During the growing seasons, from April to September, the site received 23.2% of the total precipitation in 2020 and only 2.1% in 2021 . In addition, there was minimal precipitation during data collection of this study from June to September, where only 2 mm and 1.2 mm of precipitation were received in 2020 and 2021. As for the air temperature during the growing seasons, the average maximum air temperature was slightly higher in July, August, and September in 2020 compared to 2021, but lower in March and April. The average minimum air temperature was constantly higher in 2020 compared to 2021 from March until harvest in September, except July. Similarly, the average air temperature was generally higher in 2020 than 2021 except both Julys which had the same average air temperature. As for GDD accumulation , the two seasons were slightly different. In 2020, there was 1525.4°C GDD accumulated when the berries reached 23.9°Brix on average; in 2021, there was 1292.3°C GDD accumulated when the berries reached 22.6°Brix on average. Thus, 2020 was a slightly drier and hotter season than 2021.LAI and crown porosity were assessed in both seasons, and leaf areas were calculated based on the unit ground area and LAI . In 2020, VSP80 had the most leaf area among the six trellis systems, VSP60 and GY had similar leaf areas, 25 liter pot followed by VSP . SH and HQ had the lowest leaf areas as the canopies in these two trellises still had gaps.
This was also confirmed with the fact that SH and HQ had the highest crown porosities among the six trellis systems . The other trellis systems had similar lower crown porosities than SH and HQ. There was no difference in canopy architecture among the three irrigation regimes in the first season . In 2021, all the trellis systems had similar leaf areas . HQ had higher crown porosity than VSP60, but the other trellis systems had similar crown porosities to either HQ or VSP60 . These effects were not modified by the irrigation treatments and no significant interactions between factors were found. For applied water amounts, 50% ETc had higher leaf area than 25% ETc, but there was no difference between 100% ETc with either 25% or 50% . However, 50% ETc still had the highest crown porosity compared to 100% ETc, and 25% ETc did not show any difference with the other two irrigation treatments .Grapevine leaf gas exchange was monitored throughout both seasons, and their integrals were calculated to represent the season-long plant response of grapevines for net carbon assimilation rate , stomatal conductance , and intrinsic water use efficiency . In 2020, there were no differences in gs and An among the six trellis systems . However, HQ had the highest WUEi, whereas VSP, VSP60, and SH had lower WUEi .
Regarding the irrigation treatments, there was no difference in gs integrals . However, a linear response to water amounts were observed for An and WUEi, with 100% ETc having the highest values of both gas exchange variable monitored .In 2021, there were no differences in gs, An, and WUEi among the six trellis systems . Nevertheless, a linear response to water amounts was recorded, with 100% ETc showing the highest An and gs, followed by 50% ETc, and 25% ETc which accounted for a higher WUEi in 25% ETc with 50% treatments compared with 100% ETc . The analysis of the gas exchange recorded at each measurement day indicated that in 2020, despite starting with the highest gs, SH had lower gs over the season . Contrarily, HQ trellis system showed higher gs in July and August which was connected with higher An over the season . On the other hand, GY and VSP80 systems enhanced An during some periods over the season. Regarding WUEi, VSP60 and HQ had the highest values while SH decreased it in the early season and increased it in early August . However, all these differences tended to diminish at the end of the season. For irrigation treatments, a constant effect of water amount was observed with 100% ETc increasing gs and An and decreasing WUEi . In 2021, GY and VSP60 showed higher gs and An values in general . HQ showed lower gs values and VSP had lower An values compared to the other trellis systems throughout the season. HQ increased WUEi throughout the whole season . Although GY had higher WUEi in the early season, it showed constantly lower WUEi values after 23 June 2021.
Besides GY, VSP showed lower WUEi in July and August. A similar effect of irrigation treatments was observed over the second season, with a linear response for increased gs and An and decreased WUEi when the irrigation water amount was increased .Yield components and berry quality parameters were assessed at harvest in both seasons . SH and HQ had the smallest berries among the six trellis systems in the two seasons. In 2020, SH and VSP increased the cluster number, while VSP80 and GY decreased it whereas, in 2021, SH and HQ accounted for increased the cluster number. VSP, VSP60, VSP80, and GY increased the cluster weight compared to SH in 2020. In 2021, SH showed the lowest cluster weight and skin weight. Regarding yield, differences were only significant in 2020 where SH enhanced vine yield compared to the other trellis systems. On the other hand, 100% ETc enhanced berry weight, cluster weight, and yield over the two seasons with no difference on leaf area to fruit ratio. Regarding berry quality parameters, SH had the highest TSS among and the lowest pH in 2020, whereas in 2021, VSPs and GY enhanced the TSS and the pH. Results also showed that irrigation treatments had little effect on the berry quality parameters over the two seasons with only TSS being increased in the 25% ETc treatment in the harvest of 2020.Different trellis systems affected not only the total anthocyanin concentration but also modified the anthocyanin composition, leading to modifications in the profile stability. In both seasons, SH had the highest concentrations in all the anthocyanin derivatives besides di- and tri-hydroxylated anthocyanins among the six trellis systems. In 2021, HQ also notably increased most of the anthocyanin derivatives, tri-hydroxylated, di-hydroxylated, and total anthocyanins compared to the VSP trellis systems. On the other hand, VSP trellis systems tended to decrease the anthocyanin concentrations. Regarding the irrigation treatments, 25% ETc generally showed the higher concentrations in petunidins, di- and tri-hydroxylated anthocyanins, and total anthocyanins in 2020 compared to 100% ETc. In 2021, 25% ETc increase most of the anthocyanin concentration in berries. 50% ETc performed similarly in 2021 and showed higher concentrations in malvidins, trihydroxylated anthocyanins, and total anthocyanins. In parallel with anthocyanin assessments, berry skin flavonols were measured at harvest in both seasons . In 2020, SH showed the highest concentration in myricetins. SH and HQ showed the highest concentrations in quercetins, isorhamnetins and kaempferols in both seasons. SH and HQ also showed the highest concentration in tri- and di-hydroxylated as well as total flavonols in both seasons. In 2020, there were no differences among the six trellis systems in laricetins and syringetins. While in 2021, VSPs enhanced syringetin concentration. Regarding applied water amounts, raspberry cultivation pot little effects of irrigation treatments were shown in 2020. However, in 2021, 25% ETc increased most of the flavonol derivatives except laricetins and syringetins compared to the other two treatments.The relationships between berry skin flavonol concentrations and canopy architecture were investigated in both seasons. In 2020, crown porosity had positive and significant correlations with quercetin , total flavonol concentration , R2 = 0.248, p< 0.0001, Figure 5Aa-2), and total flavonol concentration . Leaf area was also correlated with these variables, but the correlations were negative with quercetin , total flavonol concentration . In 2021, the correlations were similar but not as significant as 2020. Crown porosity still had significant and positive relationships with quercetin and total flavonols concentration . However, the relationship between crown porosity and total flavonol concentration did not persist, as was observed in 2020. The relationships between leaf area and quercetin and total flavonol concentration were significant, although not as strong . Leaf areas were negatively correlated with these two variables . The significant correlation between leaf area and total flavonol concentration did not hold in 2020 as compared to 2020 .
It was evident that when crown porosity was greater, there was greater flavonol accumulation as well greater molar percentage of quercetin.A trellis system selected in grapevine vineyard is usually aimed at optimizing canopy architecture to further maximize canopy photosynthetic activity and improve canopy microclimate, which can yield desirable production and berry composition . In historically cooler regions according to Winkler’s Index, VSPtrellis system is widely used as it offers relatively higher compatibility with mechanization and is suitable for the regional production goals . However, with the warming trend in air temperature getting more pronounced, VSPs have been showing greater chances of getting cluster overexposure, resulting in sunburnt berries with yield loss and color degradation . Under our experimental conditions, HQ trellis system showed less leaf area and greater crown porosity than the other trellis systems in 2020 in accordance with previous studies, where split trellis designs might allow more solar radiation to penetrate the canopy interior . Conversely, SH had similar leaf area but lower crown porosity in 2020. However, the differences in leaf areas and crown porosities were not as noticeable in 2021. This could be attributed to the fact that the HQ and SH might have still been filling up spaces with new growth compared to the VSPs, which might have already had relatively more established canopy architectures. In addition, the differences in leaf areas and crown porosities could be minimized by arid growing season in 2021, despite the supplemental irrigation applied to them, accounting for diminished leaf areas as shown in 2021 than 2020. Furthermore, precipitation received at the vineyard prior to bud break , as well as precipitation received immediately prior to flowering in semi-arid regions were deemed key determinants of canopy response for latter parts of the growing season.In this study, yield per vine was not constantly determined by the trellis systems in both years, although similar bud densities at pruning were achieved. Furthermore, more leaf area did not account for more yield at harvest, despite it was well established that a sufficient leaf area would support fruit development , and in contrast with some previous studies . This could be attributed to not only the total amount leaf area but also how the leaves were distributed within the canopy. Commonly, HQ would have more open space to distribute more exposed and photosynthetically active leaves to the sunlight to optimize production . Previous studies have shown that greater leaf area can also contribute to higher TSS accumulation , which was not observed in this study. On the contrary, more leaf area resulted in less TSS accumulation. This might be explained by the fact that the leaf area to fruit ratio, which represented the source-sink balance within the grapevine, might have a greater influence on the berry TSS accumulation. In this study, even though no statistical differences were observed in leaf area to fruit ratio, SH in 2020 showed relatively higher values with higher TSS accumulated at harvest. A similar situation was observed during the second season, where VSP80 showed relatively higher leaf area to fruit ratio and subsequently higher TSS at harvest. When crown porosity was considered, higher porosity resulted in greater TSS accumulation in berries, which could be attributed to the higher potential of berry exposure to the hot environment, causing the berries to experience greater dehydration . This relationship was not observed in 2021, and it might be derived from the relatively higher crop load and lower leaf area to fruit ratio in 2021 compared to 2020, especially by SH and HQ . SH and HQ did not have a similar source-sink balance as 2020, which lowered their capacity to translocate photosynthates into the berries, this might have been the reason why they had a more reduced TSS at harvest compared to the other trellis systems. Regarding the applied water amounts, the results were clear and consistent, with increased water status in grapevines irrigated with higher water amounts, and consequently, greater berry weight, cluster weight, and yield.