Dataset Information

Large seasonal swings in leaf area of Amazon rainforests.

ABSTRACT: Despite early speculation to the contrary, all tropical forests studied to date display seasonal variations in the presence of new leaves, flowers, and fruits. Past studies were focused on the timing of phenological events and their cues but not on the accompanying changes in leaf area that regulate vegetation-atmosphere exchanges of energy, momentum, and mass. Here we report, from analysis of 5 years of recent satellite data, seasonal swings in green leaf area of approximately 25% in a majority of the Amazon rainforests. This seasonal cycle is timed to the seasonality of solar radiation in a manner that is suggestive of anticipatory and opportunistic patterns of net leaf flushing during the early to mid part of the light-rich dry season and net leaf abscission during the cloudy wet season. These seasonal swings in leaf area may be critical to initiation of the transition from dry to wet season, seasonal carbon balance between photosynthetic gains and respiratory losses, and litterfall nutrient cycling in moist tropical forests.

SUBMITTER: Myneni RB

PROVIDER: S-EPMC1820882 | biostudies-literature | 2007 Mar

REPOSITORIES: biostudies-literature

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Large seasonal swings in leaf area of Amazon rainforests.

Myneni Ranga B RB Yang Wenze W Nemani Ramakrishna R RR Huete Alfredo R AR Dickinson Robert E RE Knyazikhin Yuri Y Didan Kamel K Fu Rong R Negrón Juárez Robinson I RI Saatchi Sasan S SS Hashimoto Hirofumi H Ichii Kazuhito K Shabanov Nikolay V NV Tan Bin B Ratana Piyachat P Privette Jeffrey L JL Morisette Jeffrey T JT Vermote Eric F EF Roy David P DP Wolfe Robert E RE Friedl Mark A MA Running Steven W SW Votava Petr P El-Saleous Nazmi N Devadiga Sadashiva S Su Yin Y Salomonson Vincent V VV

Proceedings of the National Academy of Sciences of the United States of America 20070313 12

Despite early speculation to the contrary, all tropical forests studied to date display seasonal variations in the presence of new leaves, flowers, and fruits. Past studies were focused on the timing of phenological events and their cues but not on the accompanying changes in leaf area that regulate vegetation-atmosphere exchanges of energy, momentum, and mass. Here we report, from analysis of 5 years of recent satellite data, seasonal swings in green leaf area of approximately 25% in a majority ...[more]

PMID: 17360360

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Project description:BackgroundThe tick Amblyomma cajennense sensu stricto (A. cajennense s.s.) frequently parasitizes animals and humans in the Amazon biome, in addition to being a vector of Rickettsia amblyommatis. In the present study, we evaluated both the population dynamics of A. cajennense s.s. in a degraded area of the Amazon biome and the presence of rickettsial organisms in this tick population.MethodsThe study was carried out in a rural area of the Santa Inês municipality (altitude: 24 m a.s.l.), Maranhão state, Brazil. Ticks were collected from the environment for 24 consecutive months, from June 2021 to May 2023. The region is characterized by two warm seasons: a rainy season (November-May) and a dry season (June-October). We characterized the temporal activity of A. cajennense s.s. on the vegetation by examining questing activity for each life stage (larvae, nymphs, adults [males and females]) in relation to the dry and rainy season. Ticks collected in this study were randomly selected and individually tested by a TaqMan real-time PCR assay that targeted a 147-bp fragment of the rickettsial gltA gene.ResultsOverall, 1843 (62.4%) adults (52.6% females, 47.4% males), 1110 (37.6%) nymphs and 398 larval clusters were collected. All adult females and nymphs were morphologically identified as A. cajennense s.s. Larval activity was observed from April to December, with a peak from June to September (dry season); nymph abundance peaked from September to November (transition period between dry and rainy seasons); and adult ticks were abundant from October to May (spring/summer/early autumn). The infection rate by R. amblyommatis in A. cajennense s.s. ticks was at least 7% (7/99).ConclusionOur data suggest a 1-year generation pattern for A. cajennense s.s., with a well-defined seasonality of larvae, nymphs and adults in the Amazon biome. Larvae predominate during the dry season, nymphs are most abundant in the dry-rainy season transition and adults are most abundant in the rainy season. The presence of R. amblyommatis in adult ticks suggests that animals and humans in the study region are at risk of infection by this species belonging to the spotted fever group of Rickettsia.

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Large seasonal swings in leaf area of Amazon rainforests.

Publications

Large seasonal swings in leaf area of Amazon rainforests.

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