Grape berry transpiration is considered an important process during maturation, but scientific evidence is scarce. In the literature, there is only one report showing reduced maturation when bunch transpiration is artificially slowed down. Traditionally, grape berry transpiration has been measured by weighing grape berries on scale for a given time, correctly assuming that the weight reduction is due to water lost. Commercially available instruments adequate to measure gas exchange in small fruits are not suitable for whole grape berry bunch. Here, we present an open differential chamber system that can be used with isolated grape berries or alternatively with a whole grape berry bunch for measuring grape berry/bunch transpiration based on the use of relative humidity sensors from Vaisala. When used with isolated grape berries, open differential chamber system validation was made by using Tempranillo grape berries collected at different phenological stages. For the whole bunch transpiration prototype, two different validations were made. Firstly, measurements were made inserting inside the chamber an increasing number of Eppendorf tubes filled with water. Secondly, transpiration was measured in whole Tempranillo bunches sampled at different phenological stages. An important output of this work is that the fact of detaching the bunch from the plant did not change the bunch gas exchange rates at least for several hours. For validations, transpiration values obtained with our prototype were compared with water losses inferred from grape berry weighing on scale for a given time, obtaining highly significant correlations. We tested the system applying to the bunch an anti-transpirant, confirming that the anti-transpirant application reduced bunch transpiration and delayed maturity.

In the Mediterranean area, climate change is associated with atmospheric CO2 concentration increases, enhanced temperatures and scarce water availability, limiting seriously crop yield and decreasing quality. The aim of this study was to investigate the effects of elevated CO2, elevated temperature and water deficit, acting individually and/or interacting, on vegetative and reproductive growth, substrate and plant water status, and must quality in fruit-bearing cuttings of two grapevine (Vitis vinifera L.) cultivars (red and white Tempranillo). In four temperature gradient greenhouses, eight treatments were applied, from fruit set to maturity: CO2 level (400 versus 700 ¿mol mol¿1), temperature (ambient versus ambient +4 °C), and water availability (full irrigation versus cyclic drought). Effects of climate change on grape yield and quality were cultivar dependent. Generally, red Tempranillo had more vegetative growth and grape yield than the white cultivar. Also, grape yield was less affected by the treatments than vegetative growth. Drought, especially under elevated temperature, drastically reduced vegetative growth, bunch fresh and dry weights in both cultivars. Interestingly, elevated CO2 attenuated these negative effects of drought. The effects of climatic factors on yield were not associated with a worse water status of the vegetative or reproductive organs. In red Tempranillo, the combination of elevated CO2, elevated temperature and drought reduced total polyphenol index (TPI), malic acid and increased color density, but did not modify anthocyanin concentration. In white Tempranillo, the combined action of the three factors associated with climate change modified only tartaric acid. In this latter cultivar, drought increased TPI under ambient temperature, regardless of CO2 level, when compared with full-irrigated plants. In conclusion, climate change-related factors (elevated CO2, elevated temperature and water deficit) individually (especially drought) and/or interacting affected to different extent red and white Tempranillo vegetative growth and yield. Drought combined with elevated temperatures reduced grapevine performance, and elevated CO2 mitigated such deleterious effect.