Browsing by Author "Chaves, Maria Manuela"
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- Control of stomatal aperture and carbon uptake by deficit irrigation in two grapevine cultivarsPublication . Souza, Cláudia R. de; Maroco, João; Santos, Tiago P.; Rodrigues, M. Lucília; Lopes, Carlos Manuel Antunes; Pereira, João Santos; Chaves, Maria Manuelaodels for the Mediterranean region. In recent years, deficit irrigation, including partial root drying (PRD), has been proposed as an irrigation technique to improve water use efficiency and standardize grapevine yield and quality. The objective of this study was to evaluate the impact of deficit irrigation on photosynthetic responses of field grown grapevines of cv. Moscatel and Castela˜o. The treatments were: full irrigation (FI), corresponding to 100% ETc; non-irrigated, but rain fed (NI) and partial root zone drying (PRD) and deficit irrigation (DI), both corresponding to an irrigation of 50% ETc. While in the DI treatment water was applied to both sides of the root system, in the PRD treatment, water was supplied to only one side of the root system, alternating sides periodically. In both cultivars, PRD and DI vines showed intermediate pre-dawn leaf water potential (ψpd) values (around -0.4 MPa) while FI vines, showed ψpd around -0.2 MPa during the growing season. NI showed the lowest cpd, reaching -0.6 MPa in Moscatel and -0.8 MPa in Castelão, at the end of growing season. Water status of PRD vines remained closer to FI than DI, especially at midday. Photosynthetic rates and fluorescence parameters of the deficit irrigation treatments (PRD and DI) did not show significant differences from FI vines, for most of the season. In Moscatel, although PRD generally showed gs, relative stomatal limitation (RSL) and intrinsic water use efficiency (A/gs) values closer to NI than DI, most of the differences between PRD and DI were not statistically significant. Our results showed a stability of the photosynthetic machinery in grapevines under low-to-moderate water availabilities, as demonstrated by the maintenance of the activity of three Calvin Cycle enzymes and of the Vcmax values. However, a decline in Jmax was observed in NI vines, that can be a result either of a decrease in ATP production or, alternatively, of decreased mesophyll conductance to CO2 diffusion. In general terms, stomatal limitation of photosynthesis is likely to be dominant in non-irrigated plants. Deficit irrigation had no negative impact on CO2 assimilation, despite less water application than in full-irrigation. Differences among varieties may be related to differences in sensitivity of stomata, shoot growth and/or the interaction between rootstock and cultivar to soil water availability.
- Deficit irrigation in grapevine improves water-use efficiency while controlling vigour and production qualityPublication . Chaves, Maria Manuela; Santos, Tiago P.; Souza, Cláudia R. de; Ortuño, M. F.; Rodrigues, M. Lucília; Lopes, Carlos Manuel Antunes; Maroco, João; Pereira, João SantosGrapevine irrigation is becoming an important practice to guarantee wine quality or even plant survival in regions affected by seasonal drought. Nevertheless, irrigation has to be controlled to optimise source to sink balance and avoid excessive vigour. The results we present here in two grapevine varieties (Moscatel and Castela ˜o) during 3 years, indicate thatwe can decrease the amount ofwater applied by 50%(as in deficit irrigation, DI, and in partial root drying, PRD) in relation to full crop’s evapotranspiration (ETc) [full irrigated (FI) vines] with no negative effects on production and even get some gains of quality (in the case of PRD).We report that in non-irrigated and in several cases in PRD vines exhibit higher concentrations of berry skin anthocyanins and total phenols than those presented by DI and FI vines.We showed that these effects on quality weremediated by a reduction in vigour, leading to an increase on light interception in the cluster zone. Because plant water status during most of the dates along the season was not significantly different between PRD and DI, and when different, PRD even exhibited a higher leaf water potential than DI vines, we conclude that growth inhibition in PRD was not a result of a hydraulic control. The gain in crop water use in DI and PRD was accompanied by an increase of the δ13 C values in the berries in DI and PRD as compared to FI, suggesting that we can use this methodology to assess the integrated water-use efficiency over the growing season.
- Drought-induced photosynthetic inhibition and autumn recovery in two Mediterranean oak species (Quercus ilex and Quercus suber)Publication . Vaz, Margarida Maria de Almeida; Pereira, João Santos; Gazarini, Luís Carlos; David, Teresa Soares; David, Jorge Soares; Rodrigues, A.; Maroco, João; Chaves, Maria ManuelaResponses of leaf water relations and photosynthesis to summer drought and autumn rewetting were studied in two evergreen Mediterranean oak species, Quercus ilex spp. rotundifolia and Quercus suber. The predawn leaf water potential (ΨlPD), stomatal conductance (gs) and photosynthetic rate (A) at ambient conditions were measured seasonally over a 3-year period. We also measured the photosynthetic response to light and to intercellular CO2 (A/PPFD and A/ Ci response curves) under water stress (summer) and after recovery due to autumn rainfall. Photosynthetic parameters, Vcmax, Jmax and triose phosphate utilization (TPU) rate, were estimated using the Farquhar model. RuBisCo activity, leaf chlorophyll, leaf nitrogen concentration and leaf carbohydrate concentration were also measured. All measurements were performed in the spring leaves of the current year. In both species, the predawn leaf water potential, stomatal conductance and photosynthetic rate peaked in spring, progressively declined throughout the summer and recovered upon autumn rainfall. During the drought period, Q. ilex maintained a higher predawn leaf water potential and stomatal conductance than Q. suber. During this period, we found that photosynthesis was not only limited by stomatal closure, but was also downregulated as a consequence of a decrease in the maximum carboxylation rate (Vcmax) and the light-saturated rate of photosynthetic electron transport (Jmax) in both species. The Vcmax and Jmax increased after the first autumnal rains and this increase was related to RuBisCo activity, leaf nitrogen concentration and chlorophyll concentration. In addition, an increase in the TPU rate and in soluble leaf sugar concentration was observed in this period. The results obtained indicate a high resilience of the photosynthetic apparatus to summer drought as well as good recovery in the following autumn rains of these evergreen oak species.
- Effects of long-term exposure to elevated CO2 and N fertilization on the development of photosynthetic capacity and biomass accumulation in Quercus suber L.Publication . Maroco, João; Breia, Elsa; Faria, T.; Pereira, João Santos; Chaves, Maria ManuelaThe effects of long-term (4 year) CO2 enrichment (70Pa versus 35 Pa) and nitrogen nutrition (8mM versus 1mM NO3–) on biomass accumulation and the development of photosynthetic capacity in leaves of cork oak (Quercus suber L., a Mediterranean evergreen tree) were studied. The evolution of photosynthetic parameters with leaf development was estimated by fitting the biochemical model of Farquhar et al. (Planta 149, 78–90, 1980) with modifications by Sharkey (Botanical Review 78, 71–75, 1985) to A–Ci response curves. CO2 enrichment had a small reduction effect on the development of the maximum CO2 fixation capacity by Rubisco (VCmax), and no effect over maximum electron transport capacity (Jmax), day-time respiration(Rd) and Triose-P utilization (TPU). However, there was a statistically significant effect of N fertilization and the interaction CO2×N over the evolution of VCmax, Jmax and TPU. Relative stomatal limitation (estimated from A–Ci curves) was higher (+20%) for plants grown under ambient CO2 than for plants grown under elevated CO2. There was a significant effect of CO2 and N fertilization over total biomass accumulation as well as leaf area. Plants grown at elevated CO2 had 27% more biomass than plants grown at ambient CO2 when given high N. However, for plants grown under low N there was no significant effect of CO2 enrichment on biomass accumulation. Plants grown under low N also had significantly higher root: shoot ratios whereas there were no differences between CO2 treatments. The larger biomass accumulation of Q. suber under elevated CO2 is attributable to a higher availability of CO2 coupled to a larger leaf area, with no significant decrease in photosynthetic capacity under CO2 enrichment and elevated N fertilization. For low N fertilization, the effects of CO2 enrichment over leaf area and biomass accumulation are lost, suggesting that in native ecosystems with low N availability, the effects of CO2 enrichment may be insignificant.
- Effects of partial root-zone drying irrigation on cluster microclimate and fruit composition of field-grown Castelão grapevinesPublication . Santos, Tiago P.; Lopes, Carlos Manuel Antunes; Rodrigues, M. Lucília; Souza, Cláudia R. de; Silva, Jorge R.; Maroco, João; Pereira, João Santos; Chaves, Maria ManuelaThe partial root-zone drying (PRD) irrigation technique has been proposed for viticulture as a possible way to save water without compromising yield. Half of the plant root system is slowly dehydrating whereas the other half is irrigated; after about two weeks the opposite side of vines is irrigated. A PRD irrigation system (50 % of the crop evapotranspiration - ETc) was installed in a vineyard (Vitis vinifera L. cv. Castelão) in Southern Portugal and compared with two other irrigation systems, deficit irrigation, DI (50 % ETc) and full irrigation, FI (100 % ETc), as well as with non-irrigated vines (NI). Water was applied twice a week, from fruit set (mid-June) until one week before harvest (September 3). While FI vines remained well watered during the ripening period, a severe water stress developed in NI plants. PRD and DI vines exhibited mild water deficits during the same period. A significant decrease in vegetative growth (shoot weight, pruning weight, leaf layer number and percentage of water shoots) was observed in NI and PRD vines when compared to DI and FI. In denser canopies (FI and DI) berry temperature was always lower than that of the more open ones (NI and PRD). The higher degree of cluster exposition in PRD and NI had a positive influence on berry composition due to temperature and incident radiation, leading to higher concentrations of anthocyanins and total phenols in the berry skin compared to DI and FI vines. Irrigation did not significantly affect berry sugar accumulation and pH in berries. Compared to FI, PRD and DI treatments water use efficiency (the amount of fruit produced per unit of water applied) was doubled since at the same yield the amount of water applied, was reduced by 50 %.
- Grape berry metabolism in field-grown grapevines exposed to different irrigation strategiesPublication . Souza, Cláudia R. de; Maroco, João; Santos, Tiago P.; Rodrigues, M. Lucília; Lopes, Carlos Manuel Antunes; Pereira, João Santos; Chaves, Maria ManuelaThe response of grape berry metabolism to vine water status was investigated in field grown grapevines (Vitis vinifera cv. Castelão) in southern Portugal. Water was supplied as: full irrigation (FI), to minimum water deficit corresponding to 100 % of crop evapotranspiration (Etc), partial rootzone drying (PRD) and deficit irrigation (DI), both corresponding to an irrigation amount of 50 % Etc, and a rainfed, i.e. no irrigation treatment (NI). In PRD, water was supplied to one side of the root system during each irrigation period, alternating sides every 15 d approximately. During the growing period, PRD and DI vines showed intermediate pre-dawn leaf water potential (Ψpd) values (around -0.4 MPa) by the end of the growing season, FI vines -0.2 MPa and NI -0.8 MPa. Berry weight as well as the content of glucose and fructose per berry increased in irrigated vines (PRD, DI, and FI) compared to NI vines. Although both malic and tartaric acid declined in non-irrigated vines, there was no significant difference between treatments at harvest. The activities of invertase, malate dehydrogenase and malic enzyme were not affected by irrigation throughout the ripening process. The contribution of other factors involved in the reduction of sugars and organic acids in berries of non-irrigated vines are discussed. These results show that deficit irrigation, like PRD and DI, do not have any negative impact on growth and quality of grape berries compared to fully irrigated vines, but may result in improved berry quality compared to rainfed vines.
- How plants cope with water stress in the field? Photosynthesis and growthPublication . Chaves, Maria Manuela; Pereira, João Santos; Maroco, João; Rodrigues, M. Lucília; Ricardo, Cândido Pereira Pinto; Osório, M. L.; Carvalho, Isabel Saraiva de; Faria, T.; Pinheiro, C.Plants are often subjected to periods of soil and atmospheric water deficit during their life cycle. The frequency of such phenomena is likely to increase in the future even outside today’s arid/semi‐arid regions. Plant responses to water scarcity are complex, involving deleterious and/or adaptive changes, and under field conditions these responses can be synergistically or antagonistically modified by the superimposition of other stresses. This complexity is illustrated using examples of woody and herbaceous species mostly from Mediterranean‐type ecosystems, with strategies ranging from drought‐avoidance, as in winter/spring annuals or in deep‐rooted perennials, to the stress resistance of sclerophylls. Differences among species that can be traced to different capacities for water acquisition, rather than to differences in metabolism at a given water status, are described. Changes in the root : shoot ratio or the temporary accumulation of reserves in the stem are accompanied by alterations in nitrogen and carbon metabolism, the fine regulation of which is still largely unknown. At the leaf level, the dissipation of excitation energy through processes other than photosynthetic C‐metabolism is an important defence mechanism under conditions of water stress and is accompanied by down‐regulation of photochemistry and, in the longer term, of carbon metabolism.
- Impact of deficit irrigation on water use efficiency and carbon isotope composition (δ13C) of field-grown grapevines under Mediterranean climatePublication . Souza, Cláudia R. de; Maroco, João; Santos, Tiago P.; Rodrigues, M. Lucília; Lopes, Carlos Manuel Antunes; Pereira, João Santos; Chaves, Maria ManuelaThe objective of this study was to evaluate the effect of deficit irrigation on intrinsic water use efficiency (A/gs) and carbon isotope composition (δ 13C) of two grapevine cultivars (Moscatel and Castelão), growing in a commercial vineyard in SW Portugal. The study was done in two consecutive years (2001 and 2002). The treatments were full irrigation (FI), corresponding to 100% of crop evapotranspiration (ETc), rain-fed (no irrigation, NI), and two types of deficit irrigation (50% ETc): (i) by supplying the water either to one side of the root system or to the other, which is partial rootzone drying (PRD), or (ii) dividing the same amount of water by the two sides of the root system, the normal deficit irrigation (DI). The water supplied to the PRD treatment alternated sides approximately every 15 d. The values of predawn leaf water potential (ψpd) and the cumulative integral of ψpd (Sψ) during the season were lower in 2001 than in the 2002 growing season. Whereas differences in Wpd and SW between PRD and DI were not significantly different in 2001, in 2002 (a dryer year) both cultivars showed lower values of SW in the PRD treatment as compared with the DI treatment. This suggests that partial rootzone drying may have a positive effect on water use under dryer conditions, either as a result of better stomatal control and/or reduced vigour. The effects of the water treatments on δ13C were more pronounced in whole grape berries and pulp than in leaves. The δ13C of pulp showed the best correlation with intrinsic water use efficiency (A/gs) as well as with Sψ. In spite of the better water status observed in PRD compared with DI in the two cultivars in 2002, no statistical differences between the two treatments were observed in A/gs and δ13C. On the other hand, they showed a higher δ13C compared with FI. In conclusion, it is apparent that the response to deficit irrigation varies with the environmental conditions of the particular year, the driest conditions exacerbating the differences among treatments. The highest values of d13C found in the pulp of NI vines in Castela˜o compared with Moscatel suggest different sensitivities to water deficits in the two cultivars, as was empirically observed.
- Impacts of experimentally imposed drought on leaf respiration and morphology in an Amazon rain forestPublication . Metcalfe, Daniel B.; Lobo-do-Vale, Raquel; Chaves, Maria Manuela; Maroco, João; Aragão, Luiz E. O. C.; Malhi, Yadvinder; Costa, António L. da; Braga, Alan P.; Gonçalves, Paulo L.; Athaydes, João de; Costa, Mauricio da; Almeida, Samuel S.; Campbell, Catherine; Hurry, Vaughan; Williams, Mathew; Meir, Patrick1. The Amazon region may experience increasing moisture limitation over this century. Leaf dark respiration (R) is a key component of the Amazon rain forest carbon (C) cycle, but relatively little is known about its sensitivity to drought. 2. Here, we present measurements of R standardized to 25 C and leaf morphology from different canopy heights over 5 years at a rain forest subject to a large-scale through-fall reduction (TFR) experiment, and nearby, unmodified Control forest, at the Caxiuana˜ reserve in the eastern Amazon. 3. In all five post-treatment measurement campaigns, mean R at 25 C was elevated in the TFR forest compared to the Control forest experiencing normal rainfall. After 5 years of the TFR treatment, R per unit leaf area and mass had increased by 65% and 42%, respectively, relative to pre-treatment means. In contrast, leaf area index (L) in the TFR forest was consistently lower than the Control, falling by 23% compared to the pre-treatment mean, largely because of a decline in specific leaf area (S). 4. The consistent and significant effects of the TFR treatment on R, L and S suggest that severe drought events in the Amazon, of the kind that may occur more frequently in future, could cause a substantial increase in canopy carbon dioxide emissions from this ecosystem to the atmosphere.
- Limitations to leaf photosynthesis in field-grown grapevine under drought - metabolic and modelling approachesPublication . Maroco, João; Rodrigues, M. Lucília; Lopes, Carlos Manuel Antunes; Chaves, Maria ManuelaThe effects of a slowly-imposed drought stress on gas-exchange, chlorophyll a fluorescence, biochemical and physiological parameters of Vitis vinifera L. leaves (cv. Aragonez, syn. Tempranillo) growing in a commercial vineyard (South Portugal) were evaluated. Relative to well-watered plants (predawn water potential, ΨPD = –0.13 ± 0.01 MPa), drought-stressed plants (ΨPD = –0.97 ± 0.01 MPa) had lower photosynthetic rates (ca 70%), stomatal conductance, and PSII activity (associated with a higher reduction of the quinone A pool and lower efficiency of PSII open centres). Stomatal limitation to photosynthesis was increased in drought-stressed plants relative to well-watered plants by ca 44%. Modelled responses of net photosynthesis to internal CO2 indicated that drought-stressed plants had significant reductions in maximum Rubisco carboxylation activity (ca 32%), ribulose-1,5-bisphosphate regeneration (ca 27%), and triose phosphate (triose-P) utilization rates (ca 37%) relative to well-watered plants. There was good agreement between the effects of drought on modelled biochemical parameters, and in vitro activities of key enzymes of carbon metabolism, namely Rubisco, glyceraldehyde-3-phosphate dehydrogenase, ribulose-5-phosphate kinase and fructose-1,6-bisphosphate phosphatase. Quantum yields measured under both ambient (35 Pa) and saturating CO2 (100 Pa) for drought-stressed plants were decreased relative to well-watered plants, as well as maximum photosynthetic rates measured at light and CO2 saturating conditions (three times ambient CO2 levels). Although stomatal closure was a strong limitation to CO2 assimilation under drought, comparable reductions in electron transport, CO2 carboxylation, and utilization of triose-P capacities were also adaptations of the photosynthetic machinery to dehydration that slowly developed under field conditions. Results presented in this study confirm that modelling photosynthetic responses based on gas-exchange data can be successfully used to predict metabolic limitations to photosynthesis.