Stem growth of multipurpose tree species: net effect of micrometeorological variability assessed by principal component regression / Crescimento do tronco de espécies de árvores de uso múltiplo: efeito líquido da variabilidade micrometeorológica avaliada por regressão de componentes principais

In a typical year in the central Amazon, there is a mild dry season, but its effect on stem growth of multipurpose forest tree species is not yet well known. This study aimed to determine the individual effect of microclimatic parameters on stem growth after removing the influence of intercorrelation among microclimatic variables. Monthly stem diameter increment was measured in six species (46 trees) from January 2018 to December 2020. Microclimatic variables recorded were irradiance, air temperature, rainfall, and vapor pressure deficit. Principal component regression was used to assess the effect of micrometeorological variability on stem growth. On average, stem growth increased with an increase in rainfall and soil water content, but decreased with rise in maximum temperature and maximum vapor pressure deficit. These findings indicate that, when removing the effect of intercorrelation between microclimatic parameters, vapor pressure deficit may, in fact, affect stem growth. We demonstrate that the reduction in stem growth during the dry season can also be related to an increase in maximum temperature and maximum vapor pressure deficit, and not only to a decline in soil water content.(AU)

Em um ano típico na Amazônia central, há uma estação seca amena, mas seu efeito sobre o crescimento do tronco de espécies de uso múltiplo ainda é pouco conhecido. Este estudo teve como objetivo determinar o efeito individual de variáveis microclimáticas sobre crescimento do tronco após remover a influência da intercorrelação entre os fatores climáticos. O incremento mensal do diâmetro do tronco foi medido em seis espécies (46 árvores) de janeiro de 2018 a dezembro de 2020. As variáveis microclimáticas medidas foram irradiância, temperatura do ar, precipitação pluvial e déficit de pressão de vapor. Utilizou-se regressão de componentes principais para avaliar o efeito da variabilidade micrometeorológica sobre crescimento do tronco. Em média, o crescimento do tronco aumentou com o aumento da precipitação e do conteúdo de água do solo, mas diminuiu com o aumento da temperatura máxima e do déficit máximo de pressão de vapor. Estes resultados indicam que, removendo o efeito da intercorrelação entre os parâmetros climáticos, o déficit de pressão de vapor pode, de fato, ter um efeito sobre o crescimento do tronco. Demonstrou-se que a redução no crescimento do caule durante a estação seca também pode estar relacionada ao aumento da temperatura máxima e do déficit máximo de pressão de vapor, e não apenas ao declínio do teor de água no solo.(AU)

Principal component regression analysis demonstrates the collinearity-free effect of sub estimated climatic variables on tree growth in the central Amazon / El análisis de regresión por componentes principales muestra el efecto libre de colinealidad de variables climáticas subestimadas sobre el crecimiento de los árboles en la Amazonía central

Abstract Introduction: Climatic variables show a seasonal pattern in the central Amazon, but the intra-annual variability effect on tree growth is still unclear. For variables such as relative humidity (RH) and air vapor pressure deficit (VPD), whose individual effects on tree growth can be underestimated, we hypothesize that such influences can be detected by removing the effect of collinearity between regressors. Objective: This study aimed to determine the collinearity-free effect of climatic variability on tree growth in the central Amazon. Methods: Monthly radial growth was measured in 325 trees from January 2013 to December 2017. Irradiance, air temperature, rainfall, RH, and VPD data were also recorded. Principal Component Regression was used to assess the effect of micrometeorological variability on tree growth over time. For comparison, standard Multiple Linear Regression (MLR) was also used for data analysis. Results: Tree growth increased with increasing rainfall and relative humidity, but it decreased with rising maximum VPD, irradiance, and maximum temperature. Therefore, trees grew more slowly during the dry season, when irradiance, temperature and VPD were higher. Micrometeorological variability did not affect tree growth when MLR was applied. These findings indicate that ignoring the correlation between climatic variables can lead to imprecise results. Conclusions: A novelty of this study is to demonstrate the orthogonal effect of maximum VPD and minimum relative humidity on tree growth.

Resumen Introducción: Las variables climáticas muestran un patrón estacional en la Amazonía central, pero el efecto de la variabilidad intra-anual en el crecimiento de los árboles aún no está claro. Para variables como la humedad relativa (HR) y el déficit de presión de vapor (VPD), cuyo efecto individual en el crecimiento de los árboles puede ser subestimada, planteamos la hipótesis de que tales influencias pueden detectarse eliminando el efecto de colinealidad entre regresores. Objetivo: Este estudio tuvo como objetivo determinar el efecto libre de colinealidad de la variabilidad climática sobre el crecimiento de los árboles en la Amazonía central. Métodos: Se midió el crecimiento radial mensual en 325 árboles desde enero 2013 hasta diciembre 2017. También se registraron datos de irradiancia (PAR), temperatura del aire, lluvia, humedad relativa (RH) y déficit de presión de vapor de aire (VPD). Se utilizó la regresión de componentes principales para evaluar el efecto de la variabilidad micrometeorológica a lo largo del tiempo sobre el crecimiento de los árboles. Para comparación, también se utilizó la regresión lineal múltiple (MLR) estándar para el análisis de datos. Resultados: El crecimiento de los árboles incrementó con el aumento de las precipitaciones y la humedad relativa, y disminuyó con el aumento de la VPD máxima, la irradiancia y la temperatura máxima. Por lo tanto, los árboles crecieron más lentamente durante la estación seca, cuando la irradiancia, la temperatura y la VPD eran más altas. La variabilidad micrometeorológica no afectó el crecimiento de los árboles cuando se aplicó MLR. Estos hallazgos indican que ignorar la correlación entre las variables climáticas puede conducir a resultados imprecisos. Conclusiones: Una novedad de este estudio es demostrar el efecto ortogonal del VPD máximo y la humedad relativa mínima sobre el crecimiento de los árboles.

Wood and bark water content and monthly stemgrowth in Amazonian tree species / Conteúdo de água de madeira e casca e crescimento mensal do tronco emespécies arbóreas amazônicas

The knowledge of how trees respond to microclimate variability is important in the face of climate changes. The objectives of this study were to examine the variation in wood water content (WWC) and bark water content (BWC) in Amazonian trees, as well as to assess the effect of microclimatic variability on monthly diameter growth rates (DGR). We extracted a core sample from each of 120 trees (28 species) and determined WWC and BWC on a fresh matter basis. DGR was measured monthly during the 12 months of 2007. The effect of microclimatic variability on DGR was analyzed by redundancy analysis. Average BWC and WWC were 53.4% and 34.7%, respectively, with a large variation in stem water content among species (BWC = 36.2−67.1%; WWC = 26.4−50.8%). There was no significant relationship between stem diameter and WWC or BWC, nor between DGR and wood density (p > 0.05). However, wood density was negatively correlated with WWC (rs = −0.69, p 0.20). The unresponsiveness of DGR to microclimatic variability, even in an above-average rainy year such as 2007, indicates that other parts of the tree may have greater priority than the stem for carbon allocation during the dry season.

O conhecimento sobre a resposta das árvores à variação microclimática é importante em face das mudanças climáticas. Os objetivos deste estudo foram examinar a variação do conteúdo de água da madeira (WWC) e do conteúdo de água da casca (BWC) em árvores amazônicas, bem como avaliar o efeito da variabilidade microclimática sobre as taxas de crescimento diamétrico (DGR). Extraímos uma amostra do tronco de 120 árvores (28 espécies) e determinamos WWC e BWC na base da matéria fresca. As medições de DGR foram realizadas mensalmente durante os 12 meses de 2007. O efeito da variabilidade microclimática sobre o crescimento das árvores foi avaliado por meio de análise de redundância. Os valores médios de BWC e WWC foram 53,4% e 34,7%, respectivamente, com uma grande variação no conteúdo de água dos tecidos entre as espécies (BWC = 36,2−67,1%; WWC = 26,4−50,8%). Não houve relação significativa entre o diâmetro do tronco e WWC ou BWC, nem entre DGR e densidade da madeira (p > 0,05). Entretanto, a densidade da madeira foi negativamente correlacionada com WWC (rs = −0,69, p 0,20). A ausência de resposta da DGR à variabilidade microclimática, mesmo em um ano chuvoso acima da média como 2007, indica que outras partes da árvore podem ter maior prioridade do que o tronco para alocação de carbono durante a época seca.

Wood and bark water content and monthly stemgrowth in Amazonian tree species / Conteúdo de água de madeira e casca e crescimento mensal do tronco emespécies arbóreas amazônicas

The knowledge of how trees respond to microclimate variability is important in the face of climate changes. The objectives of this study were to examine the variation in wood water content (WWC) and bark water content (BWC) in Amazonian trees, as well as to assess the effect of microclimatic variability on monthly diameter growth rates (DGR). We extracted a core sample from each of 120 trees (28 species) and determined WWC and BWC on a fresh matter basis. DGR was measured monthly during the 12 months of 2007. The effect of microclimatic variability on DGR was analyzed by redundancy analysis. Average BWC and WWC were 53.4% and 34.7%, respectively, with a large variation in stem water content among species (BWC = 36.2−67.1%; WWC = 26.4−50.8%). There was no significant relationship between stem diameter and WWC or BWC, nor between DGR and wood density (p > 0.05). However, wood density was negatively correlated with WWC (rs = −0.69, p < 0.001). The high BWC emphasizes the importance of the bark tissue in Amazonian trees. Contrary to expectations, variability of monthly irradiance, rainfall and temperature had no effect on DGR (p > 0.20). The unresponsiveness of DGR to microclimatic variability, even in an above-average rainy year such as 2007, indicates that other parts of the tree may have greater priority than the stem for carbon allocation during the dry season.(AU)

O conhecimento sobre a resposta das árvores à variação microclimática é importante em face das mudanças climáticas. Os objetivos deste estudo foram examinar a variação do conteúdo de água da madeira (WWC) e do conteúdo de água da casca (BWC) em árvores amazônicas, bem como avaliar o efeito da variabilidade microclimática sobre as taxas de crescimento diamétrico (DGR). Extraímos uma amostra do tronco de 120 árvores (28 espécies) e determinamos WWC e BWC na base da matéria fresca. As medições de DGR foram realizadas mensalmente durante os 12 meses de 2007. O efeito da variabilidade microclimática sobre o crescimento das árvores foi avaliado por meio de análise de redundância. Os valores médios de BWC e WWC foram 53,4% e 34,7%, respectivamente, com uma grande variação no conteúdo de água dos tecidos entre as espécies (BWC = 36,2−67,1%; WWC = 26,4−50,8%). Não houve relação significativa entre o diâmetro do tronco e WWC ou BWC, nem entre DGR e densidade da madeira (p > 0,05). Entretanto, a densidade da madeira foi negativamente correlacionada com WWC (rs = −0,69, p < 0,001). O alto valor de BWC enfatiza a importância dos tecidos da casca em árvores da Amazônia. Contrariando as expectativas, a variabilidade mensal da irradiância, precipitação e temperatura não afetou DGR (p > 0,20). A ausência de resposta da DGR à variabilidade microclimática, mesmo em um ano chuvoso acima da média como 2007, indica que outras partes da árvore podem ter maior prioridade do que o tronco para alocação de carbono durante a época seca.(AU)

Do soil fertilization and forest canopy foliage affect the growth and photosynthesis of Amazonian saplings?

Most Amazonian soils are highly weathered and poor in nutrients. Therefore, photosynthesis and plant growth should positively respond to the addition of mineral nutrients. Surprisingly, no study has been carried out in situ in the central Amazon to address this issue for juvenile trees. The objective of this study was to determine how photosynthetic rates and growth of tree saplings respond to the addition of mineral nutrients, to the variation in leaf area index of the forest canopy, and to changes in soil water content associated with rainfall seasonality. We assessed the effect of adding a slow-release fertilizer. We determined plant growth from 2010 to 2012 and gas exchange in the wet and dry season of 2012. Rainfall seasonality led to variations in soil water content, but it did not affect sapling growth or leaf gas exchange parameters. Although soil amendment increased phosphorus content by 60 %, neither plant growth nor the photosynthetic parameters were influenced by the addition of mineral nutrients. However, photosynthetic rates and growth of saplings decreased as the forest canopy became denser. Even when Amazonian soils are poor in nutrients, photosynthesis and sapling growth are more responsive to slight variations in light availability in the forest understory than to the availability of nutrients. Therefore, the response of saplings to future increases in atmospheric [CO2] will not be limited by the availability of mineral nutrients in the soil.(AU)

Do soil fertilization and forest canopy foliage affect the growth and photosynthesis of Amazonian saplings?

Most Amazonian soils are highly weathered and poor in nutrients. Therefore, photosynthesis and plant growth should positively respond to the addition of mineral nutrients. Surprisingly, no study has been carried out in situ in the central Amazon to address this issue for juvenile trees. The objective of this study was to determine how photosynthetic rates and growth of tree saplings respond to the addition of mineral nutrients, to the variation in leaf area index of the forest canopy, and to changes in soil water content associated with rainfall seasonality. We assessed the effect of adding a slow-release fertilizer. We determined plant growth from 2010 to 2012 and gas exchange in the wet and dry season of 2012. Rainfall seasonality led to variations in soil water content, but it did not affect sapling growth or leaf gas exchange parameters. Although soil amendment increased phosphorus content by 60 %, neither plant growth nor the photosynthetic parameters were influenced by the addition of mineral nutrients. However, photosynthetic rates and growth of saplings decreased as the forest canopy became denser. Even when Amazonian soils are poor in nutrients, photosynthesis and sapling growth are more responsive to slight variations in light availability in the forest understory than to the availability of nutrients. Therefore, the response of saplings to future increases in atmospheric [CO2] will not be limited by the availability of mineral nutrients in the soil.

Density, size and distribution of stomata in 35 rainforest tree species in Central Amazonia / Densidade, tamanho e distribuição estomática em 35 espécies de árvores na Amazônia Central

Stomata are turgor-operated valves that control water loss and CO2 uptake during photosynthesis, and thereby water relation and plant biomass accumulation is closely related to stomatal functioning. The aims of this work were to document how stomata are distributed on the leaf surface and to determine if there is any significant variation in stomatal characteristics among Amazonian tree species, and finally to study the relationship between stomatal density (S D) and tree height. Thirty five trees (>17 m tall) of different species were selected. Stomatal type, density (S D), size (S S) and stomatal distribution on the leaf surface were determined using nail polish imprints taken from both leaf surfaces. Irrespective of tree species, stomata were located only on the abaxial surface (hypostomaty), with large variation in both S D and S S among species. S D ranged from 110 mm-2 in Neea altissima to 846 mm-2 in Qualea acuminata. However, in most species S D ranges between 271 and 543 mm-2, with a negative relationship between S D and S S. We also found a positive relationship between S D and tree height (r² = 0.14, p < 0.01), but no correlation was found between S D and leaf thickness. The most common stomatal type was anomocytic (37%), followed by paracytic (26%) and anisocytic (11%). We conclude that in Amazonian tree species, stomatal distribution on the leaf surface is a response most likely dependent on the genetic background of every species, rather than a reaction to environmental changes, and that somehow S D is influenced by environmental factors dependent on tree height.

Estômatos são válvulas operadas a turgor que controlam a perda de água e a captura de CO2 durante a fotossíntese. Assim, as relações hídricas e o acumulo de biomassa vegetal são fortemente influenciadas pelo funcionamento estomático. Os objetivos deste trabalho foram: documentar como os estômatos estão distribuídos na superfície foliar e determinar se existe variação das características estomáticas entre espécies da Amazônia, estudar a relação entre densidade estomática (S D) e altura arbórea. Trinta e cinco árvores (>17 m de altura) de diferentes espécies foram selecionadas. Tipo de complexo estomático, S D, tamanho (S S) e distribuição na superfície foliar foram determinados utilizando impressões de ambas as superfícies foliares com esmalte incolor. Independente da espécie, os estômatos foram encontrados apenas na superfície abaxial (hipoestomatia) com ampla variação na S D e no S S entre espécies. A densidade estomática variou de 110 mm-2 em Neea altissima a 846 mm-2 em Qualea acuminata. Entretanto, a maioria das espécies apresentou S D entre 271 e 543 mm-2, com uma relação negativa entre S D e S S. Observou-se uma relação positiva entre S D e altura arbórea (r² = 0.14, p < 0.01), não havendo relação entre S D e espessura foliar. Os tipos estomáticos mais comuns foram: anomocíticos (37%), seguidos de paracíticos (26%) e anisocíticos (11%). Concluiu-se que em espécies da Amazônia, a distribuição de estômatos na superfície foliar está mais relacionada a fatores genéticos de cada espécie do que a variações ambientais. Entretanto, S D é fortemente influenciada por fatores ambientais concernentes à altura da árvore.

O SPAD-502 como alternativa para a determinação dos teores de clorofila em espécies frutíferas / The SPAD-502 as alternative for determining chlorophyll content in fruit tree species

A relação entre o teor absoluto de clorofila e o teor relativo de clorofila obtido pelo SPAD-502 foi determinada em quatro espécies frutíferas (cupuaçu, araçá-boi, limão e urucum). O teor absoluto de clorofila foi determinado usando um espectrofotômetro após a extração dos pigmentos em acetona 80 por cento. O teor de clorofila total (y) foi relacionado com os valores do SPAD (x), como segue: y = 93,95e0,0356x, r² = 0,80 para o urucum; y = 125,41e0,0205x, r² = 0,67 para o cupuaçu; y = 67,58e0,0374x, r² = 0,80 para o limão e y = 66,96e0,0365x, r² = 0,92 para o araçá-boi.

The relationship between the absolute chlorophyll content and the relative chlorophyll content (SPAD-502 values) was determined in four fruit trees species (cupuassu, araza, lemon, and annato). The absolute chlorophyll content was determined using a spectrophotometer after pigment extraction in 80 percent acetone. Chlorophyll content (y) was related to SPAD values (x) as follows: y = 93.95e0.0356x, r² = 0.80 for annato; y =125.41e0.0205x, r² = 0.67 for cupuassu; y =67.58e0.0374x, r² = 0.80 for lemon and y =66.96e0.0365x, r² = 0.92 for araza.