Estimating Water in Living Woody Stems - A Review

Abstract

Predicted climate changes due to greenhouse gas emissions will alter site and ecological conditions, increase instability in many ecosystems and expand the value of forest carbon and wood energy. Woody plants most often are faced with drought stresses, not only because of erratic rainfall, but also the result of climatic changes. Natural variability among wood species in terms of chances in induced water stress in stem moisture content is large. Under severe water deficit, plants have to face the dilemma of dying by drying or being starved of carbon. Changes in the water content of extensible tissues of the stem are readily reversible, causing diurnal variation driven by changing water potential in the xylem. This review intends: 1. to address how stems in woody species play an important role in water storage relevant to plant hydraulics, and 2. to present methodologies to estimate water content in stems of wood species. ESTIMATIVA DE ÁGUA EM CAULE LENHOSOS VIVOS -UMA REVISÃORESUMO: Mudanças climáticas previstas alterarão o local e as condições ecológicas, aumentarão a instabilidade em muitos ecossistemas e expandirão o valor do carbono florestal e da energia da madeira. Plantas lenhosas na maioria das vezes são confrontadas com deficit hídrico, não só causado por chuvas irregulares, mas também resultante das mudanças climáticas. A variabilidade natural entre as espécies lenhosas em termos de mudanças induzidas pelo estresse hídrico no teor de umidade do tronco é grande. Sob deficit hídrico severo, as plantas enfrentam o dilema de morrer por falta de água ou de carbono. Mudanças no conteúdo de água dos tecidos elásticos do caule são facilmente reversíveis, causando variação diurna impulsionadas pela mudança do potencial de água no xilema . Esta revisão pretende abordar como caules de espécies lenhosas desempenham um papel importante no armazenamento de água relevante ao sistema hidráulico das plantas e apresentar metodologias atuais para estimar o teor de água no caule de espécies lenhosas. CERNE

Pedotransfer Functions in Earth System Science: Challenges and Perspectives

“…So even though one could argue that current NDVI‐derived VWC estimates are sufficiently differentiated for global model purposes, when applied in the perspective of climate change impacts, the estimation of effects of drought stress to vegetation becomes essential. The improved understanding of responses of plants to drought stress ruled by water potentials in soils stems, strongly depending on soil type/properties (Malavasi et al, ), offers crucial information to feed such models, possible through improved parameterization of VWC with PTFs.…”

A review of time domain reflectometry (TDR) applications in porous media

“…Gibbs (1930) demonstrated a seasonal variation in tree stem water content (θstem = volume of water/total volume of stem), also referred to as stem relative water content (Malavasi et al, 2016). θstem varied with xylem water potential, and different environmental factors including soil water status, climatic conditions or present tree disease.…”

“…Methods, including the dendrometer (Turcotte et al, 2011), coring and gravimetric analysis (Clark and Gibbs, 1957;Waring and Running, 1978;Waring et al, 1979), gamma-ray attenuation (Brough et al, 1986;Edwards and Jarvis, 1983), MRI-nuclear magnetic resonance imaging (Choat et al, 2010;De Schepper et al, 2012;Reinders et al, 1988a;Reinders et al, 1988b;Windt et al, 2009), X-ray computer tomography (Raschi et al, 1995), stem diameter transduction (Cuevas Sánchez and Fernández Luque, 2010), ultrasonic echo detection (Lyu et al, 2016), TDR (Dahlen et al, 2015;Hernández-Santana and Martínez-Fernández, 2010;Irvine and Grace, 1997;Nadler et al, 2003;Wullschleger et al, 1996), FDR-frequency domain reflectometry (Beedlow et al, 2017;Kumagai et al, 2009;Zhou et al, 2018), and heat tracer methods (Trcala et al, 2015), were demonstrated to determine stem water content/storage. More details about the pros and cons of the approaches to the measurement can be found in Malavasi et al (2016).…”

“…FDR has also been used for stem water measurements (Zhou et al, 2015), and FDR may be a better choice than TDR for measuring stem water contents in trees of small diameter. In addition, maximum contact between the TDR probe and the sapwood should be made, because poor installation results in air bubbles around the TDR rods (Malavasi et al, 2016). Effects of the radial variability of stem morphology (e.g., non-uniform distribution of water in the stem, different dielectric permittivity of the sapwood and heartwood) on TDR measurements should be investigated to better understand stem water content.…”

“…A study of Zhou et al (2018) showed that the probe must sense substantial amounts of the sapwood to better account for changes in θstem. The influence of temperature on TDR coaxial cable dielectric length is another issue that should be considered (Malavasi et al, 2016).…”