Xylem sap flow and drought stress of Fraxinus excelsior saplings

Abstract

We report on diurnal and seasonal variations in sap flow rate and stem water potential of Fraxinus excelsior L. saplings growing at the edge of a Fraxino-Aceretum forest in western Germany. Because of shallow soil, the trees were subjected to drought in summer. When soil water availability was not limiting, sap flow rate was related to changes in solar radiation and vapor pressure deficit. Maximum transpiration rates per leaf area were 3.5-7.4 mmol m-2 s-1, and maximum daily totals were 1.7-3.3 kg m-2 day-1. Under drought conditions, stem water potential dropped to midday minima of -2.6 to -3.5 MPa and sap flow rate was strongly related to this parameter. After the drought period, reduced apparent (whole-plant) hydraulic conductance was observed, which was attributed to a continued reduction in stomatal conductance after the drought stress had ceased. A model was developed that linked sap flow rate directly to climatic variables and stem water potential. Good correlation between measured and simulated sap flow rates allowed the model to be used for data interpretation.

Leaf water status and stem xylem flux in relation to soil drought in five temperate broad-leaved tree species with contrasting water use strategies

“…In the case of F. excelsior, it is remarkable that even under the much lower soil moisture of the summer 2006 the trees maintained constant J sd rates throughout the drought period with flux rates comparable to the values measured by Hölscher et al (2005) under a more favorable moist soil water regime. It appears that continuous water supply is secured by the capacity of the species to develop low leaf water potentials and its ability to maintain a large and vital fine root system even during drought (Carlier et al, 1992;Korn, 2004;Stöhr and Lösch, 2004). Apparent hydraulic conductivity in the root-to-leaf flow path was not higher than in the other species, as we would have expected from a ring-porous tree.…”

Effect of fungal pathogens and climatic factors on production, biodiversity and health status of ash mountain forests

“…Fraxinus is a flexible genus which can be found over a wide range of growing conditionsfrom coastal to mountainous regions, especially on steep slopes (Stöhr & Lösch, 2004), from pioneer to mature woodland, from nutrient-rich to poorer soils (Ferrazzini et al, 2007;Dufour & Piégay, 2008). Its drought tolerance and frost sensitivity would have made ash a tree species potentially favored by the expected climate warming and drying (Scherrer et al, 2011).…”

Soil water content at the catchment level and plant water status relationships in a Mediterranean Quercus ilex forest

“…This lack of equilibrium could be better detected with the sap flow technique than based on predawn water potential measurements. A continuous record of sap flow measurement shows that it must not necessarily reflect a static situation for this physiological process, due to the fact that the W pd shoot water potential must not exactly fit to soil water potential over most of the time (Stöhr and Lösch, 2004).…”