42 Mirando la ecuación (19), w
Anexo 1: El cálculo del ITE
In figure 21 the patterns of stem water potential of each irrigation treatment during 2008 and 2009 seasons of „Cannonau‟ trials are presented. Ψstem pattern reflected both the differences
between treatments, in terms of soil moisture content and the weather conditions of the analysed period. It shows a nearly constant pattern during 2008, where the most significant differences were observed after veraison (Fig. 22A). Despite the significant differences measured after the first two measuring dates (From June 19th until September 19th), during this year, Ψstem values varied between a maximum value of -0.4 and a minimum of -1.0 MPa, which indicates a small water deficit in all treatments. DI 50 and PRD treatments presented similar values during ripening stages, and at this time, the highest values were measured in FI 100 and DI 25 (-0.6 and -0.5 MPa in the last two measuring dates). After dropping to -0.8MPa in July, FI 100 Ψstem recovered to nearly -0.5 MPa at the end of ripening, also in DI 25 plants. In the latter treatment, Ψstem remained above -
0.7MPa during the whole ripening period. This result is in accordance with the monitored soil water profiles, as in DI 25 plants important capillary water was available above 40 cm depth, which might have helped to prevent greater water stress. Regarding DI 50, after reaching the minimum value of -1.0 MPa in July 9th, Ψstem did not fully recover, remaining close to 0.9 MPa until September 19th.
As far as 2009 is concerned, there was a decreasing trend in Ψstem both in PRD (from -0.8 MPa in June 15th to -1.2 MPa in September 4th) and DI 25 (from -0.8MPa in June 15th to -1.1MPa
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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 118 of 234 in August 24th), which indicates an effective reduced plant water status. During this year PRD and DI 25 Ψstem remained under -0.8 MPa, but recovered rapidly after the heavy rain events of September. On the contrary, DI 50 values remained generally above the -0.8 MPa threshold, reaching -0.6 MPa at verasion (in July 27th) and during ripening (in August 11th), with the exception of the July 31 measurement, where it dropped to -1.0 MPa, probably due to high temperatures, strong wind conditions and high evapotranspiration rates recorded during this day and in the two previous days (Fig. 22B).
Mercenaro (2007), studying the effects of different irrigation strategies on „Cannonau‟ physiological status observed a similar pattern. In his study, the author observed a nearly constant trend of Ψstem in the irrigated control (above -0.6 MPa) and a decreasing trend in the PRD
treatments, which dropped to as much as -1.2 MPa at the end of 2005 season. In that trial, the differences between irrigation strategies were more impressive, and Ψstem data clearly showed a
moderate stress condition of the plants in the deficit irrigation treatments, due to a lower water supply.
In our experiment, at harvest time 2009, Ψstem of the „Cannonau‟ plants completely
recovered, in all the treatment, to nearly -0.4MPa, due to the have rain events registered in mid September.
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Figure 22 – Effect of irrigation treatments on „Cannonau‟ stem water potential during the seasons 2008 (A) and 2009 (B) in experimental site 1.Mean values (4 replicates/block) and standard error
(P<0.05). -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 28/5/08 19/6/08 9/7/08 29/7/08 26/8/08 19/9/08 Ψ ste m (M P a) Date
Stem Water Potential - CNN - Site 1 - 2008
FI 100 DI 50 PRD DI 25 A -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 15/6/09 21/7/09 31/7/09 11/8/09 24/8/09 4/9/09 21/9/09 Ψ ste m (M P a) Date
Stem Water Potential - CNN - Site 1 - 2009
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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 120 of 234 During the first year of the experimental trial conducted in the „Vermentino‟ vineyard of the Parteolla region, stem water potential oscillated between -0.6 and -1.0 MPa in the whole irrigation period, according to the irrigation interventions. Although the differences between treatments had been significant, the values do not indicate a decreasing trend during the dry season (Fig. 23A). Furthermore, plants recovered completely after September precipitations.
It is interesting to notice that both PRD treatment showed clearly two peaks of higher Ψstem. The first peak was detected in July 22nd (-0.6MPa in PRD treatments against -0.8MPa in the
DI ones) and the second, prior to harvest, in September 1st, as compared to the DI 40 and DI 80 treatments (nearly -0.5 MPa in PRD 40 and PRD 80 against -0.8 and -0.9 MPa of DI 40 and DI 80, respectively). Also DI 80 Ψstem reached values higher than -0.6 MPa in August 4th, dropping
sharply afterwards to -1.0 MPa. These results are consistent with the observed soil water profiles, down to 40 cm depth, since the peaks dates correspond to soil re-wetting periods, close to 40 cm depth. In fact, in July 22nd, nearly 20% moisture was registered under DI 80 plants in those soil layers, and due to capillary ascension the water supplied at 40 cm depth probably remained available to root‟s absorption during the following days. For the same reason, PRD treatments had available water during almost all the measuring period in 10 to 40 cm of depth and thus Ψstem
could recover after re-watering.
Ψstem pattern followed closely the soil drying and re-watering cycle at the 10 to 40 cm profile, suggesting that the water applied at a sub-surface level, readily available for root uptake, contributed markedly to root absorption, which prevented plants from being exposed to water stress conditions during relatively long periods of time.
During 2010, a similar fluctuating pattern was observed in stem water potential but, after July 1st, Ψstem followed a decreasing trend, reaching -1.0 MPa in the majority of treatments, except for PRD 80 where it did not drop below the -0.8 MPa threshold (Fig. 23B).
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Figure 23 – Effect of irrigation treatments on „Vermentino‟ stem water potential during the seasons 2008 (A) and 2009 (B) in experimental site 2.Mean values (4 replicates/block) and
standard error (P<0.05). -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 23/6/09 9/7/09 22/7/09 29/7/09 4/8/09 12/8/09 1/9/09 6/10/09 Ψ ste m (M P a) Date
Stem Water Potential - VRM - Site 2 - 2009
DI 80 DI 40 PRD 80 PRD 40 A -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 26/5/10 1/7/10 13/7/10 3/8/10 17/8/10 8/9/10 29/9/10 Ψ ste m (M P a) Date
Stem Water Potential - VRM - Site 2 - 2010
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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 122 of 234 The stem water potential pattern obtained in the third trial, where irrigation scheduling was determined weekly, using Ψstem as the indicator to re-watering, reflected the imposed water stress treatments during the whole season (Fig. 24).
The IC treatment, where the Ψstem was maintained above -0.8 MPa during almost all the
season, showed a decreasing tendency until veraison, and this behaviour was observed in every treatment, as the evapotranspirative demand increased. Before veraison, ED and NC treatments registered a similar decrease (from -0.7 in June 23rd to -1.6 MPa in August 11th), and both experienced severe water stress at veraison, while in LD and IC plants Ψstem remained at -1.2 MPa.
The expected decrease in the Ψstem of the LD and NC plants, after veraison, can be perceived from August 11th and 20th data (-1.2 MPa and -1.6 MPa in August 11th to -1.4 MPa and -1.7 MPa in August 20th, in LD and NC, respectively). Thereafter, plant water status recovered in every treatment, with the first rain events of September.
Furthermore, ED plants reached the IC values at the end of the season, and prior to that, NC Ψstem recovered nearly 0.9 MPa after a single irrigation intervention, even though these plants
had been subjected to water stress conditions since the beginning of July and to severe water stress in August. LD plants also recovered shortly before harvest time, but as sought, Ψstem remained
within the NC levels. These results indicate a good recover capacity of „Vermentino‟, in terms of canopy water status even after plants had been subjected to severe water and thermal stress conditions.
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Figure 24 – Effect of irrigation treatments on „Vermentino‟ stem water potential during the seasons 2011 in experimental site 3. Mean values (4 replicates/block) and standard error (P<0.05).
The use of stem water potential as a tool for irrigation scheduling shows some advantages over the ETm fractions method. Firstly, being a plant water status indicator, not only does it give a
warning signal of the evaporative demand conditions at a given time, but also indicates varietal responses to water stress. Such information can subsequently be transferred and used for scheduling in different pedo-climatic zones, since it intrinsically represents plants response to any given climate-soil situation. The ETm fractions method, although allowing for automation of the
irrigation schedule, must be locally calibrated. Even so, the desired levels of water stress may not always be achieved by the imposed deficit irrigation schemes, not only in a given phenological stage, but inclusively during the entire season.
Additionally, when water tables under the soil surface, other than irrigation water, are available to root absorption, as it happened during the first two trial of this study, plants response to irrigation treatment is much influenced by the presence of such extra water sources. In these situations, stem water potential would indicate the actual plant water status. Instead, the calculated fraction of ETm, used to schedule irrigation, have probably overestimated plants irrigation needs,
-1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 23/6/11 1/7/11 15/7/11 29/7/11 3/8/11 11/8/11 17/8/11 20/8/11 30/8/11 14/9/11 Ψ ste m (M P a) Date
Stem Water Potential - VRM - Site 3 - 2011
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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 124 of 234 since they did not take into consideration water input, other than precipitation and irrigation, to the soil-plant-atmosphere system. As a consequence, the results obtained, from physiologic responses to vegetative growth, yield and berry composition, must be carefully interpreted when it comes to transfer the knowledge and adapting it to different soil and climate situations.
4.2.3.2 Leaf Gas Exchanges
In the following analysis some of the results obtained by monitoring leaf gas exchanges during the three irrigation trials, from 2009 until 2011, are presented, starting with the first irrigation interventions and ending at harvest time. The measurements were performed at midday, as it is normally at this time of the day that plants are subjected to higher evaporative demand. As a consequence, any eventual effect of water or thermal stress conditions on photosynthetic performance and stomata behaviour could be easily detected.
It is common knowledge that leaf gas exchanges are influenced by several different factors, from the environmental to metabolic and physiologic conditions. Generally, gas exchanges decrease with leaf age and with increasing of soil water deficiency (Chaves, 1986; Lissarrague et al. 1999; Flexas et al., 1999). With Mediterranean climate conditions this process is particularly accelerated, as the hydro-meteorological balance becomes more negative and the atmospheric demand increases with the advance of the dry season.
In the present study, leaf gas exchange parameters during the first year of „Cannonau‟ trial were not presented due to a failure in the photosynthesis analysing systems (Ciras-2), that compromised all the measuring season 2008. During the second year of the first trial, the net photosynthetic rate of the „Cannonau‟ plants reached, on average, mean values of 12 μmol CO2 m-2 s-1 (in DI 50) to 14 μmol CO
2 m-2 s-1 (in PRD and DI 25) in July 31 in all treatments, decreasing 71.4% and 50% afterwards, to 4 and 6 μmol m-2 s-1, in PRD and DI 50, respectively, while in DI 25 plants, it decreased 43%, and mean values of 8 μmol CO2 m-2 s-1 were recorded (Fig. 25). A decreasing trend in Pn was observed in all treatments. Instead, stomatal conductance to water vapour remained nearly constant in the three measuring dates. At the second date, August 24th, significant differences were detected in gs between the more irrigated treatments and DI 25, with
stomata conducting at significantly lower rate in DI 25, about 25 mmol H2O m-2 s-1 less than in DI 50 and PRD.
Ana Fernandes de Oliveira - Deficit Irrigation Strategies in Grapevine (Vitis vinifera L). Ecophysiologic Responses,
Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 125 of 234 Transpiration rate followed a decreasing pattern in all treatments but as happened with gs, also T showed significant differences in August 24th, with DI 25 plants having lowers T mean values, as compared to DI 50 and PRD plants. Nevertheless, both parameters varied little from July until the end of September, and even DI 25 gs mean values remained stable, with nearly 55
mmol H2Om-2 s-1. DI 50 gs also stood steady, with nearly 80 μmol H2Om-2 s-1, and PRD presented higher variation between dates (83 to 64 μmol H2Om-2 s-1 from August 24 to September 21) but at the ending date, no significant differences were observed between treatments. It is important to take into consideration that, during this trial, at the time the first measurement was taken, gs had
probably already decreased, to values below the maximum of the growing season. The transpiration rate, which was also expected to decrease after veraison, was only slightly reduced at the end of September, maintaining mean values of 2.75 and 3.59 mmol H2O m-2 s-1 in DI 50 and DI 25 respectively, which were not statistically different.
The differences between treatments in terms of intrinsic water use efficiency increased throughout the ripening period, with DI 25 showing significantly higher values (nearly 200 μmol CO2/mol H2O) and PRD decreasing more (almost 50%), due to the sharp drop in Pn from the second to the third measuring dates in this last treatment. At veraison, WUEi values in PRD were similar to those of DI 25, but at the end, it decreased to DI 50 level (about 100 μmol CO2/mol H2O).
No significant differences between treatments were initially observed in transpiration efficiency (which varied from 2.56 of DI 50 to 3.47 of DI 25 in July 31st), but in the second and third measurements, the differences increased and were statistically relevant. DI 25 mean values of Pn/E ratio decreased 17% in September 29th, to 2.88 μmol CO
2/mol H2O, while DI 50 and PRD declined 32% and 54% presenting, in the last measuring date, mean values of 1.72 and 1.50 μmol CO2/mol H2O, respectively.
The observed reductions in leaf gas exchanges during the season might have been favoured by the reduced irrigation treatments. Nevertheless, the relatively small reduction observed both in gs, WUEi and E/Pn, namely in the less irrigated treatment, indicate that no severe water stress was imposed nor a great impact of reduced irrigation on leaf photosynthetic performance have occurred, during berry development and ripening in response to deficit irrigation. Furthermore, the recovery of stem water potential values at harvest, observed in all treatments, after the decreasing
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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 126 of 234 trend of plant water status, in response to deficit irrigation along the season, also indicates that no lasting damage was caused by drought-stress conditions.
Figure 25 – Effect of irrigation treatments on „Cannonau‟ leaf gas exchanges during season 2009 in site 1. Photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (E) and intrinsic
water use efficiency (WUEi). Mean values (4 replicates/block) and standard error (P<0.05). During the first year of the second trial, Pn of the more irrigated „Vermentino‟ vines (DI 80 and PRD 80) equally declined from July 29th (11.2 and 11.3 μmol CO2 m-2 s-1, respectively) until the last measuring date, in September 1st (7 and 7.2 μmol CO
2 m-2 s-1, respectively), with no significant differences being detected between these treatments. The highest Pn values were recorded in the second measurement date, but DI 40 plants Pn was already decreasing since the first date and always presented significantly lower values (initially 9.8 and at the end 7.0 μmol CO2 m-2 s-1). PRD 40 showed a pattern of photosynthetic rate nearly constant (around 9 to 10 μmol CO2 m-2 s-1) and 0 2 4 6 8 10 12 14 16 18 31/7/09 24/8/09 21/9/09 P n (μ m ol m -2s -1) Date
Net Photosinthetic Rate - CNN - Site 1 - 2009
DI 50 PRD DI 25 0 50 100 150 200 31/7/09 24/8/09 21/9/09 g s (m m ol m -2s -1) Date
Stomatal Conductance - CNN - Site 1- 2009
DI 50 PRD DI 25 0 1 2 3 4 5 6 7 31/7/09 24/8/09 21/9/09 E (m m ol m -2s -1) Date Transpiration - CNN - Site 1 - 2009 DI 50 PRD DI 25 0 100 200 300 400 500 600 31/7/09 24/8/09 21/9/09 WUE i ( μm ol C O2 /m ol H 2 O) Date
Intrinsic Water Use Efficiency - CNN - Site 1 - 2009
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Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 127 of 234 in September these plants presented the highest Pn (10 μmol CO2 m-2 s-1), while all the other treatment had already decreased to similar values (8 μmol CO2 m-2 s-1). This behaviour might be attributed to the presence of water sources located at deeper soil layers, which may have kept PRD 40 plants with good water status during the whole season, thus favouring leaf gas exchanges. In fact, although Ψstem had decreased to -1.0 MPa in August 12th, thereafter, in PRD 40, it increased
markedly to -0.4, in September, and even to -0.2 MPa, in October. This indicates a high capacity of these plants to reabsorb water and re-establish a good water status (Fig. 26).
Stomatal conductance highly increased after the first irrigation in all treatments, from less than 100 mmol H2O m-2 s-1 to nearly 600 and 500 mmol H2O m-2 s-1 in July 9th, in DI 80 and DI 40, respectively. The PRD treatments gs increased much less (to 350 and 450 mmol H2O m-2 s-1, in
PRD 80 and PRD 40). At veraison (July 29th measuring date) gs decreased in all the treatments, reaching 300 mmol H2O m-2 s-1 in PRD 40 and 400 mmol H2O m-2 s-1 in the other treatments (a 33% reduction in PRD 40 and DI 80, 20% in DI 40 and 11% in PRD 80) and increasing thereafter, similarly in all treatments. This seasonal pattern in gas exchange, marked by enhanced leaf gas exchanges has been observed in other studies and attributed to an enhancement of photosynthesis caused by increasing fruit-sink activity, beginning at veraison (Candolfi-Vasconcelos et al., 1994), due to increased carbon demand by the fruit (Loveys and Kriedemann, 1974).
Transpiration followed the same pattern of gs and no significant differences were found between the two 40% ETm treatments. The elevated transpiration rates observed during 2009 are
in accordance with the high temperatures and vapour pressure deficit (VPD) of this season. In fact, an intense atmospheric demand promotes transpiration rate, in order to allow for heat dissipation, when plants are in good watering conditions.
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