Plant Biosensors Analysis for Monitoring Nectarine Water Status

The real-time monitoring of plant water status is an important issue for digital irrigation to increase water productivity. This work focused on a comparison of three biosensors that continuously evaluate plant water status: trunk microtensiometers (MTs), trunk time-domain reflectometry (TDR), and LVDT sensors. During the summer and autumn seasons (DOY 150-300), nectarine trees were subjected to four different consecutive irrigation periods based on the soil Management Allowed Deficit (MAD) concept, namely: MAD₁₀ (light deficit); MAD₅₀ (moderate deficit); MAD₁₀₀ (severe deficit), and MAD₀ (full irrigation). Measurements of stem water potential (Ψ_stem) and leaf gas exchange were recorded on representative days. A continuous measurement of the plant water status of Ψ_trunk, MDS, and K_trunk revealed the water deficits imposed on the soil. The highest water deficit observed at the end of the MAD₁₀₀ period (Ψ_stem = -2.04 MPa and Ɵ_v = 17%) resulted in a minimum value of Ψ_trunk (-1.81 MPa). The maximum value of MDS (408 µm) was observed earlier than that of Ψ_trunk, motivated by the low sensitivity of MDS at Ψ_trunk < -1.2 MPa and Ψ_stem < -1.5 MPa due to a decrease in the tissue elasticity of the trunk when severe water deficit conditions are reached. Both Ψ_trunk and Ψ_stem were more dependent on soil water content, while MDS was more responsive to environmental changes. K_trunk was the weakest indicator for determining plant water status, although when expressed as a daily fraction of depletion (K_trunkFD), it improved, evidencing a process of hysteresis. Ψ_trunk showed the highest sensitivity, suggesting the potential use of MTs as a valuable biosensor for monitoring nectarine water status in digital agrosystems.