Pressure‐volume analyses on shoots ofPicea abiesand leaves ofCoffea libericaat various temperatures

Abstract

Shoots from two ecologically different evergreen tree species,Picea abies(L.) Karst andCoffea libericaHiern, were used to carry out pressure volume (PV) measurements at 5–35°C. For this purpose a pressure chamber was equipped with thermoelectric temperature regulation. The non‐linear sections of the resultant PV curves were sigmoidal for both species, with recognizable points of inflexion. These points, at around ψ= 1.12 MPa and relative water content (RWC) = 88.5% forPiceaand at ψ= 0.92 MPa and RWC = 95.5% forCoffea, were characterised by a temporary increase in the resistance to water flow of the entire shoot (R5).The maximum value of the bulk modulus of elasticity (ɛ max) was also in the region of the point of inflexion. This value was considerably higher inCoffeathan inPicea. The osmotic pressures at full water saturation (π0) and at turgor loss point (πp) showed a clear temperature dependence between 15 and 35°C differing only slightly from the theoretically expected situation. At 25°C these values were 1.72 and 2.48 MPa. respectively, forPiceaand 1.58 and 1.87 MPa. respectively, forCoffea. The turgor loss point occurred at 76–77% RWC inPiceaand at 86% RWC inCoffea, the proportion of apoplastic water varied between 22 and 25% inPiceabut was only 9–10% inCoffea. The ecological differences between the two species are reflected in their temperature dependence for R5, which was much steeper forCoffeathan forPicea. The energy of activation for the water conductance of the whole shoots was 13.0–14.4 kJ mol−1inPiceaand about 23 kJ mol−1inCoffea.