Carles M. Rubio

Response of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) to soil and atmospheric water deficits under Mediterranean mountain climate

The physiological responses to water deficits of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) were studied under Mediterranean mountain climate. Minimum leaf water potentials were −3.2 MPa for oak and −2.1 MPa for pine, with higher predawn values for pubescent oak. Relative sap flow declined in both species when vapour pressure deficit (D) went above ca. 1.2 kPa, but stomatal control was stronger for pine during the 2003 summer drought. P. sylvestris plant hydraulic conductance on a half-total leaf area basis (kL,s−1) was 1.2–2.6 times higher than the values shown by Q. pubescens, and it showed a considerably steeper decrease during summer. Leaf-level gas exchange was positively related to kL,s−1 in both species. Scots pine was more vulnerable to xylem embolism and closed stomata to prevent substantial conductivity losses. The results of this study confirm that pubescent oak is more resistant to extreme drought events.RésuméLes réponses physiologiques aux déficits hydriques du pin sylvestre (Pinus sylvestris L.) et du chêne pubescent (Quercus pubescens Wild.) ont été étudiées sous climat montagnard méditerranéen. Le potentiel hydrique foliaire minimum atteint a été de −3,2 MPa pour le chêne et de −2,1 MPa pour le pin, avec des valeurs de potentiel de base plus élevées pour le chêne pubescent. Un relatif déclin du flux de sève a été observé chez les deux espèces lorsque le déficit de vapeur d’eau dépassait 1,2 kPa, mais le contrôle stomatique a été plus fort chez le pin pendant la sécheresse de l’été 2003. La conductance hydraulique des pins, ramenée à la surface foliaire (kL, s−1) a été de 1,2 à 2,6 fois plus élevée que celle de Quercus pubescens et a présenté une rapide décroissance pendant l’été. Le niveau des échanges gazeux foliaires était positivement corrélé à kL, s−1 chez les deux espèces. Le pin sylvestre est plus vulnérable à l’embolie du xylème et a de ce fait fermé ses stomates pour empêcher une perte substantielle de conductivité hydraulique. Les résultats de cette étude confirment que le chêne pubescent est plus résistant aux épisodes d’extrême sécheresse que le pin sylvestre.

Applicability of Hydrus-1D in a Mediterranean Mountain Area Submitted to Land Use Changes

The aim of this research is to evaluate the reliability and accuracy of the Hydrus-1D model to simulate the measured dynamics of water flow in a silt loam soil profile located in an abandoned crop area. The paper includes a physical and chemical characterization of the soil, and hydraulic properties characteristics as well. Several techniques and devices were used to develop the experiment in both, field and laboratory scales. The last part of the study was the Hydrus-1D simulation using real rain events and evapotranspiration rates. In summary, it could predict accurately the water dynamics of this “natural” scenario.

The relationships among thermal resistivity, water content and a stony sandy soil

Developing soil macro-porosity could be considered to be a direct effect of physical, chemical and eco-pedological processes where the soil matrix has contact with coarse elements. Hence, macro-porosity acquires a special importance affecting the liquid phase as well as the gas phase, and therefore the soil thermal properties as well. The aim of this research is to evaluate the effect of the coarse elements on the total thermal resistivity (Rho) for a sandy soil. The experiment was carried out with several gravel masses (kggravels·kgsoil-1) mixed with soil, and repacked in a soil column device. The method used for measuring the thermal resistivity was the heat pulse, based on ASTM D5334-08. The water content (θ) was determined using capacitor probes (FDR probes). The experimental device was maintained inside a thermal chamber for controlling a minimal thermal drift. The Rho(θ) relationship presented higher variability when 35% of coarse elements were added and the water content was close to saturation.