Evapotranspiration Dynamics and Partitioning in a Grassed Vineyard: Ecophysiological and Computational Modeling Approaches

Plenty of information on evapotranspiration (ET) dynamics and partitioning into nonbiological (evaporation, E) and biological (transpiration, T) components is available in literature. However, in agro-ecosystems where more than one vegetation group is found, like intercropping or grassed orchards and vineyards, it is of great use to understand the contribution to T due to the single plant type or group of plants. We deployed empirical and modeling methods to study the ecosystem evapotranspiration (ETEC) components in a grassed vineyard in Caldaro (Italy) aiming to assess (a) which process, E or T, had greater influence on ETEC dynamics; (b) which component among grapevines and understorey portion dominated the ETEC; and (c) how rainfall influences ETEC components. A top-down approach combined the eddy covariance method to estimate ETEC, and the Transpiration Estimation Algorithm method to partition it. A bottom-up approach integrated the understorey evapotranspiration (ETu) with modeled vines transpiration (Tv((mod))). Measured and modeled fluxes showed high daily variability, consistently with meteorological conditions (vapor pressure deficit, Rn and Tair). The mean daily ETEC integrals were 3.45 and 3.40 mm d(-1) (2021 and 2022), being T-EC (estimated transpiration fraction of ETEC) the higher contributor (T-EC/ETEC of 0.77 and 0.79, same years). From the bottom-up approach, ETu assessed during ground flux chamber campaigns (0.74-1.65 mm d(-1)) was lower than Tv((mod)). A high agreement (R-2 = 0.85) was found between the eddy covariance ET hourly values and ET by summing Tv((mod)) and ETu. We concluded that the T process represented major fluxes in the agroecosystem during the warm season. Furthermore, the bottom-up approach indicated the vines as primary contributors to ecosystem T, particularly noticeable after rainfall, as the understorey T fraction (Tu) increased when the system became drier. This study helps disentangling grapevine contribution to evapotranspiration from adjacent herbaceous vegetation in a vineyard, and emphasizes the dominance of biologically mediated transpiration influenced by meteorological conditions. This novel combination of approaches not only enhances understanding of Mediterranean viticulture but also illuminates broader applications in sparsely vegetated environments, such as agroforestry systems and orchards, advancing ecological management practices.