Maria Clara Merli

An Improved Multichamber Gas Exchange System for Determining Whole-Canopy Water-Use Efficiency in Grapevine

A multichamber whole-canopy gas exchange system coupled with an automatic pot weighing device was tested for continuous 24 hr recording over 50 days in a trial comparing cv. Sangiovese vines subjected to progressive reduction of total transpiration water supply to well-watered vines. The system ran smoothly under regular maintenance for the entire period and gravimetric vine water loss was highly correlated with chamber-derived vine transpiration (r = 0.95) for data pooled over treatments. Seasonal and diurnal whole-canopy net CO2 exchange rate (NCER) and transpiration (Tc) showed that supplying 50% and 30% of daily gravimetric vine water loss (Tg) consistently corresponded to a NCER more than proportionally limited as compared to Tc, hence leading to lower canopy water-use efficiency (WUE) expressed as NCER/Tc ratio. Conversely, canopy WUE did not differ between treatments at 70% Tg restitution and rewatering. Similarly, during the most limiting water supply periods, the WUE difference between treatments was greatly reduced during cloudy days with lower vapor pressure deficit and higher diffuse-to-direct light intensity ratio. Data sets taken over different time frames on whole-canopy WUE provide a scenario different from that which might derive from traditional single-leaf assessment, reporting in almost all cases that intrinsic WUE increases under stress and suggests that the methodology used can mask or alter conclusions about adaptive response of grapevine cultivars to water stress.

Water use efficiency in Sangiovese grapes (Vitis vinifera L.) subjected to water stress before veraison: different levels of assessment lead to different conclusions

Several recent papers have shown that in grapevine (Vitis vinifera L.), interpretation of responses to drought can differ depending upon the parameter chosen to express water use efficiency (WUE). In the present paper, a series of WUE expressions, including physiological and agronomical, were compared in potted grapevines (Vitis vinifera L. cv. Sangiovese) that were either well-watered (WW) or subjected to progressive drought before veraison (WS) by supplying decreasing fractions (i.e. 70%, 50% and 30% of daily vine transpiration (Trd) determined gravimetrically before vines were fully rewatered. Although single-leaf intrinsic and instantaneous WUE increased with water stress severity, seasonal and whole-canopy WUE were similar to that before stress, at 70% Trd and upon rewatering, but dropped during severe water stress. WUE calculated as mass of DW stored in annual biomass (leaves, canes and bunches) per litre of water used did not differ on a seasonal basis, whereas WS plants showed lower must soluble solids at harvest, and unchanged colour and phenolic concentration in spite of smaller berries with higher relative skin growth. Results confirm that whole-canopy WUE is a much better index than any single-leaf based WUE parameter for extrapolation to agronomic WUE and actual grape composition. In our specific case study, it can be recommended that water supply to drought-stressed Sangiovese grapevines before veraison should not be lower than 70% of daily vine water use.

MECS-VINE®: A New Proximal Sensor for Segmented Mapping of Vigor and Yield Parameters on Vineyard Rows

Ground-based proximal sensing of vineyard features is gaining interest due to its ability to serve in even quite small plots with the advantage of being conducted concurrently with normal vineyard practices (i.e., spraying, pruning or soil tilling) with no dependence upon weather conditions, external services or law-imposed limitations. The purpose of the present work was to test performance of the new terrestrial multi-sensor MECS-VINE® in terms of reliability and degree of correlation with several canopy growth and yield parameters in the grapevine. MECS-VINE®, once conveniently positioned in front of the tractor, can provide simultaneous assessment of growth features and microclimate of specific canopy sections of the two adjacent row sides. MECS-VINE® integrates a series of microclimate sensors (air relative humidity, air and surface temperature) with two (left and right) matrix-based optical RGB imaging sensors and a related algorithm, termed Canoyct). MECS-VINE® was run five times along the season in a mature cv. Barbera vineyard and a Canopy Index (CI, pure number varying from 0 to 1000), calculated through its built-in algorithm, validated vs. canopy structure parameters (i.e., leaf layer number, fractions of canopy gaps and interior leaves) derived from point quadrat analysis. Results showed that CI was highly correlated vs. any canopy parameter at any date, although the closest relationships were found for CI vs. fraction of canopy gaps (R2 = 0.97) and leaf layer number (R2 = 0.97) for data pooled over 24 test vines. While correlations against canopy light interception and total lateral leaf area were still unsatisfactory, a good correlation was found vs. cluster and berry weight (R2 = 0.76 and 0.71, respectively) suggesting a good potential also for yield estimates. Besides the quite satisfactory calibration provided, main improvements of MECS-VINE® usage versus other current equipment are: (i) MECS-VINE® delivers a segmented evaluation of the canopy up to 15 different sectors, therefore allowing to differentiate canopy structure and density at specific and crucial canopy segments (i.e., basal part where clusters are located) and (ii) the sensor is optimized to work at any time of the day with any weather condition without the need of any supplemental lighting system.