José M. Escalona

Effects of drought on photosynthesis in grapevines under field conditions: an evaluation of stomatal and mesophyll limitations

The effect of diffusional and photochemical limitations to photosynthesis was assessed in field-grown water-stressed grapevines (Vitis vinifera L.) by combined measurements of gas exchange and chlorophyll fluorescence. Drought was slowly induced, and the progressive decline of photosynthesis was examined in different grapevine cultivars along a continuous gradient of maximum mid-morning values of stomatal conductance (g), which were used as an integrative indicator of the water-stress conditions endured by the leaves. Initial decreases of g were accompanied by decreases of substomatal CO2 concentration (Ci), the estimated chloroplastic CO2 concentration (Cc) and net photosynthesis (AN), while electron transport rate (ETR) remained unaffected. With increasing drought, g, AN, Ci and Cc further decreased, accompanied by slight decreases of ETR and of the estimated mesophyll conductance (gmes). Severe drought led to strong reductions of both g and gmes, as well as of ETR. The apparent carboxylation efficiency and the compensation point for CO2 remained unchanged under severe drought when analysed on a Cc, rather than a Ci, basis, suggesting that previously reported metabolic impairment was probably due to decreased gmes.

A ten-year study on the physiology of two Spanish grapevine cultivars under field conditions: effects of water availability from leaf photosynthesis to grape yield and quality

The effects of moderate irrigation, compared with non-irrigation, on leaf photosynthesis and transpiration, grape yield, and quality parameters, were studied over ten years in two Spanish cultivars (Tempranillo and Manto Negro) of field-grown grapevines (Vitis vinifera L.). The aim was to increase our knowledge of the relationships between water availability, canopy water losses, photosynthesis, and fruit yield and quality. A second aim was to analyse some of the mechanisms of photosynthetic down-regulation under drought, such as the capacity for RuBP regeneration and Rubisco activity.Moderate irrigation improved plant water status, leaf photosynthesis and transpiration. Considering the results over ten years, soil water availability (estimated as pre-dawn leaf water potential, ΨPD) largely determined leaf photosynthesis and leaf transpiration. Decreased photosynthesis was due to both stomatal and non-stomatal factors. The latter were related to decayed electron transport rate and reduced RuBP regeneration capacity, but not to decreased Rubisco activity.Moderate irrigation also improved grape yield, although this effect was much larger in Tempranillo than in Manto Negro. Moreover, the correlation between photosynthesis and grape yield was significant in Tempranillo, but not in Manto Negro. In contrast, the correlation between ΨPD and several parameters reflecting fruit quality (such as soluble solids and total polyphenol content) was significant only in Manto Negro. These results suggest that there is a close link between water availability and grape yield, mostly through water stress effects on photosynthesis. Drought effects on grape quality are linked to water availability but not to photosynthesis or yield.

Effects of drought on light-energy dissipation mechanisms in high-light-acclimated, field-grown grapevines

The response of several light-energy dissipation mechanisms to water shortage was analysed in a 10-year study in field-grown, high-light-acclimated grapevines, and compared with those of greenhouse-grown, low-light-acclimated grapevines. Dissipation mechanisms, except leaf photochemistry, differ among cultivars and acclimate to the prevailing light conditions during growth. However, no additional acclimation to drought was observed. The dependence of the dissipation responses on stomatal conductance suggests that low CO2 availability in the chloroplasts during drought triggers variations in the energy dissipation pattern. In irrigated grapevines under high light, more than 50% of total absorbed energy is thermally dissipated. There is evidence that implicates the xanthophyll cycle as the main thermal dissipation processes. CO2 assimilation is the most important photochemical pathway of dissipation in irrigated plants, but is replaced by photorespiration when CO2 assimilation declines under mild drought. Under moderate to severe drought, both photosynthesis and photorespiration decline, and thermal dissipation increases to account for up to 90% of total dissipation. Involvement of other processes in light dissipation is minimal in grapevines. Even in severely-stressed leaves, the incidence of photoinhibition is very low, indicating that safe dissipation of absorbed energy is very effective in grapevines.

Plasticity of vulnerability to leaf hydraulic dysfunction during acclimation to drought in grapevines: an osmotic-mediated process

Previous studies have reported correlation of leaf hydraulic vulnerability with pressure-volume parameters related to cell turgor. This link has been explained on the basis of the effects of turgor on connectivity among cells and tissue structural integrity, which affect leaf water transport. In this study, we tested the hypothesis that osmotic adjustment to water stress would shift the leaf vulnerability curve toward more negative water potential (Ψ leaf ) by increasing turgor at low Ψ leaf . We measured leaf hydraulic conductance (K leaf ), K leaf vulnerability [50 and 80% loss of K leaf (P50 and P80 ); |Ψ leaf | at 50 and 80% loss of K leaf , respectively), bulk leaf water relations, leaf gas exchange and sap flow in two Vitis vinifera cultivars (Tempranillo and Grenache), under two water treatments. We found that P50 , P80 and maximum K leaf decreased seasonally by more than 20% in both cultivars and watering treatments. However, K leaf at 2 MPa increased threefold, while osmotic potential at full turgor and turgor loss point decreased. Our results indicate that leaf resistance to hydraulic dysfunction is seasonally plastic, and this plasticity may be mediated by osmotic adjustment.

Exploring the genetic variability in water use efficiency: Evaluation of inter and intra cultivar genetic diversity in grapevines

Genetic improvement of crop Water Use Efficiency (WUE) is a general goal because the increasing water scarcity and the trend to a more sustainable agriculture. For grapevines, this subject is relevant and need an urgent response because their wide distribution in semi-arid areas. New cultivars are difficult to introduce in viticulture due to the narrow dependency of consumer appreciation often linked to a certain particular wine taste. Clones of reputed cultivars would presumably be more accepted but little is known on the intra-cultivar genetic variability of the WUE. The present work compares, on the basis of two field assays, the variability of intrinsic water use efficiency (WUEi) in a large collection of cultivars in contrast with a collection of clones of Tempranillo cultivar. The results show that clonal variability of WUEi was around 80% of the inter-cultivar, thus providing a first assessment on the opportunity for clonal selection by WUE. Plotting the WUEi data against stem water potential or stomatal conductance it was possible to identify cultivars and clones out of the confidence intervals of this linear regression thus with significantly higher and lower WUEi values. The present results contribute to open the expectative for a genetic improvement of grapevine WUE.

Water Stress Effects on Variations of Steady-State Chlorophyll Fluorescence (Fs) in Response to Light

Diurnal time course of steady-state chlorophyll fluorescence (Fs) has been shown to be an interesting tool for water-stress assessment in potted plants (1, 2, 3). Irrigated plants showed an increase of Fs in response to light intensity. The estimated electron transport rate (ETR) and non-photochemical dissipation (NPQ) also showed a positive response to light under such conditions. Water-stressed plants, however, presented a negative correlation between Fs and light intensity, together with a higher increase in NPQ. ETR was maintained almost constant or slightly reduced under such conditions. The aim of the present work is to extent the experimental basis of this approach to field measurements and to hypothesise about the causes of this phenomenon.

Leaf growth rate and nitrogen content determine respiratory costs during leaf expansion in grapevines

Respiration processes are well recognized as fundamental for the plant carbon balance, but little attention has been paid to the relationships among respiration rates, environment and genetic variability. This can be of particular interest to understand the differences in net carbon balances in crops as grapevines. Night respiration (Rn ) and its associated growth (Rg ) and maintenance (Rm ) components were evaluated during leaf expansion in two grapevine cultivars (Tempranillo cv. and Garnacha cv.) that differ in their plant growth pattern and carbon balance. Simultaneously, leaf traits as leaf mass area, nitrogen (N) and carbon (C) content were evaluated in order to relate to the respiratory processes and the leaf growth. The results showed the differences in respiration rates associated with the leaf expansion pattern. Tempranillo developed leaves with higher leaf area and lower dry weight per leaf unit than Garnacha. Although differences between cultivars were observed in terms of growth costs in expanding leaves, the maintenance costs were similar for both cultivars. Also, a significant linear regression was found between respiration rates and N content in expanding and mature leaves. The results indicate that differences in structure and nitrogen content of expanding leaves may lead to respiratory differences between cultivars. These results also demonstrate the importance of respiratory cost components in carbon balance calculations in grapevines.

Genetic Improvement of Grapevine (Vitis vinifera L.) Water Use Efficiency: Variability Among Varieties and Clones

Abstract Grapevine crop for wine is widely spread in semiarid areas where irrigation is used as a compromise for environmental sustainability and soil water availability, which is a serious limitation for yield. The improvement of water use efficiency (WUE) is a general objective for these areas, which can be largely attained by tight control of irrigation dosage and scheduling, but also by selecting cultivars with lower watering requirements. In this context, the generic improvement of grapevine WUE is a main goal to reinforce the sustainability of this crop. Genetic variability in grapevine is known to be large, as supported by the large number of cultivars and accessions around the world. However, the genetic improvement of WUE is not an easy subject, according to experience in other crops. Previous field and pot experiments showed a wide variability of intrinsic leaf WUE among grapevine cultivars. Moreover, it was demonstrated that a wide variability exists inside cultivars of the Tempranillo variety. Nowadays, there is increasing information on the genomic basis of characters related with improved resistance to water stress, highly related to WUE. This chapter shows that genetic improvement of WUE seems to be promising for grapevines to increase the sustainability of this crop in semiarid areas.

Efectos de cambio climático en el comportamiento de variedades tintas de Mallorca

En los #x00FA;ltimos cincuenta anos se ha producido un incremento de las temperaturas medias y una modificaci on del regimen de precipitacion como consecuencia del Cambio climatico. Ademas, las previsiones climaticas a futuro indican que los periodos de sequia extrema y aridez seran cada vez mas frecuentes asociadas a incrementos progresivos de la temperatura. La cuenca mediterranea es un area de especial vulnerabilidad frente al cambio climatico. En este escenario, se ha comprobado que la vid modifica su comportamiento. Numerosos estudios indican un efecto en la fenologia, con brotaciones mas tempranas, acortamiento de los ciclos de maduracion y un retraso en la finalizacion del ciclo vegetativo. Ademas, se esta produciendo un cambio en la composicion de la uva y de los vinos producidos, que comprometen la identidad de los productos. Todo ello, compromete la definicion de Terruno y la tipicidad de los productos de las regiones viticolas. En Mallorca, la actividad viticola y la produccion de vinos tiene una extensa historia. En la actualidad conviven variedades locales con variedades foraneas. Hasta ahora no se han realizado estudios de los efectos del cambio climatico en el comportamiento de estas variedades en las condiciones particulares de la Isla. Por ello, este trabajo pretende aportar nuevos conocimientos sobre dichos efectos, Los resultados muestran que en los ultimos 50 anos se ha producido un incremento de 1,5 oC en la temperatura media anual y se han repetido periodos de sequia cada vez mas prolongados en el tiempo. Como consecuencia, se ha producido un incremento significativo de la concentracion de azucares del mosto y, por ende, de la graduacion de los vinos. Por otra parte, se han adelantado las vendimias sobre todo en variedades de ciclo medio y largo de maduracion. De todas las variedades estudiadas, la variedad local Manto Negro es la que ha mostrado una mayor capacidad de adaptacion a las nuevas condiciones climaticas.