Transpiration And Plant Water Relations Of Evergreen Woody Vegetation On A Recently Constructed Artificial Ecosystem Under Seasonally Dry Conditions In Western Australia

Understanding transpiration and plant physiological responses to environmental conditions is crucial for the design and management of vegetated engineered covers. Engineered covers rely on sustained transpiration to reduce the risk of deep drainage int

A simple field validation of daily transpiration derived from sapflow using a porometer and minimal meteorological data

The original publication can be found at www.springerlink.comHeat-pulse techniques are routinely used to estimate transpiration from canopies of woody plants typically without any local calibration, mainly because of the difficulty of doing so in the field and, frequently, lack of detailed weather data. This is despite concerns that the techniques may produce erroneous values under certain conditions, such as when evaporative demand is high. In this study, we used a micrometeorological approach to validate transpiration from irrigated olives deduced from heat-pulse technique by ascertaining precise values for the parameters that are critical for converting heat-pulse velocity to sapflow. The micrometeorological approach involved limited data on stomatal conductance (gs), obtained hourly with a porometer on four contrasting days, and was used to calibrate a simple model for predicting conductance. Predicted stomatal conductance (gsm) agreed well with that measured, and when both were used to calculate hourly transpiration, they produced values that were within 10% of each other. This was despite brief underestimations of transpiration based on gsm (Tm) in the early hours of the day that arose from poor determination of incident radiation at this time. We then used Tm to iteratively set the values for the various parameters, including the time-out value that accounts for zero-flow conditions, needed to convert heat-pulse velocity to sapflow, for the four days. The best fit between Tm and transpiration from sapflow (Ts) was obtained with time-out value set to 120 s. All heat-pulse velocity data were therefore analysed with this time-out value to obtain sapflow and, hence, transpiration (Ts). Comparison of Tm and Ts for the whole season showed that the former tended to produce higher values on certain days when vapour pressure deficit (D) was high in summer (December–February). While Ts occasionally produced larger values than Tm under the mild conditions of autumn (March–April). Totals of the daily transpiration during the 190-day period were within 10% of each other.Isa A. M. Yunusa, Ian K. Nuberg, Sigfredo Fuentes, Ping Lu and Derek Eamu

Assessing sapwood depth and wood properties in Eucalyptus and Corymbia spp. using visual methods and near infrared spectroscopy (NIR)

Accurate measurement of sapwood depth (DS) is essential for calculating volumetric water use of individual trees and stands. Various methods are available to measure DS but their accuracy is rarely cross-validated. We sampled 15 Eucalyptus and 1 Corymbia species along a gradient of aridity and obtained reference values of DS in fresh wood cores using light microscopy, which represents our reference method. We compared this method to the simpler and widely used macroscopic method: visual assessment of natural or induced colour change from sapwood to heartwood. In a third method, estimation of DS was based on species-specific models that rely on wood properties measured using near infrared spectroscopy (NIR). Microscopy allowed clear identification of DS based on the presence of blocked vessels. Measurement of DS using microscopic methods was possible for 78 of a total of 80 cores and ranged from 3.6 mm (E. loxophleba) to 43.8 mm (E. viminalis). Macroscopic assessment clearly differentiated sapwood and heartwood in 60 cores. Results from microscopic and macroscopic methods agreed closely (50% deviation between estimates), macroscopic measurement across all species agreed well with microscopic assessment of DS (R2 = 0.92). Models developed for differentiation between sapwood and heartwood using NIR spectroscopy were very robust (high coefficient of determination) for four species, but DS could only be predicted well for one (E. obliqua) of the four species. Even after elimination of apparent false estimates, prediction of DS by NIR across species was not as strong as for macroscopic assessment (R2 = 0.88). DS can accurately be measured using microscopy if vessel occlusion is clearly visible. Although slightly overestimated, DS from macroscopic assessment was generally similar to that measured by microscopy. NIR spectroscopy was unable to predict DS with acceptable accuracy for the majority of species. Further improvements in the prediction of DS using NIR will require more intensive model calibration and validation, and may not be applicable to all species