Stem diameter variations as a versatile research tool in ecophysiology

Abstract

High-resolution stem diameter variations (SDV) are widely recognized as a useful drought stress indicator and have therefore been used in many irrigation scheduling studies. More recently, SDV have been used in combination with other plant measurements and biophysical modelling to study fundamental mechanisms underlying whole-plant functioning and growth. The present review aims to scrutinize the important insights emerging from these more recent SDV applications to identify trends in ongoing fundamental research. The main mechanism underlying SDV is variation in water content in stem tissues, originating from reversible shrinkage and swelling of dead and living tissues, and irreversible growth. The contribution of different stem tissues to the overall SDV signal is currently under debate and shows variation with species and plant age, but can be investigated by combining SDV with state-of-the-art technology like magnetic resonance imaging. Various physiological mechanisms, such as water and carbon transport, and mechanical properties influence the SDV pattern, making it an extensive source of information on dynamic plant behaviour. To unravel these dynamics and to extract information on plant physiology or plant biophysics from SDV, mechanistic modelling has proved to be valuable. Biophysical models integrate different mechanisms underlying SDV, and help us to explain the resulting SDV signal. Using an elementary modelling approach, we demonstrate the application of SDV as a tool to examine plant water relations, plant hydraulics, plant carbon relations, plant nutrition, freezing effects, plant phenology and dendroclimatology. In the ever-expanding SDV knowledge base we identified two principal research tracks. First, in detailed short-term experiments, SDV measurements are combined with other plant measurements and modelling to discover patterns in phloem turgor, phloem osmotic concentrations, root pressure and plant endogenous control. Second, long-term SDV time series covering many different species, regions and climates provide an expanding amount of phenotypic data of growth, phenology and survival in relation to microclimate, soil water availability, species or genotype, which can be coupled with genetic information to support ecological and breeding research under on-going global change. This under-exploited source of information has now encouraged research groups to set up coordinated initiatives to explore this data pool via global analysis techniques and data-mining.

Plant-Based Methods for Irrigation Scheduling of Woody Crops

“…De Swaef et al [130] provided an explanation on the effect of crop load on MDS and daily growth rate (DGR) in peach, with the help of a water and carbon transport model. The use of models to interpret SDV records was reviewed by De Swaef et al [131]. Other factors have been also been identified as influencing SDV records.…”

Monitoring of Freezing Dynamics in Trees: A Simple Phase Shift Causes Complexity

“…Dendrometers are commonly used to monitor growth and drought stress in woody plants (Reineke, 1932;Daubenmire, 1945;Deslauriers et al, 2007;de Swaef et al, 2015). However, upon freezing, a sharp decrease in diameter is observed in the bark of acclimated plants, which is probably caused by water fluxes toward the ice nucleation point in intercellular spaces (Zweifel and Häsler, 2000;Ball et al, 2006;Charra-Vaskou et al, 2016).…”

Low apoplastic water potential in trees - dehydration stress on living cells and embolism in xylem

“…freezing. Reversible diameter change measurements of the xylem (Irvine and Grace 1997) and living bark, consisting of the phloem and vascular cambium (Mencuccini et al 2013), have been extensively used to study changes in the water content of these tissues during summer conditions (Sevanto et al 2011;De Swaef et al 2015;Pfautsch et al 2015). Changes in the negative hydrostatic pressure of the xylem and in the positive turgor pressure of the living bark may also be derived from diameter change measurements provided that the pressurevolume relations of the tissues are known (De Schepper and Steppe 2010).…”