Plant water stress derived indexes from water potential and diameter fluctuations measurements

This work addresses the comparison between plant water status indicators from trunk diameter fluctuations measured with LVDT sensors and novel trunk microtensiometers (MTs). During the postharvest of 2022 (Day of the year, DOY, 160-350), nectarine trees were subjected to different irrigation protocols based on soil maximum allowed depletion (MAD), automatically managed by real-time soil water content values measured by capacitance probes. Three percentages of depletion of available soil water ($\alpha$) were imposed: (i) $\alpha=$10% (well-irrigated); (ii) $\alpha=$50% (moderate deficit) and (iii) $\alpha=$100%, irrigation withheld until stem water potential $(\Psi_{stem})$ reached −2.0MPa. Thereafter, irrigation was recovered to full crop water requirements. From both LVDT and MTs, real-time data, the following trunk indexes were calculated: MDS (maximum daily shrinkage, i.e. difference between the daily maximum and minimum trunk diameter), EDS (early morning daily shrinkage, from 09:00 h to midday) and LDS (late daily shrinkage, from midday to 16:00 h). The results showed that EDS was more sensitive to water deficits than MDS, and higher with MTs than LVDT. Our findings suggested the potential use of trunk microtensiometer as a valuable biosensor for monitoring the water status of nectarine trees, being the highest sensitivity in the range when EDS was calculated.