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The water balance is one of the most important factors that regulate growth, yield and quality in trees. Seasonal variations in soil water availability and also climate change play a key role in the water status of plants. Trees developed different physiological strategies in order to cope with environmental stresses. These strategies include the functional relationship between water availability, plant water status, and water consumption, which means the amount of water that is used for transpiration. In the present study, we aimed to investigate (1) the relations between tree water deficit (TWD), transpiration and stem water potential, which both can be used as parameters describing the plant water status, and (2) the functional relationships between these plant water status parameters and the transpiration rate. To analyze differences between (a) the different tree species (Pinus sylvestris, Tilia cordata, Picea abies, Malus domestica) and (b) differences between sites with the same tree species (Pinus sylvestris), we used data from dry spells of approx. 6 weeks in early summer 2023 at 3 experimental sites and one drought experiment in the greenhouse. We hypothesized that tree water deficit closely correlates with stem water potential in all trees. Yet, that tree species show different functional relationships between transpiration rate and plant water status indicators. In each tested species, the data of tree water deficit, stem water potential, and transpiration rate were recorded by automated dendrometer (DRL26D, EMS Brno), Saturas sensor (the StemSenseTM) and sap flow sensor (SFM1, ICT international), in addition to standard climatic data including soil moisture and soil matrix potential. In the preliminary results, it is observed that the functional relationship between tree water deficit, stem water potential and transpiration correlate well with each other but the trend differs between the species. Moreover, it is found that the investigated traits also closely relate to soil and atmospheric variables. However, further research should be conducted to investigate these variables over a longer period by incorporating the wet and dry events under controlled conditions.
Hayat et al. (Fri,) studied this question.