Análogo hídrico-elétrico do caule de Phaseolus vulgaris L. com capacitância hídrica variável

Abstract

In the context of the hydric-electric analogy, hydrics capacitances are treated as constant throughout the soil-plant-atmosphere continuum (SPAC). In particular, on the stem, results from experimental studies that investigated the water storage dynamics indicate that there are variations in time in this stock and in the xylem water potential, which may influence the final capacitance values. Thus, in order to improve the performance of the hydric-electric analogues, this work had the objective of developing an electric circuit analogous to the variable hydric capacitance of the stem of Phaseolus vulgaris L. in the software QUCS (Quit Universal Circuit Simulator). For this, a non-linear device defined by equation (EDD) was used, in which the volume was expanded by a polynomial function and the capacitance defined as a function of the hydric potential variation in the stem. To calibrate the model, an experiment with weighing lysimeters adapted to small plants was developed to obtain volumetric flow data and amount of water stored in the bean stem (Phaseolus vulgaris L.). For the development of the model 3 different in silico scenarios were built with modules called PVS (Parenchyma-Vessel Element System); the first, for the simulation of variable hydric capacitance; the second, for simulate the volumetric flow of water; the third, for simulation and evaluation of cavitation. Oscillatory behavior was obtained for stem hydric capacitance, which for the plant may be one of the reflexes of stem diameter variation, which is related to the differences between transpiration and absorption rates of water at the root. For volumetric water flow, there was a high correlation between simulated and experimental data (Spearman's correlation = 0.99), with a mean absolute percentage error of 17% (MAPE) and a mean absolute error of 8.75x10-11 m³ s-1 (MAE). As for the cavitation analysis, for one same PLC value (Percentage Loss in Conductivity) the different water crossing paths interfered the final values of the flows, which may mean a dependence between the water flow in the xylem and geometry of the water pathway due to cell embolism. The results obtained in this work are similar to those obtained in the literature and potentiate the use of hydric-electric modeling as an efficient technique in the study on stem hydric dynamics.