Abstract
This study aims to examine interactions between tree characteristics, sap flow, and environmental variables in an open Pinus brutia (Ten.) forest with shallow soil. We examined radial and azimuthal variations of sap flux density (Jp), and also investigated the occurrence of hydraulic redistribution mechanisms, quantified nocturnal tree transpiration, and analyzed the total water use of P. brutia trees during a three-year period. Sap flow and soil moisture sensors were installed onto and around eight trees, situated in the foothills of the Troodos Mountains, Cyprus. Radial observations showed a linear decrease of sap flux densities with increasing sapwood depth. Azimuthal differences were found to be statistically insignificant. Reverse sap flow was observed during low vapor pressure deficit (VPD) and negative air temperatures. Nocturnal sap flow was about 18% of the total sap flow. Rainfall was 507 mm in 2015, 359 mm in 2016, and 220 mm in 2017. Transpiration was 53%, 30%, and 75%, respectively, of the rainfall in those years, and was affected by the distribution of the rainfall. The trees showed an immediate response to rainfall events, but also exploited the fractured bedrock. The transpiration and soil moisture levels over the three hydrologically contrasting years showed that P. brutia is well-adapted to semi-arid Mediterranean conditions.
Highlights
Rainfall and soil moisture are generally the main limiting factors for tree transpiration in semi-arid regions
Our results show a larger increase in sapwood area with increasing diameter at breast height (DBH) for P. brutia compared to show a larger increase in sapwood area with increasing DBH for P. brutia compared to the relations for the relations for Populus euphratica
Our results show a larger increase in sapwood area with increasing DBH for P. brutia compared to Contrastingly, in Contrastingly, a study about the between area and sapwood other tree the relations for Populus euphratica
Summary
Rainfall and soil moisture are generally the main limiting factors for tree transpiration in semi-arid regions. Investigations of the movement and dynamics of sap through trees are important for advancing scientific knowledge about plants’ hydraulic functioning and growth under different spatio-temporal environmental conditions [2,3]. Sap flow instruments are widely used for the estimation of whole-plant water use and transpiration [3,4,5]. The accuracy of sap flow measurements and the upscaling of these to the whole-plant water use relies on the knowledge of species-specific physiological characteristics, as well as on information of radial and circumferential patterns of sap velocity [6,7,8]. The relationship between sap flux density and sapwood depths can be linear [6,11], exponential [4], or variable, depending on temporal or environmental changes [12,13]. Loustau et al [14] found that the variability of sap flux density of Pinus pinaster
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