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Article

Effects of Trunk Covering and Airflow Treatment on Sap Flux and Bud Burst During the Dormant Stage in ‘Fuji’ Apples

by
Young-Min Choi
1 and
Dong-Geun Choi
2,*
1
Plant Resources Research Institute, Jeonbuk State Agricultural Research & Extension Services, Namwon 55720, Republic of Korea
2
Department of Horticulture, College of Agriculture & Life Sciences, Jeonbuk National University, Jeonju 54896, Republic of Korea
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(2), 108; https://doi.org/10.3390/horticulturae11020108
Submission received: 10 December 2024 / Revised: 20 January 2025 / Accepted: 20 January 2025 / Published: 21 January 2025
(This article belongs to the Section Fruit Production Systems)
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Abstract

:
The effects of recent climate change, including warm winters and repeated temperature fluctuations during dormancy, can lead to freezing injuries that result in significant economic losses in the fruit industry. This study aimed to examine the physiological responses of ‘Fuji’/M9 apple trees to trunk covering and continuous airflow treatments over 30 days, providing insights into mitigating freezing damage. The temperature difference between the sunlit and shaded sides of the trunk was lower in the whitewashed and foam insulation-covered treatments compared to those covered with newspaper, rice straw, or left uncovered. Under airflow treatment, the temperature difference in the uncovered control was 2.2 °C lower than in the non-airflow group, while no significant difference was observed in the whitewash treatment. Sap flow initiation was observed the earliest in the foam insulation-covered treatment and the latest in the whitewashed treatment. The timing of bud burst followed the order of foam insulation, rice straw, whitewash, newspaper, and the uncovered control. Furthermore, sap flow initiation and the bud burst period were delayed under airflow treatment compared to non-airflow conditions. This study provides fundamental insights into the effects of covering materials and airflow on apple tree physiology during dormancy, offering valuable information to guide future research in this field.

1. Introduction

Dormancy in fruit trees is a survival mechanism that temporarily halts growth and is crucial for their survival during winter [1]. However, the specific molecular signals and environmental factors that regulate dormancy in fruit trees remain inadequately understood [2,3]. Adequate exposure to cold temperatures during winter has been identified as the primary factor necessary for breaking endodormancy in fruit trees [4].
In temperate climates, the cold tolerance of woody plants occurs in three distinct phases: cold acclimation or prehardening in late autumn (phase 1, 0–10 °C), dormancy during winter (phase 2, <0 °C), and loss of cold tolerance in early spring (phase 3, >0 °C) [5,6]. The endodormancy adaptation in plants is regulated by cold accumulation, whereas deacclimation is driven by high temperatures or heat accumulation [7]. In regions with mild winters, apple trees exhibit a superficial endodormancy and retain a hydrated tissue state, resulting in a shorter environmental dormancy period [8]. This condition significantly increases the risk of cold damage [7,9]. When plants lose cold tolerance, they are vulnerable to cell membrane rupture and protein denaturation caused by the formation of ice crystals, which ultimately leads to cell death [7]. The freezing tolerance of fruit trees varies depending on the variety, depth of dormancy, and specific plant organs [10]. Additionally, factors such as the tree’s moisture content, carbohydrate reserves, and weather conditions also play a critical role [11]. Several mechanisms contribute to cold tolerance or avoidance, including extracellular freezing, alterations in membrane fluidity, and osmoregulation [12,13].
Freezing damage to fruit trees can be mitigated through both passive and active methods [14]. Passive methods should account for regional and topographical factors [14], such as slope cultivation [15,16], windbreaks [17], and cover crops [18]. Active methods include heating [19], irrigation [18], ventilation [20], and trunk covering [21]. Among these methods, trunk covering has been a long-standing practice to prevent radiant heat loss, reduce heat diffusion into the atmosphere, and block cold air flow [22]. Materials commonly used for trunk covering include straw bags, shade nets [21], aluminum foil [19], fiberglass, and polyethylene [23]. Additionally, whitewash [17,24,25] and protective coatings [25,26] are applied to the trunk to prevent temperature fluctuations caused by sunlight. Covering the trunk with soil is another method, but it is labor-intensive and rarely used due to the risk of stem damage [27].
Wind significantly influences the growth and physiological responses of plants. Gentle breezes promote photosynthesis by lowering plant temperatures, facilitating the exchange of CO2 and water vapor in the atmosphere, and shaking leaves within crop canopies to ensure even sunlight distribution [28]. Conversely, strong winds disrupt stomatal gas exchange, cause moisture loss, and inflict structural damage on plant tissue [29]. A case closely related to our study is documented in the 1949 report from Fort Valley, Georgia, where thousands of peach trees perished under environmental conditions of −3 °C accompanied by an average wind velocity of 14 m·s−1 [30]. Later, it was demonstrated that at a wind velocity of 4.5 m·s−1, the surface temperature on the windward side of the tree trunk could be approximately 2 °C lower than that on the leeward side [26]. This finding supports the hypothesis that wind-induced temperature changes contributed significantly to the peach tree mortality observed in 1949. Although wind impacts fruit trees throughout the growing season, research on this subject remains limited. Most existing studies focus on its role in mechanical harvesting, particularly in apples [31,32] and citrus fruits [33].
The Jangsu region is a major apple-producing area in South Korea, with approximately 850 hectares cultivated with apple trees [34]. Analyzing historical weather patterns in key apple cultivation regions offers critical insights for formulating future cultivation strategies and implementing effective measures to mitigate the impacts of extreme weather events. Global climate change has significantly affected growing seasons of fruit trees, contributing to the occurrence of meteorological and physiological disorders at various growth stages. In particular, low-temperature damage during the early spring bud burst and flowering periods in apples has become increasingly unpredictable, with no effective countermeasures currently available. Although traditional approaches, such as covering tree trunks, have been employed to prevent frost damage, these approaches have notable limitations. This study aims to provide insights into mitigating desiccation and low-temperature damage during the dormant and bud burst stages of ‘Fuji’ apples. Specifically, it investigates the effect of trunk covering materials combined with continuous airflow treatments during February and March, a critical period when cold tolerance is gradually lost.

2. Materials and Methods

2.1. Plant Materials

This experiment was conducted in an apple orchard (35°37′59″ N, 127°30′47″ E, 439 m above sea level) located in Jangsu, Jeonbuk state, South Korea. The experimental materials consisted of 2-year-old ‘Fuji’/M9 apple trees selected for uniform vigor, with five trees per treatment. Prior to the experiment, fertilization, pruning, and pest management were conducted in accordance with conventional management practices. The schematic diagram of the experiment designed to verify the effects of experimental treatments is shown in Figure 1.

2.2. Trunk Covering and Airflow Treatment During the Dormant Stage

The selected experimental trees were treated with various trunk covering materials on a 60 cm portion of the trunk, starting from ground level, for 30 days (25 February to 24 March). The whitewash treatment was uniformly applied to the surfaces of tree trunks in two coats using a solution diluted at a 1:2 ratio of water and water-based acrylic paint (Soon & Soo, Noroo Paint & Coatings Co., Ltd., Anyang, Republic of Korea). Additionally, newspaper, rice straw, and foam insulation materials were wrapped around the same section as the whitewash and secured with string (Figure 2A). Each covering material was composed of newspaper with a thickness of 5 mm, rice straw with a thickness of 2 cm, and foam insulation with a thickness of 2 cm. All materials were applied to a 60 cm portion of the tree trunk in the same manner as the whitewash treatment.
Airflow treatment was conducted using an industrial fan (SF-360, Golden Tech Inc., Yeoju, Republic of Korea) at an average wind speed of approximately 2 m·s−1 for 7 h per day (10:00 to 17:00) over the 30-day experimental period (February 25 to March 24). Wind speed was measured using a portable anemometer (Testo 435, TestoAG, Schwarzwald, Germany).
All covering material treatments were applied to ten apple trees, with five trees subjected to airflow treatment and the remaining five left untreated. Each apple tree was treated as a single replication in the experiment.

2.3. Collection of Temperature and Humidity Data

For meteorological analysis of the Jangsu region in South Korea, weather data were obtained from the Korea Meteorological Administration (KMA) Open MET Data Portal https://data.kma.go.kr (accessed on 1 April 2023), which provides historical temperature data from February and March over the past 30 years (1994–2023). The automatic weather station (AWS, observation point 248) is located at 35°39′24″ N, 127°31′13″ E, approximately 2.7 km from the experimental orchard in a straight line, at an elevation of 408 m above sea level.
During the experimental period, air temperature and humidity data were collected using a Hobo Pro V2 device (Onset Computer Corp., Bourne, MA, USA). The sensor was installed at a height of 1.5 m above ground level and protected by a radiation shield. Additionally, a similar sensor was placed between the tree trunk and the covering material to monitor the internal temperature and humidity. All data were recorded at 1-min intervals.

2.4. Measurement of Surface Temperature of the Trunk

The surface temperature of the tree trunk was measured using a thermal imaging camera (Testo 882, TestoAG, Schwarzwald, Germany) positioned 30 cm from the trunk, with the emissivity set to 0.95. Data analysis was performed using IRSoft 4.0 software (TestoAG, Schwarzwald, Germany) to extract temperatures from a minimum of 15 points on each image (per tree), with the average value calculated from five replicates.
The measurement of the surface temperature of the trunk under airflow treatment was conducted exclusively to the no-covering and whitewash treatments. Tree trunks in the other treatment were excluded as the covering materials were assumed to negate the effects of wind.

2.5. Observation of Bud Burst and Measurement of Xylem Sap Flow

The bud burst period (Figure 2B,C) was determined as the stage at which flower buds opened to more than 2 mm, following the Standard Research Investigation Analysis Guidelines 2023 published by the Rural Development Administration of Korea. Additionally, the bud burst period for each treatment was defined as the day on which more than 80% of the flower buds per tree, across five trees, had sprouted.
To measure xylem sap flow, a Flow32 sensor (Dynamax Inc., Houston, TX, USA) was installed on the trunk of an apple tree with a diameter of 12–16 mm. The trunk surface was smoothed using sandpaper, oil was applied to the surface, and the sensor was securely affixed to ensure full contact with the surface of the trunk. Gaps between the upper and lower parts of the sensor were sealed using rubber clay, and the entire sensor was insulated with protective material to minimize internal heat loss and prevent exposure to solar radiation. A fixed voltage of 4 V was applied to the trunk, and the average ksh value (gage zero set constant) recorded between 4:00 AM and 6:00 AM the following day was used for calibration. Data measurements were recorded every 20 min using a CR1000 data logger (Campbell Scientific Inc., Logan, UT, USA).

2.6. Data Analysis

The arithmetic mean and standard deviation of the data were calculated using Microsoft Excel 2019 (Microsoft Corp., Redmond, WA, USA). Duncan’s multiple range test at the p < 0.05 level and the F-test were conducted using SAS 9.4 (SAS Institute Inc., Cary, NC, USA). Additionally, 30-year meteorological averages were calculated by dividing the data into 5-year intervals. Data visualization was conducted using SigmaPlot 14.0 (Systat Software Inc., Chicago, IL, USA).

3. Results

3.1. Analysis of Meteorological Factors in Jangsu, Korea from February to March over the Past 30 Years (1994–2023)

The results of a 30-year weather analysis for the Jangsu region in Jeonbuk State, South Korea, one of the country’s primary apple-producing areas, are presented in Table 1. From 1994 to 2023, the average temperatures for February and March showed a gradually increasing trend, with the 30-year averages being −0.7 °C and 6.4 °C, respectively. There was no significant change in the average high temperature, the highest recorded temperature, or the day of the highest temperature record in February over the 30-year period. However, in the past five years (2019−2023), the values were 7.1 °C, 15.3 °C, and 52.6 Julian days, respectively, all of which exceeded the 30-year averages (6.0 °C, 14.6 °C, and 59.8 Julian days, respectively). In addition, the average minimum temperature and the lowest recorded temperature in February (2019−2023) were both lower than the 30-year average. The average and maximum wind speeds over the past 30 years showed no significant change, at 1.8 m·s−1 and 8.0 m·s−1, respectively. From 1994 to 2023, all temperature measures, average temperature, average maximum temperature, highest recorded temperature, average minimum temperature, and lowest recorded temperature, demonstrated a gradual increase at five-year intervals for March.
Recent observations suggest that the growth stages of apple trees are occurring earlier than in the past, likely due to the rising temperatures associated with climate change [35]. This phenomenon aligns with the findings in the Intergovernmental Panel on Climate Change (IPCC) report, which indicates that the average temperature in South Korea has increased by 1.7 °C over the past 100 years (1906–2005). Rising temperatures can negatively impact the dormant buds of apple trees [36], potentially causing bud necrosis in severe cases due to ice crystal formation within the buds [37]. Frost injury is particularly significant not only because of weather conditions but also in relation to the developmental stage of the plant [38]. Apple trees may be exposed to sudden low temperatures as their cold tolerance weakens and their development progresses, and damage after the bud burst stage can result in economic losses equivalent to winter freezing injury [39]. In other words, the rise in average temperatures in apple-growing regions during February and March signifies an earlier transition from dormancy, leading to an earlier loss of cold tolerance compared to the past. This implies that freezing damage may occur even at relatively high temperatures during early spring.

3.2. Effects of Covering Materials on the Surface Temperature of the Trunk in ‘Fuji’ Apples

Temperature and humidity were measured using sensors installed between the covering material and the tree trunk (Table 2). The results indicated that the average temperature was 9.0 °C for the uncovered and whitewashed treatments, 8.8 °C for the newspaper-covered treatment, 9.3 °C for the rice straw-covered treatment, and 8.9 °C for the foam insulation-covered treatment. Although the temperature in the rice straw covering treatment was 0.3 °C higher than that of the uncovered and whitewashed treatments, no statistically significant differences were observed among the various covering materials. For the newspaper-covered treatment, the temperature on rainy or humid days was up to 5 °C lower compared to the air temperature and other covering materials. This effect is believed to be due to the newspaper’s ability to absorb moisture, which then freezes at low temperatures. Humidity, similar to temperature, showed no statistically significant differences among treatments. All treatments exhibited a typical diurnal variation pattern, with humidity decreasing during the daytime and increasing at night.
The surface temperature difference between the sunlit (positive light) and shaded (negative light) sides of the apple tree trunks was lowest in the whitewashed (1.6 °C) and foam insulation-covered (1.9 °C) treatments, showing a difference of 3.1–4.6 °C compared to the other treatments. The temperature differences between the newspaper (5.0 °C) and rice straw-covered (5.7 °C) treatments and the uncovered control (6.2 °C) were statistically significant, ranging from 0.5 to 1.2 °C. However, these differences were smaller compared to those observed in whitewashed or foam insulation-covered treatments. This can be attributed to the insufficient blocking of radiant heat from the sun compared to the whitewashed and foam insulation-covered treatments. On clear winter days, the surface temperature of tree trunks can be up to 15 °C higher than the air temperature [25], with temperature differences between the sunlit and shaded sides of the trunks reaching 25 °C or more [24,26]. In other research reports, covering tree trunks with insulation or thermal materials has been shown to store heat within the covering during the day and gradually release it at night [40]. In kiwifruit trees, foam insulation has been reported to provide a slightly better thermal effect compared to rice straw [41]. However, covering the trunk of a fruit tree is intended to prevent freezing damage by reducing the temperature difference between the sunlit and shaded sides of the trunk, rather than providing insulation. In this study, whitewashed and foam insulation-covered treatments were the most effective in minimizing the temperature difference between the sunlit and shaded sides of the tree trunk. Additionally, there are reports suggesting that whitewashed tree trunks can prevent temperature increases in the bark and inhibit pathogen invasion [42].

3.3. Effects of Airflow Treatment on the Surface Temperature of the Trunk in ‘Fuji’ Apples

Most studies on the effects of wind on fruit trees focus on changes in physiological and ecological characteristics [43,44], fruit drop [31,45], and physical damage [28,44]. However, research on its impact during dormancy is lacking. The wind speed used in this experiment was set to 2 m·s−1, which corresponds to the average wind speed observed in Jangsu, South Korea, in February and March (Table 1). The changes in the surface temperature of the trunk of ‘Fuji’ apple trees under airflow treatment are summarized in Table 3.
The air temperature and humidity under airflow treatment (including uncovered and whitewashed treatments) were 10.5 °C and 50.1%, respectively, showing no significant difference compared to the non-airflow treatment (10.7 °C and 51.0%). The temperature of the sunlit side of the tree trunk was statistically lower in the whitewashed treatment compared to the uncovered control, as well as in the airflow treatment compared to the non-airflow treatment. However, the temperature of the shaded side of the trunk in the uncovered and whitewashed trees did not differ significantly between the airflow and non-airflow treatments. For uncovered trees, the temperature difference between the sunlit and shaded sides of the trunk was 2.2 °C between the airflow (4.4 °C) and non-airflow (6.6 °C) treatments. In contrast, for whitewashed trees, no statistically significant difference was observed between the airflow and non-airflow treatments. These results not only highlight the effect of whitewash application in reducing the temperature difference between the sunlit and shaded sides of the trunk during the dormancy period of apple trees, but also confirm that wind can lower the surface temperature of the tree, in addition to its previously reported effects on leaves and fruits [26,28].

3.4. Effects of Trunk Covering Materials and Airflow Treatment on Xylem Sap Flow and Bud Burst in ‘Fuji’ Apples

The xylem sap flow in the trunk of ‘Fuji’ apple trees, influenced by different covering materials (Figure 3A), was observed in the following order: foam insulation (March 3), rice straw (March 5), newspaper (March 4), no covering (March 6), and whitewashed treatment (March 11). The bud burst period (Figure 3B) was recorded in the order of foam insulation (March 23), rice straw (March 26), whitewashed treatment (March 27), newspaper (March 30), and no covering (April 3). As shown in Figure 3, the foam insulation-covered treatment, which exhibited the smallest temperature difference between the sunlit and shaded sides of the trunk, also demonstrated the earliest sap flow and bud burst. In contrast, the whitewashed treatment, which had the smallest temperature difference in comparison with other treatments, exhibited sap flow approximately five days after the no-covering treatment but achieved bud burst (March 27) approximately six days earlier. This observation is likely attributed to residual whitewashing material or bark detachment from the trunk caused by exposure to environmental conditions during winter, or possibly to the effects of natural wind. Furthermore, as deacclimation is influenced by cumulative high temperatures and heat accumulation [7], further research, including the continuous monitoring of surface temperature, is deemed necessary. The sap flow in the xylem of the trunk was delayed by 18 days and 12 days in the uncovered and whitewashed treatments, respectively, under airflow conditions compared to non-airflow conditions. Across all treatments, the bud burst period was delayed by approximately 1 to 3 days due to the airflow treatment. Furthermore, no significant differences in bud burst rates were observed among the treatments.
These results indicate that trunk covering and airflow treatments during February and March, when ‘Fuji’ apples gradually lose cold tolerance, affect sap flow and bud burst by altering the internal and surface temperatures of the trunk covering materials. The covering materials blocked the transfer of thermal energy from the sun [22], resulting in the temperature difference between the sunlit and shaded sides of the tree trunk in the covered treatments compared to the uncovered treatment. Freezing injury to the shaded sides of the trunk of fruit trees can significantly reduce the tree’s lifespan [26]. Furthermore, continuous airflow was observed to have a delaying effect on bud burst. Changes in ambient air temperature significantly influence phenological traits such as bud burst in apple trees [36]. Therefore, to mitigate damage caused by recent climate changes or extreme weather events, further research is needed to develop adaptive strategies and investigate the precise timing of physiological changes across growth stages.

4. Conclusions

The results of the weather analysis for February and March over the past 30 years indicate a consistent increase in temperatures. Recent abnormal phenomena during the apple dormancy period have manifested in various forms, including warm winters, repeated temperature fluctuations, and extreme high and low temperatures. In South Korea, winter freezing damage in apple trees is conventionally mitigated by covering the trunk. However, there are no reported studies on the physiological responses of apple trees to different covering materials. Furthermore, the effects of cold winter wind on the physiology of apple trees remain unexplored. This study demonstrated that during February and March, a critical period when apple trees lose cold tolerance and initiate growth activity, trunk surface temperature is influenced by covering materials and airflow. Additionally, the study revealed variations in sap flow timing and bud burst stages among the different treatments. These findings indicate that trunk coverings and wind exposure influence the cold tolerance of apple trees. To mitigate freezing damage, reducing trunk temperature differences proved to be the most effective with whitewash and foam insulation materials. Furthermore, in regions where low temperatures are expected in early spring, the selection of covering materials should account for the timing of the bud burst stage. This study confirmed that sustained wind during dormancy delays the initiation of sap flow and the bud burst period. However, its precise impact on freezing injury in fruit trees remains unclear. Nonetheless, considering the role of wind in reducing trunk surface temperatures, implementing windbreaks should be prioritized in regions where freezing injury is a recurring and severe issue. Our findings provide foundational insights into the physiological effects of trunk covering materials and wind exposure on apple trees. Future studies should investigate the impacts of various covering materials and their application timing on dormancy and overall tree physiology.

Author Contributions

Conceptualization, Y.-M.C. and D.-G.C.; methodology, Y.-M.C. and D.-G.C.; software, Y.-M.C.; validation, Y.-M.C. and D.-G.C.; formal analysis, Y.-M.C.; investigation, Y.-M.C., resources, Y.-M.C.; data curation, Y.-M.C.; writing—original draft preparation, Y.-M.C.; writing—review and editing, D.-G.C.; visualization, Y.-M.C.; supervision, D.-G.C.; project administration, Y.-M.C.; funding acquisition, D.-G.C. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Rural Development Administration of Korea (grant number PJ008224).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Schematic diagram of the test setup for evaluating the trunk covering and airflow treatments on apple trees during the dormant stage.
Figure 1. Schematic diagram of the test setup for evaluating the trunk covering and airflow treatments on apple trees during the dormant stage.
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Figure 2. Photographs of the trunk covering (A) and determination of bud burst in ‘Fuji’ apples. (A): Covering materials, from left to right, are untreated, whitewash, foam insulation, rice straw, and newspaper. (B,C) Show dormant and bud burst flower buds, respectively. The bud burst period was determined when the bud scale of flower buds was separated by more than 2 mm.
Figure 2. Photographs of the trunk covering (A) and determination of bud burst in ‘Fuji’ apples. (A): Covering materials, from left to right, are untreated, whitewash, foam insulation, rice straw, and newspaper. (B,C) Show dormant and bud burst flower buds, respectively. The bud burst period was determined when the bud scale of flower buds was separated by more than 2 mm.
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Figure 3. Differences in sap flow (A) and bud burst period (B) according to the covering materials and airflow treatment on the trunk in ‘Fuji’ apples. The two letters in the abbreviation in the diagram represent the covering materials and airflow treatment, respectively. The dates in parentheses indicate the time at which sap flow in the xylem was observed. UN: uncovered, non-airflow; UA: uncovered, airflow; WN: whitewash, non-airflow; WA: whitewash, airflow; NN: newspaper, non-airflow; NA: newspaper, airflow; RN: rice straw, non-airflow; RA, rice straw, airflow; FN: foam insulation, non-airflow; FA: foam insulation, airflow.
Figure 3. Differences in sap flow (A) and bud burst period (B) according to the covering materials and airflow treatment on the trunk in ‘Fuji’ apples. The two letters in the abbreviation in the diagram represent the covering materials and airflow treatment, respectively. The dates in parentheses indicate the time at which sap flow in the xylem was observed. UN: uncovered, non-airflow; UA: uncovered, airflow; WN: whitewash, non-airflow; WA: whitewash, airflow; NN: newspaper, non-airflow; NA: newspaper, airflow; RN: rice straw, non-airflow; RA, rice straw, airflow; FN: foam insulation, non-airflow; FA: foam insulation, airflow.
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Table 1. Changes in meteorological characteristics observed in Jangsu in Korea from February to March over the past 30 years (1994–2023).
Table 1. Changes in meteorological characteristics observed in Jangsu in Korea from February to March over the past 30 years (1994–2023).
MonthYearMean
Value		Mean
Maximum
Value		Maximum ValueMean
Minimum
Value		Minimum ValueMean Wind
Velocity
(m·s−1)		Maximum Wind Velocity
(m·s−1)
HighestDate
(Julian Day)		LowestDate
(Julian Day)
February1994–1998−1.3 ± 1.7 z6.1 ± 1.515.2 ± 3.247.0 ± 6.5−7.6 ± 1.9−15.9 ± 1.837.0 ± 5.21.7 ± 0.27.6 ± 0.9
1999–2003−1.2 ± 1.15.4 ± 1.412.8 ± 1.852.8 ± 5.9−6.9 ± 1.3−16.3 ± 3.036.0 ± 4.31.6 ± 0.38.7 ± 1.8
2004–2008−0.9 ± 2.15.5 ± 2.814.2 ± 3.747.4 ± 6.1−6.8 ± 2.0−14.9 ± 3.439.6 ± 4.12.0 ± 0.28.9 ± 0.8
2009–2013−0.4 ± 2.16.0 ± 2.315.9 ± 2.353.6 ± 6.3−6.0 ± 2.2−15.6 ± 2.337.8 ± 7.91.7 ± 0.37.5 ± 1.0
2014–2018−0.5 ± 1.25.7 ± 1.114.1 ± 3.545.6 ± 9.7−6.2 ± 1.6−13.1 ± 2.134.2 ± 2.82.0 ± 0.27.7 ± 0.8
2019–20230.3 ± 1.77.1 ± 1.915.3 ± 3.152.6 ± 5.6−5.7 ± 2.0−12.3 ± 1.437.2 ± 6.21.7 ± 0.37.8 ± 0.8
Mean−0.7 ± 0.66.0 ± 0.614.6 ± 1.149.8 ± 3.5−6.5 ± 0.7−14.7 ± 1.637.0 ± 1.81.8 ± 0.28.0 ± 0.6
March1994–19983.5 ± 1.310.7 ± 1.819.1 ± 2.382.4 ± 7.4−2.5 ± 1.3−8.2 ± 1.569.6 ± 12.71.9 ± 0.18.9 ± 0.8
1999–20034.2 ± 1.211.3 ± 1.519.6 ± 1.484.2 ± 5.4−2.3 ± 1.1−8.4 ± 1.667.0 ± 7.81.9 ± 0.210.2 ± 1.9
2004–20084.1 ± 1.111.1 ± 1.419.3 ± 1.279.4 ± 7.2−2.4 ± 1.1−9.5 ± 1.665.4 ± 3.62.1 ± 0.29.0 ± 1.2
2009–20134.1 ± 1.310.5 ± 2.021.0 ± 2.479.8 ± 9.0−2.0 ± 1.3−7.8 ± 0.969.0 ± 7.12.4 ± 0.19.0 ± 0.4
2014–20185.0 ± 1.112.4 ± 1.021.3 ± 1.785.6 ± 5.0−1.7 ± 1.1−9.4 ± 2.362.4 ± 3.41.9 ± 0.28.3 ± 0.7
2019–20236.4 ± 1.013.8 ± 1.421.1 ± 1.582.4 ± 5.7−0.7 ± 0.8−6.8 ± 1.265.0 ± 4.51.7 ± 0.28.0 ± 0.4
Mean4.6 ± 1.011.6 ± 1.220.2 ± 1.082.3 ± 2.4−1.9 ± 0.7−8.4 ± 1.066.4 ± 2.72.0 ± 0.28.9 ± 0.8
z Mean ± S.D. (n = 5).
Table 2. Differences in temperature, humidity during the experimental period, and surface temperature inside the covering materials on the trunk in ‘Fuji’ apples.
Table 2. Differences in temperature, humidity during the experimental period, and surface temperature inside the covering materials on the trunk in ‘Fuji’ apples.
Covering
Materials		Mean Temperature
(°C)		Mean Humidity
(%)		Trunk Surface Temperature (°C)
Positive LightNegative LightDifference
Uncovered9.0 ± 6.9 z78.9 ± 25.115.9 ± 1.0 a y9.7 ± 1.0 a6.2 ± 1.1 a
Whitewash11.2 ± 0.6 c9.6 ± 0.3 a1.6 ± 0.9 c
Newspaper8.8 ± 6.372.3 ± 25.313.5 ± 0.7 b8.5 ± 0.3 b5.0 ± 0.7 b
Rice straw9.3 ± 6.876.3 ± 22.913.5 ± 1.0 b7.9 ± 0.7 c5.7 ± 1.1 ab
Foam insulation8.9 ± 6.874.0 ± 25.49.7 ± 0.9 d7.8 ± 1.0 c1.9 ± 1.3 c
z Mean ± S.D. (n = 15). y p < 0.05. Same letters within each column indicate that values are not significantly different.
Table 3. Differences in air temperature and humidity during the experimental period, and surface temperature according to the application of whitewash and airflow treatment on the trunk in ‘Fuji’ apples.
Table 3. Differences in air temperature and humidity during the experimental period, and surface temperature according to the application of whitewash and airflow treatment on the trunk in ‘Fuji’ apples.
Airflow
Treatment		Trunk
Treatment		Mean
Temperature (°C)		Mean
Humidity (%)		Trunk Surface Temperature (°C)
Positive LightNegative LightDifference
Non-airflowUncovered10.7 ± 5.5 z51.0 ± 24.215.5 ± 0.6 a y8.9 ± 1.2 b6.6 ± 1.3 a
Whitewash12.5 ± 0.5 c11.6 ± 0.7 a0.8 ± 0.7 c
AirflowUncovered10.5 ± 5.550.1 ± 24.213.1 ± 0.4 b8.7 ± 1.5 b4.4 ± 1.4 b
Whitewash11.5 ± 0.7 d11.1 ± 0.6 a0.4 ± 0.6 c
Significance
Airflow Treatment (A)--nsnsns
Trunk Treatment (B)--ns*ns
A × B--**ns**
z Mean ± S.D. (n = 15). y p < 0.05. Same letters within each column indicate that values are not significantly different. ns, *, ** Non-significant or significant at p < 0.05, 0.01.
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Choi, Y.-M.; Choi, D.-G. Effects of Trunk Covering and Airflow Treatment on Sap Flux and Bud Burst During the Dormant Stage in ‘Fuji’ Apples. Horticulturae 2025, 11, 108. https://doi.org/10.3390/horticulturae11020108

AMA Style

Choi Y-M, Choi D-G. Effects of Trunk Covering and Airflow Treatment on Sap Flux and Bud Burst During the Dormant Stage in ‘Fuji’ Apples. Horticulturae. 2025; 11(2):108. https://doi.org/10.3390/horticulturae11020108

Chicago/Turabian Style

Choi, Young-Min, and Dong-Geun Choi. 2025. "Effects of Trunk Covering and Airflow Treatment on Sap Flux and Bud Burst During the Dormant Stage in ‘Fuji’ Apples" Horticulturae 11, no. 2: 108. https://doi.org/10.3390/horticulturae11020108

APA Style

Choi, Y.-M., & Choi, D.-G. (2025). Effects of Trunk Covering and Airflow Treatment on Sap Flux and Bud Burst During the Dormant Stage in ‘Fuji’ Apples. Horticulturae, 11(2), 108. https://doi.org/10.3390/horticulturae11020108

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