil: Martinelli, L. A.. Universidade de Sao Paulo; Brasi

Large emissions from floodplain trees close the Amazon methane budget

Wetlands are the largest global source of atmospheric methane (CH4), a potent greenhouse gas. However, methane emission inventories from the Amazon floodplain, the largest natural geographic source of CH4 in the tropics, consistently underestimate the atmospheric burden of CH4 determined via remote sensing and inversion modelling, pointing to a major gap in our understanding of the contribution of these ecosystems to CH4 emissions. Here we report CH4 fluxes from the stems of 2,357 individual Amazonian floodplain trees from 13 locations across the central Amazon basin. We find that escape of soil gas through wetland trees is the dominant source of regional CH4 emissions. Methane fluxes from Amazon tree stems were up to 200 times larger than emissions reported for temperate wet forests6 and tropical peat swamp forests, representing the largest non-ebullitive wetland fluxes observed. Emissions from trees had an average stable carbon isotope value (δ13C) of −66.2 ± 6.4 per mil, consistent with a soil biogenic origin. We estimate that floodplain trees emit 15.1 ± 1.8 to 21.2 ± 2.5 teragrams of CH4 a year, in addition to the 20.5 ± 5.3 teragrams a year emitted regionally from other sources. Furthermore, we provide a ‘top-down’ regional estimate of CH4 emissions of 42.7 ± 5.6 teragrams of CH4 a year for the Amazon basin, based on regular vertical lower-troposphere CH4 profiles covering the period 2010–2013. We find close agreement between our ‘top-down’ and combined ‘bottom-up’ estimates, indicating that large CH4 emissions from trees adapted to permanent or seasonal inundation can account for the emission source that is required to close the Amazon CH4 budget. Our findings demonstrate the importance of tree stem surfaces in mediating approximately half of all wetland CH4 emissions in the Amazon floodplain, a region that represents up to one-third of the global wetland CH4 source when trees are combined with other emission sources

Overexpression of a soybean Globin (GmGlb1-1) gene reduces plant susceptibility to Meloidogyne incognita.

Na publicação: Isabela Tristan Lourenço-Tessutti; Leonardo Lima Pepino Macedo; Francismar Corrêa Marcelino-Guimaraes; Maria Cristina Mattar Silva; Maria Fatima Grossi-de-Sa

Global carbon dioxide efflux from rivers enhanced by high nocturnal emissions

Carbon dioxide (CO2) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO2 concentrations. Using a global compilation of high-frequency CO2 measurements, we demonstrate that nocturnal CO2 emissions are on average 27% (0.9 gC m−2 d−1) greater than those estimated from diurnal concentrations alone. Constraints on light availability due to canopy shading or water colour are the principal controls on observed diel (24 hour) variation, suggesting this nocturnal increase arises from daytime fixation of CO2 by photosynthesis. Because current global estimates of CO2 emissions to the atmosphere from running waters (0.65–1.8 PgC yr−1) rely primarily on discrete measurements of dissolved CO2 obtained during the day, they substantially underestimate the magnitude of this flux. Accounting for night-time CO2 emissions may elevate global estimates from running waters to the atmosphere by 0.20–0.55 PgC yr−1