The influence of bamboo culm water content on sap flux measurements with thermal dissipation probes: observations and modeling

Abstract

Water content fluctuations in bamboo culms significantly influence sap flux measurements with thermal dissipation probes, as indicated and quantified by experimental, monitoring and model analyses. Bamboos and other plants may substantially rely on stem water storage for transpiration. Fluctuations in wood water content (θwood) may lead to errors when estimating transpiration based on sap flux (Js) measurements with the widely used thermal dissipation probe (TDP) method. To test the effects of θwood on Js, we conducted a culm dehydration experiment, monitored bamboos with TDPs, and implemented a steady-state thermal model. Based on the model simulation, a mathematical correction method was built. Central to the calculation of Js, and thus a major potential source of error, is the maximum temperature difference between probes (ΔTmax) which is often referred to as ‘zero flow’ conditions. In the culm dehydration experiment, we observed that ΔTmax decreased when θwood increased. In long-term field monitoring, ΔTmax decreased when soil moisture content increased, potentially indicating changes in θwood and a seasonal decrease in stem water storage. The steady-state model reproduced the θwood to ΔTmax relationship of the dehydration experiment and underlined a considerable sensitivity of Js estimates to θwood. Fluctuations in θwood may lead to a substantial underestimation of Js, and subsequently of transpiration, in commonly applied estimation schemes. However, our model results suggest that such underestimation can be quantified and subsequently corrected for with our correction equations when key wood properties are known. Our study gives insights into the relationship between θwood and TDP-derived Js and examines potential estimation biases. The influence of bamboo culm water content on sap flux measurements with thermal dissipation probes: observations and modeling (PDF Download Available). Available from: https://www.researchgate.net/publication/321136319_The_influence_of_bamboo_culm_water_content_on_sap_flux_measurements_with_thermal_dissipation_probes_observations_and_modeling [accessed Jan 16 2018].