Background and Aims Measuring the carbon assimilation and respiration during vine phenology can provide an understanding of the dynamics of carbon fluxes from different organs and their relationship. Most field studies to date do not consider the respiratory losses of different plant organs and their variability under environmental, genetic and phenological changes. The aim of this study was to investigate the effect of genotype and water regime on carbon assimilation, respiration and allocation during vine phenology. Methods and Results Field trials were carried out during 2013 and 2014 to study the effect of genotype and water status on carbon assimilation, respiratory losses from leaves, shoots, fruits and roots during the vine phenological cycle, and on biomass production. Carbon respiration varied during plant phenology and represented a significant proportion of the total vine carbon assimilation. The integrated carbon respiratory loss in leaves, fruits and roots was greater in irrigated vines than in non-irrigated vines. Tempranillo recorded the highest carbon assimilation, leaf and stem respiration, as well as the highest above-ground biomass. Garnacha showed a higher root respiration loss and allocated more biomass to the permanent organs. Accumulation of above-ground biomass was influenced by plant carbon budgets during the growing season. Conclusions Vine phenology, cultivar and plant water status affected carbon assimilation, carbon loss and carbon allocation. Non-irrigated vines had a higher respiratory carbon loss in respect to the total carbon assimilation by photosynthesis. Above- and below-ground carbon fluxes were coupled during vine phenology. Significance of the Study The present work illustrates the importance of respiratory processes on the carbon balance and the relationship among different carbon balance components during vine phenology.

Grapevine water use efficiency (WUE) is becoming a key issue in semi-arid areas as the production and quality of a harvest largely depends on the use of important water volumes in areas that are typically characterised by water scarcity during the grapevine growing season. Therefore, improving water use efficiency is a challenge to secure the environmental sustainability of viticulture in these areas. WUE is commonly measured at the leaf level because portable equipment of leaf gas exchange rates facilitates the simultaneous measurement of photosynthesis and transpiration. However, when those measurements are compared to the daily integrals or whole plant estimations, the relationship sometimes results in high and sometimes in low correspondence. Scaling up from single leaf to whole plant WUE was attempted by comparing daily integrals of AN/E with midday values, showing a poor relationship that impoverished as water stress intensified. The main objective of the present work was to evaluate the importance of the spatial and time variations of carbon and water balances at the leaf and plant level. The leaf position inside the canopy showed a marked effect on the instantaneous and daily integrals of leaf WUE. The night transpiration and respiration rates were also evaluated, as were the shoot and root respiration contributions to the total carbon balances. Two main components were identified to solve the gap between leaf and whole plant WUE, the important effect of leaf position on the daily carbon gain and transpiration and the large flux of carbon losses by dark respiration. Moreover, these results also showed the importance of some as yet unexplored targets to improve the WUE in grapevines.

Background and Aims: An understanding of spatial variation in soil respiration is critical to determining the carbon balance in grapevines. The effect of soil water content on soil respiration during different phenological stages in two grapevine cultivars, Grenache and Tempranillo, was studied over two seasons (2013 and 2014).Methods and Results: Soil respiration was measured from five locations confined to within and between rows of vines at five phenological stages between budburst and postharvest under irrigated and non-irrigated conditions. Vine phenology influenced the in-row soil CO2 efflux to a greater extent than the between-row CO2 efflux, while irrigation resulted in in-row soil respiration 65% higher than that of the between-row positions. In contrast, the flux from the in-row positions of the non-irrigated treatment was only 25% higher than that of the between-row positions. Soil moisture and vine phenological stages appeared to have a greater influence on soil respiration than soil temperature.Conclusions: Significant correlations existed among soil respiration, irrigation and the vine phenological stages. Soil respiration increased from budburst to pea-size berry stage; thereafter, it decreased until the ripening stage before increasing again during the postharvest stage.Significance of the Study: The study showed that soil water availability and vine phenology play an important role in influencing soil respiration under field conditions.

The effect of water stress on photosynthesis and transpiration has been largely studied in the past. However, there is a lack of research on water stress effects on root respiration and vine carbon balance even though the importance of root respiration on the final carbon balance has been clearly shown. An experiment was carried out during 2013 to determine the effect of different levels of water availability on root respiration and plant carbon balance on two important grapevine cultivars ('Grenache' and 'Tempranillo'). Two irrigation treatments were established (moderate irrigation and drought or rain-fed). Root respiration and soil water content were measured at different phenological stages and different soil positions from each vine monitored. Results showed that root respiration rates for 'Tempranillo' and 'Grenache' were higher in the initial growth stages, with 'Tempranillo' exhibiting the highest levels. A decline in respiration rates was observed in both cultivars and treatments at veraison. Soil moisture heterogeneity around the irrigated vines determined changes in root respiration, being higher in the portion of soil close to the dripper than between rows. This could be explained by the distribution of root system activity according to greater moisture availability in these zones. The present study showed that about 15% of carbon fixed by photosynthesis was lost by root respiration.

Water limitation is a major global constraint for plant productivity that is likely to be exacerbated by climate change. Hence, improving plant water use efficiency (WUE) has become a major goal for the near future. At the leaf level, WUE is the ratio between photosynthesis and transpiration. Maintaining high photosynthesis under water stress, while improving WUE requires either increasing mesophyll conductance (gm ) and/or improving the biochemical capacity for CO2 assimilation-in which Rubisco properties play a key role, especially in C3 plants at current atmospheric CO2 . The goals of the present analysis are: (1) to summarize the evidence that improving gm and/or Rubisco can result in increased WUE; (2) to review the degree of success of early attempts to genetically manipulate gm or Rubisco; (3) to analyse how gm , gsw and the Rubisco's maximum velocity (Vcmax ) co-vary across different plant species in well-watered and drought-stressed conditions; (4) to examine how these variations cause differences in WUE and what is the overall extent of variation in individual determinants of WUE; and finally, (5) to use simulation analysis to provide a theoretical framework for the possible control of WUE by gm and Rubisco catalytic constants vis-à-vis gsw under water limitations.

The measurement of the carbon balances is necessary to evaluate the contribution of different biomes to carbon sequestration and therefore to mitigate the global climate change effects. Carbon balance of grapevine is of major interest because of the extension and wide distribution of this crop, but also to characterize its sustainability and to satisfy increasing demands about the environmental footprint of wine production. However, references accounting for the carbon balance for different grapevine genotypes and environments are scarce. Carbon balance is an integration of two key physiological processes: photosynthesis (carbon uptake) and respiration (carbon release). Both largely depend on genotype, environmental conditions and agronomic practices. Different methodologies to measure carbon balance in grapevines are summarized, together with the practical difficulties of obtaining reliable field data. On the other hand, the increasing interest of whole plant chambers to evaluate the dynamics of responses to environmental, genetic and agronomic variables is discussed.

Evaluation of different mechanisms adopted by grapevine cultivars to deal with drought is of major importance to carry out more efficient cultivar selection. In this report, 23 cultivars, including local and foreign grape cultivars, were studied under field conditions in order to identify the different behaviors in response to water deficit, and how it can affect water use efficiency (WUE) at leaf level (intrinsic water use efficiency (WUEi) and leaf carbon isotope-composition (delta C-13)). Psi(stem) was used to assess plant water status. Under a common environment, a high variability was found in photosynthetic parameters, stomatal response, WUEi and leaf delta C-13. This large variability observed represents an opportunity for genotype selection. Using different physiological traits we were able to select suitable cultivars for current and future viticulture. Under non-water stress situation the cultivar Escursac combined high rates of net photosynthesis with low stomatal conductance, resulting in high WUEi. In response to drought, strong, and moderate water saving behavior of local cultivars Manto Negro, Giro Ros, Argamussa and Vinater Negre resulted in higher WUEi. Long-term WUE (leaf delta C-13) corroborate these cultivars as high water use efficient. (C) 2015 Elsevier B.V. All rights reserved.

Knowledge about regulation of stomatal conductance is necessary to improve grapevine water use efficiency. The vast range of grapevine cultivars may allow choosing the best-performing ones to global changing conditions provided the understanding and characterization of their physiological responses. In this study, a comparison between two cultivars (Tempranillo and Grenache) with different reputation in water use efficiency was performed during two experimental years in field-conditions. Water relations, leaf gas exchange and abscisic acid (ABA) dynamics were measured at different phenological stages along the growing seasons. A clear difference in the regulation of leaf water relations was observed between cultivars under water stress conditions. Specifically, results showed that there is a clear relationship between hydraulic conductance (K-h) and stomata! regulation. However, ABA can exert a differentiating role on stomatal control during different stages within the grapevine growth period. Furthermore, this study showed that differences in osmotic adjustment could lead to substantial differentiation in the stomatal regulation and the leaf water use efficiency. (C) 2015 Elsevier B.V. All rights reserved.

Background and Aims Stomatal (gs) and mesophyll conductance (gm) limit photosynthesis significantly and consequently, apart from gs, gm is also a physiological process that could affect leaf water use efficiency (WUE). The aims of the present study were to analyse the genetic variability of gm in the grapevine, to relate the variability of leaf WUE with relative changes in gs and gm and to analyse the importance of leaf structural parameters in the variability of gm. Methods and Results The gm in seven potted grapevine cultivars (Vitis viniferaL.) were compared in three experiments under irrigation and moderate water stress treatments. Significant variability of gm was observed among cultivars associated with change in intrinsic WUE. No clear relationship with anatomical traits was found. Conclusions Variability of gm was associated with leaf WUE, although it could not be explained by anatomical variability. It is likely that biochemical mechanisms play an additional important role in the diffusion of CO2 in grapevines. Significance of the Study This study shows that the variability of gm in different grapevine cultivars offers a potential target for improving leaf WUE by increasing net photosynthesis (AN) without increasing plant water losses.

Ferns are thought to have lower photosynthetic rates than angiosperms and they lack fine stomatal regulation. However, no study has directly compared photosynthesis in plants of both groups grown under optimal conditions in a common environment. We present a common garden comparison of seven angiosperms and seven ferns paired by habitat preference, with the aims of (1) confirming that ferns do have lower photosynthesis capacity than angiosperms and quantifying these differences; (2) determining the importance of diffusional versus biochemical limitations; and (3) analysing the potential implication of leaf anatomical traits in setting the photosynthesis capacity in both groups. On average, the photosynthetic rate of ferns was about half that of angiosperms, and they exhibited lower stomatal and mesophyll conductance to CO2 (gm ), maximum velocity of carboxylation and electron transport rate. A quantitative limitation analysis revealed that stomatal and mesophyll conductances were co-responsible for the lower photosynthesis of ferns as compared with angiosperms. However, gm alone was the most constraining factor for photosynthesis in ferns. Consistently, leaf anatomy showed important differences between angiosperms and ferns, especially in cell wall thickness and the surface of chloroplasts exposed to intercellular air spaces.

Climate change models predict that Mediterranean region, where the most important wine-producer countries worldwide are present, will experience increased frequency and severity of drought periods. Consequently, there is an increased requirement for improvement in the irrigation assessment of vineyards. It was described that grapevine water status can be determined as a function of stomatal conductance (g(s)), with values of this parameter below 100 mmol H(2)0 m(-2) s(-1) indicating that grapevines are under drought. Stomatal conductance is a physiological parameter that can also be estimated remotely by correlation with canopy temperatures. Therefore, remote thermal sensing of gs can then be used to develop an irrigation scheduling based on physiological plant status of drought stress. Multicopter RPA (Remote Piloted Aircraft) combined with aerial thermographic imagery open a new opportunity for water stress detection in vineyards. High-resolution thermal images acquired from the multicopter were used to generate three different thermal indexes and three basic alternative methods developed from leaf energy balance equation to correlate with gs. The use of this technology for irrigation assessment in vineyards is discussed.

A comparative study on water-use-efficiency (WUE) under severe water deficit and recovery was conducted on potted grapevines of 'Grenache', 'Syrah' and 'Chardonnay' cultivars grown in Mallorca (Spain). Deficit irrigation was established according to the leaf maximum daily g(s) to achieve severe water deficit conditions in the lapse of one week.The goal was to analyze how g(s) is regulated under water stress and recovery, as well as how water stress affects the adjustments of WUE at leaf and whole plant level. Soil water content, climatic conditions, leaf photosynthesis, transpiration, g(s) and mesophyll conductance (g(m)) were recorded daily throughout the experiment. Water relations and plant hydraulic conductivity (Kh(Plant)), were performed on five specific sampling days: the day the desired stomatal conductance (50 mmol m(-2) s(-1)) was first achieved (day 0), seven days after sustaining the plants at constant soil moisture, just before re-watering (day 7), and then 1, 2 and 7 days after re-watering.The relative contribution of g(s) and g(m) limitations during acclimation to water stress changes from predominant g(s) early during water stress to similar g(s) and g(m) after acclimation. Nonetheless during re-watering photosynthesis recovery was mostly limited by g(s), since stomatal closure recovered much more slowly than g(m). Water stress induced an increase in WUE, which interestingly persisted many days after re-watering. Kh(Plant) variations during drought and recovery were in accordance with gs values. However, the relationship with g(m) variations was lower.'Chardonnay' showed the largest differences between water stress and irrigated plants and the lowest leaf water potential. Under drought and recovery this cultivar maintained lower g(s) and leaf photosynthesis (A(N)) but their WUE values were not the highest.

Conferencia presentada en el 28th International Horticultural Congress, celebrado del 22 al 27 de agosto de 2010 en Lisboa (Portugal)

Background and Aims: Improving water-use efficiency (WUE) is desirable for future grapevine growth and grape production, especially in Mediterranean areas where water is predicted to be limiting. Understanding the genetic variability in WUE is important to identify the most appropriate cultivars to be used in semi-arid areas. Most previous studies have focused at leaf-level WUE, while information on whole-plant level is scarce. This study explored the genetic variability of grapevine in whole-plant WUE (WUEWP) to determine whether several leaf WUE (WUEl) indicators are suitable as proxies of WUEWP. Methods and Results: Three similar experiments were performed to compare WUE in up to eight different grapevine cultivars under irrigation and water-stress treatments. Although WUEl and WUEWP varied with cultivar and treatment, WUEl was not a reliable parameter to predict WUEWP. Conclusions: Large variability in WUEWP between grapevine cultivars was observed, although this variability was not described by leaf-level indicators of WUE. Significance of the Study: This study showed that the large variability existing for WUEWP in different cultivars offers an potential method for selecting the more suitable cultivars to grow in water-scarce viticulture areas, although WUEl is not reliable for estimating WUEWP.

Background and Aims: Net carbon gain commonly estimated from leaf photosynthesis measurements often overestimates grapevine production. This is usually attributed to canopy complexity and a lack of plant respiration data. The present study evaluates the significance of plant respiration in correcting this overestimation. Methods and Results: Non-grafted and non-productive young plants of four grapevine varieties were grown either under irrigation or controlled water stress for 30 days. Daily time courses of leaf photosynthesis and transpiration were determined along with measurements of leaf, stem and root respiration, from which whole plant carbon balance was estimated. Up to 3060% of carbon obtained by photosynthesis is used in respiration, with root respiration being the largest user of fixed carbon (up to 75%). Conclusions: Whole plant respiration represents a significant part of total carbon balance and accounts for the largest part of the discrepancy between photosynthesis-based estimates of plant production and actual plant production. Significance of the Study: The present study presents a quantitative evaluation of the importance of plant respiration in grapevine carbon balance and biomass production, highlighting that gas exchange studies aiming predict plant production should include estimates of respiration, especially of roots.

Poster presentado en el 28th International Horticultural Congress, celebrado del 22 al 27 de agosto de 2010 en Lisboa (Portugal)

Aims: In temperate climates, cover crops are mainly used to reduce excess soil water and nutrient availability to grapevines, which otherwise could decrease grape quality. In Mediterranean climates, where water is a limiting factor, the use of cover crops is not as straightforward. However, in this scenario, summer senescent and self-seeding herbaceous cover crops could also help to decrease soil erosion as well as to reduce excessive early vegetative vigour, which could restrict grape water availability at later phenological stages. The aim of this experiment was to study the effects of particular cover crops in Mediterranean vineyards on grapevine vegetative growth, gas exchange, yield and grape quality. Methods and results: The experiment was carried out over three consecutive years in an organic vineyard (cv. Manto Negro) in central Majorca, Spain. Three treatments (three cover cropping rows per treatment) were established: perennial grass and legume mixture (PM), no tillage, i.e., with permanent resident vegetation (NT), and traditional tillage or ploughed soil (TT). The grapevines were rain fed until veraison, and then drip irrigation was applied (30% potential evapotranspiration; ETP) until harvest. Plant water status was established according to a defined value of maximum daily leaf stomatal conductance (gs). Cover crops reduced total leaf area (LA), gs and grapevine vigour at early growth stages. gs and net photosynthesis (AN) were higher in cover crop treatments during the veraison and ripening stages, likely because of the reductions in LA. Intrinsic water use efficiency increased from flowering to veraison-maturity in all treatments. Yield was lower in the cover crop treatments (PM and NT) compared to TT for all years, but these differences were only significant in 2007. However, grape quality parameters slightly improved in the PM treatment. Conclusion: The use of cover crops decreased LA, helping to avoid dramatic reductions of stomatal conductance in mid-summer, but decreased yield and only slightly increased grape quality. Significance and impact of the study: This study showed that the use of specific cover crops in vineyards under Mediterranean climates helps to reduce vegetative vigour. Nevertheless, yield reduction and slight quality improvement suggest that cover crops should be adjusted in order to reduce competition for water and thus prevent these negative effects of water scarcity.

Three autochthonous grapevine varieties of Majorca (Spain) were analyzed for the presence of viruses listed by the international certification programs. Enzyme-Linked Immuno-Sorbent Assay (ELISA) screenings were performed in 193 vines from 46 vineyards included in a clonal selection. Virus-free vines were only 6.4%, 9.6% and 11.5%, in Manto Negro, Callet and Moll, respectively. Infections by grapevine leafroll associated viruses (GLRaVs) were ascertained in 71%, 78% and 60% of Manto Negro, Callet and Moll vines, respectively. Each variety was also highly infected by Grapevine fanleaf virus (GFLV) and Grapevine fleck virus (GFkV). The percentage of plants displaying multiple infections was 58.4% in Manto Negro, 63.8% in Callet and 42.6% in Moll. Thus, it was very difficult to identify virusfree clones with suitable agronomic characteristics to be considered as a reference for the grape market. In order to obtain certified propagation material under such conditions of endemic viral infection, sanitation should be the main focus in clonal selection processes. However, the time and financial requirements for proper sanitation process bring to consideration the need to use, at least temporarily, standard multiplication material while certified clones are achieved.

Improving water use efficiency (WUE) in grapevines is essential for vineyard sustainability under the increasing aridity induced by global climate change. WUE reflects the ratio between the carbon assimilated by photosynthesis and the water lost in transpiration. Maintaining stomata partially closed by regulated deficit irrigation or partial root drying represents an opportunity to increase WUE, although at the expense of decreased photosynthesis and, potentially, decreased yield. It would be even better to achieve increases in WUE by improving photosynthesis without increasing water loses. Although this is not yet possible, it could potentially be achieved by genetic engineering. This review presents current knowledge and relevant results that aim to improve WUE in grapevines by biotechnology and genetic engineering. The expected benefits of these manipulations on WUE of grapevines under water stress conditions are modelled. There are two main possible approaches to achieve this goal: (i) to improve CO2 diffusion to the sites of carboxylation without increasing stomatal conductance; and (ii) to improve the carboxylation efficiency of Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The first goal could be attained by increasing mesophyll conductance to CO2, which partly depends on aquaporins. The second approach could be achieved by replacing Rubisco from grapevine with Rubiscos from other C3 species with higher specificity for CO2. In summary, the physiological bases and future prospects for improving grape yield and WUE under drought are established.