Photosynthetic resilience of dry‐farmed ‘Pedro Ximénez’ grapevines under organic versus conventional management in a warm Mediterranean vineyard

Abstract

BACKGROUND

Organic viticulture is expanding across Mediterranean wine regions, driven by EU sustainability policies and increasing consumer demand. However, comparative studies assessing both physiological performance and productivity of grapevines under organic and conventional management while maintaining similar soil and climatic conditions remain limited, particularly in dry‐farmed warm Mediterranean environments. This study evaluated the physiological and agronomic responses of the grapevine cultivar ‘Pedro Ximénez’ over two consecutive seasons (2022–2023) in a commercial dry‐farmed vineyard in south‐western Spain managed under certified organic and conventional management systems.

RESULTS

Leaf gas‐exchange parameters including net photosynthetic rate (A _N), stomatal conductance (g _s), intrinsic water‐use efficiency (_iWUE), and the stomatal stress integral (SI _gs) were monitored alongside agronomic parameters such as bunch number, bunch weight, and pruning weight. Across both seasons, organically managed vines showed lower cumulative stomatal stress (SI _gs reduced by 37% in 2022 and 14% in 2023) while maintaining similar seasonal iWUE values. During high vapor pressure deficit episodes, electron transport rate (ETR) remained comparable between management systems whereas A _N declined, indicating that photosynthetic reductions were mainly associated with CO₂ diffusional or biochemical limitations rather than photochemical impairment. Yield components were comparable between systems, although organic vines produced more clusters per plant in 2023 (17 ± 0.9 vs 15 ± 0.8; Tukey test, P < 0.05).

CONCLUSION

Under the conditions of this commercial, warm Mediterranean vineyard, organic management was associated with reduced seasonal stomatal stress while maintaining comparable productivity, suggesting that organic viticulture may represent a viable strategy for dry‐farmed vineyards in warm Mediterranean regions. © 2026 Society of Chemical Industry.

INTRODUCTION

As the EU redefines its agricultural policies to meet contemporary challenges, there is a growing recognition of the need to prioritize sustainable practices. For this reason, the Common Agricultural Policy (CAP), ¹ implemented through Member States' National Strategic Plans, focuses on advancing research, knowledge sharing, and innovation. The 25% organic‐area objective is an EU‐wide target set by the European Commission Organic Action Plan for 2030, ² to which Spain's National Strategic Plan contributes.

Grapevines are one of the main fruit crops, with a global surface area under cultivation of 7 201 944 ha in 2023. ³ Spain is the European Union country with the largest grapevine cultivation area, accounting for 945 061 ha. ³ However, only 149 934 ha were certified as organic in 2022, corresponding to 18.5%. ⁴ These figures are below the targets set by EU agricultural policies, and therefore research funding has been prioritized to help meet the established goals.

Additional challenges facing the viticulture sector include adapting to the negative effects of climate change. In this context, organic viticulture has emerged as a strategy for mitigating climate‐induced stressors in vineyards. ⁵ This type of viticulture is characterized by reducing synthetic inputs, enhancing biodiversity, and promoting soil conservation practices – thus emerging as a cornerstone in this paradigm shift. ⁶ Organic systems contribute to soil health, reduce greenhouse gas emissions, and enhance biodiversity. ⁶ These attributes are critical for building resilient agricultural systems capable of withstanding the uncertainties posed by climate change. ⁷ Despite skepticism regarding the economic feasibility of organic farming, evidence suggests that organic agriculture can be economically viable and also contribute to rural development. ⁸

Within this context, other climate‐change adaptation strategies include the use of grapevine cultivars or clones grown in warm climate zones.^{9, 10, 11, 12} In this regard, the ‘Pedro Ximénez’ grape cultivar – which has been cultivated for centuries in Spain – has attracted scientific inquiry. This cultivar has historically been associated with the production of sweet wines, such as those produced in the Designations of Origin (D.O.) Montilla‐Moriles, Málaga, and Jerez‐Xérès‐Sherry. ¹³ However, beyond its traditional use, this grapevine cultivar demonstrates remarkable adaptability to diverse climates and soil types, making it a versatile option for viticulturists seeking resilience in varying terroirs. ¹⁴ Acknowledged for its adaptability and resilience, the ‘Pedro Ximénez’ cultivar has shown promise in withstanding environmental stressors, making it a compelling focus for research. ¹⁵

This cultivar has received relatively limited attention in physiological studies compared with other grape cultivars. This lack of comprehensive research has hindered the elucidation of critical physiological aspects, such as water relations,^{16, 17} photosynthetic characteristics, ¹⁸ responses to environmental conditions, ¹⁹ or the influence of soil management on vegetative growth. ²⁰ Quantitative assessments of intrinsic water use efficiency (_iWUE) and the seasonal stomatal‐stress integral (SI _gs) are lacking for ‘Pedro Ximénez’ and other minor cultivars, despite their recognized value as drought‐adapted genotypes. This scarcity of research leaves viticulturists without important information for crop management.

It was therefore hypothesized that organic management in a Mediterranean dry‐farmed vineyard would: (i) reduce the cumulative SI _gs, (ii) enhance _iWUE, (iii) maintain yield components relative to conventional management, and (iv) preserve electron transport rate (ETR) during episodes of high atmospheric demand indicating non‐photochemical limitations to the net photosynthetic rate (A _N). To test this hypothesis, leaf gas exchange (A _N and g _s), ETR, _iWUE and seasonal SI _gs were monitored together with yield components in ‘Pedro Ximénez’ grapevines over two consecutive seasons under certified organic and conventional management systems. This study addresses the evidence gap for ‘Pedro Ximénez’ cultivar by quantifying cultivar‐specific physiological responses to management.

MATERIAL AND METHODS

Experimental site

The experiment was conducted from August to November 2022 and from April to August 2023, in a private vineyard (Dos Mercedes, Jerez de la Frontera, Cadiz, Spain) belonging to Williams & Humbert, SW Spain (36° 44′ 53.88″ N, 6° 7′ 42.53″ W) at 100 m above sea level.

Seven‐year‐old grapevines (Vitis vinifera L., ‘Pedro Ximénez’) grafted on 161‐49 Couderc rootstock were used in the study. The grapevines were trained to a single Cordon de Royat system with eight buds per vine. They grew in an albariza soil, with a row‐to‐vine spacing of 2.40 × 1.10 m. Albariza soil is characterized by high calcium carbonate content, with 25% to 40% active limestone, low organic matter and nitrogen levels, and a high level of porosity, which helps to retain moisture. ²¹ The training system was a vertical shoot positioning (VPS) system with movable wires. No irrigation or fertilization treatments were applied during the study. Inter‐row vegetation was absent during the experiment, and the soil surface between vine rows remained bare, following the traditional soil management practices used in albariza vineyards. Plant protection practices were carried out by the vineyard management team of Williams & Humbert according to their standard protocols for conventional and certified organic production. These operations were not controlled by the researchers but followed the routine management of the commercial vineyard.

The climatic classification of the study area was typical Mediterranean (Csa). ²² The average historical data for the 2012‐2022 period indicate an annual reference evapotranspiration (ETo) of 1308 mm and an accumulated rainfall of 458 mm. Over this period, the temperature ranged from 8.82–26.95 °C, and the relative humidity ranged from 50.72% to 91.59% (data obtained from the Agroclimatic Information Network of Andalusia (RIA), Basurta Station, Jerez de la Frontera, Cádiz, Spain).

Plant measurements

During the experiment, leaf stomatal conductance (g _s) and net photosynthetic capacity (A _N) were measured weekly between 10:00 a.m. and 12:00 p.m. GMT in a marked, fully expanded leaf on each side of the canopy. Measurements were taken using an open gas‐exchange system (Li‐6800; Li‐Cor, Inc., Lincoln, NE, USA) equipped with a fluorescence chamber, utilizing saturating radiation light at 1200 μmol m⁻² s⁻¹ and a CO₂ reference of 400 μmol mol⁻¹. These measurements were performed on a total of 24 vines with an agronomic management system. Physiological measurements were conducted during two consecutive seasons (2022 and 2023). In the figures, data from both seasons are displayed along a common day‐of‐year (DOY) axis to facilitate visualization of the seasonal dynamics of grapevine gas‐exchange variables. Simultaneously with the physiological measurements, temperature and humidity were recorded with a data logger (LOG‐210 Labprocess, Barcelona, Spain) to analyze the plant–atmosphere response. Intrinsic water‐use efficiency (_iWUE) was calculated for every leaf as the ratio A _N/g _s (μmol CO₂ mol⁻¹ H₂O). The relative electron‐transport rate (ETR) was obtained from the simultaneous chlorophyll fluorescence signal of the LI‐6800 chamber.

To quantify total water stress supported by the crop in both years, the stomatal‐stress integral (SI _gs) was calculated from the g _s data, following the methodology proposed by Myers, ²³ as shown in Eqn (1):

$${\mathit{SI}}_{\mathrm{gs}}=\sum \left(g_s^{\mathit{max}}-g_s^{\mathit{av}}\right)·n$$ (1)

where ${\mathit{SI}}_{\mathit{gs}}$ is the stress integral in terms of stomatal conductance values and $g_s^{\mathit{av}}$ is the mean stomatal conductance measured during each sampling interval; $g_s^{\mathit{max}}$ is the maximum value of stomatal conductance during the monitoring period, and n is the number of days between consecutive measurements. In this study, $g_s^{\mathit{max}}$ was defined as the maximum g _s value recorded across the entire dataset and was used as a common reference for both management systems.

At harvest (236 DOY in 2022 and 240 DOY in 2023) the bunch numbers were counted and the weight of each of the physiologically monitored vines was determined using a hanging balance (Kern, HDB 10 K‐2XL, Balingen, Germany). After grapevine winter stoppage, pruning was performed when all the leaves had fallen (DOY 356 in 2022 and DOY 152024), recording the pruning weight of each of the physiologically monitored vines determined using the hanging balance mentioned above.

From February to August in 2023, phenological monitoring of the grapevines was carried out on a weekly basis. The scale described by Baggiolini ²⁴ was used to determine the phenological stage visually (Fig. 1). To establish the phenological stage of each vine, buds on the four central spurs were counted, identifying the phenological stage that was present in more than 50% of the buds. These observations were performed on a total of 50 vines per management.

Figure 1.

Phenology described by Baggiolini ²⁴ and illustrated with original photographs taken by the authors. (A) Winter rest. (B1) Weeping. (B2) Swollen bud. (C) Green tip. (D) Incipient leaves. (E) Spreading leaves. (F) Clusters visible. (G) Separated clusters. (I1) Beginning of flowering. (I2) Total flowering. (J) Full flowering. (K) Pea size grain. (L) Cluster compaction. (M1) Start of veraison. (M2) Full veraison. (N) Ripening.

Experimental design and statistical analysis

The study was conducted in two adjacent plots within the same commercial vineyard, both planted with the same cultivar, rootstock, training system, and planting geometry. One plot was managed under conventional practices and the other followed certified organic management established in 2016. Because the comparison involved one plot per management system, the study should be interpreted as a field comparison under commercial vineyard conditions rather than as a fully replicated plot‐scale experiment.

Within each plot, three rows were selected and eight vines per row were monitored for physiological and agronomic measurements (n = 24 vines per management). Vines were selected following the methodology described by Santesteban et al. ²⁵ to ensure representative plants within each plot. Repeated measurements were performed on the same tagged vines throughout the study period.

Statistical analyses were performed using R statistical software (R Core Team, version 4.4.0, Vienna, Austria; RStudio (Posit) version 2026.01.1 + 403 ‘Apple Blossom’, Boston, MA, USA). Descriptive analyses of all physiological and agronomical variables were first conducted by sampling date across the two growing seasons. Homogeneity of variances was assessed using Levene's test.

Physiological variables (A _N, g _s, _iWUE, and ETR) were analyzed using linear mixed‐effects (LMM) models to account for the repeated measurements performed on the same vines over time. Management (organic vs conventional), sampling date (DOY), and their interaction were considered as fixed effects, whereas vine identity was included as a random factor. The DOY was treated as a categorical temporal factor within each monitoring period. Temporal autocorrelation structures were explored during model fitting but were not retained because they did not improve model performance according to the Akaike information criterion (AIC).

When significant effects were detected, pairwise comparisons between management systems at each sampling date were performed using Tukey‐adjusted contrasts. Yield‐related variables were analyzed using two‐way analysis of variance (ANOVA) with management and season as fixed factors. The relationship between A _N and g _s was analyzed by linear regression, and differences between management systems were evaluated using ANCOVA to test for differences in slopes and intercepts.

RESULTS AND DISCUSSION

Experimental conditions

Table 1 summarizes the monitoring periods, DOY range, and climatic conditions associated with each experimental season. The mean air temperature during the monitoring period was 26.5 °C in 2022 and 18.5 °C in 2023. In 2022, the average daily maximum temperature was 32.0 °C and the minimum was 18.2 °C, whereas in 2023, the maximum was 26.42 °C and the minimum was 9.83 °C. The total rainfall during the monitoring period was 182.0 mm in 2022 and 144.81 mm in 2023, distributed from January to June. Accumulated reference ETo during the experiment was 410 in 2022 and 1063.7 mm in 2023. The vapor pressure deficit (VPD) ranged from 0.64 to 2.82 kPa in 2022 and 0.21–1.72 kPa in 2023, with higher values observed during summer. This ‘Csa’ Mediterranean climate is typical for warm‐zone cultivars such as ‘Pedro Ximénez’. ²²

Table 1.

Monitoring periods, day‐of‐year (DOY range) and climatic conditions associated with each experimental season

	2022	2023
T min (°C)	18.2	9.8
T max (°C)	32.0	26.4
T avg (°C)	26.5	18.5
RHmin (%)	28.0	35.6
RHmax (%)	70.1	81.8
RHavg (%)	50.0	61.4
Rainfall (mm)	182.0	144.8
ETo (mm)	410.0	1063.7
VPDmin (kPa)	0.6	0.2
VPDmax (kPa)	2.8	1.7
DOY range	214–314	103–240
Main physiological measurements	A N, g s, iWUE, ETR	A N, g s, iWUE, ETR, phenology

ETo, reference evapotranspiration; RH_avg, average relative humidity; RH_max, maximum relative humidity; RH_min, minimum relative humidity; T _avg, average temperature; T _max, maximum temperature; T _min, minimum temperature; VPD, vapor pressure deficit.

Grapevine physiological characterization during the experiment

The A _N peaked at 16.06 μmol m⁻² s⁻¹ on DOY 136 under conventional management, and at 13.83 μmol m⁻² s⁻¹ on DOY 164 under organic management (Fig. 2). Linear mixed‐effects models revealed that management system, DOY, and their interaction significantly affected A _N, with distinct variations between the two systems on multiple sampling dates, excluding DOY 164, 171, 180, 235, and 240. In June (DOY 164, 171, and 180), rising temperatures and falling humidity levels coincided with similar photosynthetic behavior in both management systems.

Figure 2.

Temporal evolution of the photosynthetic rate in both management systems during the 2 years of the experiment. Conventional management (●) and organic management (△). Asterisks (*) indicate significant differences between management systems at each sampling date according to Tukey‐adjusted pairwise comparisons derived from linear mixed‐effects models (P < 0.05). DOY, day of the year.

From DOY 158 to 164, A _N began to decrease, coinciding with increases in VPD despite slightly lower air temperatures (DOY 158 = 27.4 °C; DOY 164 = 26.3 °C) and higher humidity (61.7% and 71.4%, respectively). From DOY 164 until harvest (DOY 236–240), A _N decreased progressively under both management systems. Previous studies by Greer and Weedon ²⁶ reported a 15% to 30% drop in A _N for ‘Semillon’ at leaf temperatures around 25 °C, supporting these observations.

Regarding g _s (Fig. 3), significant differences appeared on DOY 136, 151, 199 and 214; on those dates the conventional management system showed, on average, 26% higher g _s than the organic management system. Throughout the experiment g _s ranged from 0.016–0.439 mol m⁻² s⁻¹ and tended to decline as temperature rose, which is consistent with Greer and Weedon, ²⁶ who found a decrease of 0.0016 ± 0.0002 mol m⁻² s⁻¹ per 5 °C increase.

Figure 3.

Temporal evolution of the stomatal conductance (g _s) in both management systems: conventional management (●) and organic management (△). Asterisks (*) indicate significant differences between management systems at each sampling date according to Tukey‐adjusted pairwise comparisons derived from linear mixed‐effects models (P < 0.05). DOY, day of the year.

On DOY 144, g _s increased in both management systems, matching the phenological shift from fruit set (Stage I) to pea‐size berries (Stage II) ²⁷ (Fig. 4). This increase matched an increase in A _N under both management systems, reaching the seasonal maximum in the conventional grapevines (Fig. 3).

Figure 4.

Evolution of the phenological stages in both management systems: conventional management (●) and organic management (△). A, winter rest; B2, swollen bud; D, incipient leaves; F, inflorescences visible; G, separated clusters; I1, beginning of flowering; J, full flowering; K, pea‐size berries; L, cluster compaction; M1, start of veraison; M2, full veraison; N, ripening. DOY, day of the year.

The vines remained at winter bud stage (A) until DOY 82, when swelling began. Within a few days, they reached the incipient‐leaf (D) and spreading‐leaf (E) stages, with 50% of shoots at stage E on DOY 103. Flowering started on DOY 123, and only 8 days later (DOY 131) fruit‐set was already evident, suggesting a compressed anthesis window. Such compression can promote more synchronous fruit set and earlier cluster compaction, as observed by DOY 158 (stage L), and may reduce the duration for which flowers are exposed to adverse weather. Fruit development progressed more slowly, with clusters remaining pea‐sized (K) from DOY 144 to 151; by DOY 158 most clusters were compact (L). Ripening (N) occurred between DOY 221 and 235, a period that overlaps with the seasonal thermal peak and highest VPD at the site (Table 1), particularly in early to mid‐August, which underscores the importance of characterizing less‐studied cultivars like ‘Pedro Ximénez’ under warm‐climate ripening conditions given the industry‐relevant risk of heat‐associated ripening issues such as sugar–acid imbalance or phenolic decoupling.^{28, 29, 30} This phenological calendar closely matches that reported by Martínez‐Bracero et al. ³¹ for the same cultivar in the D.O. Montilla‐Moriles, differing only by a 5 day advance in budbreak and flowering there, attributable to slightly higher early season temperatures. The similar behavior of ‘Pedro Ximénez’ in both wine regions likely reflects the shared classification of those regions within the same warm‐dry Mediterranean agroclimatic zone defined by Resco et al. ³²

Regarding the relationship between A _N and g _s, a curvilinear response between A _N and g _s under moderate water stress has been widely reported.^{33, 34, 35} However, the relationship found in this study was strictly linear, suggesting that non‐stomatal (biochemical) constraints contributed to the decline in A _N alongside stomatal limitations. When data from both experimental seasons were analyzed together, a robust linear correlation between A _N and g _s was observed (r ² = 0.771 for organic management and r ² = 0.714 for conventional management) (Fig. 5).

Figure 5.

Correlation between the net photosynthetic rate (A _N) and stomatal conductance (g _s) during the 2 year experiment (2022–2023) under both management systems: conventional management (●) and organic management (△). The regression equation for conventional management is shown in the black box. The dotted ellipse corresponds to low values of g _s from 0.05 to 0.15 mol m⁻² s⁻¹. The solid ellipse corresponds to moderate stress with g _s from 0.15 to 0.30 mol m⁻² s⁻¹. The dotted line represents organic management, and the solid line represents conventional management.

According to Medrano et al., ³⁶ g _s can serve as an integrative indicator of plant water status. Following their g _s‐based zoning, two domains are evident in Fig. 5. The first domain (dotted ellipse) corresponds to low g _s values (0.05–0.15 mol m⁻² s⁻¹) where both stomatal and non‐stomatal limitations prevail. The second domain (solid ellipse) represents moderate stress (g _s = 0.15–0.30 mol m⁻² s⁻¹) dominated mainly by stomatal limitation.

Within the first domain, conventional management exhibited higher A _N at a given g _s, whereas in the second domain organic vines achieved an A _N comparable with that of conventional vines. This pattern implies that vines in the organically managed plot appeared to experience lower cumulative stress, or recovered more rapidly, once stomatal control became the primary limitation. Plants under organic management could have experienced lower cumulative physiological stress, allowing them to maintain photosynthesis rate despite tighter stomatal regulation.

Table 2 shows the cumulative SI _gs values recorded under both management systems. In this index, higher SI _gs values indicate greater cumulative water stress experienced by the crop. This index allows for the quantification of the water stress resulting from water restriction beyond its temporal distribution, integrating the overall stress sustained by the crop in comparison with single‐point measurements. At the end of the season this index was significantly higher under conventional management than under organic management in both years. Both systems accumulated more stress in 2023 than in 2022, with the largest increase observed under conventional management.

Table 2.

Stress integral in terms of stomatal conductance (SI _gs) values during both years

SI gs (mmol m−2 s−1 day)	2022	2023
Conventional management	4.216a	16.773c
Organic management	2.642b	14.475d

Different letters indicate significant differences between management systems and seasons according to a Tukey test.

Stomatal conductance is a sensitive indicator of plant water status, and its reduction is closely linked to stress conditions. ³⁵ Higher SI _gs values therefore reflect a longer duration and/or greater severity of stomatal stress over time. ³⁶ The lower SI _gs recorded under organic management suggests improved _iWUE or reduced exposure to environmental stress. This pattern could be associated with soil properties often reported in organically managed systems, such as greater soil porosity, higher organic matter content, and enhanced biological activity, ³⁷ which may favor water retention and mitigate short‐term climatic extremes. However, soil physical or biological properties were not measured directly in this study; this interpretation should therefore be considered as a plausible explanation rather than a demonstrated mechanism. These findings align with earlier reports indicating that organically managed vineyards can develop physiological adaptations, such as enhanced _iWUE and faster post‐stress recovery, which lessen their sensitivity to drought. ³⁸ Consequently, organic management may represent a promising agronomic option in regions where water availability is limited or increasingly unpredictable under climate change scenarios.

Regarding _iWUE, the values followed the same seasonal course as g _s but did not show a consistent overall advantage for either management system (Fig. 6). The mean _iWUE across the 2023 season was 82 ± 4 μmol CO₂ mol⁻¹ H₂O under conventional management and 79 ± 5 μmol CO₂ mol⁻¹ H₂O under organic management. This difference was not statistically significant as LMM models indicated no significant overall effect of management on _iWUE (P = 0.28). Nevertheless, conventional vines exhibited 15% to 20% higher _iWUE on hot, high‐VPD dates (DOY 199–214; Tukey‐adjusted contrasts, P < 0.05), whereas early season (DOY 123–136) and post‐veraison (DOY 249) conditions favored organic management by 10% to 15% _iWUE. These alternating peaks indicate that management affected intrinsic efficiency mainly during short stress pulses rather than in an additive manner over the whole season.

Figure 6.

Seasonal course of intrinsic water‐use efficiency (_iWUE) in ‘Pedro Ximénez’ vines under conventional management (●) and organic management (△) during the 2022–2023 seasons. The absence of asterisks indicates no significant differences between management systems at each sampling date according to Tukey‐adjusted pairwise comparisons derived from linear mixed‐effects models (P < 0.05).

Such transient advantages mirror results obtained by Gaudillère et al. ³⁸  and Bellvert et al., ²⁷ who reported management‐dependent shifts in _iWUE only under specific VPD–temperature combinations. Overall, the similarity of season‐integrated _iWUE values supports the conclusion drawn from SI _gs; both systems maintained comparable water‐use efficiency at the whole‐canopy scale, with conventional vines responding to acute stress through sharper, short‐lived increases in efficiency, and organic vines compensating through a steadier daily performance.

The relationship between A _N and the relative electron‐transport rate (ETR) was virtually identical in both management systems (Fig. 7). Linear regression slopes did not differ (ANCOVA, P = 0.18), indicating that ETR responded similarly to changes in carbon assimilation regardless of agronomic practice. These patterns support hypothesis (iv): ETR was preserved under high‐VPD episodes, indicating that observed declines in A _N were not driven by impaired electron transport and are consistent with CO₂‐diffusional and/or biochemical limitation.

Figure 7.

Relationship between the relative electron‐transport rate (ETR) and net photosynthetic rate (A _N) for individual leaves of ‘Pedro Ximénez’ under conventional (●) and organic (△) management during 2022–2023. The equation for conventional management is shown in the black box. The dotted line represents organic management and the solid line represents conventional management. Regression slopes did not differ significantly (ANCOVA, P = 0.18).

Under water‐limited conditions, divergence in A _N‐ETR slopes usually signals impaired photochemistry or photo‐protective down‐regulation.^{39, 40} The similarity observed here suggests that non‐stomatal limitations affecting A _N at low g _s were more likely related to biochemical factors, such as reduced Rubisco activity or mesophyll conductance, than to damage or down‐regulation of the electron transport chain.^{36, 41} Nevertheless, further measurements of leaf nitrogen, mesophyll conductance or hydraulic traits would be required to confirm the exact nature of the biochemical limitation in the present study.

Although midday g _s did not differ significantly on most sampling dates (Fig. 3), the lower seasonal SI _gs under organic management (Table 2) indicates a shorter cumulative exposure to low g _s across the season. Thus, the stomatal ‘signal’ emerges in the integrated metric rather than in single‐date means, whereas the preserved ETR rules out electron‐transport impairment as the primary cause of A _N declines under high VPD.

Agronomical parameters

The average number of bunches per vine differed significantly between management systems in 2023 (Table 3). Organic vines carried 17 ± 0.9 bunches per plant, whereas conventional vines bore 15 ± 0.8 bunches per plant (Tukey test, P < 0.05). This higher cluster count, combined with similar bunch weights, explains why total yield per vine was numerically greater in the organic block, confirming that organic management can maintain yield levels comparable to conventional management under warm, dry conditions (Table 3).

Table 3.

Bunch weight, number of bunches per vine at harvest, and pruning weight per plant after harvest

Management system	Average bunch weight (kg)	Number of bunches (average) per plant	Pruning weight (kg per plant)
2022
Conventional	2.72 ± 1.17a	*	0.99 ± 0.30a
Organic	2.32 ± 0.80a	*	0.82 ± 0.16a
2023
Conventional	4.19 ± 0.28a	15 ± 0.8b	0.47 ± 0.03a
Organic	4.74 ± 0.33a	17 ± 0.9a	0.52 ± 0.04a

Different superscript letters indicate significant differences between management systems within each parameter and year (P < 0.05, determined by a two‐way ANOVA followd by Bonferroni‐adjusted post hoc comparisons).

^*For experimental organizational reasons, the number of bunches was not counted in 2022.

Merot and Smits ⁸ reported that in a 4 year trial, yield fell only in the second season after conversion to organic management; across the full study period, total production was maintained because improvements in grape quality compensated for the transient drop in quantity. Likewise, Vitali Čepo et al. ⁴² showed that wines from organically grown grapes contained significantly fewer pesticide residues than wines from conventional grapes. Borsato et al. ⁴³ demonstrated, using a multifactorial life‐cycle approach, that organic vineyard management sustained economic productivity while reducing environmental impacts.

As the study compared one organically managed plot and one conventionally managed plot within the same vineyard, management effects cannot be fully separated from potential plot‐level differences (e.g., soil heterogeneity or field history). The results should therefore be interpreted as evidence from a commercial vineyard case study.

CONCLUSIONS

This study assessed the physiological and agronomic performance of the ‘Pedro Ximénez’ grapevine cultivar under organic and conventional management in a warm climate region over two consecutive years. The following conclusions can be drawn:

(1) At the physiological level, conventional management displayed higher photosynthetic rates only when both stomatal and non‐stomatal limitations coincided; under purely stomatal limitation, organically managed vines matched those rates. This pattern may indicate a potential physiological adjustment in organically managed vines that could help them cope with moderate stress.

(2) The cumulative stomatal‐stress integral (SI _gs) was consistently lower in organic plots in both seasons, indicating reduced exposure to water‐related stress. This difference could be associated with soil structure and water retention properties frequently reported in organically managed systems.

(3) Agronomically, organic vines produced significantly more clusters per plant in 2023, whereas bunch weight and pruning weight were statistically similar between systems, showing that organic management‐maintained yield components comparable with those under conventional management.

(4) Electron transport rate remained comparable between management systems across high‐VPD episodes. Reductions in A _N therefore chiefly reflected CO₂‐diffusional and/or biochemical limitations rather than photochemical impairment.

(5) Phenological timing was identical in both treatments, entirely driven by climate, showing that management system did not alter developmental pace.

Overall, these results support the viability of organic viticulture for ‘Pedro Ximénez’ in warm Mediterranean climates: organic management does not compromise productivity or phenology and may enhance physiological resilience to water stress. These results contribute to an understanding of organic vineyard management as a potential strategy to improve physiological resilience of grapevines under warm Mediterranean conditions.

FUNDING INFORMATION

Data originated from the GOPC‐CA‐20‐0008 (GO INVITECPX) project. This was financed by the European Agricultural Fund for Rural Development (Fondo Europeo Agrícola de Desarrollo Rural, FEADER), the Regional Ministry of Agriculture, Livestock, Fisheries, Water and Sustainable Development of the Government of Andalusia (Consejería de Agricultura, Ganadería, Pesca y Agua y Desarrollo Sostenible de la Junta de Andalucía), and the Integrated Territorial Investment of the Province of Cadiz (Inversión Territorial Integrada Provincia de Cádiz).

CONFLICT OF INTEREST

The authors declare no conflict of interest.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.