Species-specific shifts in diurnal sap velocity dynamics and hysteretic behavior of ecophysiological variables during the 2015–2016 el niño event in the amazon forest

Bruno O. Gimenez, Kolby J. Jardine, Niro Higuchi, Robinson I. Negrón-Juárez, Israel de Jesus Sampaio-Filho, Leticia O. Cobello, Clarissa G. Fontes, Todd E. Dawson, Charuleka Varadharajan, Danielle S. Christianson, Gustavo C. Spanner, Alessandro C. Araújo, Jeffrey M. Warren, Brent D. Newman, Jennifer A. Holm, Charles D. Koven, Nate G. McDowell, Jeffrey Q. Chambers

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20 Scopus citations

Abstract

Current climate change scenarios indicate warmer temperatures and the potential for more extreme droughts in the tropics, such that a mechanistic understanding of the water cycle from individual trees to landscapes is needed to adequately predict future changes in forest structure and function. In this study, we contrasted physiological responses of tropical trees during a normal dry season with the extreme dry season due to the 2015–2016 El Niño-Southern Oscillation (ENSO) event. We quantified high resolution temporal dynamics of sap velocity (Vs), stomatal conductance (gs) and leaf water potential (ΨL) of multiple canopy trees, and their correlations with leaf temperature (Tleaf) and environmental conditions [direct solar radiation, air temperature (Tair) and vapor pressure deficit (VPD)]. The experiment leveraged canopy access towers to measure adjacent trees at the ZF2 and Tapajós tropical forest research (near the cities of Manaus and Santarém). The temporal difference between the peak of gs (late morning) and the peak of VPD (early afternoon) is one of the major regulators of sap velocity hysteresis patterns. Sap velocity displayed species-specific diurnal hysteresis patterns reflected by changes in Tleaf. In the morning, Tleaf and sap velocity displayed a sigmoidal relationship. In the afternoon, stomatal conductance declined as Tleaf approached a daily peak, allowing ΨL to begin recovery, while sap velocity declined with an exponential relationship with Tleaf. In Manaus, hysteresis indices of the variables Tleaf-Tair and ΨL-Tleaf were calculated for different species and a significant difference (p < 0.01, α = 0.05) was observed when the 2015 dry season (ENSO period) was compared with the 2017 dry season (“control scenario”). In some days during the 2015 ENSO event, Tleaf approached 40°C for all studied species and the differences between Tleaf and Tair reached as high at 8°C (average difference: 1.65 ± 1.07°C). Generally, Tleaf was higher than Tair during the middle morning to early afternoon, and lower than Tair during the early morning, late afternoon and night. Our results support the hypothesis that partial stomatal closure allows for a recovery in ΨL during the afternoon period giving an observed counterclockwise hysteresis pattern between ΨL and Tleaf.

Original languageEnglish
Article number830
JournalFrontiers in Plant Science
Volume10
DOIs
StatePublished - May 31 2019

Funding

The authors are thankful to the logistical and scientific support provided by the Laboratório de Manejo Florestal (LMF) and the Large-Scale Biosphere-Atmosphere Program (LBA) at the National Institute of Amazonian Research (INPA). This material is based upon work supported as part of the Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics), as part of DOE’s Terrestrial Ecosystem Science Program – Contract No. DE-AC02-05CH11231. Additional funding for this research was provided by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).

FundersFunder number
Laboratório de Manejo Florestal
NGEE-Tropics
Next Generation Ecosystem Experiments-Tropics
U.S. Department of EnergyDE-AC02-05CH11231
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Instituto Nacional de Pesquisas da Amazônia

    Keywords

    • Direct solar radiation
    • Hysteresis
    • Leaf temperature
    • Sap velocity
    • Stomatal conductance
    • Tropical forests
    • Vapor pressure deficit

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