Hipólito Medrano

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.

The Effects of Water Stress on Plant Respiration

Plant growth can be limited by several factors, among which a lack of water is considered of major importance. Despite the vast knowledge of the effect of water stress on photosynthesis, there is much less known about its effect on respiration. Respiration, unlike photosynthesis, never halts, and it reflects the overall metabolism. However, the data available on the effect of water stress on respiration show large variation, from inhibition to stimulation under different water-stress conditions. This chapter combines a review of the latest studies of the effect of water stress on plant respiration with the compilation of data from different authors and recent results to develop a working hypothesis to explain how respiration is regulated under water stress. Leaf respiration shows a biphasic response to Relative Water Content (RWC), decreasing in the initial stages of water stress (RWC > 60%), and increasing as RWC decreases below 50%. Under this hypothesis, the initial decrease in respiration would be related to the immediate inhibition of leaf growth and, consequently, the growth respiration component. The increase of respiration at lower RWC would relate to an increasing metabolism as the plant triggers acclimation mechanisms to resist water stress. These mechanisms would increase the maintenance component of respiration, and, as such, the overall respiration rate. This hypothesis aims to give a metabolic explanation for the observed results, and to raise questions that can direct future plant respiration experiments.

Mesophyll conductance to CO2 and Rubisco as targets for improving intrinsic water use efficiency in C3 plants

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 Rubiscos 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 Response of Photosynthesis to Soil Water Stress

The physiological and molecular basis of photosynthetic responses to limited soil water availability (water stress) has been intensively examined over the last decade(s). Therefore, this chapter highlights the major achievements of the underlying processes of photosynthetic limitation under drought, an increasingly important issue within the context of climate change. Restricted CO2 diffusion to the sites of carboxylation inside the chloroplast has been demonstrated to be the main limiting factor for photosynthesis, particularly during the early phases of stress. Stomatal (g s ) and mesophyll conductance (g m ), the two leaf diffusion components, contribute differently to this limitation, being largely influenced by the degree of water deficit. Thus, photosynthetic acclimation to drought and its recovery from drought depend primarily on the capacity to adjust g m and g s rapidly. The basis of g m and g s regulation is not fully understood, but several genetic, metabolic, and structural factors involved have been recently described. Secondary stress factors such as excessive light and elevated temperatures affect photosynthetic performance too, implying efficient photoprotection a necessary feature for stress-resistant plants.

Trade-offs between seedling growth, plant respiration and water-use efficiency in two Mediterranean shrubs Rhamnus alaternus and Rhamnus ludovici-salvatoris

Seedling recruitment is a critical developmental stage in regeneration of plant populations under Mediterranean conditions that strongly depends on water availability. Seed mass and relative growth rate (RGR) may affect the early establishment of seedlings through different physiological processes. Here, we examined the effects of the seed mass and carbon balance on seedling growth under two water regimes in Rhamnus alaternus L. and Rhamnus ludovici-salvatoris, two Mediterranean shrubs, showing a different ability to recruit seedlings. Plant water consumption and biomass accumulation (ΔB) were measured during three periods of the growth in order to estimate water use efficiency (WUE), RGR, and its components. Additionally, net photosynthesis and leaf, stem, and root respiration were measured in plants grown in pots well watered and under progressive drought. Rhamnus alaternus showed the higher seed mass, ΔB, and plant WUE than that of R. ludovici-salvatoris in all periods and water regimes. The higher RGR of R. alaternus was observed during the first and the second period, but the reverse trend was registered during the third period as a consequence of the higher initial biomass of R. alaternus. Also, R. alaternus showed a higher specific leaf area and estimated carbon balance than that of R. ludovicisalvatoris. The observed differences in ΔB, estimated carbon balance, seed mass, and WUE between both species could explain their different distribution and ability to recruit seedlings under natural conditions.

Seed germination at different temperatures and seedling emergence at different depths of Rhamnus spp

Rhamnus alaternus and R. ludovici-salvatoris, two Mediterranean shrubs with different geographic distributions, have shown important differences in seedling recruitment capacity. The objectives of this work were to determine the ability of these species to germinate seeds under different temperature ranges, as well as the capacity of seedlings to emerge from different burial depths, in order to better understand their regeneration processes. Two different experiments were performed. In the first one, seed germination was studied in Petri dishes and in the dark at different temperature regimes: a) 5–15°C, b) 10–20°C and c) 15–25°C (12h/12h). In the second experiment, seedling emergence capacity from different burial depths (0.5, 2 and 5 cm) was tested. R. ludovici-salvatoris showed a significantly higher final germination rates, a lower dormancy period, and average time response at 10–20°C than at other temperature ranges, although differences were much greater when seeds were subjected to the 5–15°C temperature regime. By contrast, R. alaternus did not show significant differences between treatments (5–15°C and 10–20°C) in germination behavior. Seedling emergence of both species was lower and slower when seeds were buried at 5 cm. However, R. ludovici-salvatoris always showed a lower seedling emergence capacity than R. alaternus at any burial depth. The low ability of R. ludovici-salvatoris to germinate seeds and emerge between 5–15°C, even from shallow depths, is discussed in relation to its low regeneration capacity and declining geographic distribution.

Influence of water availability and grapevine phenological stage on the spatial variation in soil respiration

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.

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.