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Article

Species- and Provenance-Specific Leaf Phenological Responses to Drought and Elevated Phosphorus in Fagus sylvatica and Quercus petraea

by
Marko Bačurin
,
Krunoslav Sever
,
Ida Katičić Bogdan
and
Saša Bogdan
*
Forest Genetics, Dendrology and Botany Department, Faculty of Forestry and Wood Technology, University of Zagreb, Svetošimunska Cesta 23, 10000 Zagreb, Croatia
*
Author to whom correspondence should be addressed.
Forests 2025, 16(9), 1402; https://doi.org/10.3390/f16091402
Submission received: 14 July 2025 / Revised: 20 August 2025 / Accepted: 31 August 2025 / Published: 2 September 2025
(This article belongs to the Special Issue Tree Growth and Physiological Properties Under Ongoing Global Climate Change: 2nd Edition)
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Abstract

Leaf phenology is a crucial functional trait in temperate forest trees that integrates environmental signals and reflects species’ adaptive capacity to stress. This study examined how moderate drought and elevated phosphorus availability, alone and in combination, affect the spring and autumn phenology of juvenile Fagus sylvatica and Quercus petraea saplings from two climatically distinct Croatian provenances. In a common garden experiment, saplings were subjected to four treatments involving drought and phosphorus addition. Phenological stages were scored using standardized ordinal scales across two growing seasons. Results revealed that phosphorus consistently advanced autumn leaf senescence in both species, independent of drought, while drought effects were species- and provenance-specific. Spring phenology was more sensitive to drought: beech from the drier provenance advanced budburst, suggesting an escape strategy, whereas oak delayed leaf-out under the same conditions. Notably, combined drought and phosphorus treatments often neutralized individual effects, indicating physiological compensation. Provenance-level differences highlighted contrasting strategies—phenotypic plasticity versus stress tolerance—under multi-stressor conditions. These findings underscore the dominant role of phosphorus in regulating phenology and the complex, non-additive nature of drought–nutrient interactions, emphasizing the need for integrative approaches in predicting phenological responses under climate change.

1. Introduction

In recent decades, global climate change has amplified the intensity and frequency of abiotic stressors such as drought, posing critical challenges to the stability, productivity, and regeneration of temperate forest ecosystems [1]. Altered precipitation regimes and rising temperatures intensify drought events while simultaneously disturbing nutrient stoichiometry in forest soils, particularly the balance between nitrogen and phosphorus [2,3]. Leaf phenology—the seasonal timing of leaf development and senescence—has therefore emerged as a key functional trait of temperate forest trees, integrating environmental cues and mediating tree performance under changing conditions [4].
The timing of phenological events is traditionally governed by photoperiod and temperature [5], yet additional environmental drivers—especially water and nutrient availability—can substantially modulate developmental transitions [6,7]. Among nutrients, phosphorus (P) is increasingly recognized as a central regulator of phenological timing. Beyond its role in metabolism and growth, P influences hormonal pathways and gene expression, including senescence-associated genes, and can shape chromatin-level control through SPX-domain signaling [8,9]. Empirical work shows that higher P availability can accelerate vegetative development and advance the onset of senescence by enabling earlier completion of developmental phases [6]. However, the extent to which P-driven phenological shifts are modulated by co-occurring drought stress remains poorly resolved. Some studies indicate that P may buffer drought impacts by sustaining metabolic function [10], whereas others report antagonistic or context-dependent outcomes [11].
Drought itself exerts complex—and sometimes opposing—effects on phenology, advancing or delaying developmental phases depending on species identity, stress timing, and severity [12,13,14,15]. Despite this, most studies still consider spring and autumn phenology separately, rather than as components of an integrated seasonal cycle [16,17]. This separation hampers our ability to understand transitional dynamics linking leaf flushing and senescence and to predict whole-season responses under multiple stressors. In addition to interspecific variation, local adaptation contributes to divergent phenological strategies among provenances: geographic origin reflects climatic history and ecological filtering, shaping phenotypic plasticity and stress tolerance [18,19]. Yet, provenance-based phenological responses under combined drought and nutrient stress, particularly during juvenile stages, remain underexplored.
To address these gaps, we investigated how elevated phosphorus availability and moderate drought—alone and in combination—affect the spring and autumn leaf phenology of juvenile Fagus sylvatica and Quercus petraea from two ecologically contrasting Croatian provenances in a common-garden experiment. Based on the background above, we hypothesized that: (i) elevated P generally accelerates phenological development, leading to earlier transitions in both spring and autumn [6,8,9]; (ii) drought modifies leaf phenology in a species- and provenance-dependent manner, reflecting divergent adaptive strategies shaped by climatic origin [12,13,14,15,18,19]; and (iii) combined drought–phosphorus effects are non-additive (interactive), potentially buffering or amplifying single-stressor impacts rather than summing linearly [10,11].
We tested these hypotheses using repeated phenological scoring across two growing seasons, enabling an integrated assessment of multi-stressor influences on the full seasonal cycle. Our findings contribute to a better understanding of functional adaptation in temperate tree species and offer insights for climate-resilient forest management.

2. Materials and Methods

2.1. Plant Material and Provenance Sites

This study was conducted on naturally regenerated four-year-old saplings of common beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Matt.) Liebl.) originating from two mature, mixed forest stands located in the continental region of Croatia. The age of the saplings (approximately four years) was determined by counting annual growth rings on a subsample of 25 individuals per each species. The first provenance was located near Karlovac (KA) in the northwest (45.466° N, 15.522° E; 170–185 m a.s.l.), characterized by deeper soils, north–northeast exposure, and higher precipitation. The second provenance was near Slavonski Brod (SB) in the east (45.273° N, 17.973° E; 230–255 m a.s.l.), with shallower soils, south–southeast exposure, and drier conditions.
In March 2021, saplings were collected from both stands beneath 50 mature mother trees (25 per species). A total of 640 saplings were excavated (160 per species per site), ensuring minimal root damage and even spatial distribution to reduce genetic relatedness. Saplings were temporarily stored in moist sand and shade before being transplanted.
Climatic classification at both sites was humid temperate (Cfwbx” and Cfwb”x) per Köppen. Mean annual precipitation (1949–2019) was higher at KA (≈1112 mm) than SB (≈770 mm). Between 2016 and 2020, KA experienced more drought months (17 total, 9 during growing season) than SB (9 total, 4 during growing season). Mean growing season temperature was 18.8 °C, relative humidity 66.7%, and solar radiation 7.6 h/day [20].

2.2. Experimental Design

The experiment was established in mid-March 2021 at the Faculty of Forestry and Wood Technology, University of Zagreb (45.821° N, 16.023° E; 120 m a.s.l.) as a common garden trial. Saplings were planted into four large wooden boxes (155 × 275 × 80 cm; 3.41 m3 each), filled with commercial Klasmann-Deilmann TS 3 substrate (initially containing 160 mg/L P2O5).
Each box contained 100 saplings—25 of each species from each provenance—randomly arranged at 20 × 18 cm spacing. Two boxes received phosphorus fertilization (1182 g of Triplex, 45% P2O5) to raise P2O5 levels to 300 mg/L (+P treatment), while two boxes remained unfertilized −P treatment).
During 2021, saplings were exposed to natural conditions with regular watering. In 2022, all boxes were covered with a transparent PVC roof to exclude rainfall, and four treatments were applied:
  • +PW: elevated phosphorus + regular watering (40 L every 4 days).
  • Control: no phosphorus + regular watering.
  • +PD: elevated Phosphorus + drought (minimal watering triggered by visible wilting).
  • −PD: no phosphorus + drought.

2.3. Leaf Phenology Scoring

Autumn leaf phenological phases were scored twice a week in 2022 using a 0–5 ordinal scale: 0—leaves completely green with no visible discoloration; 1—up to 25% of plant leaves show discoloration; 2—up to 50% of plant leaves show discoloration; 3—more than 50% of plant leaves show discoloration; 4—more than 75% of plant leaves show discoloration; and 5—leaves shed.
Spring leaf phenology was scored twice a week (during the process in 2023) on all plants in the trial using a 1–7 ordinal scale: 1—bud scales completely closed, dormant buds; 2—buds swelling, scales slightly spaced; 3—bud burst, green leaf tips visible; 4—folded leaves visible. 5—leaves unfolding but not yet flattened, small. 6—leaves still relatively small but with flattened blades, blade edges bent downward, withered, lighter green or reddish; and 7—leaves appear developed, larger but more tender than fully developed leaves and lighter green or reddish.
All phenological scorings were performed by one experienced person. In this study, the term phenophase refers to discrete ordinal stages of leaf development or senescence, scored on a predefined scale. The phenological phase scores (i.e., phenophases) served as input data for subsequent statistical analyses.

2.4. Statistical Analyses

All statistical analyses and visualizations were performed in R (version 4.5.1; R Development Core Team, 2025). Data processing relied on the tidyverse (version 2.0.0) and dplyr (version 1.1.4) packages. Assumptions of normality and homogeneity of variance were evaluated using the Shapiro–Wilk and Levene’s tests implemented in rstatix (version 0.7.2). Data visualization was conducted using ggplot2 (version 3.5.1) and ggstatsplot (version 0.12.3).
Statistical analyses examined the effects of treatment (+PW, –PD, +PD, control), provenance, and species during two observation seasons (autumn 2022 and spring 2023). To assess multivariate phenological responses, we applied a Permutational Multivariate Analysis of Variance (PERMANOVA) using the adonis2 function from the vegan package (version 2.7.1), with Bray–Curtis dissimilarity and 999 permutations. Analyses were conducted separately for each season (autumn 2022 and spring 2023). The initial model included the main effects (Species, Provenance, Treatment) and all possible two- and three-way interactions. In subsequent models, provenance was nested within species (Species + Species:Provenance + Treatment) to reflect the hierarchical structure of the experimental design.
The same saplings were monitored repeatedly across calendar dates within each season. To account for non-independence, permutations in PERMANOVA were constrained within individuals using the strata = TreeID option, ensuring shuffling only among units sharing the same subject identifier. This yields valid permutation p-values in a repeated-measures design while preserving full multivariate phenology trajectories.
For univariate, date-wise comparisons of ordinal phenophase scores among treatments, analyses were performed separately for each season, and independently within each species and provenance. Each observation date was analyzed as a cross-section using the Kruskal–Wallis test, followed by Dunn’s post hoc with Benjamini–Hochberg FDR correction. Treating each date as a cross-section avoids violating independence across repeated dates (i.e., no across-date pooling of the same subject within the same test). Differences between treatments were considered statistically significant when p < 0.05 on at least two calendar dates.

3. Results

3.1. Autumn Phenology

The PERMANOVA analysis of autumn phenological data revealed that both species and treatment had statistically significant effects on leaf phenology (Table 1). The effect of species was highly significant (p = 0.001), explaining 6.3% of the total phenological variation. Likewise, the treatment effect was also highly significant (p = 0.001), accounting for 11.7% of the observed variation. This indicates that drought and phosphorus treatments significantly influenced autumn leaf phenological patterns.
The effect of provenance, although not statistically significant at the conventional 0.05 level (p = 0.069), explained an additional 1.1% of the variation and may represent a biologically relevant source of variability.
All interaction terms—including Species × Provenance, Species × Treatment, Provenance × Treatment, and the three-way interaction—were statistically non-significant (p > 0.1), suggesting that the effects of treatment and species on autumn phenology were generally additive and consistent across provenances.
The residual variation remained high (75.96%), reflecting expected biological variability and potentially unmeasured environmental factors.

3.1.1. The Treatment Effects on Autumn Phenology in European Beech

Differences in the timing and progression of autumn leaf senescence between drought-exposed and control European beech saplings were not statistically significant (Figure 1). However, provenance SB showed a slight advancement, entering phenophase 3 (>50% discolored leaves) approximately two days earlier under drought conditions compared to the control (Figure 1a). In contrast, leaf senescence dynamics for provenance KA saplings subjected to drought closely matched those of the control (Figure 1b). Thus, it can be concluded that drought had a negligible effect on autumn leaf senescence in European beech saplings, irrespective of provenance.
Saplings of European beech exposed to combined elevated soil phosphorus and drought conditions (+PD treatment, Figure 1) showed significantly earlier leaf senescence compared to the control in both provenances. The onset of phenophase 3 (>50% discolored leaves) occurred on average 14 and 19 days earlier (provenances KA and SB, respectively). However, the +PD treatment did not significantly differ from the elevated phosphorus alone (+PW treatment). Thus, the interaction effect between drought and elevated phosphorus was not confirmed, indicating that elevated phosphorus predominantly influenced autumn leaf senescence in European beech independently of drought.

3.1.2. The Treatment Effects on Autumn Phenology in Sessile Oak

Differences in the dynamics of autumn leaf senescence between sessile oak saplings exposed to drought and control saplings were also not statistically significant (Figure 2). Similarly to European beech, saplings of provenance SB exhibited slightly earlier leaf senescence under drought conditions, with phenophase 3 occurring on average 2–3 days earlier compared to control saplings (Figure 2a); however, this difference was not significant. Saplings from provenance KA showed an even less pronounced response to drought (Figure 2b). Overall, drought had a negligible effect on autumn leaf senescence in sessile oak saplings, irrespective of provenance.
Similarly to European beech, saplings of sessile oak from provenance SB exposed to combined elevated soil phosphorus and drought (+PD treatment, Figure 1a) showed significantly earlier leaf senescence compared to the control. Phenophase 3 occurred on average 29 days earlier in the +PD treatment than in the control (Figure 1a). However, no interaction effect was observed here either; instead, elevated phosphorus predominantly influenced autumn leaf senescence since no significant differences were found between +PD and elevated phosphorus alone (+PW treatment). Conversely, provenance KA showed no significant shifts in autumn leaf senescence timing in either elevated phosphorus (+PW) or combined phosphorus and drought (+PD) treatments. Although phenophase 3 occurred on average 7 days earlier in the +PD treatment, variations in the timing of other phases and within-treatment variability resulted in no statistically significant differences.

3.2. Spring Phenology

The PERMANOVA analysis of spring phenological data showed that species had a dominant and statistically significant effect on leaf phenology (p = 0.001), explaining 33.7% of the total multivariate variation (Table 2). This highlights a substantial divergence in spring phenological patterns between Fagus sylvatica and Quercus petraea.
The effect of treatment was also statistically significant (p = 0.005), contributing 3.7% of the phenological variation. This confirms that drought and phosphorus treatments continued to exert measurable influence on spring leaf phenology, albeit to a lesser extent than in autumn.
By contrast, the effects of provenance and all interaction terms (Species × Provenance, Species × Treatment, Provenance × Treatment, and the three-way interaction) were statistically non-significant (p > 0.1). The three-way interaction (Species × Provenance × Treatment) was marginally non-significant (p = 0.099), explaining 1.9% of the variation, and may suggest subtle combined effects worth further investigation.
Overall, a large portion of variation (58.7%) remained unexplained (residual), likely reflecting individual variability and environmental noise.

3.2.1. The Treatment Effects on Spring Phenology in European Beech

The effect of drought on leaf unfolding in European beech saplings was statistically significant for provenance SB (Figure 3a) but not for provenance KA (Figure 3b). In drought-exposed saplings of provenance SB, phenophase 3 (budburst) occurred on average about 5 days earlier compared to control saplings, and subsequent leaf-unfolding phases also started earlier. Saplings of provenance KA subjected to drought exhibited slightly earlier bud swelling (phenophase 2), but differences in subsequent phenophases compared to the control were negligible. Thus, drought significantly accelerated the spring phenology of leaf unfolding only in saplings of provenance SB.
The combined phosphorus and drought treatment (+PD) significantly differed from both drought alone (−PD) and elevated phosphorus alone (+PW) treatments, but not from the control in the provenance SB (Figure 3a). Therefore, the combined treatment neutralized the individual effects of drought and elevated phosphorus, indicating an interaction effect between drought and elevated phosphorus on leaf unfolding in this provenance. However, such an interaction effect was not observed in provenance KA, nor were there significant individual effects, as none of the treatments significantly differed from the control (Figure 3b).

3.2.2. The Treatment Effects on Spring Phenology in Sessile Oak

In sessile oak, results similar to those observed for European beech were recorded. In provenance SB, the combined phosphorus and drought treatment (+PD) significantly differed from both drought alone (-PD) and elevated phosphorus alone (+PW) treatments, but not from the control (Figure 4a). This result again suggests an interaction effect between drought and elevated phosphorus on leaf unfolding, whereby the combined treatment neutralized the individual effects of drought and elevated phosphorus. It is important to note that both drought and elevated phosphorus individually significantly delayed leaf unfolding in provenance SB. In provenance KA, there were no significant differences among treatments, indicating the absence of individual or interaction effects. Nevertheless, a potential interaction effect is indicated by the similarity between the +PD treatment and control relative to the -PD treatment (Figure 4b). However, the lack of statistical significance precludes definitive conclusions regarding the interaction effect on leaf unfolding in provenance KA.
Contrary to the response observed in European beech, drought significantly delayed leaf unfolding in sessile oak saplings of provenance SB (Figure 4a). On average, phenophase 3 occurred approximately 6 days later in drought-exposed saplings compared to the control, with delays also apparent in subsequent leaf-unfolding phenophases. Although provenance KA saplings exposed to drought exhibited slightly earlier leaf unfolding compared to the control, these differences were not statistically significant (Figure 4b). Notably, control saplings of the two provenances differed significantly from each other (compare control curves in Figure 4a,b), with provenance SB exhibiting earlier leaf unfolding than provenance KA. This provenance difference was not observed in European beech saplings.

4. Discussion

4.1. Autumn Phenology: Negligible Effects of Drought

The PERMANOVA analysis confirmed that both species identity and treatment significantly shaped autumn phenological variation, whereas provenance and interaction effects were weak (Table 1). This statistical outcome supports the interpretation that phosphorus availability, rather than drought or provenance, was the main driver of autumn senescence dynamics. Our experiment revealed negligible drought effects on autumn senescence in both species. Although minor advances were recorded, they were not statistically significant and indicate that the applied drought regime may not have reached thresholds necessary to trigger phenological shifts. Previous studies report highly context-dependent responses: Fagus sylvatica sometimes delays senescence after summer drought, especially when rewatering occurs [21], and similar patterns are found in Quercus petraea [22]. Other work shows delayed senescence in Betula pendula [11] or apple trees [23], while Bačurin et al. [7] observed drought-induced delays in Q. robur. Importantly, several studies emphasize that only moderate to severe drought during sensitive stages significantly alters senescence [11,21,23]. Thus, our results likely reflect that the moderate stress applied, though ecologically relevant, was insufficient to disrupt hormonal and metabolic cues governing leaf senescence. Although our findings suggest a limited impact of drought on autumn leaf senescence, it is important to recognize that leaf phenology does not fully capture the complexity of tree developmental dynamics. Studies on mature F. sylvatica and Q. petraea demonstrated that both extremely dry and extremely wet years significantly altered cambial activity, growth rate, and the timing of cambium cessation, even when leaf phenology showed only minor shifts [24]. These results indicate that photoperiod exerts a stronger control over leaf senescence than water availability, while wood formation processes remain more sensitive to climatic extremes. Consequently, leaf and cambium phenology can diverge, especially in oak, underscoring the need for integrative assessments that combine anatomical and foliar observations.

4.2. Dominant Influence of Elevated Phosphorus on Autumn Senescence

In contrast, elevated phosphorus consistently advanced autumn senescence in both species, particularly in SB provenance of Q. petraea. This supports growing evidence that phosphorus acts as a developmental signal beyond its metabolic role. Plants sense phosphorus via signaling cascades that regulate senescence-associated genes [8], while elevated P accelerates growth completion and resource reallocation [25]. At the molecular level, SPX-domain pathways and hormone interactions underpin earlier senescence [9]. The similarity of +PW and +PD treatments suggests phosphorus was the dominant driver, overriding drought effects, consistent with studies showing nutrient stoichiometry—especially N:P imbalance—can induce early senescence [26]. Our findings confirm phosphorus as a critical regulator of autumn phenology, with strong capacity to reshape developmental timing.

4.3. Spring Phenology: Contrasting Species Responses to Drought

In spring, PERMANOVA revealed a dominant species effect explaining over 30% of total variation, with additional but smaller contributions of treatments (Table 2). Provenance effects were not significant, highlighting that the contrasting drought responses observed between F. sylvatica and Q. petraea primarily reflect species-specific strategies rather than geographic origin. Spring phenology showed stronger drought sensitivity and clear interspecific divergence. In F. sylvatica (SB provenance), drought advanced budburst by several days, consistent with an “escape” strategy enabling early growth before summer droughts [27]. While potentially adaptive, this increases frost risk and ecological mismatches. In contrast, Q. petraea from the same provenance delayed budburst under drought, reflecting a conservative avoidance strategy typical for oaks with deeper rooting and stronger stomatal control [4,28]. Such divergence may stem from species-specific chilling and heat requirements [29] and different hormonal regulation, particularly abscisic acid [30]. Legacy effects from previous seasons may also shape responses [15]. KA provenance in both species showed minimal change, indicating lower phenological plasticity. These contrasting strategies highlight how temperature cues, water status, and hormonal pathways interact to shape spring development [31].

4.4. Interactive Effects of Drought and Phosphorus: Physiological Compensation

The combined drought + phosphorus treatment (+PD) frequently neutralized single-factor effects, resulting in phenological timing close to controls, especially in SB provenances. This suggests compensatory physiological mechanisms where phosphorus mitigates drought stress. Possible processes include improved ATP availability, enhanced root growth, and modulation of ABA signaling [32,33]. Phosphorus is increasingly recognized as a signal regulating development and nutrient balance [8,26], which may explain the observed buffering. Such non-additive interactions are common in multi-stressor contexts [34] and underscore the need for models that integrate nutrient–water–signaling interactions to predict phenological shifts.

4.5. Provenance Differences: Role of Local Adaptation

Clear provenance differences underline the role of local adaptation. SB provenance exhibited greater phenological plasticity: drought advanced budburst in F. sylvatica but delayed it in Q. petraea. KA provenance, by contrast, remained phenologically stable. Physiological studies support these contrasting strategies: KA saplings display stronger antioxidant defenses [10] and greater biomass allocation to roots [20], consistent with stress tolerance and drought avoidance. Although KA appears wetter on an annual scale, its soils are shallow and drought-prone during growing seasons, favoring conservative phenotypes. SB’s higher plasticity aligns with previous reports that southern provenances of beech show stronger responsiveness [18,19]. Together, SB represents a responsive, plastic strategy, while KA reflects conservative stability based on morphology and physiology. These alternative adaptive pathways resonate with ecological trade-offs between plasticity and tolerance [35,36].

5. Conclusions

This study demonstrates that phosphorus availability is a dominant regulator of leaf phenology in Fagus sylvatica and Quercus petraea, advancing autumn senescence and altering spring development regardless of drought. In contrast, drought effects were weaker and strongly species-specific, with F. sylvatica from drier origins showing accelerated budburst, while Q. petraea exhibited delayed flushing. Provenances further revealed contrasting adaptive strategies: the Slavonski Brod population expressed higher phenological plasticity, whereas the Karlovac provenance maintained stable phenological timing supported by physiological and morphological stress tolerance traits.
Most importantly, combined drought and phosphorus treatments frequently neutralized single-factor effects, highlighting the non-additive nature of multi-stressor interactions. These findings emphasize that predictions of climate-change impacts on forest phenology cannot rely on single-factor experiments, but must integrate nutrient and water dynamics together with intraspecific variation. From a management perspective, both plastic and conservative provenances provide complementary adaptive value. Their joint use in reforestation may enhance the resilience of European temperate forests under increasing climatic uncertainty.

Author Contributions

Conceptualization, K.S. and S.B.; methodology, M.B., I.K.B. and S.B.; validation, M.B. and S.B.; formal analysis M.B. and S.B.; investigation, M.B., I.K.B. and S.B.; resources, K.S. and S.B.; data curation, M.B. and S.B.; writing—original draft preparation, M.B. and S.B.; writing—review and editing, K.S. and I.K.B.; visualization M.B. and S.B.; supervision S.B. and K.S.; project administration, K.S.; funding acquisition, K.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Croatian Science Foundation, grant number IP-2020-025204: project title: “Phenotypic response of common beech and sessile oak provenances to long-lasting drought in interaction with different phosphorus concentrations in the soil”.

Data Availability Statement

The data used in this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Forests 16 01402 g001
Figure 1. Progression of autumn leaf senescence phenology in European beech saplings exposed to drought (−PD), elevated phosphorus (+PW), combined drought and elevated phosphorus (+PD), and control conditions: (a) provenance SB; (b) provenance KA. Significant differences (p < 0.05) indicate that leaf senescence occurred significantly earlier in the +PD and +PW treatments compared to the −PD treatment and control.
Figure 1. Progression of autumn leaf senescence phenology in European beech saplings exposed to drought (−PD), elevated phosphorus (+PW), combined drought and elevated phosphorus (+PD), and control conditions: (a) provenance SB; (b) provenance KA. Significant differences (p < 0.05) indicate that leaf senescence occurred significantly earlier in the +PD and +PW treatments compared to the −PD treatment and control.
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Forests 16 01402 g002
Figure 2. Progression of autumn leaf senescence phenology in sessile oak saplings subjected to drought (−PD), elevated phosphorus (+PW), combined drought and elevated phosphorus (+PD), and control conditions: (a) provenance SB; (b) provenance KA. Significant differences (p < 0.05) indicate earlier leaf senescence in the +PD and +PW treatments compared to the −PD treatment and control.
Figure 2. Progression of autumn leaf senescence phenology in sessile oak saplings subjected to drought (−PD), elevated phosphorus (+PW), combined drought and elevated phosphorus (+PD), and control conditions: (a) provenance SB; (b) provenance KA. Significant differences (p < 0.05) indicate earlier leaf senescence in the +PD and +PW treatments compared to the −PD treatment and control.
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Figure 3. Progression of spring leaf unfolding phenology in European beech saplings subjected to drought (−PD), elevated phosphorus (+PW), combined drought and elevated phosphorus (+PD), and control conditions: (a) provenance SB; (b) provenance KA. Significant differences (p < 0.05) indicate earlier leaf unfolding in the drought treatment (−PD) compared to all other treatments.
Figure 3. Progression of spring leaf unfolding phenology in European beech saplings subjected to drought (−PD), elevated phosphorus (+PW), combined drought and elevated phosphorus (+PD), and control conditions: (a) provenance SB; (b) provenance KA. Significant differences (p < 0.05) indicate earlier leaf unfolding in the drought treatment (−PD) compared to all other treatments.
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Forests 16 01402 g004
Figure 4. Progression of spring leaf unfolding phenology in sessile oak saplings subjected to drought (−PD), elevated phosphorus (+PW), combined drought and elevated phosphorus (+PD), and control conditions: (a) provenance SB; (b) provenance KA. Significant differences (p < 0.05) indicate delayed leaf unfolding in the −PD and +PW treatments compared to the +PD treatment and control.
Figure 4. Progression of spring leaf unfolding phenology in sessile oak saplings subjected to drought (−PD), elevated phosphorus (+PW), combined drought and elevated phosphorus (+PD), and control conditions: (a) provenance SB; (b) provenance KA. Significant differences (p < 0.05) indicate delayed leaf unfolding in the −PD and +PW treatments compared to the +PD treatment and control.
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Table 1. PERMANOVA Results—Autumn 2022.
Table 1. PERMANOVA Results—Autumn 2022.
EffectDfSum of SquaresR2Fp-Value
Species10.59830.0629115.40330.001
Provenance10.10580.011122.72380.069
Treatment31.11150.116879.53920.001
Species × Provenance10.00500.000530.12940.921
Species × Treatment30.07660.008050.65700.617
Provenance × Treatment30.18840.019811.61700.160
Species × Provenance × Treatment30.20080.021111.72320.117
Residual1867.22420.75960
Total2019.51051.00000
Note: Results are based on PERMANOVA analysis (Bray–Curtis distance, 999 permutations). Significance of effect is indicated with red bold p-value.
Table 2. PERMANOVA Results—Spring 2023.
Table 2. PERMANOVA Results—Spring 2023.
EffectDfSum of SquaresR2Fp-Value
Species10.884370.33749110.31810.001
Provenance10.004200.001600.52450.489
Treatment30.097350.037154.04790.005
Species × Provenance10.003730.001430.46580.519
Species × Treatment30.019850.007570.82530.527
Provenance × Treatment30.021540.008220.89560.435
Species × Provenance × Treatment30.050200.019162.08750.099
Residual1921.539180.58738
Total2072.620431.00000
Note: Results are based on PERMANOVA analysis (Bray–Curtis distance, 999 permutations). Significance of effect is indicated with red bold p-value.
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MDPI and ACS Style

Bačurin, M.; Sever, K.; Katičić Bogdan, I.; Bogdan, S. Species- and Provenance-Specific Leaf Phenological Responses to Drought and Elevated Phosphorus in Fagus sylvatica and Quercus petraea. Forests 2025, 16, 1402. https://doi.org/10.3390/f16091402

AMA Style

Bačurin M, Sever K, Katičić Bogdan I, Bogdan S. Species- and Provenance-Specific Leaf Phenological Responses to Drought and Elevated Phosphorus in Fagus sylvatica and Quercus petraea. Forests. 2025; 16(9):1402. https://doi.org/10.3390/f16091402

Chicago/Turabian Style

Bačurin, Marko, Krunoslav Sever, Ida Katičić Bogdan, and Saša Bogdan. 2025. "Species- and Provenance-Specific Leaf Phenological Responses to Drought and Elevated Phosphorus in Fagus sylvatica and Quercus petraea" Forests 16, no. 9: 1402. https://doi.org/10.3390/f16091402

APA Style

Bačurin, M., Sever, K., Katičić Bogdan, I., & Bogdan, S. (2025). Species- and Provenance-Specific Leaf Phenological Responses to Drought and Elevated Phosphorus in Fagus sylvatica and Quercus petraea. Forests, 16(9), 1402. https://doi.org/10.3390/f16091402

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