Effect of smoke on the transmissivity of photosynthetically active radiation inside the canopy

International audienceBiomass burning activities emit high concentrations of aerosol particles to the atmosphere. Such particles can interact with solar radiation, decreasing the amount of light reaching the surface and increasing the fraction of diffuse radiation through scattering processes. This work reports results from photosynthetic active radiation (PAR) and aerosol optical depth (AOD) measurements conducted simultaneously at Reserva Biológica do Jaru (Rondonia State, Brazil) during LBA/SMOCC (Large-Scale Biosphere-Atmosphere Experiment in Amazonia/ Smoke, Aerosols, Clouds, Rainfall, and Climate) and RaCCI (Radiation, Cloud, and Climate Interactions in the Amazon during the Dry-to-Wet Transition Season) field experiments from 15 September to 15 November 2002. AOD values were retrieved from an AERONET (Aerosol Robotic Network) radiometer, MODIS (Moderate Resolution Spectroradiometer) and a portable sunphotometer from the United States Department of Agriculture-Forest Service. Daily mean downward PAR irradiance at the top of canopy was reduced by up to 50% due to the smoke aerosol particles. This radiation reduction affected turbulent fluxes of sensible and latent heats at the surface, observed particularly for high values of aerosol optical depth. The increase of aerosol optical depth also enhanced the transmission of photosynthetic active radiation inside the canopy. This result was a consequence of enhanced availability of diffuse radiation due to light scattering by the aerosol particles. A complex relationship was identified between light availability inside the canopy and net ecosystem exchange (NEE). The results showed that the increase of aerosol optical depth corresponded to an increase on CO2 exchange, indicating more CO2 uptake by the vegetation. However, for a higher AOD value, the corresponding NEE was lower than for intermediate values. Further studies are needed to better understand these findings, which were reported for the first time for the Amazon region under smoky conditions

Fluorescence-Based Phenotypic Selection Allows Forward Genetic Screens in Haploid Human Cells

The isolation of haploid cell lines has recently allowed the power of forward genetic screens to be applied to mammalian cells. The interest in applying this powerful genetic approach to a mammalian system is only tempered by the limited utility of these screens, if confined to lethal phenotypes. Here we expand the scope of these approaches beyond live/dead screens and show that selection for a cell surface phenotype via fluorescence-activated cell sorting can identify the key molecules in an intracellular pathway, in this case MHC class I antigen presentation. Non-lethal haploid genetic screens are widely applicable to identify genes involved in essentially any cellular pathway

Recruitment of TBK1 to cytosol‐invading Salmonella induces WIPI2‐dependent antibacterial autophagy

Mammalian cells deploy autophagy to defend their cytosol against bacterial invaders. Anti-bacterial autophagy relies on the core autophagy machinery, cargo receptors, and "eat-me" signals such as galectin-8 and ubiquitin that label bacteria as autophagy cargo. Anti-bacterial autophagy also requires the kinase TBK1, whose role in autophagy has remained enigmatic. Here we show that recruitment of WIPI2, itself essential for anti-bacterial autophagy, is dependent on the localization of catalytically active TBK1 to the vicinity of cytosolic bacteria. Experimental manipulation of TBK1 recruitment revealed that engagement of TBK1 with any of a variety of Salmonella-associated "eat-me" signals, including host-derived glycans and K48- and K63-linked ubiquitin chains, suffices to restrict bacterial proliferation. Promiscuity in recruiting TBK1 via independent signals may buffer TBK1 functionality from potential bacterial antagonism and thus be of evolutionary advantage to the host

Ecological research in the Large Scale Biosphere Atmosphere Experiment in Amazonia: A discussion of early results

The Large-scale Biosphere–Atmosphere Experiment in Amazonia (LBA) is a multinational, interdisciplinary research program led by Brazil. Ecological studies in LBA focus on how tropical forest conversion, regrowth, and selective logging influence carbon storage, nutrient dynamics, trace gas fluxes, and the prospect for sustainable land use in the Amazon region. Early results from ecological studies within LBA emphasize the variability within the vast Amazon region and the profound effects that land-use and land-cover changes are having on that landscape. The predominant land cover of the Amazon region is evergreen forest; nonetheless, LBA studies have observed strong seasonal patterns in gross primary production, ecosystem respiration, and net ecosystem exchange, as well as phenology and tree growth. The seasonal patterns vary spatially and interannually and evidence suggests that these patterns are driven not only by variations in weather but also by innate biological rhythms of the forest species. Rapid rates of deforestation have marked the forests of the Amazon region over the past three decades. Evidence from ground-based surveys and remote sensing show that substantial areas of forest are being degraded by logging activities and through the collapse of forest edges. Because forest edges and logged forests are susceptible to fire, positive feedback cycles of forest degradation may be initiated by land-use-change events. LBA studies indicate that cleared lands in the Amazon, once released from cultivation or pasture usage, regenerate biomass rapidly. However, the pace of biomass accumulation is dependent upon past land use and the depletion of nutrients by unsustainable land-management practices. The challenge for ongoing research within LBA is to integrate the recognition of diverse patterns and processes into general models for prediction of regional ecosystem function

Monitoramento dos fluxos de radiação, energia, CO2 e vapor d'água em superfícies vegetadas.

Aplicações micrometeorológicas; Aspectos metodológicos; Componentes do balanço de radiação e de energia; Fluxos de CO2, vapor d?água e balanço de energia pelo método das Covariâncias dos Vórtices Turbulentos; Características aerodinâmicas e perfil logarítmico do vento; Técnicas de medidas

Comportamento do albedo durante o período chuvoso em uma área de Caatinga degradada na região da Chapada do Araripe, PE.

O objetivo deste trabalho foi analisar o comportamento do albedo para uma área de caatinga degradada durante o periodo chuvoso na região da Chapada do Araripe ?PE. Para tanto, foi conduzido um experimentodurante o primeiro trimestre do ano de 2012 em uma área com caatinga degradada localizada na Empresa Pernambucana de Pesquisa Agropecuária -IPA (7o27?S; 40o24?W, 828 m).As medidas da radiação foram obtidas por meio da instalação de um radiômetro (CNR1, Campbell scientific), instalado a uma altura de 6,7 metros. O albedo (α, %), foi obtido por meio da relação entre os dados de radiação refletida e incidente.Pode-se observar que houve uma grande variação dos valores horários de albedo associadas a variaçãodo ângulo de elevação solar, com valores médios diários em torno de 16%. Estes resultados podem ser utilizados como parâmetros de entrada em modelos de simulação climática

Effect of smoke and clouds on the transmissivity of photosynthetically active radiation inside the canopy

Biomass burning activities emit high concentrations of aerosol particles to the atmosphere. Such particles can interact with solar radiation, decreasing the amount of light reaching the surface and increasing the fraction of diffuse radiation through scattering processes, and thus has implications for photosynthesis within plant canopies. This work reports results from photosynthetically active radiation (PAR) and aerosol optical depth (AOD) measurements conducted simultaneously at Reserva Biológica do Jaru (Rondonia State, Brazil) during LBA/SMOCC (Large-Scale Biosphere-Atmosphere Experiment in Amazonia/ Smoke, Aerosols, Clouds, Rainfall, and Climate) and RaCCI (Radiation, Cloud, and Climate Interactions in the Amazon during the Dry-to-Wet Transition Season) field experiments from 15 September to 15 November 2002. AOD values were retrieved from an AERONET (Aerosol Robotic Network) radiometer, MODIS (Moderate Resolution Spectroradiometer) and a portable sunphotometer from the United States Department of Agriculture – Forest Service. Significant reduction of PAR irradiance at the top of the canopy was observed due to the smoke aerosol particles layer. This radiation reduction affected turbulent fluxes of sensible and latent heats. The increase of AOD also enhanced the transmission of PAR inside the canopy. As a consequence, the availability of diffuse radiation was enhanced due to light scattering by the aerosol particles. A complex relationship was identified between light availability inside the canopy and net ecosystem exchange (NEE). The results showed that the increase of aerosol optical depth corresponded to an increase of CO₂ uptake by the vegetation. However, for even higher AOD values, the corresponding NEE was lower than for intermediate values. As expected, water vapor pressure deficit (VPD), retrieved at 28m height inside the canopy, can also affect photosynthesis. A decrease in NEE was observed as VPD increased. Further studies are needed to better understand these findings, which were reported for the first time for the Amazon region under smoky conditions

Aplicação do modelo de vegetação dinâmica IBIS às condições de floresta de terra firme na região central da Amazônia.

É fundamental para os Modelos de Vegetação Dinâmica Global (DVGM na sigla em inglês) representar corretamente o ciclo diário, as variações sazonais e interanuais das trocas de massa e energia entre o ecossistema e a atmosfera, a hidrologia do solo, a fenologia das plantas e a evolução do estoque de carbono do ecossistema. Este estudo dedica-se a validação e calibração do DVGM IBIS (Integrated Biosphere Simulator) para um ecossistema de floresta tropical úmida de terra firme, localizada na Reserva Biológica do Cuieiras do INPA. Foram utilizados nove anos de dados meteorológicos da torre de fluxo K34, como também dados de diâmetro de árvores, medidas de sonda de nêutrons, de liteira fina e foi realizado um ajuste nos parâmetros físicos do solo do modelo. Os resultados indicam que o modelo representa bem o balanço hídrico, assim como o saldo de radiação e o fluxo de calor latente, porém não representa tão bem os fluxos de calor sensível e de CO2, o índice de área foliar (LAI) e os estoques de liteira fina e biomassa. Os resultados mostram a necessidade de definir um tipo funcional de planta específico para representar a floresta tropical úmida de terra firme da Amazônia e a inclusão de uma subrotina de eventos severos

Intradiurnal and seasonal variability of soil temperature, heat flux, soil moisture content, and thermal properties under forest and pasture in Rondônia.

Soil temperatures depend on the soil heat flux, an important parameter in meteorological and plant growth-energy balance models. Thus, they were measured, together with soil moisture contents, within the LBA program at forest (Reserva Jaru) and pasture (Fazenda Nossa Senhora) sites in Rondônia, Brazilian Amazonia during wet (February) and dry (August) periods of 1999. The wet period showed maxima of the heat flux into the soil around five to six times smaller at the forest than at the pasture, except for some spikes that are related to stronger solar forcing, such as those due to sunspecks in the forest. This pattern remained during the dry period, but with doubled maximum values. Also, the soil heat flux and the soil temperatures responded very significantly to the passage of cold fronts in both periods at both sites. Temperature profiles measured in the 0.10-0.40 m soil layer showed daily averages and ranges smaller at the forest than at the pasture. The daily average of the soil moisture content in the same layer, during the wet season, increased with depth at both sites, with consistently lower values at the forest. However, their ranges were smaller at the pasture, except for the 0.40 m depth. During the dry period, these ranges were much higher at the pasture, but with nearer average values. Finally, the computed daily apparent soil thermal diffusivities, volumetric heat contents, and thermal conductivities are presented, with the first ones crossed with the measured soil moisture content