Dynamics of soil and canopy temperature: a conceptual approach for Alentejo vineyards

Abstract

Context and purpose of the study – Climate change imposes increasing restrictions and risks to Mediterranean viticulture. Extreme heat and drought stress events are becoming more frequent which puts in risk sustainability of Mediterranean viticulture. Moreover row crops e.g. grapevine for wine, are increasingly prone to the impact of more intense/longer exposure time to heat stress. The amplified effects of soil surface energy reflectance and conductance on soil-atmosphere heat fluxes can be harmful for leaf and berry physiology. Leaf/canopy temperature is a biophysical variable with both physiological and agronomic meaning. Improved comprehension of spatial and temporal dynamics of soil and leaf/canopy temperature (thermal microclimate) in irrigated vineyards can support improved crop and soil monitoring and management under more extreme and erratic climate conditions. In this work we propose a conceptual approach to integrate information on major soil-vine-atmosphere interactions under deficit irrigation. Ultimately a conceptual model based on temperature relations is proposed to support assessment of the impact of air and soil temperatures on canopy and berry temperatures, leaf senescence and gas exchange. This model may support Decision Support Systems (DSS) for canopy and soil management and irrigation scheduling in Mediterranean vineyards. In addition a set of temperatures (e.g. canopy, soil) are proposed to feed the conceptual models to support the DSS.

Material and methods – Location & plant material: South Portugal (38º22’ N 7º33’ W); cvs Touriga N. (TOU) & Aragonez (ARA) (syn. Tempranillo), 2,200 pl/ha, 1103-P rootstock, VSP, bilateral Royat Cordon training system, N-S ORIENTATION. Sandy to silty-clay-loam soil, pH=7-7.6, low OM; Irrigation treatments: DI1 -sustained deficit irrigation strategy used by the farm consisting of an equal proportion of crop evapotranspiration (ETc) (0.28 in 2014 and 0.36 in 2015) applied along irrigation period; DI2 – similar to DI1 but with reduced volume applied (0.18 in 2014 and 0.24 in 2015). Measurements: Diurnal courses (8-20h, every 3h) of leaf water potential (ΨPD, Ψleaf), leaf gas exchange (Licor 6400, Licor, USA) and canopy TC (B20, Flir Systems, 7-13 μm, ε=0.96) and Tberry (thermocouples) were determined. Statistics: Randomized complete block design (2 irrigation treat., 4 blocks). Pearson correlations between variables (TC, ψ, gs, An), measured on the west exposed side of the canopy, and between the variables and TS, TC and Tberry were done (Statistix 9.0 software).

Results – The strong correlations between Tleaf and water status in grapevine support the parameter Tc as good predictor of plant water status (Garcia-Tejero et al. 2016; Costa et al. 2019). In parallel, TS was shown to positively influence TC especially at the cluster zone and at the warmest conditions of the day (Costa et al., 2019). Therefore, TS can used as another variable to model and predict thermal stress in vineyards. Better comprehension of thermal and water fluxes in the vineyard mat be predicted on the basis of temperature. Thermal variables such as Tair, TC, Tberry and TS can be used in models and DSS to support water and canopy management.