How did DANA event affect water status and thermal response of fruit crops?

In recent years, associated extreme events to climate change are being experienced more frequently and with greater intensity, worldwide but particularly affecting to Mediterranean basin countries. The DANA phenomenon (Spanish acronym for depresión aislada en niveles altos, meaning upper-level isolated atmospheric depression) occurs normally in autumn due to convective storms generated by the existence of cold air in the upper layers of the atmosphere combined with warm winds coming from the Mediterranean Sea. Its effects are devastating, provoking storms of great intensity that cause violent flash-flooding and run-off with a huge capacity for soil erosion. This field experiment focuses on the effects of DANA event of 12-13 September 2019 in Southern Spain on plant water status and thermal response of nectarine trees. Two irrigation treatments were applied during the summer-autumn postharvest (DOY, Day of the year, 158-329): well-irrigated (CTL) and non-irrigated (DRY). Volumetric soil water content (θ_v), air temperature (Ta) and canopy temperature (Tc) were real-time monitored and the crop water stress index (CWSI) was calculated. Stem water potential (Ψ_stem) and leaf gas exchange were measured on representative days of the experimental period. The effects of DANA forced to disconnect the soil water content sensors, precluding to measure Ψ_stem and leaf gas exchange from DOY 255 to 275. Before DANA, withholding irrigation caused a gradual decline in soil and plant water status in the DRY treatment. Minimum values of Ψ_stem = -2.63 MPa and θ_v = 13% were obtained at DOY 246. Significant differences were obtained in the Tc, Tc-Ta, and CWSI between treatments. CWSI in the DRY treatment was maximum (0.94) at DOY 232. The effects of DANA reduced the differences between treatments in thermal data, what required to establish different baselines for CWSI calculation. In this sense, the relationship Tc-Ta vs. VPD improved the coefficient of determination after DANA (from R²=0.71*** to 0.83***) in well-irrigated trees. Similar values of Ψ_stem and leaf gas exchange were found in both treatments after DANA. Only thermal indices showed significant differences between treatments. Furthermore, the strong relationship found between Tc-Ta vs. Ψ_stem worsened after DANA event (from R²=0.81*** to 0.32*). This work underlined the robustness of infra-red thermography to continuously monitor plant water status under this type of natural weather disaster.  

 

Acknowledgements: This work was funded by Spanish Agencia Estatal de Investigación (PID2019-106226RB-C21/AEI/10.13039/501100011033). MR. Conesa thanks to the Spanish Juan de la Cierva programme (IJC2020-045450-I) funded by MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR.