Caracterização diurna e sazonal da condutância estomática de indivíduos arbóreos em resposta à variáveis ambientais na a Amazônia Central

Understanding the interactions of the continuous soil-plant-atmosphere to ecosystem environmental changes is a prerequisite for models that predict carbon balance in tropical forests. In this context, the objective of this study was to characterize the influence of meteorological variables in the Baixio and Platô on leaf water potential (Ψf), stomatal conductance (gs) and leaf temperature (Tf) considering different techniques of two tree species, respectively in the canopy of a primary forest in Central Amazonia and to understand biochemical mechanisms such as abscisic acid production (ABA) and the relationship with stomatal regulation. The species studied were the Eschweilera cyathiformis and Pouteria anomala (in the plateau), and Peltogyne excelsa and Micropholis guyanensis (in the Baixo). The species studied in the biochemical experiment were Cariniana legalis, Handroanthus serratifolius and Astronium fraxinifolium, performed in Trancoso-BA in 2018. The meteorological variables were obtained from the instrumentation installed in two monitoring towers K34 (plateau) and B34 (Baixo). The behavior of the daily progression of Ψf of the different species in the evaluation was significant, so that the species P. anomala and E. ciathiformis in K34 is different in relation to the species P. excelsa and M. guyanensis in the Baixo, this may be related to isohydric and anisohydric behavior of the species in the plateau and shallow, respectively. For the gs dynamics of the species in response to the different rainy and dry periods there was significant difference, it was observed that gs decreased considerably in the dry period when compared to the rainy season and followed the same pattern in the plateau and shallow. The results of the measurements of Tf in the species of the basin and plateau, and for the rainy and dry periods, show significant differences so that the measurement with the porometer was more significant when compared with the techniques of Thermovisor (Flir), Thermocouples and Sensor InfraRed, as well as in relation to the air temperature measurements with Thermohygrometers. There was variation of the optimal values of Tf in the plateau relative to gs seasonally. For the entire collection period, the configuration of hysteresis behavior between stomatal conductance and VPD and Tf is obscured. In the plateau, for P. anomala, it was observed that the VPD and Tf was not sufficient to predict a greater effect on gs in the rainy season, while in the dry period VPD showed a greater effect on gs. In the Baixo, for P. excelsa and M. guyanensis, it was observed that the VPD showed to have a greater effect on gs in the rainy and dry periods. As for the biochemical experiment, it was observed that only the species Handroanthus serratifolius presented a considerable ABA concentration in the leaf and showed a diurnal variation with higher values occurring at 2:00 PM compared to the times of 12:00 AM and 6:00 PM. The concentration of ABA responded more intensely to non-irrigated treatment. Thus, speciesspecific variations in ABA biosynthesis sensitivities to environmental variables such as VPD, Tf, PAR and Ψf may help to explain the stomatal behavior of Amazonian forest species. Therefore, we conclude that environmental factors and physiological aspects alone do not explain the diurnal variation in stomatal movement. Thus, it is likely that biochemical factors such as ABA production, associated to environmental variations and their interactions with the physiology of canopy trees in the Amazon forest, are of extreme relevance to be explored to improve the understanding of how tropical forests respond to climate changes.O entendimento das interações do contínuo solo-planta-atmosfera frente às mudanças ambientais do ecossistema é pré-requisito para modelos que preveem o balanço de carbono em florestas tropicais. Neste contexto, este trabalho teve por objetivo caracterizar a influencia de variáveis meteorológicas no Baixio e Platô sobre o potencial hídrico foliar (Ψf), a condutância estomática (gs) e temperatura foliar (Tf) considerando diferentes técnicas, de duas espécies arbóreas respectivamente no dossel de uma floresta primária na Amazônia Central e entender mecanismos bioquímicos como produção de acido abscísico (ABA) e sua relação com a regulação estomática. A pesquisa foi realizada na Reserva Biológica do Cuieiras (2º35’22’’S, 60º06’55’’W) em 2017. As espécies estudadas foram a Eschweilera cyathiformis e Pouteria anomala (no platô) Peltogyne excelsa e Micropholis guyanensis (no baixio). As espécies estudadas no experimento bioquímico foram Cariniana legalis, Handroanthus serratifolius e Astronium fraxinifolium, realizado em Trancoso-BA em 2018. As variáveis meteorológicas foram obtidas a partir da instrumentação instalada em duas torres de monitoramento K34 (platô) e B34 (baixio). O comportamento da progressão diária de Ψf das diferentes espécies na avaliação foi significativo, de modo que a espécie P. anomala e E. ciathiformis na K34 é diferente em relação às espécies P. excelsa e M. guyanensis no baixio, isso pode estar relacionado a um comportamento isohídrico e anisohídrico das espécies no platô e baixio, respectivamente. Para a dinâmica de gs das espécies em resposta aos diferentes períodos chuvoso e seco houve diferença significativa, observou-se que gs diminuiu consideravelmente no período seco quando comparado ao período chuvoso e seguiu o mesmo padrão no platô e baixio. Os resultados das medidas de Tf nas espécies do baixio e platô, e para os períodos chuvoso e seco, mostram diferenças significativas de modo que a medida com o porômetro foi mais significativa quando comparadas com as técnicas do Termovisor (Flir), Termopares e Sensor InfraRed, bem como em relação as medidas de temperatura do ar com Termohigrômetros. Observaram-se variação dos valores ótimos de Tf no platô em relação gs sazonalmente. Para todo o período de coleta se obsreva a configuração de comportamento de histerese entre a condutância estomática e DPV e Tf. No platô, para P. anomala, observou-se que o DPV e Tf não foi suficiente para predizer um maior efeito sobre gs, no período sazonal chuvoso, enquanto no período seco DPV demonstrou maior efeito sobre gs. Já no baixio, para P. excelsa e M. guyanensis, observou-se que o DPV demonstrou ter um maior efeito sobre gs, nos períodos chuvoso e seco. Quanto ao experimento bioquímico observou-se que apenas a espécie Handroanthus serratifolius apresentou concentração de ABA consideráveis na folha e demonstrou variar diurnamente com maiores valores ocorrendo as 2:00PM comparado aos horários de 12:00AM e 18:00PM. A concentração de ABA respondeu mais intensamente ao tratamento não irrigado. Assim, variações específicas da espécie nas sensibilidades de biossíntese de ABA às variáveis ambientais como DPV, Tf, PAR e Ψf, podem ajudar a explicar o comportamento estomático de espécies florestais da Amazônia. Portanto, conclui-se que fatores ambientais e aspectos fisiológicos por si só não explicam a variação diurna no movimento estomático. Assim, é provável que fatores bioquímicos como a produção de ABA, associadas às variações ambientais e suas interações com a fisiologia das árvores de dossel na floresta Amazônica é tema de extrema relevância a ser explorado, para melhorar o entendimento de como as florestas tropicais respondem as mudanças climáticas

Below versus above ground plant sources of abscisic acid (ABA) at the heart of tropical forest response to warming

Warming surface temperatures and increasing frequency and duration of widespread droughts threaten the health of natural forests and agricultural crops. High temperatures (HT) and intense droughts can lead to the excessive plant water loss and the accumulation of reactive oxygen species (ROS) resulting in extensive physical and oxidative damage to sensitive plant components including photosynthetic membranes. ROS signaling is tightly integrated with signaling mechanisms of the potent phytohormone abscisic acid (ABA), which stimulates stomatal closure leading to a reduction in transpiration and net photosynthesis, alters hydraulic conductivities, and activates defense gene expression including antioxidant systems. While generally assumed to be produced in roots and transported to shoots following drought stress, recent evidence suggests that a large fraction of plant ABA is produced in leaves via the isoprenoid pathway. Thus, through stomatal regulation and stress signaling which alters water and carbon fluxes, we highlight the fact that ABA lies at the heart of the Carbon-Water-ROS Nexus of plant response to HT and drought stress. We discuss the current state of knowledge of ABA biosynthesis, transport, and degradation and the role of ABA and other isoprenoids in the oxidative stress response. We discuss potential variations in ABA production and stomatal sensitivity among different plant functional types including isohydric/anisohydric and pioneer/climax tree species. We describe experiments that would demonstrate the possibility of a direct energetic and carbon link between leaf ABA biosynthesis and photosynthesis, and discuss the potential for a positive feedback between leaf warming and enhanced ABA production together with reduced stomatal conductance and transpiration. Finally, we propose a new modeling framework to capture these interactions. We conclude by discussing the importance of ABA in diverse tropical ecosystems through increases in the thermotolerance of photosynthesis to drought and heat stress, and the global importance of these mechanisms to carbon and water cycling under climate change scenarios. © 2018 by the authors. Licensee MDPI, Basel, Switzerland

Hysteresis area at the canopy level during and after a drought event in the Central Amazon

Understanding forest water limitation during droughts within a warming climate is essential for accurate predictions of forest-climate interactions. In hyperdiverse ecosystems like the Amazon forest, the mechanisms shaping hysteresis patterns in transpiration relative to environmental factors are not well understood. From this perspective, we investigated these dynamics by conducting in situ leaf-level measurements throughout and after the 2015 El Niño-Southern Oscillation (ENSO) drought. Our findings indicate a substantial increase in the hysteresis area (Harea) among transpiration (E), vapor pressure deficit (VPD), and stomatal conductance (gs) at canopy level during the ENSO peak, attributed to both temporal lag and differences in magnitude between gs and VPD peaks. Specifically, the canopy species Pouteria anomala exhibited an increased Harea, due to earlier maximum gs rates leading to a greater temporal lag with VPD compared to the post-drought period. Additionally, leaf water potential (ΨL) and canopy temperature (Tcanopy) showed larger Harea during the ENSO peak compared to post-drought conditions across all studied species, suggesting that stomatal closure, particularly during the afternoon, acts to minimize water loss and may explain the counterclockwise hysteresis observed between ΨL and Tcanopy. The pronounced Harea during the drought points to a potential imbalance between water supply and demand, underlining the role of stomatal behavior of isohydric species in response to drought

Below versus above Ground Plant Sources of Abscisic Acid (ABA) at the Heart of Tropical Forest Response to Warming.

Warming surface temperatures and increasing frequency and duration of widespread droughts threaten the health of natural forests and agricultural crops. High temperatures (HT) and intense droughts can lead to the excessive plant water loss and the accumulation of reactive oxygen species (ROS) resulting in extensive physical and oxidative damage to sensitive plant components including photosynthetic membranes. ROS signaling is tightly integrated with signaling mechanisms of the potent phytohormone abscisic acid (ABA), which stimulates stomatal closure leading to a reduction in transpiration and net photosynthesis, alters hydraulic conductivities, and activates defense gene expression including antioxidant systems. While generally assumed to be produced in roots and transported to shoots following drought stress, recent evidence suggests that a large fraction of plant ABA is produced in leaves via the isoprenoid pathway. Thus, through stomatal regulation and stress signaling which alters water and carbon fluxes, we highlight the fact that ABA lies at the heart of the Carbon-Water-ROS Nexus of plant response to HT and drought stress. We discuss the current state of knowledge of ABA biosynthesis, transport, and degradation and the role of ABA and other isoprenoids in the oxidative stress response. We discuss potential variations in ABA production and stomatal sensitivity among different plant functional types including isohydric/anisohydric and pioneer/climax tree species. We describe experiments that would demonstrate the possibility of a direct energetic and carbon link between leaf ABA biosynthesis and photosynthesis, and discuss the potential for a positive feedback between leaf warming and enhanced ABA production together with reduced stomatal conductance and transpiration. Finally, we propose a new modeling framework to capture these interactions. We conclude by discussing the importance of ABA in diverse tropical ecosystems through increases in the thermotolerance of photosynthesis to drought and heat stress, and the global importance of these mechanisms to carbon and water cycling under climate change scenarios

Below versus above Ground Plant Sources of Abscisic Acid (ABA) at the Heart of Tropical Forest Response to Warming.

Warming surface temperatures and increasing frequency and duration of widespread droughts threaten the health of natural forests and agricultural crops. High temperatures (HT) and intense droughts can lead to the excessive plant water loss and the accumulation of reactive oxygen species (ROS) resulting in extensive physical and oxidative damage to sensitive plant components including photosynthetic membranes. ROS signaling is tightly integrated with signaling mechanisms of the potent phytohormone abscisic acid (ABA), which stimulates stomatal closure leading to a reduction in transpiration and net photosynthesis, alters hydraulic conductivities, and activates defense gene expression including antioxidant systems. While generally assumed to be produced in roots and transported to shoots following drought stress, recent evidence suggests that a large fraction of plant ABA is produced in leaves via the isoprenoid pathway. Thus, through stomatal regulation and stress signaling which alters water and carbon fluxes, we highlight the fact that ABA lies at the heart of the Carbon-Water-ROS Nexus of plant response to HT and drought stress. We discuss the current state of knowledge of ABA biosynthesis, transport, and degradation and the role of ABA and other isoprenoids in the oxidative stress response. We discuss potential variations in ABA production and stomatal sensitivity among different plant functional types including isohydric/anisohydric and pioneer/climax tree species. We describe experiments that would demonstrate the possibility of a direct energetic and carbon link between leaf ABA biosynthesis and photosynthesis, and discuss the potential for a positive feedback between leaf warming and enhanced ABA production together with reduced stomatal conductance and transpiration. Finally, we propose a new modeling framework to capture these interactions. We conclude by discussing the importance of ABA in diverse tropical ecosystems through increases in the thermotolerance of photosynthesis to drought and heat stress, and the global importance of these mechanisms to carbon and water cycling under climate change scenarios

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

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. © 2019 Gimenez, Jardine, Higuchi, Negrón-Juárez, Sampaio-Filho, Cobello, Fontes, Dawson, Varadharajan, Christianson, Spanner, Araújo, Warren, Newman, Holm, Koven, McDowell and Chambers