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Article

Influence of Canopy Vineyard Management on Physiological Behaviour and Radiation Interception Efficiency in Syrah

by
Mario de la Fuente
1,*,
Rubén Linares
1,
José Ramón Lissarrague
1,
Sara Sánchez-Élez
2 and
Pilar Baeza
1
1
CEIGRAM—Departamento de Producción Agraria, Escuela Técnica Superior de Ingeniería Agronómica, Alimentaria y de Biosistemas, Universidad Politécnica de Madrid, Ciudad Universitaria sn, 28040 Madrid, Spain
2
Instituto Madrileño de Investigación y Desarrollo Rural, Agrario y Alimentario (IMIDRA), 28013 Madrid, Spain
*
Author to whom correspondence should be addressed.
Horticulturae 2026, 12(2), 242; https://doi.org/10.3390/horticulturae12020242
Submission received: 19 December 2025 / Revised: 9 February 2026 / Accepted: 11 February 2026 / Published: 18 February 2026
(This article belongs to the Special Issue Vitis Genetic Resources: Phenotyping, Genotyping, and Utilization for Sustainable Viticulture)
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Abstract

Historically, certain physiological behaviours were typically attributed to genetic factors. However, some grape varieties exhibit different responses depending on crop management and environmental conditions. The present study examines whether the physiological responses of grapevines traditionally attributed to genotypic traits (near-isohydric or near-anisohydric behaviour) can instead be substantially modified by canopy architecture. The objective was to determine how canopy management influences water relations (leaf water potential—ΨL), physiological plant responses (water use efficiency (WUE), stomatal conductance (gs), transpiration (E) and photosynthetic (A) rates), and radiation interception efficiency (εi), particularly under warm Mediterranean conditions. To test this, two training systems were evaluated in a Syrah vineyard: a vertical shoot position (VSP1) and a sprawl (S1) system with 12 shoots·m−1, under the same irrigation regime. The results showed that under stressed conditions (high vapor pressure deficit [VPD] and relatively lower ΨL, from −1.4 to −0.6 MPa), the S1 system—despite a similar leaf area index, LAI—exhibited lower gs values than those of the VSP1 system (10–30%), with plants closing their stomata to reduce water consumption and prevent their dehydration caused by steep E rates. Meanwhile, the VSP vines exhibited higher gs values (isohydric-like response), indicating higher E rates, which reduced their WUE and intrinsic water-use efficiency (IE). This strategy (similar to the anisohydric one) allowed the S1 treatment to obtain higher WUE and interception radiation efficiency (εi) ratios, even at low ΨL (more efficient), produced by the higher canopy demand (more exposed surface area [SA]). These contrasting behaviours indicate that sprawl systems can enhance radiation interception and WUE compared with vertical systems under semiarid Mediterranean conditions.

Graphical Abstract

1. Introduction

Water availability in food production is highlighted in the latest IPCC report [1] as the main adverse loss- and damage-related impact of climate change, which will continue to intensify. Therefore, there is unlikely to be sufficient water for food production in 2050 due to increased agricultural and ecological droughts, causing water scarcity that will impact the world’s food production [2]. Water-use efficiency (WUE; A/E), which is important for preventing the depletion of natural resources, is one of the most valued objectives in grapevine cultivation under Mediterranean climates [3].
During the growing season, in semiarid Mediterranean conditions, the total water available for plants in the soil is significantly lower than the evaporative demand, thereby limiting the quality of production. This is even more pronounced in the current water scarcity context, caused by summer drought periods, which have been longer than usual [3,4]. Consequently, plants have developed various physiological adaptation strategies to enhance their water-consumption efficiency, particularly under conditions of water deficit or scarcity. Plant responses to water deficit are complex and involve both adaptive changes and deleterious effects, with vine response to water stress influenced by numerous factors, including genotype, climate, soil, and vineyard management [4].
Plants have evolved several drought-adaptation strategies across ecology, biology, physiology and agronomy [5]. These strategies encompass both rapid responses to low soil moisture (dehydration escape or avoidance) and major survival mechanisms for coping with drought (dehydration tolerance, dormancy, cavitation tolerance, desiccation tolerance). Nevertheless, one of the most common plant adaptation strategies in response to drought or increased vapour pressure deficit (VPD) is stomatal closure, a potential indicator of water stress. In the short term, stomatal conductance (gs) is among the first physiological processes in expanded leaves to respond to drought [6]. Plants have two different daily patterns of water relations based on their ability to decouple their leaf water potential from atmospheric demand. The terms iso/anisohydric were introduced by Berger Landefeldt [7] to describe these patterns.
Isohydric plants are those that close their stomata in response to a relevant drop in soil water potential or increased atmospheric demand. Through stringent stomatal control, they maintain their leaf water potential (LWP; ΨL) at a high level, with the objective of avoiding the depletion of available water. These varieties (e.g., Grenache) respond to water stress by modifying their growth and physiology, including rapid stomatal regulation, high sensitivity and high stem conductivity, to maintain leaf water potential constant (ΨL) during the day. Therefore, they close their stomata to high ΨL, avoiding damage from water stress [8].
In contrast, anisohydric plants do not close their stomata and maintain transpiration activity, even when soil water content decreases, thereby keeping stomata open at high levels of water deficit, resulting in a decrease in leaf water potential [9]. These varieties (e.g., Syrah) allocate all the available water to growth and physiological processes, even when this availability is not guaranteed throughout the cycle. This behaviour can compromise the plant’s survival, maximising stomatal opening and, consequently, CO2 assimilation, at the risk of embolism. Additionally, high temperatures and VPD reduce stomatal sensitivity to abscisic acid (ABA) [10]. Consequently, their ΨL falls more than that of isohydric cultivars, exposing them to more severe effects of water stress [11].
Traditionally, this behaviour has been attributed to genetic or varietal factors. In Vitis vinifera L., varieties have usually been classified as isohydric or anisohydric based on their physiological response to water deficit [8,9,10].
Nevertheless, some varieties, such as Sangiovese, Grenache, Cabernet Sauvignon, Semillon, Merlot, Chardonnay, Airén, and of course, Syrah, exhibit different behaviours under varying environmental, climatic and edaphic conditions [7,12,13,14,15]. Other authors note that the plant’s anatomical architecture (xylem vessel diameter, hydraulic conductivity, and stomatal density) is the main determinant of this behaviour [16]. These differences are not limited to wine grape varieties; both behaviours can also be found in table grapes, even within the same variety [17].
This genotype classification can vary, leading to conflicting results for the same cultivar, mainly due to differences in growing conditions, hydraulic conductance control on gs, and the degree of water deficit [9]. As a result, varietal classification based on this criterion is vague and is now questioned [7,18].
The Syrah cultivar usually exhibits low stomatal regulation at low potentials, depending on the evapotranspirative demand, which causes characteristic near-anisohydric behaviour [8] in response to soil water stress. However, other factors could shift this response toward a near-isohydric behaviour, such as irrigation, root development and ABA physiology [10]; partial rootzone drying and deficit irrigation [12]; adaptation to drought and soil water deficit [19]; environmental conditions and water management [14] or soil water-holding capacity and stomatal hydraulic control [20].
Among these factors, training and trellising systems are among the most relevant for managing plant water consumption and sunlight interception, because canopy modifications affect the clusters’ microclimate [3,21,22]. Canopy management (the placement of leaves, branches and clusters within the plant) can modulate processes, such as transpiration, photosynthesis, and stomatal conductance, among others, by altering the total leaf-area surface exposed, particularly in response to variables such as temperature and sun-exposure duration [23]. Severe water deficit reduces leaf area, thereby decreasing intercepted light, which, in turn, combines with stomatal closure to limit photosynthesis and assimilate production [6].
Therefore, this work hypothesises that plant physiology (conductance, net photosynthesis and transpiration) can be seriously modified by the training system (surface leaf area exposition), causing variations in intercepted radiation efficiency, photosynthesis, stomatal conductance and, consequently, different patterns in plant–water relations (water use efficiency (WUE) and intrinsic water use efficiency (IE; A/gs), leaf water potential), which are similar to near-isohydric or anisohydric behaviours, especially in warm, dry climates or under water scarcity conditions.

2. Materials and Methods

2.1. Field Trial Design

This trial was conducted (2005– 2007) in a commercial vineyard located in the Castilla la Mancha Region (Spain; 44°15′ N, 3°59′ W and 488 m above sea level). The vineyard was planted in 2001 on a fine clay-sandy soil (Palexeralf, Soil Survey Staff, USDA classification) with a 50 cm-deep superficial clay horizon (50–55% clay). The weather conditions were typical for a Mediterranean semiarid climate (Papadakis classification). The cultivar was Syrah, grafted onto 110R with 1.2 m spacing, in NW–SE (+8.3° to West) orientated rows with 2.7 m between rows. Irrigation system drippers (3 L·h−1) were spaced at 1.2 m along the planting line, and the amount applied during the cycle (231, 248 and 162 mm annually for 2005, 2006 and 2007, respectively) started before veraison and was equal across all treatments. Climatic conditions (Table 1) during these years were extremely warm and dry, particularly in 2005 and 2006. Differences can be observed mainly in accumulated degree days (2413, 2525 and 2030 °C per year, respectively), low rainfall (199, 271 and 274 mm per year, respectively) and evapotranspiration reference (ET0; calculated via the FAO Penman-Monteith method [24]: 1269, 1211.1 and 1064.6 mm per year, respectively) index.
The experimental design comprised two treatments, which were completely randomised into four blocks. Each plot had four vine rows (two central and two external), with 20 plants per row. Grapevine measurements were taken from the two central rows, with the external rows, as well as the first and last vines of each row, acting as buffers. The examined treatments (to assess the impact of the training system) were: (i) VSP1, vertical positioned system with 12 shoots·m−1 of crop load and (ii) S1, sprawl with 12 shoots·m−1 of crop load. Plants were spur-pruned and trained to a bilateral cordon at 1.40 m (Figure 1). The sprawl system had a single pair of vegetation wires from 0.4 m to the basal wire, spaced 0.6 m apart. The VSP1 system had two wires from 0.3 m to the basal wire, and a higher wire at 1.5 m.

2.2. Surface Leaf Area and Intercepted Radiation Efficiency (εi)

Intercepted radiation by the plant. To assess the relationship between leaf surface area (vegetation and porosity) and the radiation intercepted by the plant, the most reliable indicator is the real exposed surface area [25]. This ratio integrates the total leaf area (Leaf Area Index, LAI; m2 leaf area/m2 ground area) and the percentage of photosynthetically active radiation intercepted (PAR; µmol·m−2·s−1) by the plant.
LAI was measured during the ripening-maturity period (DOY 216, 241 and 240 for 2005, 2006 and 2007, respectively). Total LAI (m2 leaf-area m−2 soil area) was determined by measuring four representative shoots (mains and secondary) per plant, across two plants per treatment and block, following the methodology described by Carbonneau (1976), which was modified by Sánchez de Miguel et al. in 2011 [26] based on the field measurement of the main vein length.
Percentage of photosynthetically active radiation intercepted. The radiation measurements were carried out on a clear day at 8 solar time (s.t.), 12 s.t. and 16 s.t., during the ripening period (207, 208 and 228 DOY for 2005, 2006 and 2007, respectively), using a LI-191 SA Line Quantum Sensor (LICOR©, Lincoln, NE, USA), one metre in length and equipped with a high-sensitivity silicon photovoltaic detector. Data were automatically recorded using a portable data logger (LI-1000, LICOR©, Lincoln, NE, USA), which allowed for direct readings of the PAR (µmol·m−2·s−1) intercepted by the vine canopy. The fraction of PAR intercepted by the canopy was calculated as the ratio between intercepted PAR (incident PAR—transmitted PAR; Ri-Rt) and incident PAR and was measured at solar noon on each sampling date, always under clear sky conditions.
Surface exposed area (SA; m2 external foliar·m−2 surface soil) was calculated based on the inner geometric parameters of each system at ripening-maturity period (DOY 216, 241 and 240 for 2005, 2006 and 2007, respectively). Five width measures were taken at two different heights, across two vines per treatment and block. For the VSP treatment, the area was likened to a parallelepiped, and measurements were taken from the vegetation lateral wall (total vegetation height, basal vegetation zone and fruiting zone) and the width of row vegetation. In the sprawl system, the perimeter was estimated by using flexible tape to closely follow the external border of the vine, and a vector graphics program (ACad v.17.1; 2008®) was used to calculate the circular section of the plant wall along the row.
Intercepted radiation efficiency (εi). This efficiency is defined as the ratio between incident radiation and intercepted radiation [27]:
εi = 1 − (Rt/Ri),
where Ri is the incident radiation reaching the system, and Rt is the radiation transmitted through the canopy to the soil. This value ranges from 0 (bare soil) to 1 (completely opaque canopy).

2.3. Plant Physiology

Plant water status was estimated by measuring leaf water potential at pre-dawn (Ψaa), at maximum photosynthesis rate (08:00 s.t; Ψmax), at midday (12:00 s.t; Ψ12h) and stem water potential (12:00 s.t; Ψstem) using a Scholander type pressure chamber (PMS®, Portland, OR, USA). At the same time, the leaves were covered with a plastic bag before the petiole was severed. The gas flow was limited to 0.2 bar s−1, and the measurement was performed within 1–1.5 min after detaching the leaf from the plant. To measure the Ψstem, leaves were covered with aluminium foil approximately 90–120 min before midday. All measurements were taken on clear days, using mature, healthy leaves exposed to direct sunlight and located on primary shoots in the bunch zone. Each measure (Ψaa, Ψmax and Ψ12h and Ψstem) was carried out on six leaves per treatment (two leaves in three blocks) at three phenological stages: fruitset (DOY 160, 151 and 163 for 2005, 2006 and 2007, respectively), veraison (DOY 201, 208 and 212 for 2005, 2006 and 2007, respectively), and end-of-ripening (DOY 229, 241 and 240 for 2005, 2006 and 2007, respectively).
Physiological responses. Photosynthesis or net CO2 assimilation rate (A), transpiration rate (E), stomata conductance (gs), water use efficiency (A/E; WUE) and intrinsic water use efficiency (A/gs; IE) measures were determined using healthy, mature and well sun-exposed leaves that were located on primary shoots in the bunch zone. Measurements were taken at maximum photosynthetic activity (08:00 s.t.) and at midday (12:00 s.t.), at three phenological stages (fruitset, veraison, and end-of-ripening; same dates that plant water status measures), and were replicated with six different leaves for each date and treatment (two replicates per block) using portable IRGA equipment (Li-6400, LI-COR© Inc.; Lincoln, NE, USA).

2.4. Statistical Analysis

Finally, all data were analysed using analysis of variance (ANOVA) in SPSS® v.26.0 (IBM, Armonk, NY, USA) at the 5% significance level to compare means between treatments.

3. Results

Our results are discussed and evaluated based on the three-year trial period. In the first section, surface leaf-area exposure, radiation and interception efficiency are examined. Following this, the second section focuses on plant physiological responses (leaf water potential, photosynthesis, transpiration, conductance, etc.).

3.1. Surface Leaf Area and Intercepted Radiation Efficiency (εi)

Photosynthesis processes depend on radiation, temperature, and atmospheric CO2 concentration. Yield depends on three factors: radiation interception, radiation use efficiency (RUE) and harvest index (HI) (RUE (units of g/(MJ PAR) is the slope or ratio between biomass and intercepted radiation. HI is the fraction of biomass that is harvested (HI = Y/B) [28]), all of which can be modified by the training system [28]. Radiation interception is also a key factor in determining crop yield and depends on incident radiation, leaf area index (LAI) and extinction coefficient (K). Different training systems can modify LAI and K values, and differences in solar interception may explain improved use of natural resources [29]. Consequently, the canopy plays a key role in determining how effectively the vineyard captures and utilises available solar energy, shaping the vine’s physiological behaviour and overall productivity.

3.1.1. Total Surface Leaf Area (LAI) and Exposed Surface Area (SA)

Regarding the LAI (Figure 2), although it was expected, VSP1 and S1 showed similar values across all seasons. These results can be explained by both treatments having the same crop load (12 shoots m−1) and irrigation regime/doses. Nevertheless, the exposed surface area was higher in the open system than in the vertical system (VSP1 had 82% of S1’s exposed surface area).

3.1.2. Intercepted Radiation Efficiency (εi)

Under warm climatic conditions, when most physiological processes are limited by frequent water stress, temperature, relative humidity, and atmospheric evaporative demand, the optimal use of soil water reserves and the efficiency of radiation interception become critically important.
Regarding the daily mean radiation balance (Table 2), the open system (S1) tended to intercept higher levels of radiation (+18%) during the hours before harvest. Although no differences between treatments were observed in the average or cumulative balance, S1 demonstrated a higher average efficiency (+19%) than VSP1.
However, when we examined the hourly balance, we observed notable afternoon differences (Figure 3) and a general trend, but no other significant differences during the day. At 16:00 s.t., S1 intercepted 40% more radiation than VSP1 and with superior efficiency (35%).
It should be remarked that, in the split year analysis, at the end of the day, the S1 treatment intercepted higher radiation than the vertical system (Ri-Rtac values in VSP1 represented 52% and 77% of S1 in 2006 and 2007, respectively; p < 0.05), especially with the same LAI, but not in 2005 (first year of the trial; Table 3), when no differences between treatments were found.

3.2. Plant Physiology

3.2.1. Leaf and Stem Water Potential

Leaf water potential measurements indicated that both treatments showed similar nocturnal rehydration, suggesting that conditions at the onset of photosynthetic activity were comparable. No significant differences between treatments were observed in leaf water potential, as measured at predawn and at the hour of maximum photosynthesis over three years, with only a minor difference at fruit set, when S1 showed a lower value than VSP1.
Although no statistically significant differences were found (Table 4), a slight trend was observed. The midday values (Ψ12h) tended to differ slightly, with lower values in S1 than in VSP1. Notably, under the same water-availability conditions, the smallest differences in midday measures were observed between fruit set and veraison (but not in stem water potential-Ψstem), suggesting a likely higher water-stress level in the sprawl treatment. This is in line with previous studies in which Ψ12h was among the most reliable indicators of vine water status [30,31]. At the end of ripening, no differences were detected. Depending on the year (between veraison and harvest), leaf water potential values recorded during most of the ripening period correspond to stress conditions according to Van Leeuwen et al. [29]. These severe environmental conditions may have minimised differences among treatments due to extreme temperatures or drought (see 2005 and 2006 values). Even when differences were not statistically significant, S1 tended to have lower VSP1 values, closer to −1.5 MPa, which could represent a limiting factor for physiological processes [29,32].

3.2.2. Physiological Responses

Several studies have identified stomatal conductance and leaf water potential responses to vapour pressure deficit (VPD) as key variables for distinguishing between isohydric and anisohydric behaviours [7,8,10,33,34,35,36]. In particular, the regression between stomatal conductance and soil water potential, or minimal day leaf water potential/midday [37], can elucidate both. Isohydric-like vines typically exhibit stomatal closure at relatively high midday leaf water potential, whereas anisohydric-like vines maintain stomatal opening until much lower values are reached. Our results (Figure 4) indicated that at low leaf water potentials (red zone: <−1.4 MPa), both treatments exhibit similar responses, closing stomata to prevent embolism under severe stress conditions.
However, at high potentials (yellow area: from −1.2 to −1.4 MPa), S1 began to exhibit lower stomatal conductance values, approximately 10–20% below those of VSP1. At even higher potentials (green area: from −1.0 to −0.6 MPa), S1 maintained stomatal conductance values below 0.2 (mol m−2 s−1), representing a 20–30% reduction compared to VSP1. This pattern suggests that S1 closes stomata earlier, reducing transpiration and enhancing water-use efficiency, under certain leaf water potential values.
The relationship between net photosynthesis (A) and stomatal conductance (gs) over the three years (Figure 5) supports this fact. S1 consistently achieved higher A values regardless of the stomatal conductance aperture compared with VSP1. These differences may be explained by the more stressful microclimatic conditions (leaves and clusters Tª; Hr) experienced within the VSP1 canopy as previously reported by de la Fuente et al. in their 2016 paper on cluster microclimate (temperature and relative humidity) [38].
WUE in leaves is strongly influenced by vapour pressure deficit (VPD), temperature and air CO2 concentration, due to their impact on stomatal conductance (gs) [9,19,39]. In our study, WUE (defined as the ratio of net photosynthesis to transpiration rate [Table 5]) was generally higher in S1 than in VSP1, with increases of approximately 10% at 8:00 s.t. and 17% at 12:00 s.t.
WUE is widely recognised as a useful and reliable indicator of vineyard sustainability, particularly under adverse climate change conditions like drought [9]. Intrinsic water-use efficiency (A/gs) is a ratio that better explains the stomatal regulation. No differences were observed at 8:00 s.t., when vines reached maximum net photosynthesis assimilation. However, as temperature and VPD increased during the morning, the plants’ transpiration rates also increased, until reaching a threshold where gas exchange with the atmosphere was restricted (to prevent embolism). Under these conditions, VSP1 consistently had lower A/gs values (−27%) than S1 at 12:00 s.t. (across all seasons), suggesting a less efficient stomatal response under stress.

4. Discussion

4.1. Surface Leaf Area, Radiation and Intercepted Radiation Efficiency (εi)

The LAI/SA relationship (Figure 2) suggests that the S1 system may support a greater number of exposed and active leaves than VSP1, giving more photo-assimilates to the plant, due to the larger (+18%) exposed leaf area, despite similar LAI values. These results are consistent with previous work reporting that the sprawl trellis is more efficient than VSP, with higher net A per LAI unit and greater resilience under progressive water deficit [40].
Although Syrah generally maintains relatively uniform photosynthetic activity throughout the canopy under high-temperature conditions [41], some differences in intercepted radiation were observed during the day (Table 2). On average, S1 exhibited 19% higher efficiency than VSP1, with higher mean levels of intercepted radiation (+18%). Furthermore, in an hourly balance, S1 intercepted 40% more radiation than VSP1. It achieved higher efficiency (35%) in the first hour of the afternoon (Figure 3), when environmental conditions are more demanding for the plant than in the morning. This delayed efficiency during the afternoon can be explained by the row orientation (NW-SE; +8.3° to West), which maximises the difference with this exposition under Mediterranean conditions, because row orientation towards the west can increase the leaf area exposed, yield, and water use efficiency [42]. In addition, principal shoots are usually more active than secondary shoots during the first stages of the growth cycle. However, secondary shoots and leaves can exhibit equal or even greater photosynthetic activity under certain conditions (e.g., basal position, morning sun), with secondary leaf-surface development being key to global photosynthesis in the cycle. Even if the developmental differences between main and lateral shoots are less pronounced in Syrah than in other varieties [41], the impact of secondary leaves on the plant physiological parameters and, therefore, its global productivity, could be relevant in sprawl training systems.
Accumulated interception radiation values recorded in 2006 and 2007 indicate greater interception efficiency in the sprawl-trained system compared to the vertically trained trellis system. The interannual differences (higher radiation interception in 2006 and 2007 than in 2005) are attributable to the transformation of the S1 treatment from a VSP training system to a sprawl system in 2004–2005. These differences can be relevant (depending on seasonal conditions), with the canopy system intercepting up to 33–48% more radiation and with higher efficiency (Table 3). Many previous studies [21,25,27,33,40] have highlighted the direct relationship between SA and canopy interception of radiation, particularly in free and open systems, where total diffuse radiation plays a more significant role [40] and is a key factor for improving process efficiency. According to del Zozzo et al. [40], under well-watered conditions, sprawl systems achieved significantly higher A rates per LAI than VSP, and total direct light was strongly correlated with this ratio. In our trial, both treatments received the same irrigation doses and amounts, thereby avoiding severe stress, and both had similar LAI values (but not SA). Therefore, the higher radiation interception efficiency in the open system (S1) may directly improve water-use efficiency (A/E) and intrinsic water use efficiency (A/gs) relative to the VSP1 system. Additionally, the sprawl system may have a slight influence on dry matter accumulation and yield, but evidently affects berry quality, mainly by increasing total anthocyanin content more than the VSP system [22].

4.2. Plant Physiology

Leaf water potential showed no significant differences between treatments; only S1 tended to have slightly lower values relative to VSP1 from fruit set to veraison, being closer to −1.5 MPa at veraison (Table 4). This could constitute a limiting factor for physiological processes [29,30] but does not indicate severe stress in the plants. The interannual differences in leaf water potential indicate that, at fruit set, leaf water potential was lower in the warmer and drier (2005, 2006; Table 1) years than in the mild and moderate year (2007). These differences diminished at veraison, becoming marked again as ripening progressed toward harvest.
These results are consistent with those of Baeza et al. [43] and del Zozzo et al. [40], who reported that free and open systems (bush, curtain, etc.) exhibited higher water potentials in their plants than VSP, likely related to differences in water availability according to the leaf surface exposed area (Figure 2). In our trial, S1 had a larger exposed surface area and consequently required more available water during the day.
The stomatal conductance (gs)/leaf water potential (Ψ12h) curves (Figure 4) help to explain different behaviours under varying stress levels. In stressed plants (red area: <−1.4 MPa), there were no differences in gs. However, at higher potentials (yellow area: from −1.2 to −1.4 MPa and green area from −1.0 to −0.6 MPa), the open system (S1) exhibited a stomatal conductance value approximately 10–30% lower than that of VSP1. This suggests that, because S1 has a higher leaf surface area and therefore requires daily water availability, it needs to maintain low transpiration rates. Therefore, S1 closed their stomata earlier than VSP1, upon reaching a certain minimum leaf water potential level, resulting in greater water use efficiency. In parallel, the VSP near-anisohydric-like response was also demonstrated in our study, as indicated by a higher stomatal aperture at the same time, consistent with previous findings [14]. These results, according to previous studies [7,15,37,41,44], demonstrate that both like-behaviors—nearly anisohydric (VSP1) and nearly isohydric (S1)—can occur under the same conditions (environment, irrigation regime, rootstock, etc.) and even within the same variety [17,45,46], and may be modulated depending on soil and environmental conditions (temperature, relative humidity, water availability, etc.). This undermines the general assumption that Syrah is a strictly anisohydric variety [8,19,44,47,48] and also provides evidence supporting near-isohydric-like behaviour [14] under particular conditions. Additionally, the same cultivar under severe thermic [49] or hydric [45,46,50] stress can vary its anisohydric-like to isohydric-like behaviour.
Data on WUE (Table 5) showed that the S1 system was more efficient than VSP1, despite receiving the same irrigation amount. These differences were most pronounced in the morning, reaching up to 17% by midday. Although gaps remain in scaling from single-leaf to whole-plant responses [49], WUE estimation provides valuable insights into efficiency in biomass accumulation., especially for cultivars grown in warmer, drier regions, which usually exhibit traits that would reduce transpiration and preserve the soil water content longer into the growing season but could potentially increase stomatal and temperature limitations on photosynthesis under future, hotter conditions [43]. It should be noted that interannual differences in both efficiencies indicate that, even though 2006 was a warm year with high ET0 (Table 1), the radiation values and, perhaps above all, the greater water availability (Pe above 270 mm), resulted in higher efficiency values compared with the other two years (2005 with low Pe and 2007 with lower radiation and temperature). These differences diminished at veraison, becoming marked again as ripening progressed toward harvest.
Closing stomata at high leaf water potential may reduce a plant’s resistance to embolism and increase reliance on a water-saving stomatal strategy. This suggests that cultivars grown in warm regions (where evaporative demand is high) that rely on this strategy will be more vulnerable to temperature fluctuations and to CO2-related limitations on photosynthesis under future environmental scenarios [42].
Nevertheless, the intrinsic water use efficiency values (IE) indicate that faster stomatal closure makes open systems (S1) more efficient throughout the morning (lower leaf transpiration, higher photosynthetic rate, superior intrinsic water use efficiency and water use efficiency) than the vertical trellis (VSP1) because they maintain their gs values as low as possible between reasonable limits for the Syrah variety (close to 350 mmol m−2 s−1; [43]). S1 achieved high net photosynthesis (A) ratios even at low Ψ12h (more efficient). This aligns with the findings of Baeza et al. [43], who reported that lower water availability per exposed leaf area leads to stomatal regulation that decreases conductance more markedly than photosynthetic activity, resulting in higher efficiency values. Furthermore, these results align with those of Cogato et al. [45], who reported that, at high Tª, the Syrah variety had higher E ratios than the near-isohydric variety (Grenache). Still, the decline in A was lower; consequently, its IE was higher.
This suggests that stomatal conductance and/or the net photosynthesis rate slowed down in VSP1 (see Figure 5), where no matter the rate, the VSP1 conductance always remained higher than S1 due to lower canopy demand (the same LAI but less SA). Stomatal conductance (gs), which declines as soil water content decreases, plays a pivotal role in plant drought regulation [6] and may affect net photosynthesis (A) more than transpiration rate under high evaporative demand [43]. Therefore, canopy management strategies are increasingly relevant given current climate change projections for the growing period, including rising average temperatures and greater heterogeneity in summer precipitation patterns (i.e., reduced water availability) in Mediterranean climates.
Although previous studies on Syrah have examined its physiological behaviour and radiation interception efficiency under Mediterranean climates [14,16,30,44], far fewer have compared vertically oriented and fixed training systems (VSP) with more porous, free-growth, and open canopies such as sprawl [42]. Therefore, the present study provides an important precedent for understanding the behaviour of Syrah under these conditions and across different canopy management practices.

5. Conclusions

This study highlights the significant influence of canopy management (particularly total leaf area and exposed surface area) on key processes, such as radiation interception, which directly affect grapevine physiological performance (net photosynthetic accumulation, water-use efficiency, and intrinsic water-use efficiency).
Despite similar leaf area index and identical irrigation regimes, the S1 system intercepts more radiation than the VSP1 system. This results in higher transpiration rates and, consequently, slightly lower midday water potentials throughout the growing season. However, due to earlier stomatal closure at even relatively high Ψ12h values and improvements in its microclimate (due to open, porous canopy management), S1 results in greater interception capacity and supports higher net photosynthetic rates for a given stomatal conductance.
Although no statistically significant differences in leaf water potential were detected, S1 consistently exhibited slightly lower midday Ψ12h values, reflecting its greater transpiration, which is linked to its larger exposed surface area. Importantly, stomatal behaviour clearly differed between systems. S1 reduced stomatal conductance at comparatively higher water potentials, thereby improving both water-use efficiency (WUE) and intrinsic water use efficiency (IE) during periods of high atmospheric demand. This response is consistent with a more water-conservative strategy resembling near-isohydric behaviour. Conversely, VSP1 maintained higher stomatal conductance at similar water potentials, aligning with a near-anisohydric pattern.
Furthermore, the correlations between gs and Ψ12h indicate that both physiological behaviours—near-anisohydric-like (VSP1) and near-isohydric-like (S1)—can be observed under the same conditions (environment, irrigation regime, rootstock, etc.) and even within the same variety.
Overall, the findings indicate that open, free-growth systems such as S1 can improve radiation interception efficiency, water-use efficiency, and intrinsic water-use efficiency in warm, dry Mediterranean climates without inducing severe water stress. However, further research integrating plant productivity (dry matter partitioning and yield) and berry composition is required to determine whether these physiological advantages translate into consistent agronomic benefits across seasons.

Author Contributions

Conceptualisation, M.d.l.F., J.R.L. and R.L.; methodology, J.R.L. and P.B.; software, M.d.l.F.; validation, M.d.l.F., S.S.-É. and R.L.; formal analysis, M.d.l.F.; investigation, M.d.l.F. and R.L.; data curation, M.d.l.F.; writing—original draft preparation, M.d.l.F.; writing—review and editing, M.d.l.F., R.L., S.S.-É. and P.B.; supervision, P.B. and J.R.L.; funding acquisition, J.R.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Osborne Distribuidora S.A. and the Spanish Ministry of Science within the framework of a public–private project (MEC. IDI: P030260221).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

The authors gratefully acknowledge the effort of Osborne Distribuidora S.A. for technical support on the implementation of this project. The first (and corresponding) author conducted this work during their research and doctoral studies at U.P.M (2004–2008) and gratefully acknowledges the effort of the people who collaborated in the field trials: Luis E. Moraleda Román, Isaac Esteban Vázquez and Sergio Ortiz Arribas. The authors have reviewed and edited the output and take full responsibility for the content of this publication.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

VSPvertical shoot positioned system
Ssprawl system
gsstomatal conductance
Aphotosynthesis or net CO2 assimilation rate
ETranspiration rate
VPDvapor pressure deficit
WUEwater use efficiency
LWP/ΨLleaf water potential
ABAAbscisic acid
IEIntrinsic water use efficiency
TmMean temperature
GDDGrowing degree days
PePrecipitations
ET0Mean reference evapotranspiration
Ψaaleaf water potential at pre-dawn
ΨmaxLeaf water potential at maximum photosynthesis rate (08:00 solar time)
ΨstemStem leaf water potential
Ψ12hLeaf water potential at midday (12:00 solar time)
L.A.I.Leaf Area Index
PARphotosynthetically active radiation
S.A.Surface exposed area
fIPAR or Ri-Rtphotosynthetically active radiation (PAR) intercepted by the canopy
εiIntercepted radiation efficiency

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Figure 1. Theoretical models based on average surface area (SA) measures (cm) for the training systems: VSP (left) and Sprawl (right).
Figure 1. Theoretical models based on average surface area (SA) measures (cm) for the training systems: VSP (left) and Sprawl (right).
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Figure 2. Leaf area index (LAI) and exposed surface area (SA). *** and ns indicate significance at p ≤ 0.001 and not significant, respectively. 1 VSP1, vertical positioned system with 12 shoots·m−1 of crop load, 2 S1, sprawl with 12 shoots·m−1 of crop load.
Figure 2. Leaf area index (LAI) and exposed surface area (SA). *** and ns indicate significance at p ≤ 0.001 and not significant, respectively. 1 VSP1, vertical positioned system with 12 shoots·m−1 of crop load, 2 S1, sprawl with 12 shoots·m−1 of crop load.
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Figure 3. Hourly mean radiation balance (Ri-Rt4) at the maturity period. 1 VSP1, vertical positioned system with 12 shoots·m−1 of crop load, 2 S1, sprawl with 12 shoots·m−1 of crop load. Sig: significant differences; * indicate significance at p ≤ 0.05. Hourly mean radiation balance (Ri-Rt; µmol/h), PAR-photosynthetically active radiation intercepted; µmol/h) and s.t. solar time.
Figure 3. Hourly mean radiation balance (Ri-Rt4) at the maturity period. 1 VSP1, vertical positioned system with 12 shoots·m−1 of crop load, 2 S1, sprawl with 12 shoots·m−1 of crop load. Sig: significant differences; * indicate significance at p ≤ 0.05. Hourly mean radiation balance (Ri-Rt; µmol/h), PAR-photosynthetically active radiation intercepted; µmol/h) and s.t. solar time.
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Figure 4. Relationship between conductance (gs; mol m−2 s−1) and leaf water potential at midday (Ψ12h 5; MPa). VSP1, vertical positioned system with 12 shoots·m−1 of crop load, S1, sprawl with 12 shoots·m−1 of crop load; * and ** indicate a significant linear relationship at p ≤ 0.05 and at p ≤ 0.01, respectively. Leaf water potential area: red zone (<−1.4 MPa); yellow area (from −1.2 to −1.4 MPa), and green area (from −1.0 to −0.6 MPa).
Figure 4. Relationship between conductance (gs; mol m−2 s−1) and leaf water potential at midday (Ψ12h 5; MPa). VSP1, vertical positioned system with 12 shoots·m−1 of crop load, S1, sprawl with 12 shoots·m−1 of crop load; * and ** indicate a significant linear relationship at p ≤ 0.05 and at p ≤ 0.01, respectively. Leaf water potential area: red zone (<−1.4 MPa); yellow area (from −1.2 to −1.4 MPa), and green area (from −1.0 to −0.6 MPa).
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Figure 5. Intrinsic water use efficiency. Relationship between conductance (gs; mmol m−2 s−1) and net photosynthesis (A; µmol m−2 s−1). VSP1, vertical positioned system with 12 shoots·m−1 of crop load, S1, sprawl with 12 shoots·m−1 of crop load; *** indicates a significant linear relationship at p ≤ 0.001 (n = 110).
Figure 5. Intrinsic water use efficiency. Relationship between conductance (gs; mmol m−2 s−1) and net photosynthesis (A; µmol m−2 s−1). VSP1, vertical positioned system with 12 shoots·m−1 of crop load, S1, sprawl with 12 shoots·m−1 of crop load; *** indicates a significant linear relationship at p ≤ 0.001 (n = 110).
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Table 1. Climatic conditions of each year in the experimental trial (Toledo, Spain).
Table 1. Climatic conditions of each year in the experimental trial (Toledo, Spain).
YearJAN 2FEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
2005Tm 1 (°C)15.04.05.09.514.319.125.526.925.920.515.18.65.8
GDD (°C)2412.60.00.044.4155.2437.7902.51426.71920.62234.92393.12409.82412.6
Pe (mm)199.30.017.10.00.03.63.60.022.022.081.118.531.4
ET0 (mm)1269.031.047.967.9130.2172.1196.5207.4176.1120.657.233.428.5
2006Tm (°C)15.74.96.110.614.319.623.627.325.121.616.912.15.7
GDD (°C)2525.20.00.043.7172.9471.3879.11416.81886.12235.22449.12519.52525.2
Pe (mm)271.58.617.521.20.00.04.90.00.00.0115.895.48.1
ET0 (mm)1211.125.041.881.1115.4163.3184.1193.3171.2115.767.533.019.7
2007Tm (°C)14.35.29.210.212.516.920.724.823.721.114.58.35.2
GDD (°C)2030.10.013.837.5125.3329.2635.31084.41526.31863.52016.52029.42030.1
Pe (mm)274.30.026.00.039.536.245.00.036.95.653.223.88.1
ET0 (mm)1064.616.343.887.9101.6142.5158.6182.8163.8111.056.30.00.0
1 Tm: Mean temperature; GDD: Growing degree days; Pe: Precipitation and ET0: Mean reference evapotranspiration. 2 January, February, March, April, May, Jun, July, August, September, October, November and December.
Table 2. Daily mean radiation balance (Ri-Rt) at maturity, accumulated (Ri-Rt ac) and intercepted radiation efficiency (εi) for both treatments.
Table 2. Daily mean radiation balance (Ri-Rt) at maturity, accumulated (Ri-Rt ac) and intercepted radiation efficiency (εi) for both treatments.
Ri-Rt 4 (mol/h)Ri-Rt ac (mol/h)εi
VSP1 10.664.460.27
S1 20.845.290.33
SEM 5 (82)0.070.450.02
Treatment* 3ns*
20050.63 b3.61 b0.31 a
20060.77 a5.44 a0.24 b
20070.85 a5.59 a0.35 a
SEM (60)0.080.520.03
Year***
Treatment * Yearns*ns
1 VSP1, vertical positioned system with 12 shoots·m−1 of crop load, 2 S1, sprawl with 12 shoots·m−1 of crop load, 3 Significant differences; * and ns indicate significance at p ≤ 0.05 and not significant, respectively. Means followed by the same letter were not significantly different at p ≤ 0.05 according to Tukey’s test. 4 Daily mean radiation balance (Ri-Rt; mol/h), accumulated (Ri-Rt ac; mol/h) and intercepted radiation efficiency (εi). 5 SEM, standard error of the mean, number of samples in brackets.
Table 3. Radiation accumulated balance (Ri-Rt ac) and intercepted radiation efficiency (εi) at the maturity period and each year.
Table 3. Radiation accumulated balance (Ri-Rt ac) and intercepted radiation efficiency (εi) at the maturity period and each year.
YearTreatmentRi-Rt 4 ac (mol/h)εi
2005VSP1 15.910.50
S1 27.630.87
Sig 3nsns
2006VSP13.740.18
S17.15 0.29
Sig***
2007VSP14.88 0.38
S16.29 0.32
Sig*ns
1 VSP1, vertical positioned system with 12 shoots·m−1 of crop load, 2 S1, sprawl with 12 shoots·m−1 of crop load, 3 Sig: significant differences; *, ** and ns indicate significance at p ≤ 0.05; 0.01 and not significant, respectively. 4 Radiation balance accumulated (Ri-Rt ac; mol/h) and intercepted radiation efficiency (εi).
Table 4. Leaf water potential (MPa) at fruit set, veraison and harvest.
Table 4. Leaf water potential (MPa) at fruit set, veraison and harvest.
LWPTreatmentFruitsetVeraisonHarvest
Ψaa 5Ψ8h 5Ψ12h 5Ψstem 5ΨaaΨ8hΨ12hΨstemΨaaΨ8hΨ12hΨstem
TreatmentVSP1 1−0.25−0.71−0.89−0.39−0.41−0.93−1.41−0.77−0.45−0.92−1.30−0.57
S1 2−0.27−0.65−0.93−0.40−0.39−0.90−1.47−0.77−0.41−0.90−1.33−0.49
SEM 3 (n = 18)0.040.020.020.080.040.070.020.110.030.030.040.11
Sig. 4ns*nsnsnsnsnsnsnsnsnsns
Year2005−0.27−0.80 c −1.10 c−0.49−0.31 a−1.05 b−1.51 b−0.67−0.45 b−0.93 b−1.33 b−0.50
2006−0.33−0.65 b−0.90 b−0.42−0.56 b−0.63 a−1.35 a−1.02−0.59 c−1.09 c−1.42 c−0.60
2007−0.18−0.60 a−0.74 a−0.28−0.33 a−1.07 b−1.46 b−0.63−0.26 a−0.72 a−1.19 a−0.50
SEM (n = 12)0.040.020.020.100.050.090.030.130.040.040.050.13
Sig.ns******ns******ns********ns
Year * TreatmentSig.nsnsnsnsnsnsnsnsnsnsnsns
1 VSP1, vertical positioned system with 12 shoots·m−1 of crop load, 2 S1, sprawl with 12 shoots·m−1 of crop load, 3 EEM: standard average error for n = 6 samples per treatment. 4 Sig: significant differences; * indicates significance at p ≤ 0.05, **, *** and ns indicate significance at p ≤ 0.01, 0.001 and not significant, respectively. Means followed by the same letter were not significantly different at p ≤ 0.05 according to Tukey’s test. 5 Ψaa, predawn leaf water potential, Ψ8h, leaf water potential measured at maximum (8 h), Ψ12h, leaf water potential measured at midday and Ψstem, stem water potential measured at midday.
Table 5. Water use efficiency (WUE; A/E) and intrinsic water use efficiency (IE; A/gs).
Table 5. Water use efficiency (WUE; A/E) and intrinsic water use efficiency (IE; A/gs).
WUE 3 (A/E)IE (A/gs)
8:00 s.t. 412:00 s.t.8:00 s.t.12:00 s.t.
VSP1 14.13 2.27 0.100.08
S1 24.58 2.710.110.11
Treatment* 5**ns ***
20054.03 b2.00 b0.10 b0.10 b
20065.01 a2.83 a0.13 a0.11 a
20073.98 b2.64 b0.09 b0.09 b
Year***********
Year * Treatmentnsnsnsns
1 VSP1, vertical positioned system with 12 shoots·m−1 of crop load, 2 S1, sprawl with 12 shoots·m−1 of crop load, 3 Water use efficiency (WUE) and intrinsic water use efficiency (IE) (A/gs); 4 Solar time (st). 5 Significant differences; *, **, *** and ns indicate significance at p ≤ 0.05, 0.01, 0.001 and not significant, respectively. Means followed by the same letter were not significantly different at p ≤ 0.05 according to Tukey’s test.
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de la Fuente, M.; Linares, R.; Lissarrague, J.R.; Sánchez-Élez, S.; Baeza, P. Influence of Canopy Vineyard Management on Physiological Behaviour and Radiation Interception Efficiency in Syrah. Horticulturae 2026, 12, 242. https://doi.org/10.3390/horticulturae12020242

AMA Style

de la Fuente M, Linares R, Lissarrague JR, Sánchez-Élez S, Baeza P. Influence of Canopy Vineyard Management on Physiological Behaviour and Radiation Interception Efficiency in Syrah. Horticulturae. 2026; 12(2):242. https://doi.org/10.3390/horticulturae12020242

Chicago/Turabian Style

de la Fuente, Mario, Rubén Linares, José Ramón Lissarrague, Sara Sánchez-Élez, and Pilar Baeza. 2026. "Influence of Canopy Vineyard Management on Physiological Behaviour and Radiation Interception Efficiency in Syrah" Horticulturae 12, no. 2: 242. https://doi.org/10.3390/horticulturae12020242

APA Style

de la Fuente, M., Linares, R., Lissarrague, J. R., Sánchez-Élez, S., & Baeza, P. (2026). Influence of Canopy Vineyard Management on Physiological Behaviour and Radiation Interception Efficiency in Syrah. Horticulturae, 12(2), 242. https://doi.org/10.3390/horticulturae12020242

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