PosterPDF Available

Alfonso Zambrano NGEE-Tropics Poster 2022 Annual Meeting

September 2022

DOI:10.13140/RG.2.2.28103.27049

Conference: NGEE Annual Meeting 2022

Authors:

Alfonso Zambrano

Smithsonian Tropical Research Institute

Pacific Northwest National Laboratory

Louisiana State University

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Tree water use is the dominant terrestrial hydrologic flux globally, and has a dominant regulatory influence over the carbon cycle. Sap flow through the tree is also a useful model diagnostic for FATES-Hydro. Our objective is to quantify variation in tree water use at three sites across a rainfall gradient in Panama. Our ultimate goals are to understand the hydraulic regulation of water use and carbon uptake as a function of climate and plant traits, and to aid in improved modeling of tropical forest function.

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Poster

Full-text available

Regulation of whole-tree hydraulic conductance in tropical forests across a steep climatic gradient

October 2023

This study aimed to understand how transpiration (J s) and crown conductance (G s) of tropical trees are impacted by environmental and physiological traits across a gradient from seasonally dry, intermediate, and ever-wet tropical forests (Fig. 1), and to quantify how leaf-to-air temperature decoupling impacts G s. Main hypotheses: H1: High vapor pressure deficit (VPD) in seasonally dry ... [Show full abstract] tropical forests results in lower G s than in wetter forests. Likewise, drier periods cause lower G s within sites. H2: Decoupling of leaf and air temperature directly impacts G s. H3: Environmental conditions provide a stronger control on G s than species functional traits.

Article

Full-text available

Short‐term variation in leaf‐level water use efficiency in a tropical forest

January 2023 · New Phytologist

The representation of stomatal regulation of transpiration and CO2 assimilation is key to forecasting terrestrial ecosystem responses to global change. Given its importance in determining the relationship between forest productivity and climate, accurate and mechanistic model representation of the relationship between stomatal conductance (gs) and assimilation is crucial. We assess possible ... [Show full abstract] physiological and mechanistic controls on the estimation of the g1 (stomatal slope, inversely proportional to water use efficiency) and g0 (stomatal intercept) parameters, using diurnal gas exchange surveys and leaf‐level response curves of six tropical broadleaf evergreen tree species. g1 estimated from ex situ response curves averaged 50% less than g1 estimated from survey data. While g0 and g1 varied between leaves of different phenological stages, the trend was not consistent among species. We identified a diurnal trend associated with g1 and g0 that significantly improved model projections of diurnal trends in transpiration. The accuracy of modeled gs can be improved by accounting for variation in stomatal behavior across diurnal periods, and between measurement approaches, rather than focusing on phenological variation in stomatal behavior. Additional investigation into the primary mechanisms responsible for diurnal variation in g1 will be required to account for this phenomenon in land‐surface models.

Article

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Hydraulic architecture explains species moisture dependency but not mortality rates across a tropica...

June 2021 · Biotropica

Intensified droughts are affecting tropical forests across the globe. However, the underlying mechanisms of tree drought response and mortality are poorly understood. Hydraulic traits and especially hydraulic safety margins (HSMs), that is, the extent to which plants buffer themselves from thresholds of water stress, provide insights into species‐specific drought vulnerability. We investigated ... [Show full abstract] hydraulic traits during an intense drought triggered by the 2015–2016 El Niño on 27 canopy tree species across three tropical forest sites with differing precipitation. We capitalized on the drought event as a time when plant water status might approach or exceed thresholds of water stress. We investigated the degree to which these traits varied across the rainfall gradient, as well as relationships among hydraulic traits and species‐specific optimal moisture and mortality rates. There were no differences among sites for any measured trait. There was strong coordination among traits, with a network analysis revealing two major groups of coordinated traits. In one group, there were water potentials, turgor loss point, sapwood capacitance and density, HSMs, and mortality rate. In the second group, there was leaf mass per area, leaf dry matter content, hydraulic architecture (leaf area to sapwood area ratio), and species‐specific optimal moisture. These results demonstrated that while species with greater safety from turgor loss had lower mortality rates, hydraulic architecture was the only trait that explained species’ moisture dependency. Species with a greater leaf area to sapwood area ratio were associated with drier sites and reduced their transpirational demand during the dry season via deciduousness. Abstract in Spanish is available with online material.

Thesis

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Impact of tree species diversity on water and carbon relations in European forests

October 2014

Charlotte Grossiord

Biodiversity is known to support and boost a wide range of forest ecosystem functions and services like productivity and resistance against insect pests and diseases. However, whether tree species diversity also promotes water and carbon acquisition and use in forest ecosystems is still unclear. Furthermore, in the current context of global warming, information on how tree species diversity can ... [Show full abstract] influence the response of forest ecosystems to extreme climatic events such as drought are urgently needed. In this framework, the objective of my PhD thesis was to determine how tree species diversity influences important functions of the water and carbon cycle including transpiration, carbon isotope composition and water extraction depth at the tree- and ecosystem-scale under contrasting soil water conditions. My work was conducted within the FunDivEUROPE project in a network of permanent forest stands and tree plantations across a North-South gradient in Europecovering a wide range of climatic conditions. I found considerable variability among species or forest types in the response of transpiration and carbon isotope composition at the tree- and ecosystem-scale across Europe. Species diversity did not affect the water and carbon relations of tree species and forest ecosystems under non-limiting soil water conditions. However, a strong effect of species diversity was observed under drought conditions in some forest types. Based on these data, I discuss the potential mechanisms of species interactions that may explain the observed patterns. I also point out that the influence of species diversity is highly context-dependent, and changes with local environmental and climatic conditions. In terms of forest management applications, I suggest that, at least in some regions, controlling for tree species diversity along with stand density and total basal area could be recommended to help forests adapt to drier conditions