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Article

Influence of the Invasive Species Ailanthus altissima (Tree of Heaven) on Yield Performance and Olive Oil Quality Parameters of Young Olive Trees cv. Koroneiki Under Two Distinct Irrigation Regimes †

by
Asimina-Georgia Karyda
* and
Petros Anargyrou Roussos
Laboratory of Pomology, Department of Crop Science, Agricultural University of Athens (AUA), Iera Odos 75, 118 55 Athens, Greece
*
Author to whom correspondence should be addressed.
†
This paper is an extension of a conference paper: Karyda, A.-G.; Roussos, P.A. Effect of Ailanthus altissima on photosynthetic activity, yield and olive oil quality characteristics under two irrigation regimes. In Proceedings of the XIV International Scientific Agriculture Symposium “AGROSYM 2023”, Jahorina, Bosnia and Herzegovina, 5–8 October 2023; pp. 134–139.
Appl. Sci. 2025, 15(14), 7678; https://doi.org/10.3390/app15147678
Submission received: 13 May 2025 / Revised: 4 July 2025 / Accepted: 7 July 2025 / Published: 9 July 2025
(This article belongs to the Section Chemical and Molecular Sciences)
Versions Notes

Abstract

Ailanthus altissima (AA) is an invasive tree species rapidly spreading worldwide, colonizing both urban and agricultural or forestry environments. This three-year study aimed to assess its effects on the growth and yield traits of the Koroneiki olive cultivar under co-cultivation in pots, combined with two irrigation regimes, full and deficit irrigation (60% of full). Within each irrigation regime, olive trees were grown either in the presence or absence (control) of AA. The trial evaluated several parameters, including vegetative growth, yield traits, and oil quality characteristics. Co-cultivation with AA had no significant impact on tree growth after three years, though it significantly reduced oil content per fruit. Antioxidant capacity of the oil improved under deficit irrigation, while AA presence did not significantly affect it, except for an increase in o-diphenol concentration. Neither the fatty acid profile nor squalene levels were significantly influenced by either treatment. Fruit weight and color were primarily affected by deficit irrigation. During storage, olive oil quality declined significantly, with pre-harvest treatments (presence or absence of AA and full or deficit irrigation regime) playing a critical role in modulating several quality parameters. In conclusion, the presence of AA near olive trees did not substantially affect the key quality indices of the olive oil, which remained within the criteria for classification as extra virgin.

1. Introduction

Ailanthus altissima (Mill.) Swingle, commonly known as the tree of heaven, is a fast-growing, deciduous, invasive tree species belonging to the Simaroubaceae family [1,2,3]. It exhibits remarkable adaptability to diverse soil types and climatic conditions [3]. The rapid spread of Ailanthus is facilitated by its vigorous vegetative propagation, prolific seed production, and tolerance to various abiotic stresses [2,4,5]. Its seeds are dispersed over long distances by wind, and the tree readily regenerates from root suckers and cut stumps [4,5].
A key mechanism contributing to Ailanthus expansion is its allelopathic capacity, which is the release of phytotoxic compounds that suppress the growth of nearby plant species [2,5,6]. These compounds are mostly concentrated in the roots and bark [1,3,6], although they are also present, to a lesser extent, in the shoots, seeds, and wood [6]. The presence of Ailanthus has been shown to negatively affect neighboring vegetation through reduced photosynthetic activity, altered soil pH, and depleted soil fertility [3,4].
Controlling Ailanthus is particularly challenging, as both mechanical and chemical control measures often prove ineffective [7,8,9]. In recent decades, its spread has intensified across urban, forest, and agricultural landscapes, where it displaces native and economically important plant species [7].
The olive tree (Olea europaea L.) is considered one of the earliest domesticated tree crops [10,11]. Approximately 85% of global olive groves are concentrated in the Mediterranean basin, with Spain, Greece, and Italy leading in the production of both olive oil and table olives [12].
Extra virgin olive oil (EVOO) is widely recognized for its high nutritional value and exceptional oxidative stability, making it a premium vegetable oil. This stability is attributed to its fatty acid composition [13,14,15] and to a variety of secondary natural antioxidants, including squalene, carotenoids, tocopherols, and phenolic compounds [14,15,16]. The degradation rate of these compounds during storage is influenced by their initial concentrations [15], but storage conditions also play a critical role in determining the chemical stability and quality of EVOO over time [14,15].
Olive oil production—both in terms of yield and quality—is affected by numerous factors, including environmental conditions, cultivation practices, and genetic characteristics [17]. While the olive tree is considered drought-tolerant due to its adaptive mechanisms for coping with limited water supply [18], its performance can still be impacted by climatic variability. It is well adapted to the Mediterranean climate [10,19,20], which features dry, hot summers and cool, wet winters, and can produce high-quality products under such conditions [10]. However, intensified cultivation [21], combined with the effects of climate change—such as increased temperatures and irregular rainfall during critical phenological stages [19,21]—may compromise both yield and oil quality [21]. In response, modern irrigation strategies have been developed to optimize water use while maintaining production levels and quality [20,22].
Another factor that can adversely affect olive production is weed competition. Depending on species and density [23,24], weeds compete with olive trees for vital resources like water and nutrients, ultimately reducing fruit yield and quality [25]. Effective weed management is therefore crucial to maintaining high productivity [23].
Given the limited data available on the impact of Ailanthus on tree crops, the observations from this experiment are interpreted in the context of its broader ecological behavior as an invasive species. Like other aggressive weeds, Ailanthus poses a significant challenge to agricultural production, as it can compete with crops for essential resources such as water, light, nutrients, and space [26,27]. This competition can result in reduced crop yield and quality. As a fast-growing species with high adaptability to harsh environments, Ailanthus may outgrow cultivated plants, causing shading, reduced photosynthesis, stunted growth, and lower fruit quality [8]. In terms of water management, its presence may increase the need for irrigation to meet crop demands and could also negatively affect plant nutrition [28]. In this context, the findings of the present experiment offer valuable insights into the potential competitive and ecological impacts of Ailanthus on neighboring crops.
In Greece—currently the second-largest olive oil producer in Europe [12]—the spread of Ailanthus poses a growing threat to olive cultivation [3]. The olive tree holds significant cultural and economic value in the country. Among the various cultivars, ‘Koroneiki’ stands out globally for producing high-quality olive oil. Given that many Greek olive groves are rainfed, competition from Ailanthus could exacerbate water stress and further threaten productivity.
The objective of this study was to investigate the potential stress effects of Ailanthus altissima on the yield and oil quality characteristics of the ‘Koroneiki’ olive cultivar, under both full and deficit irrigation conditions.

2. Materials and Methods

2.1. Plant Material and Experimental Design

The experiment was carried out at the orchard of the Agricultural University of Athens (latitude: 37°59′1.19″ N, longitude: 23°42′11.99″ E). The trees used were 12-month-old self-rooted olive trees cv. Koroneiki, growing in the nursery in 1.5 L pots.
The olive trees were planted in the spring of 2020 in 45 L black plastic pots filled with soil substrate with and without (control) Ailanthus plants. The Ailanthus plants used were rooted offshoots of similar growth derived from mature trees. One plant per pot was planted at a distance of approximately 10 cm from the olive trees, and the trees were fully watered till a slight leaching was observed. Thereafter, two irrigation regimes were applied, one full, in which each pot received an average of 2 L of water per watering event—maintaining the substrate at its water-holding capacity without causing leaching—and a deficit one, applying 60% of the water volume of the first regime. Irrigation events were adjusted as needed, based on the climatological conditions and on soil moisture sensors inserted to the substrate of each treatment (two sensors per treatment) (WaterScout SM100 Soil Moisture Sensors, Spectrum Technologies, Inc., Aurora, IL, USA). Irrigation was administered through an automatic watering system, through one self-adjustable dripper. The trial lasted three years, and a total of 40 plants (10 plants per treatment, five replicates of two plants each) were used. Trees were randomly divided into five replicates, with two trees per replicate (control (C) and presence of Ailanthus (A)) and per irrigation regime (full (F) and deficit (D)).

2.2. Tree Growth Measurements

During the experiment, all necessary cultural practices were applied to ensure unhindered growth and production. The trees were allowed to grow naturally without any pruning, only removing offshoots produced.
Tree height measurements were taken at the beginning (just after planting and acclimatization) and at the end of the experimental period to calculate the increment. Additionally, trunk diameter measurements at a specific height were taken using a digital caliper (Starrett, 727 Series, Athol, New England, MA, USA) after each harvest to calculate the trunk cross-sectional area (TCSA).

2.3. Harvest and Olive Oil Extraction

The harvest took place on the following dates: 10 November 2020 for the first year, 26 November 2021 for the second year, and 16 November 2022 for the third year. Each plot was harvested separately (five samples per treatment), and the fruits were transferred to the Laboratory of Pomology for the oil extraction. The olives were crushed using a semi-industrial Abencor-type olive mill (Callis S.A., Athens, Greece). The crusher operated at 2800 rpm, and the resulting paste was transferred to a malaxer, where it was malaxed for 35 min at 50 rpm and 25–27 °C. Following malaxation, 50 g of the paste was transferred to a Falcon-type tube and centrifuged at 2500× g for 15 min to accurately determine the oil percentage in the paste. The remaining paste was centrifuged at 1400× g for 3–4 min using the semi-industrial centrifuge of the Abencor-type olive mill, and the oil produced was stored in filled bottles at 4 °C in the dark until analysis. Additionally, in the first year, samples were kept in half-filled test tubes (head-space occupied by air) in darkness at room temperature for 6 and 12 months to evaluate oil quality degradation, simulating oil consumption under household conditions. The yield (mass of fruit produced), oil content, and olive oil production per tree were evaluated.

2.4. Fruit Characteristics Determination

Five fruits per replicate were retained for measurements to assess physical characteristics. Fruit weight, diameter, and length were recorded using an electronic balance (Kern 470, Kern and Sohn, GmbH, Balingen, Germany) and a digital caliper (Starrett, 727 Series, Athol, New England, MA, USA), respectively. The ratio of flesh fresh weight to flesh dry weight was also determined.
The color of the peel was measured using a chroma meter (CR-300, Minolta, Ahrensburg, Germany) under dark conditions. From the provided CIE L* a* b* values, the hue angle and chroma value were calculated [29].
In the laboratory, the maturity index of the fruits was determined based on the peel and pulp color on a scale from 0 (deep green peel color) to 7 (all purple or black peel color with all the flesh purple) [30].

2.5. Olive Oil Analysis

The extracted oils were analyzed for acidity, peroxide value, and UV spectrophotometric indices (K232, K270, and ΔK) using the standard methods outlined by the European Union (Regulation EEC 2568/1991; Regulation CE 1989/2003) [31].

2.6. Total Phenol Content and Antioxidant Capacity Determination

After adding hexane to remove fats, 2 mL of 80% v/v methanol in water was used to extract the phenolic compounds from the olive oil samples. After centrifugation and removal of the supernatant phase, total phenol content and antioxidant capacity were determined in the methanolic extracted samples.
The total phenolic compounds (mg gallic acid equivalents per kg of olive oil) were determined using the method of Waterman and Mole (1994) [32]. Total o-diphenols (mg caffeic acid equivalents per kg of olive oil) were measured following the procedure of Gutfinger (1981) [33], while the total flavonoids (mg equivalent catechin kg−1 olive oil) were calculated using the modified protocol described by Dewanto et al. (2002) [34]. The antioxidant capacity was measured using three different methods. The Klimczak et al. (2007) [35] protocol was used for the FRAP (ferric reducing antioxidant powder) and DPPH (2,2-diphenyl-1-picrylhydrazyl) methods, while the ABTS [2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] method followed the protocol of Re et al. (1999) [36]. The results were expressed as µmol Trolox kg−1 olive oil. All measurements were taken using the Unicam Helios Y Gamma Spectrophotometer (Thermo Spectronic, Helios Gamma, Cambridge, UK).

2.7. Fatty Acids and Squalene Determination

The composition of fatty acids, expressed as a percentage (%) of methyl esters (FAMES), was determined following the guidelines of Regulation EEC 2568/91 [31]. To achieve this, 0.5 g of oil was diluted in 5 mL hexane; then, 0.5 mL of 0.2 N methanolic solution of KOH was added, and the solution was vigorously shaken. The methyl-esters were analyzed using Shimadzu GC-2030 (Shimadzu Corporation, Kyoto, Japan) equipped with a Split/Splitless injector and a flame ionization detector (FID), using a Supelco SP®-2340 (Supelco Inc., Bellefonte, PA, USA) fused silica capillary column (60 × 0.32 mm × 0.2 μm film thickness). The injector temperature was set at 249 °C. FID was used for the identification and quantification of fatty acid methyl ester peaks using a detector temperature of 249 °C. An amount of 1.0 µL of sample was injected at an initial column temperature of 150 °C (using a split ratio of 1:80), which was held for a constant 18 min. The temperature was then increased at a rate of 2 °C min−1 to 175 °C and held for 5 min and then raised at a rate of 5 °C min−1 to the final temperature of 200 °C, which was held for 22 min. The identified fatty acids were palmitic (C16:0), palmitoleic (C16:1), heptadecanoic (C17:0), heptadecenoic (C17:1), stearic (C18:0), oleic (C18:1), linoleic (C18:2), linolenic (C18:3), arachidic (C20:0), gadoleic (C20:1), behenic (C22:0), and lignoceric (C24:0) acids. FAMES were identified using the 37 component FAME mix of Supelco (Merck Group, St. Louis, MO, USA). Squalene was also determined under the same conditions (the area of its peak was not taken into account for the calculation of the total area of FAMES) [31,37], and its concentration was determined by an external calibration curve (Sigma, Merck Group, St. Louis, MO, USA) [37] and expressed as mg per 100 g of olive oil.

2.8. Statistical Analysis

The experiment was arranged as a completely randomized design. The study was conducted for 3 years, with the last olive crop harvested in November 2022. The raw data from all the years were combined and analyzed as a two-way analysis of variance (ANOVA), with the two factors being the presence of Ailanthus or not (C—control treatment and A—Ailanthus treatment) and the irrigation regime (F—full irrigation and D—deficit irrigation). Significant differences were determined using Student’s t-test for the main factors and Tukey HSD for their interaction, at a significance level of α = 0.05.
To evaluate the effects of different treatments (CF—control and full irrigation, CD—control and deficit irrigation, AF—Ailanthus presence and full irrigation, AD—Ailanthus presence and deficit irrigation) and storage period (0—Harvest, 6 months, and 12 months), the raw data were analyzed by two-way analysis of variance (ANOVA) (factors being the treatments and the storage period). Significant differences were determined using Tukey HSD at a significance level of α = 0.05. The comparison of regression lines, assuming equal intercepts, was employed to detect possible significant differences among treatments concerning olive oil quality degradation throughout the storage period. The statistical analysis was conducted using the JMP Pro 16 (SAS institute, Cary, NC, USA) statistical software.

3. Results

3.1. Effect of the Treatments on the Growth, Yield, and Fruit Characteristics of the Olive Tree and Quality Parameters of the Olive Oil over a Period of 3 Years

The growth and production of the trees were not significantly affected by the presence of Ailanthus or the implementation of deficit irrigation (Table 1). However, both treatments, individually, resulted in a reduction in oil content compared to the control, while the combination of Ailanthus presence under deficit irrigation resulted in the lowest olive oil percentage.
Deficit irrigation resulted in a significant reduction in fruit weight and dimensions compared to full irrigation (Table 2). In particular, deficit irrigation, irrespective of the presence of Ailanthus, resulted in smaller fruits with reduced length and diameter. In addition, fruit length was significantly reduced by deficit irrigation in the presence of Ailanthus.
Full irrigation resulted in lower fruit color parameters but in an increased maturity index compared to deficit irrigation (Table 3). When applied in the presence of Ailanthus, deficit irrigation significantly increased the chroma value of fruits and decreased the maturity index, compared to the combination of full irrigation in the absence of Ailanthus.
Regardless of the irrigation system used, the presence of Ailanthus increased the K232 and K270 values compared to the control (Table 4), but it did not have any significant impact on peroxide value and acidity. This increase was also observed when full irrigation was applied in the presence of Ailanthus. Furthermore, the application of deficit irrigation, regardless of the presence of Ailanthus, resulted in a reduction of oil acidity, while no significant differences were detected regarding the peroxide value.
Under deficit irrigation (irrespective of Ailanthus presence), the concentration of total flavonoids increased (Table 5). The presence of Ailanthus (irrespective of the irrigation regime employed) led to an increase in the concentration of total o-diphenols too. The lowest values of total phenolics and total flavonoids were recorded when Ailanthus was absent and full irrigation was applied, with a significant difference from the control under deficit treatment. In contrast, the combination of Ailanthus and deficit irrigation led to the highest concentration of total o-diphenols. The highest values of all three antioxidant capacity assays (DPPH, FRAP, ABTS) were detected when deficit irrigation was applied in the absence of Ailanthus.
Regarding the free fatty acid content (Table 6), the presence of Ailanthus (irrespective of irrigation regime) resulted in oils rich in C16:1, C18:3, and C24:0. Deficit irrigation (irrespective of Ailanthus presence) increased the percentages of C17:1, C18:3, C20:1, and C22:0 in olive oils produced, while it reduced the percentage of C18:0. Furthermore, oils produced under deficit irrigation in the presence of Ailanthus were found to be rich in C16:1 (compared to control deficit irrigation), C17:1 (compared to control full irrigation), C18:3, and C20:1 (compared to Ailanthus presence under deficit irrigation). Olive oil produced under deficit irrigation in the absence of Ailanthus exhibited a low C18:0 percentage.
Overall, deficit irrigation when applied resulted in oils low in SFAs and with a low SFAs:UFAs ratio (Table 6). No other statistically significant differences in fatty acids and squalene concentrations were observed.

3.2. Effects of Treatments on the Quality of Olive Oil over a 12-Month Storage Period

The lowest peroxide value and acidity, K232, and K270 values were recorded at harvest, with significant differences from 6 to 12 months (Table 7). Furthermore, after six months of storage, the K270 value was still at a low level comparable to that determined at harvest. After 12 months of storage, however, peroxide value, acidity, K232, and K270 values were increased, especially compared to harvest (Figure S1). The olive oil obtained from the CD treatment was characterized by a high peroxide value and a decrease in the K270 value. On the other hand, the olive oil obtained from the CF treatment showed the highest acidity. The analysis of regression lines indicates that the olive oil obtained from the CD treatment had the highest degradation rate based on the peroxide value within 12 months (Figure S1a). Similarly, the olive oil produced under CF treatment showed the highest degradation in terms of the K232 value (Figure S1c) and the ΔK index (Figure S1e). Significant differences emerging from the interaction of treatments and time of storage were determined concerning all parameters studied (Table S1).
The highest concentrations of total phenolics, total o-diphenols, and total flavonoids, as well as the highest antioxidant capacity, according to all three measurement methods used (DPPH, FRAP, ABTS), were detected at harvest (Table 8 and Figure S2). During the storage period, these values decreased significantly (apart from FRAP at 12 months). Olive oil obtained from the CD treatment presented the lowest concentrations of polyphenols tested and the highest antioxidant capacity, according to all three measurements (DPPH, FRAP, ABTS), compared to olive oil from all the other treatments (Table 8). Furthermore, it is clear that this specific olive oil experienced the greatest degradation over the period of 12 months in terms of total phenolics (Figure S2a), total o-diphenols (Figure S2b), total flavonoids (Figure S2c), and antioxidant capacity, as measured by the FRAP method (Figure S2e). Significant differences emerging from the interaction of treatments and time of storage were determined concerning all parameters studied (Table S2).
According to the data presented in Table 9 and Figure S3, the concentration of C18:1 was at its lowest point at the time of harvest, and it subsequently increased during the storage period. Conversely, a decrease in the concentrations of C16:1, C18:0, C20:0, and C20:1 was observed during storage. CD and AD treatments resulted in oils rich in C16:0. AF treatment led to a decrease in C18:3, but it significantly increased C18:1. Olive oil produced by the CF treatment, irrespective of the time of sampling, was rich in C18:0 and C18:2.
The olive oils produced exhibited the highest concentrations of squalene and PUFAs, along with a high C18:1/C18:2 ratio, at harvest (Table 9). Conversely, oils at harvest had the lowest concentrations of MUFAs, UFAs, and the MUFAs/PUFAs ratio. These parameters fluctuated during the storage period. Olive oils produced by CD and AD treatments were low in UFAs but high in SFAs and the SFAs/UFAs ratio. Moreover, AF treatment increased MUFAs concentration and the MUFAs/PUFAs ratio. In addition, CF treatment resulted in oils rich in PUFAs with a high C18:1/C18:2 ratio. Significant differences emerging from the interaction of treatments and time of storage were determined concerning all parameters studied (Table S3).
The analysis of regression lines did not reveal any significant difference regarding the degradation grade of both individual free fatty acids (Figure S3) and their various groups and squalene (Figure S4).

4. Discussion

4.1. Effects of the Treatments on the Growth, Yield, and Fruit Characteristics of the Olive Tree and Quality Parameters of the Olive Oil

Both deficit irrigation and the presence of Ailanthus led to a reduction in oil content. Although several studies have reported increased oil content under deficit irrigation [38,39], the observed decrease in this trial is likely the result of combined stress caused by both Ailanthus presence and imposed water limitations. Moreover, water stress alone has been shown to reduce oil content compared to full irrigation conditions [18,40]. Olive trees subjected to water deficits often exhibit reduced photosynthetic rates, primarily due to stomatal closure and limitations in mesophyll conductance [41,42]. These physiological constraints lead to lower carbohydrate availability, directly impairing oil synthesis. Prolonged drought conditions can also trigger oxidative stress, which damages cellular structures and further reduces photosynthetic efficiency [41]. In addition to competing for water, Ailanthus may negatively impact carbon assimilation through shading and nutrient competition, both of which can contribute to decreased oil content. In the present experiment, during the third year, Ailanthus height reached, in most plots, almost half the height of the olive trees, generating in general a slight shading effect. Sofo et al. [43] found that shaded olive trees display lower photosynthetic rates and increased photoinhibition, especially under drought stress. Shading has also been shown to hinder oil accumulation, as oil biosynthesis between late summer and early winter relies heavily on photosynthetic activity [44]. A reduction in photosynthetically active radiation (PAR) limits carbohydrate reserves, which negatively affects oil accumulation in the fruit [44]. Nutrient imbalances may further exacerbate this effect. Adequate levels of calcium (Ca), potassium (K), and boron (B) have been positively correlated with higher oil content [45]. Potassium, in particular, is essential for stomatal regulation and enzyme activation during photosynthesis; its deficiency can impair photosynthetic efficiency and fruit development [46]. Likewise, nitrogen (N) and phosphorus (P) are critical for chlorophyll synthesis and energy transfer, and their limited availability can significantly constrain the plant’s photosynthetic capacity [47]. Finally, beyond these direct competitive effects, the presence of Ailanthus may also influence olive tree health and oil yield through its allelopathic properties [2,5,6].
In the present trial, deficit irrigation resulted in reduced fruit size, regardless of the presence of Ailanthus. This finding aligns with previous studies [18,48], which reported greater fruit weight in trees under full irrigation. Similarly, Sánchez-Rodríguez et al. [49] observed that Manzanilla cultivar trees subjected to severe water stress produced the smallest fruits in terms of both weight and dimensions. Moreover, fruit growth parameters—such as diameter, length, and weight—have been shown to correlate directly and positively with plant water consumption [50]. Deficit irrigation also led to a lower fruit maturity index. Water deprivation has been shown to delay fruit ripening, resulting in a lower maturity index at harvest and altering the pace of fruit development, as observed in ‘Arbequina’ olives [51]. García et al. [52] similarly reported changes in fruit characteristics associated with reduced irrigation. These findings suggest that limiting water availability can slow the maturation process, ultimately leading to a lower maturity index. Additionally, a significantly lower chroma value was recorded in fruits from fully irrigated trees, consistent with the findings of Gonçalves et al. [48], which may indicate an advancement in fruit maturation.
Deficit irrigation significantly reduced the free acidity of olive oil compared to full irrigation, while it had no effect on peroxide value or ultraviolet absorbance indices, in agreement with Rinaldi et al. [38]. Olive oils produced under deficit irrigation showed improved oxidative stability, as indicated by antioxidant capacity data, which is partly attributed to the higher concentration of phenolic compounds. These phenolics play a vital role in inhibiting the hydrolytic breakdown of triglycerides into free fatty acids, thereby protecting the oil from oxidation and helping to maintain low acidity levels [53]. In contrast, the presence of Ailanthus led to increased ultraviolet absorbance indices. The competitive stress imposed by Ailanthus, an invasive weed [26,27], may subject olive trees to various forms of physiological stress—such as water scarcity, nutrient imbalances, or potential toxicity—which can accelerate lipid oxidation and result in elevated extinction values in the extracted oil. Similar oxidative trends were reported by García et al. [54] in oils from olive trees exposed to severe water deficit, reinforcing the connection between environmental stress and oil quality deterioration. Additionally, Lémole et al. [55] observed increases in both K232 and K270 values in olives grown under prolonged shading, which is a condition comparable to the canopy interference caused by fast-growing Ailanthus stands. Likewise, Silva et al. [56] demonstrated that potassium deficiency, a form of nutritional stress, can significantly raise K270 values. These findings support the idea that various abiotic stressors, including competition from invasive species, can negatively affect oil quality. The qualitative parameters of the olive oil analyzed in this study—including free acidity, peroxide value, K232, K270, and ΔK—fall within the ranges reported in previous studies [57,58,59,60]. Nonetheless, all oil quality parameters remained within the limits set by European Community regulations [31], confirming that all oils produced were of extra virgin quality.
Deficit irrigation was found to significantly increase both the total polyphenol content and the antioxidant capacity of the olive oils produced in the present study. This result aligns with numerous previous studies that have reported a positive correlation between water stress and the accumulation of phenolic compounds in olive oil [39,51,61,62]. The underlying physiological mechanism is believed to involve the activation of the enzyme phenylalanine ammonia-lyase (PAL), which plays a key role in the biosynthetic pathway of polyphenols. Water stress is known to enhance PAL activity, thereby promoting the accumulation of phenolic compounds in fruit tissues and, subsequently, in the resulting olive oil [63]. Furthermore, in the current study, deficit irrigation was associated with significant increases in both total ortho-diphenols and total flavonoids, which are two major subclasses of polyphenols known for their potent antioxidant properties. These findings are consistent with earlier research [61,64], which also demonstrated that deficit irrigation enhances the biosynthesis and accumulation of specific polyphenolic classes. Τhe concentrations of total polyphenols measured in the present study fall within the range previously reported for the same olive cultivar in various regions of the country [59,60], as well as in studies conducted in other countries [57]. Moreover, the findings are comparable to those documented for Mediterranean olive oils produced from other cultivars [65,66,67,68].
The fatty acid profile, on the other hand, was not significantly affected by either the presence of Ailanthus or deficit irrigation. However, Ben-Gal et al. [69] and Grattan et al. [70] highlighted that limited irrigation can influence the fatty acid composition of olive oil. The ratio of monounsaturated to polyunsaturated fatty acids (MUFAs/PUFAs) appeared to remain unaffected by the irrigation regime, which aligns with the findings of Patumi et al. [21]. The compositional profile of Koroneiki cultivar olive oil, characterized by elevated levels of oleic acid (C18:1) and low concentrations of linolenic acid (C18:3), was confirmed in this study and is consistent with previously reported data [71]. However, under deficit irrigation and in the presence of Ailanthus, the oils produced were richer in linolenic acid (C18:3) and palmitoleic acid (C16:1). These findings are in agreement with Stefanoudaki et al. [18] and García et al. [54], who reported similar increases in these fatty acids under water stress conditions. Supporting this trend at the molecular level, Hernández et al. [72] demonstrated that water stress upregulates genes involved in the biosynthesis of linolenic acid (C18:3), leading to enhanced accumulation in the oil. Conversely, deficit irrigation was associated with a reduction in stearic acid (C18:0) content, a finding consistent with the observations of Gucci et al. [73], who reported a similar decline under restricted water supply conditions. While stearic acid tends to remain relatively stable, its levels can decrease under more severe water stress, reflecting changes in lipid metabolism. Furthermore, elevated levels of both linolenic (C18:3) and palmitoleic (C16:1) acids have also been observed in oils from shaded trees, as documented by Lémole et al. [55]. Additionally, Kattmah et al. [74] reported an inverse relationship between nitrogen availability and linolenic acid (C18:3) concentration, suggesting that nutrient imbalances may further influence fatty acid biosynthesis. The rapid growth and substantial biomass of Ailanthus create a high nitrogen demand, with the plant competing for this resource with neighboring vegetation. This competition likely reduced nitrogen availability to the olive trees, potentially contributing to the observed increase in C18:3 in the olive oil produced. Thus, the results of the current study may be partially explained by the competitive and stress-inducing effects of Ailanthus as an invasive species, which is known to negatively affect crop water, light, and nutrient availability [26,27].

4.2. Effects of Treatments on the Quality of Olive Oil over a 12-Month Storage Period

Peroxide value, free acidity, and ultraviolet absorbance indices (K232 and K270) increased significantly after 12 months of storage. These results are consistent with the findings of Yildirim [75], who observed notable increases in peroxide values after 7 months, particularly in oils stored at room temperature compared to those under refrigeration. The rise in free acidity is primarily attributed to the hydrolysis of triglycerides, which leads to the release of free fatty acids. This reaction is accelerated by oxygen exposure, even in the absence of light, as shown in the samples stored in half-filled test tubes with air headspace at room temperature for 6 and 12 months, which are conditions that mimic typical household storage. Oxygen promotes both oxidative and enzymatic degradation, contributing to overall quality deterioration, resulting in increases of oil acidity as reported by others too [76,77]. Additionally, the progressive degradation of phenolic compounds during storage weakens the oil’s antioxidant defense system, further accelerating oxidation and increasing acidity [78]. Pristouri et al. [79] found that oils stored in partially filled containers—similar to the conditions in the present trial—showed a sharp rise in peroxide values after 12 months, underscoring the importance of minimizing oxygen exposure. Recent studies reinforce these observations and emphasize the critical role of oxygen in olive oil degradation. Gündüz and Baştürk [80] reported that air exposure significantly increased peroxide values and free acidity. Similarly, Averbuch et al. [78] and Safarzadeh Markhali and Teixeira [81] found that oxygen exposure during storage accelerated oxidation, as indicated by higher K232 and K270 values, and contributed to phenolic degradation. Ghreishi Rad et al. [82] also confirmed that oxidative markers increased with both storage duration and oxygen contact. These results corroborate the findings of the present study.
The concentration of total polyphenols and the antioxidant capacity of the olive oil showed a marked decrease during storage. These results align with Yildirim [75], who reported up to a 70% reduction in total phenolic content over time. A detailed analysis of individual phenolics revealed increases in hydroxytyrosol and tyrosol concentrations, while other phenolic compounds declined. This shift suggests that storage not only reduces overall phenolic content, but it also alters the qualitative composition of the phenolic profile. Daskalaki et al. [13] similarly showed that changes in phenolic compounds during storage are closely linked to the peroxide value. Specifically, when peroxide values remained below the acceptable threshold (20 meq O2/kg olive oil), a significant portion of hydroxytyrosol and tyrosol derivatives persisted. These findings highlight the scavenging role of phenolic compounds and their interaction with peroxide formation in shaping the phenolic profile. Moreover, phenolic degradation during storage—even in the absence of light—is strongly influenced by key factors such as the degree of fatty acid unsaturation, the volume of headspace oxygen, and ambient temperature. These variables directly affect hydroperoxide formation, which in turn accelerates phenolic oxidation and contributes to the overall decline in oil quality [13]. The reduction of antioxidant compounds, particularly phenolics, was expected, given their central role in maintaining oxidative stability. These compounds protect fatty acids from oxidative degradation and help prevent deterioration of the oil through both oxidative and hydrolytic reactions [60].
Among the treatments examined, the CD treatment exhibited the highest rate of degradation in total phenols, o-diphenols, flavonoids, and antioxidant capacity (as measured by FRAP) as indicated by the significant differences in the corresponding regression lines. This accelerated deterioration is likely due to the initially low phenolic content, which resulted in insufficient oxidative protection. The reduced antioxidant capacity, reflected in the FRAP values, corresponded with an elevated peroxide value, highlighting the critical role of phenolics in suppressing lipid peroxidation [83]. Supporting this, Fotiadou et al. [84] demonstrated that enzymatic enrichment with natural antioxidants improved oxidative resistance and limited peroxide formation. Likewise, Giannakopoulos et al. [85] and Averbuch et al. [78] reported that oils with higher initial phenolic content oxidized more slowly and maintained better quality over time.
The concentrations of squalene and polyunsaturated fatty acids (PUFAs) declined significantly during storage. These findings are consistent with the results reported by Rastrelli et al. [86] and Stefanoudaki et al. [77], who showed that the degradation of PUFAs—particularly linolenic acid (C18:3)—can be mitigated by displacing headspace oxygen with an inert gas such as nitrogen in partially filled containers. In the present study, the observed increase in the relative concentration of oleic acid (C18:1) over the storage period is likely due to the oxidative degradation of more unsaturated fatty acids, namely linolenic (C18:3) and, to a lesser extent, linoleic acid (C18:2) [75]. This compositional shift highlights the differential oxidative stability of fatty acids and emphasizes the importance of appropriate storage conditions for maintaining oil quality [87]. Furthermore, the high oleic acid content of olive oil plays a crucial role in enhancing its oxidative stability.

5. Conclusions

The results of this study indicate that both deficit irrigation and the presence of Ailanthus can influence the quality of olive oil from the ‘Koroneiki’ variety, as reflected by increases in K232 and K270 values associated with Ailanthus presence, and elevated C18:3 levels under deficit irrigation. However, the combined exposure of olive trees to both stress factors did not produce an additive negative effect, as some oil quality parameters remained unaffected or even showed a slight improvement. Importantly, the measured quality indicators determined in this study at harvest remained within the limits established by the European Union for extra virgin olive oil for these olive oil quality traits. Furthermore, the findings regarding the effects of the storage period on olive oil quality underscore the importance of proper storage conditions to preserve oil quality and prevent oxidative degradation, while also highlighting the critical role of initial oil quality in ensuring successful preservation. Further research is recommended, involving additional olive cultivars and diverse abiotic stress conditions, to fully elucidate the effects of Ailanthus on both tree physiology and oil quality.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/app15147678/s1, Figure S1: Effects of time and treatments and analysis of regression lines (the small square within each figure) for: (a) peroxide value; (b) acidity; (c) K232 value; (d) K270 value; (e) ΔK index; Table S1: Interaction of treatments on quality characteristics of olive oil over time; Figure S2: Effects of time and treatments and analysis of regression lines (the small square within each figure) for: (a) total phenol concentration; (b) total o-diphenols concentration; (c) flavonoids concentration; (d) antioxidant capacity measured by DPPH method; (e) antioxidant capacity measured by FRAP method; (f) antioxidant capacity measured by ABTS method; Table S2: Interaction of treatments on total phenolics, total o-diphenols and total flavonoids content and on antioxidant capacity of olive oil according to the DPPH, FRAP and ABTS methods over time; Figure S3: Effects of time and treatments and analysis of regression lines (the small square within each figure) for: (a) C16:0 concentration; (b) C16:1 concentration; (c) C18:0 concentration; (d) C18:1 concentration; (e) C18:2 concentration; (f) C20:0 concentration; (g) C18:3 concentration; (h) C20:1 concentration; Figure S4: Effects of time and treatments and analysis of regression lines (the small square within each figure) for: (a) SFAs concentration; (b) MUFAs concentration; (c) PUFAs concentration; (d) UFAs concentration; (e) SFAs/UFAs ratio; (f) MUFAs/PUFAs ratio; (g) C18:1/C18:2 ratio; (h) squalene concentration; Table S3: Interaction of treatments on fatty acids profile and squalene concentration in olive oil over time.

Author Contributions

Conceptualization, A.-G.K. and P.A.R.; methodology, A.-G.K. and P.A.R.; software, A.-G.K. and P.A.R.; validation, P.A.R.; formal analysis, A.-G.K.; investigation, A.-G.K.; resources, P.A.R.; data curation, A.-G.K.; writing—original draft preparation, A.-G.K.; writing—review and editing, A.-G.K. and P.A.R.; visualization, A.-G.K.; supervision, P.A.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

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

Acknowledgments

The olive trees used in the experiment were donated by G. Kostelenos Nurseries, which is located in Galata, Trizinia. This paper is an extended version of our paper published in Karyda, A.-G.; Roussos, P.A. Effect of Ailanthus altissima on photosynthetic activity, yield, and olive oil quality characteristics under two irrigation regimes. In Proceedings of the XIV International Scientific Agriculture Symposium “AGROSYM 2023”, Jahorina, Bosnia and Herzegovina, 5–8 October 2023.

Conflicts of Interest

The authors declare no conflicts of interest.

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Table 1. Effect of treatments on growth and production parameters over a period of 3 years.
Table 1. Effect of treatments on growth and production parameters over a period of 3 years.
Increment (cm)TCSA (cm2)Fruit Yield/Tree (kg)Olive Oil
(% w/w of Olive Paste)		Olive Oil/Tree (kg)
Treatment
C (Control)15.72 a0.55 a0.21 a15.91 a0.03 a
A (Ailanthus)10.65 a0.46 a0.22 a12.85 b0.03 a
Irrigation regime
F (Full)13.17 a0.48 a0.21 a16.24 a0.03 a
D (Deficit)13.20 a0.53 a0.22 a12.52 b0.03 a
Treatment × Irrigation regime
C × F13.71 a0.52 a0.18 a16.44 a0.02 a
C × D17.73 a0.58 a0.23 a15.37 a0.03 a
A × F12.63 a0.45 a0.24 a16.04 a0.03 a
A × D8.67 a0.48 a0.20 a9.66 b0.02 a
TCSA is the trunk cross-sectional area expressed in cm2. Means within the same column followed by the same letter are not significantly different according to Student’s t-test (for Ailanthus treatment and irrigation regime) and Tukey’s multiple range test (interaction) at a significance level of α = 0.05.
Table 2. Effect of treatments on fruit characteristics over a period of 3 years.
Table 2. Effect of treatments on fruit characteristics over a period of 3 years.
Fruit Weight (g)Diameter (mm)Length (mm)Flesh Fresh Weight/Dry Weight% Stone Weight/Fruit Weight% Flesh Weight/Fruit Weight
Treatment
C (Control)1.17 a11.26 a16.66 a2.75 a33.47 a66.53 a
A (Ailanthus)1.14 a11.18 a16.53 a2.54 a32.12 a67.88 a
Irrigation regime
F (Full)1.26 a11.60 a17.11 a2.65 a33.16 a66.84 a
D (Deficit)1.05 b10.85 b16.08 b2.65 a32.43 a67.57 a
Treatment × Irrigation regime
C × F1.24 a11.55 a16.93 a2.74 a34.05 a65.95 a
C × D1.09 b10.97 b16.39 ab2.76 a32.89 a67.11 a
A × F1.28 a11.64 a17.30 a2.55 a32.27 a67.73 a
A × D1.00 b10.72 b15.77 b2.53 a31.96 a68.04 a
Means within the same column followed by the same letter are not significantly different according to Student’s t-test (for Ailanthus treatment and irrigation regime) and Tukey’s multiple range test (interaction) at a significance level of α = 0.05.
Table 3. Effects of treatments on fruit color parameters and maturity index over a period of 3 years.
Table 3. Effects of treatments on fruit color parameters and maturity index over a period of 3 years.
L*Hue Angle (h°)Chroma ValueMaturity Index
Treatment
C (Control)58.10 a102.87 a26.30 a2.3 a
A (Ailanthus)58.61 a106.86 a30.59 a2.1 a
Irrigation regime
F (Full)56.16 b97.64 b25.07 b2.5 a
D (Deficit)60.54 a112.10 a31.81 a1.9 b
Treatment × Irrigation
C × F56.14 a96.19 a22.79 b2.6 a
C × D60.06 a109.56 a29.81 ab2.0 ab
A × F56.19 a99.09 a27.36 ab2.4 ab
A × D61.03 a114.64 a33.82 a1.8 b
Means within the same column followed by the same letter are not significantly different according to Student’s t-test (for Ailanthus treatment and irrigation regime) and Tukey’s multiple range test (interaction) at a significance level of α = 0.05.
Table 4. Effects of treatments on quality characteristics of olive oil over a period of 3 years.
Table 4. Effects of treatments on quality characteristics of olive oil over a period of 3 years.
Peroxides (meq. O2/kg oil)Acidity
(g Oleic Acid/100 g oil)		K232K270ΔK
Treatment
C (Control)14.5 a0.40 a1.10 b0.11 b0.00
A (Ailanthus)15.7 a0.39 a1.60 a0.17 a0.00
Irrigation regime
F (Full)16.7 a0.47 a1.39 a0.14 a0.00
D (Deficit)13.5 a0.32 b1.31 a0.25 a0.00
Treatment × Irrigation regime
C × F12.7 a0.48 a1.05 b0.10 c0.00
C × D11.9 a0.32 b1.16 b0.13 bc0.00
A × F16.2 a0.45 ab1.73 a0.18 a0.01
A × D15.1 a0.33 b1.47 a0.16 ab0.00
Means within the same column followed by the same letter are not significantly different according to Student’s t-test (for Ailanthus treatment and irrigation regime) and Tukey’s multiple range test (interaction) at a significance level of α = 0.05.
Table 5. Effects on total phenolics, total o-diphenols, and total flavonoids content and on antioxidant capacity of olive oil according to the DPPH, FRAP, and ABTS methods over a period of 3 years.
Table 5. Effects on total phenolics, total o-diphenols, and total flavonoids content and on antioxidant capacity of olive oil according to the DPPH, FRAP, and ABTS methods over a period of 3 years.
Total
Phenols (mg Gallic Acid/kg oil)		Total o-
Diphenols
(mg Caffeic Acid/kg oil)		Total
Flavonoids (mg
Catechin/kg oil)		DPPH (μmol Trolox/kg oil)FRAP
(μmol Trolox/kg oil)		ABTS
(μmol Trolox/kg oil)
Treatment
C (Control)227.47 a34.54 b164.60 a850.53 a1005.45 a1041.97 a
A (Ailanthus)209.93 a52.04 a141.16 a696.92 a934.60 a983.27 a
Irrigation regime
F (Full)187.00 a36.43 a121.91 b598.51 b728.85 b865.73 b
D (Deficit)250.40 a50.15 a183.84 a948.95 a1211.20 a1159.52 a
Treatment × Irrigation regime
C × F157.79 b33.91 b107.48 b522.99 b649.17 b799.18 b
C × D297.16 a35.17 b221.71 a1178.07 a1361.74 a1284.76 a
A × F216.22 ab38.94 ab136.35 ab674.02 b808.54 b932.27 b
A × D203.65 ab65.13 a145.97 ab719.82 ab1060.66 ab1034.28 ab
Means within the same column followed by the same letter are not significantly different according to Student’s t-test (for Ailanthus treatment and irrigation regime) and Tukey’s multiple range test (interaction) at a significance level of α = 0.05.
Table 6. Effects of treatments on fatty acids profile (%) and squalene concentration in olive oil over a period of 3 years.
Table 6. Effects of treatments on fatty acids profile (%) and squalene concentration in olive oil over a period of 3 years.
TreatmentIrrigation RegimeTreatment × Irrigation Regime
C (Control)A (Ailanthus)F (Full)D (Deficit)C × FC × DA × FA × D
C16:014.01 a14.16 a14.28 a13.90 a14.20 a13.83 a14.36 a13.96 a
C16:10.98 b1.08 a1.03 a1.04 a1.01 ab0.95 b1.04 ab1.12 a
C17:00.04 a0.05 a0.04 a0.05 a0.04 a0.04 a0.04 a0.05 a
C17:10.07 a0.07 a0.07 b0.08 a0.07 b0.07 ab0.07 ab0.08 a
C18:02.61 a2.66 a2.81 a2.45 b2.86 a2.36 b2.78 a2.54 ab
C18:171.92 a71.76 a71.47 a72.21 a70.79 a73.05 a72.15 a71.37 a
C18:27.90 a7.49 a7.84 a7.56 a8.60 a7.21 a7.08 a7.91 a
C20:00.37 a0.43 a0.39 a0.41 a0.38 a0.37 a0.40 a0.45 a
C18:30.89 b1.04 a0.89 b1.04 a0.88 b0.89 b0.89 b1.19 a
C20:10.26 a0.27 a0.25 b0.28 a0.25 ab0.26 ab0.24 b0.30 a
C22:00.13 a0.13 a0.12 b0.14 a0.12 a0.14 a0.13 a0.14 a
C24:00.05 b0.06 a0.06 a0.06 a0.06 a0.05 a0.06 a0.06 a
SFAs17.12 a17.39 a17.61 a16.90 b17.55 ab16.69 b17.67 a17.11 ab
MUFAs73.20 a73.18 a72.79 a73.59 a72.10 a74.31 a73.48 a72.87 a
PUFAs8.79 a8.54 a8.73 a8.61 a9.48 a8.10 a7.97 a9.11 a
UFAs81.99 a81.71 a81.51 a82.20 a81.58 a82.41 a81.45 a81.98 a
SFAs/
UFAs		0.21 a0.21 a0.22 a0.21 b0.22 a0.20 a0.22 a0.21 a
MUFAs/
PUFAs		8.79 a8.88 a8.82 a8.85 a8.19 a9.39 a9.45 a8.31 a
C18:1/
C18:2		2.57 a2.82 a2.42 a2.97 a2.05 a3.09 a2.79 a2.85 a
Squalene (mg/100 g oil)408.29 a484.67 a384.50 a508.46 a317.41 a499.18 a451.60 a517.74 a
Means within the same row followed by the same letter are not significantly different according to Student’s t-test (for Ailanthus treatment and irrigation regime) and Tukey’s multiple range test (interaction) at a significance level of α = 0.05.
Table 7. Effects of storage period and treatments on quality characteristics of olive oil over time.
Table 7. Effects of storage period and treatments on quality characteristics of olive oil over time.
FactorsPeroxides
(meq. O2/kg Oil)		Acidity
(g Oleic Acid/100 g Oil)		K232K270ΔK
Storage period
Harvest17.50 c0.25 b1.35 c0.16 b0.00
6 months35.63 b0.47 a2.14 b0.15 b0.01
12 months51.75 a0.45 a2.89 a0.25 a0.01
Treatments
CF36.07 b0.45 a2.17 a0.20 a0.03
CD42.77 a0.35 b2.12 a0.17 b0.00
AF27.73 d0.38 b2.15 a0.19 ab0.01
AD33.27 c0.38 b2.07 a0.19 a0.01
The definitions of the letters are listed as follows: CF: control treatment and full irrigation; CD: control treatment and deficit irrigation; AF: Ailanthus presence and full irrigation; AD: Ailanthus presence and deficit irrigation. The factor “storage period” refers to storage period irrespective of the treatment employed and the factor “treatment” to each specific treatment irrespective of the storage period. Means within the same column followed by the same letter are not significantly different (separately for storage period and treatments) according to Tukey’s multiple range test at a significance level of α = 0.05.
Table 8. Effects of storage period and treatments on total phenolics, total o-diphenols, and total flavonoids content and on the antioxidant capacity of olive oil according to the DPPH, FRAP, and ABTS methods over time.
Table 8. Effects of storage period and treatments on total phenolics, total o-diphenols, and total flavonoids content and on the antioxidant capacity of olive oil according to the DPPH, FRAP, and ABTS methods over time.
Total Phenols (mg
Gallic Acid/kg Oil)		Total o-
Diphenols
(mg Caffeic Acid/kg Oil)		Total
Flavonoids (mg
Catechin/kg Oil)		DPPH (μmol Trolox/kg Oil)FRAP
(μmol Trolox/kg Oil)		ABTS
(μmol Trolox/kg Oil)
Storage period
Harvest269.84 a51.82 a223.71 a1043.4 a1017.46 a1059.71 a
6 months195.00 b20.26 b118.41 b512.62 b783.2 b781.57 b
12 months138.37 c12.74 c97.89 b610.69 b870.56 ab684.69 b
Treatments
CF210.83 b34.06 a170.43 a816.59 b991.82 b936.97 a
CD106.09 c18.21 c68.38 b321.66 c524.91 c587.23 b
AF250.93 a31.28 b168.55 a833.33 b973.14 b900.76 a
AD236.43 ab29.54 b179.31 a917.38 a1071.77 a942.99 a
The definitions of the letters are listed as follows: CF: control treatment and full irrigation; CD: control treatment and deficit irrigation; AF: Ailanthus presence and full irrigation; AD: Ailanthus presence and deficit irrigation. The factor “storage period” refers to storage period irrespective of the treatment employed and the factor “treatment” to each specific treatment irrespective of the storage period. Means within the same column followed by the same letter are not significantly different (separately for storage period and treatments) according to Tukey’s multiple range test at a significance level of α = 0.05.
Table 9. Effects of storage period and treatments on fatty acid profile (%) and squalene concentration in olive oil over time.
Table 9. Effects of storage period and treatments on fatty acid profile (%) and squalene concentration in olive oil over time.
Storage PeriodTreatments
Harvest6 Months12 MonthsCFCDAFAD
C16:014.81 b16.52 a15.23 b14.93 b16.30 a15.00 b15.85 a
C16:11.21 a1.08 b0.96 c1.09 ab1.08 ab1.05 b1.10 a
C18:02.53 a2.36 b2.26 c2.48 a2.31 c2.40 b2.35 bc
C18:169.89 c71.77 b73.25 a70.88 c70.35 c73.19 a72.12 b
C18:27.09 a6.95 a7.04 a8.32 a7.54 b6.12 c6.12 c
C20:00.42 a0.33 b0.29 b0.35 ab0.35 ab0.32 b0.37 a
C18:30.90 a0.85 a0.78 b0.82 b0.91 a0.76 c0.88 a
C20:10.27 a0.18 b0.20 b0.21 a0.22 a0.22 a0.21 a
SFAs17.92 b19.21 a17.78 b17.79 b19.02 a17.76 b18.64 a
MUFAs71.43 c73.02 b74.40 a72.19 c71.67 c74.48 a73.46 b
PUFAs7.98 a7.80 b7.82 b9.14 a8.45 b6.88 c7.00 c
UFAs79.41 c80.82 b82.22 a81.34 a80.11 b81.35 a80.45 b
SFAs/
UFAs		0.23 b0.24 a0.22 c0.22 b0.24 a0.22 b0.23 a
MUFAs/
PUFAs		9.13 b9.50 a9.69 a7.90 d8.50 c10.84 a10.50 b
C18:1/
C18:2		0.04 a0.03 b0.03 c0.04 a0.03 b0.03 b0.03 b
Squalene (mg/100 g oil)740.86 a200.38 b199.48 b286.31 a396.32 a403.93 a434.39 a
The definitions of the letters are shown as follows: CF: control treatment and full irrigation; CD: control treatment and deficit irrigation; AF: Ailanthus presence and full irrigation; AD: Ailanthus presence and deficit irrigation. The factor “storage period” refers to storage period irrespective of the treatment employed and the factor “treatment” to each specific treatment irrespective of the storage period. Means within the same row followed by the same letter are not significantly different (separately for storage period and treatments) according to Tukey’s multiple range test at a significance level of α = 0.05.
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Karyda, A.-G.; Roussos, P.A. Influence of the Invasive Species Ailanthus altissima (Tree of Heaven) on Yield Performance and Olive Oil Quality Parameters of Young Olive Trees cv. Koroneiki Under Two Distinct Irrigation Regimes. Appl. Sci. 2025, 15, 7678. https://doi.org/10.3390/app15147678

AMA Style

Karyda A-G, Roussos PA. Influence of the Invasive Species Ailanthus altissima (Tree of Heaven) on Yield Performance and Olive Oil Quality Parameters of Young Olive Trees cv. Koroneiki Under Two Distinct Irrigation Regimes. Applied Sciences. 2025; 15(14):7678. https://doi.org/10.3390/app15147678

Chicago/Turabian Style

Karyda, Asimina-Georgia, and Petros Anargyrou Roussos. 2025. "Influence of the Invasive Species Ailanthus altissima (Tree of Heaven) on Yield Performance and Olive Oil Quality Parameters of Young Olive Trees cv. Koroneiki Under Two Distinct Irrigation Regimes" Applied Sciences 15, no. 14: 7678. https://doi.org/10.3390/app15147678

APA Style

Karyda, A.-G., & Roussos, P. A. (2025). Influence of the Invasive Species Ailanthus altissima (Tree of Heaven) on Yield Performance and Olive Oil Quality Parameters of Young Olive Trees cv. Koroneiki Under Two Distinct Irrigation Regimes. Applied Sciences, 15(14), 7678. https://doi.org/10.3390/app15147678

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