A bacia amazônica tem mais de seis milhões de quilômetros quadrados e abriga a maior floresta tropical do mundo, sendo particularmente importante pela sua biodiversidade e pelo seu papel na ciclagem de água e carbono. Fotossíntese, condutância estomática e fluxo de seiva de espécies florestais da Amazônia apresentam variação ao longo do dia seguindo a variação diurna observada na irradiância, temperatura e o déficit de pressão de vapor. Em decorrência da fotorrespiração, cerca de 25% do carbono fixado é retornado para a atmosfera. Os aumentos na concentração de CO2 na atmosfera previstos para as próximas décadas poderão apresentar efeito positivo na assimilação de carbono deste ecossistema florestal. Em comparação à época chuvosa, redução da umidade do solo e aumento no déficit de pressão de vapor (associado à baixa umidade do ar e alta temperatura) favorecem o fechamento dos estômatos em detrimento da fotossíntese. Desse modo, em comparação com a estação chuvosa, a fotossíntese líquida é menor no período seco. No geral, na Amazônia as árvores que atingem o dossel da floresta crescem a taxas maiores na época chuvosa. Exceto em anos de menor precipitação, o ecossistema florestal atua como sumidouro de carbono na época chuvosa. Mais estudos são necessários para determinar como e de que forma fatores específicos do ambiente físico influenciam a assimilação de carbono e o crescimento de árvores nos diversos grupos funcionais na Amazônia.

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Biogeosciences and Forestry Biogeosciences and Forestry Gas exchange, biomass allocation and water-use efficiency in response to elevated CO 2 and drought in andiroba (Carapa surinamensis, Meliaceae) Marcilia Freitas de Oliveira (1) , Ricardo Antonio Marenco (2) Prolonged droughts are predicted for some parts of the Amazon; however, it is still unclear how Amazonian trees will respond to water stress under the ongoing increase in CO2 concentration. The aim of this study was to assess the effect of elevated CO2 (eCO2) and drought on photosynthetic rates, water-use efficiency, and biomass allocation in andiroba (Carapa surinamensis). The plants were grown in pots at ambient (400 ppm CO2) and eCO2 (700 ppm) at two water regimes, soil at 50% field capacity, FC (drought) and soil at 100% FC for 163 days. We measured light saturated photosynthesis on a mass basis (Asat-mass), stomatal conductance to CO2 on a mass basis (gsCO2-mass), whole-plant water-use efficiency (WUEP), biomass accumulation, specific leaf area (SLA) and total leaf area. At eCO2, Asat-mass increased 28% in well-watered plants and 93% under drought, whereas gsCO2-mass declined 39% in well-watered plants at eCO2, with no effect of drought on gsCO2-mass at eCO2. The total biomass gain improved 73% at eCO2 and over CO2 levels it was reduced (54%) by drought. WUEP improved (188%) at eCO2 in well-watered plants and 262% under drought. SLA declined 23% at eCO2, but the effect of drought on SLA was null. On the contrary, total leaf area was greatly reduced (67%) by drought, but it was not affected by eCO2. The large increase in total biomass and the substantial improvement in WUEP under eCO2, and the sharp decline in leaf area under water stress widen our knowledge on the physiology of this important species for the forest management of large areas in the Amazon region.

Climate models predict an increase in atmospheric CO2 concentration and prolonged droughts in some parts of the Amazon, but the effect of elevated CO2 is still unknown. Two experiments (ambient CO2 -400 ppm and elevated CO2 -700 ppm) were conducted to assess the effect of drought (soil at 50% field capacity) on physiological parameters of Carapa. At ambient CO2 concentration, light-saturated net photosynthetic rate (PNsat) was reduced by 33.5% and stomatal conductance (gs) by 46.4% under drought, but the effect of drought on PNsat and gs was nullified at elevated CO2. Total plant biomass and leaf area production were also reduced (42-47%) by drought. By changing leaf traits, Carapa is able to endure drought, as the consumptive use of water was reduced under drought (32-40%). The improvement of PNsat under elevated CO2 and water stress and the leaf plasticity of Carapa broaden our understanding of the physiology of Amazonian trees.Additional key words: chlorophyll fluorescence; leaf water potential; nonphotochemical quenching; water-use efficiency. use of water; ETRelectron transport rate; FC -field capacity; Fm -maximal fluorescence yield of the dark-adapted state; Fm' -maximal fluorescence yield of the light-adapted state; Fs -steady-state fluorescence yield; Fv/Fm -maximal quantum yield of PSII photochemistry; Fv -variable fluorescence; gs -stomatal conductance; Jmax -maximum electron transport rate; F0 -minimal fluorescence yield of the dark-adapted state; Jmax25 -Jmax at 25°C; LMA -leaf mass per area ratio; NPQ -nonphotochemical quenching; T -temperature in Kelvin; PN -net photosynthetic rate; PNsat -light-saturated PN; PNmax -light-and CO2-saturated PN; RH -relative humidity; TNC -total non-structural carbohydrates; Vcmax -maximum carboxylation rate of Rubisco; Vcmax25 -Vcmax at 25°C; VPDL -leaf-to-air vapor pressure difference; WT -total dry matter (biomass); WUEi -intrinsic water-use efficiency; Γ -CO2-compensation point; Γ* -Γ in absence of mitochondrial respiration; ΨL -leaf water potential; ФPSII -effective quantum yield of PSII photochemistry. Acknowledgments: To the Ministry of Science, Technology, Innovations and Communications (MCTIC/ INPA PRJ 15.120), National Council for Scientific and Technological Development -CNPq (Grant 302041/2015-0 and scholarship for MFO) and Fundação de Amparo à Pesquisa do Estado do Amazonas (FAPEAM) for supporting this research. We thank the Editor and the anonymous reviewers and for their constructive and useful comments.

root-knots. The life cycle comprises the eggs, four juvenile stages and adult male or female. Eggs are enclosed in gelatinous egg sacs that are usually deposited on the surface of galled roots. The first moult occurs within the egg giving rise to the second-stage juvenile (J2), which is the infective stage. Three other moults occur within the roots allowing the nematode to go through the stages J3, J4, and adults (Karssen and Moens, 2006). The species M. enterolobii was detected for the first time in Brazil in the states of Pernambuco and Bahia, causing severe damages in guava orchards (Carneiro and Almeida, 2001). In vegetables, it was detected for the first time in the state of São Paulo, parasitizing green pepper (Capsicum annuum) cultivar Silver and tomato (Solanum lycopersicum) cultivars ' Andrea' and 'Debora', all known to be resistant to M. incognita and M. javanica (Carneiro et al., 2006). This ability of M. enterolobii to parasite plants resistant to other species of Meloidogyne makes it a difficult-to-control nematode (Bitencourt and Silva, 2010). This species presents a wide polyphagia and highly aggressive behavior for most vegetable species in comparison to M. incognita and M. javanica (Pinheiro and Pereira, 2012). Cultivars of tomato and pepper that have resistance to M. incognita, M. javanica and M. arenaria carry the Mi gene that gives the plant a hypersensitivity reaction (HR) causing histological changes, such as cell death near the infection site (Dropkin, 1969). This usually occurs 12 hours after attempted infection. However, the resistance conferred by the Mi-1 gene is unstable and can be compromised by soil temperatures above 28°C (Dropkin, 1969). In addition, there are species and races of Meloidogyne that have the ability to break the resistance conferred by the Mi gene, which makes