Calibration and evaluation of a STELLA software-based daily CO2 balance model in Vitis vinifera L

This paper describes and evaluates the reliability of a model for prediction of daily carbon balance and dry matter (DM) accumulation in vertically shoot positioned grapevine (Vitis vinifera L.) canopies based on the user-friendly STELLA simulation software. Validation of the model was produced for potted 'Cabernet Sauvignon' grapevines at both low canopy density [LD (≈10 shoots/m of row)] and high canopy density [HD (≈20 shoots/m of row)] by comparing, on a seasonal basis, the modelled daily CO2 balance with the diurnal net carbon exchange rate (NCER) measured using a whole-canopy enclosure method. Estimated daily total photosynthesis (Pn) was linearly correlated with measured NCER for LD (r2 = 0.87) and HD (r2 = 0.86), thereby indicating that despite its simplicity the model led to a fairly good degree of precision, although it tended to slightly underestimate (5% to 8% less) the measured rates and scattering increased at high values of CO2 fixations. Daily total respiration (R) for LD treatment was 29.0% of total daily Pn, with clusters, leaves and stems accounting for 11.8%, 46.7%, and 41.5%, respectively. Daily total R was 24.2% of total daily Pn in HD treatment and single organs contributed 22.3% (clusters), 41.6% (leaves), and 36.1% (stems). The model estimated that 1604 and 1893 g DM per vine accumulated at harvest for LD and HD treatment, respectively, whereas destructive sampling of leaves, stems and clusters yielded 1475 ± 64 g per vine for LD treatment and 1730 ± 96 g per vine for HD treatment, respectively, corresponding to the 91% and 92% of the DM estimated with STELLA, which in its present version does not take into account root respiration.