Leaf flush drives dry season green-up of the Central Amazon

Pontes‐Lopes, Aline; Nelson, Bruce; Wu, Jin; Graça, Paulo Maurı́cio Lima de Alencastro; Tavares, Julia Valentim; Prohaska, N.; Martins, Giordane; Saleska, S. R.

doi:10.1016/j.rse.2016.05.009

Cited by 117 publications

(159 citation statements)

References 36 publications

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“…Our results are coherent with previous studies using EVI to estimate photosynthetic capacity in the Amazon forest [9][10][11][12][13][14][15][16]54]. These studies showed an increase in photosynthesis during the dry season in areas without water limitation, as observed here.…”

Section: When Is the Peak Of Maximum Photosynthesis Activity In Amazoniasupporting

confidence: 93%

“…The positive relationship between ChlF and radiation observed for 76% of the Amazon forest suggests that photosynthesis responds to an increase in radiation and is coherent with independent results obtained with Enhanced Vegetation Index (EVI), which is a proxy for photosynthetic capacity [9][10][11][12][13][14][15][16]50] and Leaf Area Index (LAI) [10,13]. Both EVI and LAI exhibit an increase with sunlight during the dry season in central and eastern Amazon rainforests [7,[9][10][11][12][13][14][15][16][19][20][21].…”

Section: How Does Photosynthesis Varies As a Function Of Climate Seassupporting

confidence: 83%

“…Both EVI and LAI exhibit an increase with sunlight during the dry season in central and eastern Amazon rainforests [7,[9][10][11][12][13][14][15][16][19][20][21]. Groundbased eddy flux towers data [6] support our findings of an increasing level of photosynthesis during the dry season (Figure 2b) in the equatorial portion of Amazonian forests (5°N-5°S).…”

Section: How Does Photosynthesis Varies As a Function Of Climate Seassupporting

confidence: 80%

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Chlorophyll Fluorescence Data Reveals Climate-Related Photosynthesis Seasonality in Amazonian Forests

et al. 2017

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Amazonia is the world largest tropical forest, playing a key role in the global carbon cycle. Thus, understanding climate controls of photosynthetic activity in this region is critical. The establishment of the relationship between photosynthetic activity and climate has been controversial when based on conventional remote sensing-derived indices. Here, we use nine years of solar-induced chlorophyll fluorescence (ChlF) data from the Global Ozone Monitoring Experiment (GOME-2) sensor, as a direct proxy for photosynthesis, to assess the seasonal response of photosynthetic activity to solar radiation and precipitation in Amazonia. Our results suggest that 76% of photosynthesis seasonality in Amazonia is explained by seasonal variations of solar radiation. However, 13% of these forests are limited by precipitation. The combination of both radiation and precipitation drives photosynthesis in the remaining 11% of the area. Photosynthesis tends to rise only after radiation increases in 61% of the forests. Furthermore, photosynthesis peaks in the wet season in about 58% of the Amazon forest. We found that a threshold of ≈1943 mm per year can be defined as a limit for precipitation phenological dependence. With the potential increase in the frequency and intensity of extreme droughts, forests that have the photosynthetic process currently associated with radiation seasonality may shift towards a more water-limited system.

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Section: When Is the Peak Of Maximum Photosynthesis Activity In Amazoniasupporting

confidence: 93%

Section: How Does Photosynthesis Varies As a Function Of Climate Seassupporting

confidence: 83%

Section: How Does Photosynthesis Varies As a Function Of Climate Seassupporting

confidence: 80%

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Chlorophyll Fluorescence Data Reveals Climate-Related Photosynthesis Seasonality in Amazonian Forests

et al. 2017

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“…During the dry seasons, the chemodiversity seems relatively similar (39.4 ± 4 % for α-pinene, 20.3 ± 3 % for limonene), whereas it slightly changes during the wet season and dramatically changes during the wet-dry transition. The reason for this difference in June could be related to changes in the phenology, as demonstrated at a central Amazonian site (Alves et al, 2016;Lopes et al, 2016). Furthermore, during the dry season of 2015, a very strong El Niño event took place, leading to extremely dry conditions observed region-wide (Jardine et al, 2017).…”

Section: Seasonalitymentioning

confidence: 98%

“…Such a behaviour could explain the lower mixing ratios and different chemodiversity found in June. During this time of the year, leaf flushing takes place in the central Amazon region (Alves et al, 2016;Lopes et al, 2016). Under these conditions, lower α-pinene mixing ratios were found as compared to the dry season, when young leaves reach mature levels.…”

Section: Seasonalitymentioning

confidence: 99%

Monoterpene chemical speciation in a tropical rainforest:variation with season, height, and time of dayat the Amazon Tall Tower Observatory (ATTO)

et al. 2018

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Abstract. Speciated monoterpene measurements in rainforest air are scarce, but they are essential for understanding the contribution of these compounds to the overall reactivity of volatile organic compound (VOC) emissions towards the main atmospheric oxidants, such as hydroxyl radicals (OH), ozone (O 3 ) and nitrate radicals (NO 3 ). In this study, we present the chemical speciation of gas-phase monoterpenes measured in the tropical rainforest at the Amazon Tall Tower Observatory (ATTO, Amazonas, Brazil). Samples of VOCs were collected by two automated sampling systems positioned on a tower at 12 and 24 m height and analysed using gas chromatography-flame ionization detection. The samples were collected in October 2015, representing the dry season, and compared with previous wet and dry season studies at the site. In addition, vertical profile measurements (at 12 and 24 m) of total monoterpene mixing ratios were made using proton-transfer-reaction mass spectrometry. The results showed a distinctly different chemical speciation between day and night. For instance, α-pinene was more abundant during the day, whereas limonene was more abundant at night. Reactivity calculations showed that higher abundance does not generally imply higher reactivity. Furthermore, inter-and intra-annual results demonstrate similar chemodiversity during the dry seasons analysed. Simulations with a canopy exchange modelling system show simulated monoterpene mixing ratios that compare relatively well with the observed mixing ratios but also indicate the necessity of more experiments to enhance our understanding of in-canopy sinks of these compounds.

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Water stress detection in the Amazon using radar

Emmerik

Steele‐Dunne

Paget

et al. 2017

Geophysical Research Letters

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The Amazon rainforest plays an important role in the global water and carbon cycle, and though it is predicted to continue drying in the future, the effect of drought remains uncertain. Developments in remote sensing missions now facilitate large‐scale observations. The RapidScat scatterometer (Ku band) mounted on the International Space Station observes the Earth in a non‐Sun‐synchronous orbit, which allows for studying changes in the diurnal cycle of radar backscatter over the Amazon. Diurnal cycles in backscatter are significantly affected by the state of the canopy, especially during periods of increased water stress. We use RapidScat backscatter time series and water deficit measurements from dendrometers in 20 trees during a 9 month period to relate variations in backscatter to increased tree water deficit. Morning radar bacskcatter dropped significantly with increased tree water deficit measured with dendrometers. This provides unique observational evidence that demonstrates the sensitivity of radar backscatter to vegetation water stress, highlighting the potential of drought detection and monitoring using radar.

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Leaf flush drives dry season green-up of the Central Amazon

Cited by 117 publications

References 36 publications

Chlorophyll Fluorescence Data Reveals Climate-Related Photosynthesis Seasonality in Amazonian Forests

Chlorophyll Fluorescence Data Reveals Climate-Related Photosynthesis Seasonality in Amazonian Forests

Monoterpene chemical speciation in a tropical rainforest:variation with season, height, and time of dayat the Amazon Tall Tower Observatory (ATTO)

Water stress detection in the Amazon using radar

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