Comparative Analysis of the Effects of Different Mulching Materials on Microclimate and Fruit Quality in Apricot Orchards

Abstract

The ‘Diaoganxing’ is the experimental material, with natural grass cover as the control, to compare the effects of 5 different mulching materials. The aim was to identify the most effective mulching type for improving orchard microenvironments and fruit quality. The results demonstrated that waterproof, breathable film and reflective film significantly enhanced orchard microenvironments and fruit quality (p ≤ 0.05). Specifically, the waterproof, breathable film effectively regulated soil temperature and moisture, reducing soil temperature by 4.60% and increasing soil moisture by 17.09% in the 0–60 cm soil layer. Meanwhile, the reflective film optimized light distribution in the mid-lower canopy, increasing light intensity by 161.04–208.71% and reflectance by 2.6–3.3 times. In terms of fruit quality, the reflective film accelerated ripening by 10 d, increased carotenoid content by 15.34%, and achieved a peel color index (CCI) of 6.23. On the other hand, the waterproof breathable film advanced maturation by 7 d and significantly improved vitamin C, soluble sugar, and soluble solids content by 23.26%, 30.77%, and 12.76%, respectively. This study provides a scientific basis for the efficient and high-quality production of apricots in southern Xinjiang through the use of mulching practices.

1. Introduction

Apricot (Prunus armeniaca L.), a drupe of significant nutritional and economic importance, belongs to the Rosaceae family. Xinjiang, with over 3000 years of documented cultivation history, has a cultivated area of 1.16 × 10⁵ ha and an annual production of 9.37 × 10⁵ tons [1]. Moreover, the ‘Diaoganxing’ cultivar, valued for its superior marketability and extended postharvest shelf life, has been widely adopted for commercial cultivation. ‘Diaoganxing’ is a dual-purpose apricot germplasm suitable for both fresh consumption and drying. The fruit features orange-red flesh and is rich in nutritionally valuable compounds. Both the flesh and apricot seeds are edible. Due to its excellent marketability and superior storage characteristics, it has been widely introduced and cultivated. By 2020, the planting area of this variety in the Fourth Regiment of the First Division has expanded to 4359 hectares [2].

In the orchard management practices of apricot orchards in southern Xinjiang, clean tillage and natural grass cover are the most common methods. Zhang [3] found that plowing could maintain soil looseness and suppress weed growth in the short term, but in the long term, it easily damaged the soil structure and was time-consuming and labor-intensive. Wang [4] found that while the natural grass cover method in apricot orchards could reduce surface temperature, mitigate evaporation, and enhance soil water retention capacity, it also facilitated the proliferation of pests and diseases, increased management expenses, intensified competition for soil nutrients, and raised irrigation demands.

Compared to the aforementioned two orchard soil management practices, ground mulching exhibits distinct advantages in regulating soil temperature and moisture [5], optimizing light distribution within the orchard rows [6], and suppressing weed proliferation [7]. Ground mulching can be categorized into organic and inorganic types, with their material properties differentially influencing soil conditions and environmental outcomes. While organic mulching (e.g., straw or wood chips) is widely recognized for enhancing soil fertility and microbial activity [8], inorganic mulching materials such as plastic films have gained prominence due to their precision in microclimate regulation [9]. Dong [10] conducted a study on plastic film mulching in apple orchards and found that the mulching practices exhibited a more pronounced regulatory effect on shallow soil layers, and the efficacy varied significantly among plastic films of different colors. Zhou [11] observed that after the implementation of ground mulching in orchards, the soil moisture evaporation rate decreased significantly, effectively reducing evaporative water loss and maintaining higher soil moisture compared to unmulched conditions. Furthermore, Wang [12] and Chen [13] found that Tyvek^® moisture—permeable reflective film markedly improved the light environment in citrus orchards, thereby enhancing citrus fruit quality. With the progress of science and technology, some studies have demonstrated that using new mulch materials can enhance fruit quality. Wang [14] reported that white plastic mulch significantly increased the vitamin C content and sugar-acid ratio of jujube fruits. Tang [15] utilized reflective insulation film to improve grape berry coloration. Jia [16] demonstrated that white non-woven mulch film effectively accelerated citrus ripening and improved fruit flavor. In the arid regions of southern Xinjiang, the efficacy of various mulching materials in apricot orchards for reducing soil water loss, modifying soil properties, and improving fruit quality remains unclear.

Therefore, investigating these advanced mulching materials is of significant scientific and practical importance. Based on this, the present study investigates the effects of five mulching materials (white plastic film, black plastic film, vapor barrier film, waterproof and breathable film, and reflective and heat-insulating film) versus natural grass cover (control) on orchard microclimate (soil temperature/moisture, canopy light environment) and fruit quality (appearance characteristics, internal quality) in apricot of Southern Xinjiang. This research innovatively delves into screening uniquely suitable mulching materials for apricot orchards, thus laying an original foundation for optimizing orchard management and upgrading fruit quality.

2. Materials and Methods

2.1. Materials

Field experiments were conducted in an apricot orchard located in the Second Company of the Eleventh Regiment, Alar, Xinjiang (40°37′ N, 81°32′ E, average elevation 1003 m). The region experiences a temperate continental climate, with a mean annual temperature of 10.1 °C, annual solar radiation exceeding 2900 h, total annual precipitation ranging from 40.1 to 82.5 mm [17], annual evapotranspiration ranging from 1876.6 to 2558.9 mm, and a frost-free period of 195 days. The apricot orchard was established in 2007, with the primary cultivar ‘Diaoganxing’ and the pollinizer ‘Meixing’. The trees were planted at a density of 3 m × 4 m and pruned to an open-center canopy architecture. The orchard showed no incidence of pests or diseases. The soil is sandy loam. Drip irrigation lines were installed 0.5 m from the tree rows, with the lines placed underneath plastic mulch.

2.2. Experimental Design

The experiment began on 5 April 2024, and data analysis was conducted while collecting data and measuring fruit quality. The experimental design in the apricot orchard included six treatments: a natural grass cover control (CK) and five plastic mulch treatments (F1–F5) (

Table 1. Specifications of Mulching Materials.

Treatment	Mulch Materials and Treatments	Film Color (Number of Layers)	Material Quality	Mulch Thickness (μm)	Effective Width (m)	Water Vapor Transmission Rate g/(m2·24 h)	Manufacturer
CK	natural grass cover	-	-	-	-	-	-
F1	white plastic film	white transparent (One Layers)	PE	10	2	0	Jiangsu Taika Greenhouse Equipment Co., Ltd., Suqian, China
F2	black plastic film	black (One Layers)	PE	10	2	0	Jiangsu Taika Greenhouse Equipment Co., Ltd., Suqian, China
F3	vapor barrier film	white (Two Layers)	PP + PE	30	1.5	1.38	Shanghai Jiakun Material Science & Technology Co., Ltd., Shanghai, China
F4	waterproof and breathable film	white (Three Layers)	PP + PE/PP copolymer + PP	30	1.5	1207	Shanghai Jiakun Material Science & Technology Co., Ltd., Shanghai, China
F5	reflective and heat-insulating film	silver and white (three Layers)	PET/AI + PE + PP	50	1.5	0.12	Shanghai Jiakun Material Science & Technology Co., Ltd., Shanghai, China

Polyethylene, abbreviated as PE; Polypropylene (non-woven fabric), abbreviated as PP; Polypropyl ene and polyethylene copolymer layer, abbreviated as PE/PP copolymer; Polyester aluminum-plastic, abbreviated as PET/AI.

).

The mulch was applied on 5 April (post-bloom stage), covering both the tree basins and inter-row spaces, and secured using ground stakes. This study involved a total of 90 apricot trees across 18 experimental areas, with each experimental area covering 64 m² and containing 5 trees. The orchard was irrigated three times during the growing season, on 22 April, 28 May, and 27 June. The irrigation amount for each experimental area is 6.6 m³.

2.3. Measurements

2.3.1. Data Collection of Environmental Factors in the Apricot Orchard

A light-intensity, temperature, and humidity meter GSP-8G (Jiangsu Jingchuang Co., Ltd., Xuzhou, China) was used to monitor environmental parameters. The temperature and humidity probes were placed at different soil depths: the soil surface, 0–20 cm, 20–40 cm, and 40–60 cm, to continuously collect soil temperature and moisture data. The monitoring instrument collected data every 5 min, summarized the data, and calculated the average daily data for future use. Additionally, the light-intensity probe was positioned 50 cm vertically from the trunk in the inter-row space to continuously measure light intensity at heights of 50 cm and 100 cm above the ground.

Following the method described by Tang [10], a light meter AS823 (Dongguan Wanchuang Electronic Products Co., Ltd., Dongguan, China) was used to measure the light intensity of both reflected and incident light at the soil surface. The light intensity measurement locations were consistent with those used for light intensity monitoring. The reflectance (R) was calculated using the formula:

$$\mathit{R} ={\displaystyle \frac{{\mathit{R}}_{\mathit{l}}}{{\mathit{R}}_{\mathit{i}}}}\times 100\%$$

(1)

where R is the reflectance, R_l is the light intensity of reflected light, and R_i is the light intensity of incident light.

2.3.2. Fruit Quality Measurement

In order to determine the specific developmental stages of apricot, this study recorded the sixth to eighth stages according to the BBCH developmental stages for stone trees (flowering stage, fruit growth stage, fruit ripening stage). Fruit sampling commenced on the 41st day (fruit growth stage) after the full bloom stage of ‘Diaoganxing’ (14 May) and was conducted at 9 d intervals, totaling 7 sampling events after flowering until fruit maturity. For each treatment, the 3 trees were randomly selected from 3 experimental areas, and the 20 fruits were harvested from 4 cardinal directions of each tree. After harvest, the fruits were immediately transported to the laboratory and randomly divided into two groups; 180 fruits were randomly selected for evaluation of external fruit quality, while the remaining fruits were used for assessment of internal fruit quality.

The appearance characteristics of each treatment were repeated 10 times per sample, and the contents were repeated 3 times per sample. The single fruit weight was measured using an electronic balance LC-FA004 ( Shanghai Lichen Instrument Technology Co., Ltd., Shanghai, China) with an accuracy of 0.01 g; the fruit’s longitudinal diameter, transverse diameter and lateral diameter were measured using an electronic digital caliper X-RAY (Nanjing Suce Measurement Instrument Co., Ltd., Nanjing, China) with an accuracy of 0.01 mm; the fruit skin hardness was measured using a handheld fruit hardness tester GY-4 (Beijing Jinkelida Electronic Technology Co., Ltd., Beijing, China) in kg/cm²; the fruit volume was determined by the water displacement method [18] in cm³; the fruit skin brightness (L*), red-green color difference (a*), and yellow-blue color difference (b*) were measured using a handheld colorimeter CR-400 (Konica Minolta Co. Ltd., Tokyo, Japan), and the comprehensive color index (CCI) was calculated [19]; vitamin C was determined by the molybdenum blue colorimetric method [20]; soluble sugar (SS) was determined by the anthrone sulfuric acid method [21]; titratable acid (TA) was determined by the NaOH acid-base titration method [22]; carotenoids were determined by the acetone colorimetric method [23]; and soluble solids (TSS) were measured using a portable handheld refractometer PAL-1 (ATAGO Co., Ltd., Tokyo, Japan) [24]. The formulas for the shape index (S_i) [25], fruit density (ρ) [26], and comprehensive color index (CCI) [19] are as follows:

$${\mathit{S}}_{\mathit{i}} (\mathrm{Shape} \mathrm{index}) ={\displaystyle \frac{{\mathit{D}}_{\mathit{t}}}{{\mathit{D}}_{\mathit{l}}}} \times 100\%$$

(2)

where S_i is the fruit shape index, D_t is the fruit longitudinal diameter, and D_l is the fruit transverse diameter.

$$\mathit{\rho }(\mathrm{Fruit} \mathrm{density}) ={\displaystyle \frac{\mathit{M}}{\mathit{V}}}$$

(3)

where ρ is the fruit density, M is the fresh weight of the fruit, and V is the fruit volume.

$$\mathit{CCI} (\mathrm{Comprehensive} \mathrm{Color} \mathrm{Index})=1000 \times {\displaystyle \frac{\mathit{a}\mathit{*}}{\mathit{L}\mathit{*}\times \mathit{b}\mathit{*}}}$$

(4)

where L* represents brightness; a positive a* indicates red, a negative a* indicates green, a positive b* indicates yellow, and a negative b* indicates blue.

2.3.3. Data Analysis

Organization was performed using Microsoft Excel 2024; descriptive statistics, one-way ANOVA, Duncan’s multiple range test for significant differences (p ≤ 0.05), and correlation analysis were conducted using IBM SPSS Statistics 27; chart plotting was performed using Origin 2024.

3. Results

3.1. The Effects of Mulching on Environmental Factors

To investigate the effects of different mulching materials on the light conditions of apricot trees, the average daily light intensity at 2 heights (50 cm and 100 cm) in the inter-row space was compared (Figure 1).

The light intensity at 100 cm was significantly higher than that at 50 cm, showing a gradual decline and stabilizing after 22 May. The light intensity in the middle and lower canopy layers under the F5 treatment was significantly higher than that of the other treatments, with increases of 161.04% and 208.71%, respectively, followed by the F4 treatment, which showed increases of 154.60% and 175.00%, respectively.

The reflectance of each treatment at heights of 50 cm and 100 cm above the ground was measured at 12:00 on both cloudy and sunny days using an illuminometer. Significant differences were observed among the treatments (p ≤ 0.05). The results indicated that F5 had the highest reflectance enhancement effect, ranging from 44.21% to 51.33%, which was significantly higher than that of the other treatments. In contrast, F2 had the lowest reflectance, ranging only from 6.39% to 8.28%. On cloudy days, the reflectance of all treatments was slightly lower compared to sunny days. Among them, F5 exhibited the highest reflectance on cloudy days, with an enhancement of 3.2–3.3 times, while on sunny days, the enhancement was similar, ranging from 2.6 to 3.0 times. In summary, F5 significantly improved light reflectance in the lower and middle canopy layers of apricot trees. In comparison, the F1, F2, and F3 treatments did not show a significant effect on reflectance enhancement (Figure 2).

The effects of different mulching films on soil temperature showed significant differences (p ≤ 0.05). The results indicated that the soil surface temperature exhibited pronounced fluctuations, with an increase observed under all treatments in the 0–20 cm, 20–40 cm, and 40–60 cm soil layers. Within the 0–60 cm soil depth range, F4 and F5 reduced soil temperature, while F1, F2, and F3 contributed to an increase in soil temperature. In the 0–20 cm, 20–40 cm, and 40–60 cm soil layers, F2 had the highest average daily temperature, increasing soil temperature by 3.14–3.93 °C, whereas F5 decreased it by 1.95–2.26 °C. Additionally, within the 0–60 cm soil depth range, the soil temperature changes under all treatments gradually decreased with increasing soil depth (Figure 3a).

Soil moisture was significantly influenced by different mulching materials. The soil moisture content under all mulching treatments remained at a high level across all soil layers. Among them, F4 exhibited the highest average soil moisture content in all soil layers, with an increase of 17.56%, and was significantly different from other treatments (p ≤ 0.05). In contrast, F2 showed the lowest increase, with only a 3.77% rise (Figure 3b).

The effects of different mulching films on soil temperature showed significant differences (p ≤ 0.05). The results indicated that the soil surface temperature exhibited pronounced fluctuations, with an increase observed under all treatments in the 0–20 cm, 20–40 cm, and 40–60 cm soil layers. Within the 0–60 cm soil depth range, F4 and F5 reduced soil temperature, while F1, F2, and F3 contributed to an increase in soil temperature. In the 0–20 cm, 20–40 cm, and 40–60 cm soil layers, F2 had the highest average daily temperature, increasing soil temperature by 3.14–3.93 °C, whereas F5 decreased it by 1.95–2.26 °C.

Additionally, within the 0–60 cm soil depth range, the soil temperature changes under all treatments gradually decreased with increasing soil depth (Figure 3a). Soil moisture was significantly influenced by different mulching materials. The soil moisture content under all mulching treatments remained at a high level across all soil layers. Among them, F4 exhibited the highest average soil moisture content in all soil layers, with an increase of 17.56%, and was significantly different from other treatments (p ≤ 0.05). In contrast, showed the lowest increase, with only a 3.77% rise (Figure 3b).

3.2. The Effects of Mulching on Appearance Characteristics

During the fruit expansion period of ‘Diaoganxing’, external indices such as fruit dimensions (longitudinal, transverse, and lateral diameters), single fruit mass, fruit firmness, and fruit volume exhibited varying trends. As shown in Figure 4a–c, with the gradual increase in fruit maturity, the longitudinal, transverse, and lateral diameters of the fruit showed an increase, while the fruit shape index gradually decreased during fruit development. Specifically, the longitudinal diameter of the fruit exhibited a double S-shaped growth curve, whereas the transverse and lateral diameters displayed a single S-shaped growth curve. The longitudinal, transverse, and lateral diameters increased progressively with fruit development, entering a rapid growth phase from 59 to 86 d after anthesis. Among them, F4 showed significant differences (p ≤ 0.05) compared to the other five treatments after 59 d post-anthesis, and by 95 d post-anthesis, the mean values of the longitudinal diameter, transverse diameter and lateral diameter for F4 reached 35.01 mm, 35.67 mm, and 31.08 mm, representing increases of 10.42%, 10.67%, and 7.66%, respectively.

The longitudinal diameter increased most rapidly between 68 and 77 d post-anthesis, reaching a maximum value of 35.01 mm in F4 at 95 d post-anthesis. Throughout the experimental period, the longitudinal diameter of F1 remained at the minimum value, reaching 30.19 mm at 95 d post-anthesis, which was 4.82 mm smaller than the maximum value (F4) (Figure 4a). The transverse diameter increased gradually with fruit development, with the greatest growth rate observed between 77 and 86 d post-anthesis. At 95 d post-anthesis, the transverse diameter of F4 reached the maximum value of 35.67 mm, showing significant differences (p ≤ 0.05) compared to other treatments, while F1 had the minimum value of 30.39 mm (Figure 4b). The lateral diameter also increased with fruit development, entering a rapid growth phase at 68 d post-anthesis, transitioning to a slow growth phase at 86 d post-anthesis, and reaching the maximum value at 95 d post-anthesis, with F4 achieving a lateral diameter of 31.08 mm (Figure 4c). A comparison of the three graphs revealed that the growth of the longitudinal and lateral diameters of F4 gradually stagnated between 86 and 95 d post-anthesis, indicating that fruit expansion in F4 tended to stabilize after 86 d post-anthesis.

The fruit shape index of ‘Diaoganxing’ apricot gradually decreased during fruit development. By 86 d post-anthesis, the fruit shape indices of F4 (1.01) and F5 (1.00) approached 1, indicating that the fruit shape tended to become more spherical. By 95 d post-anthesis, the fruit shape index of all treatments was less than 1, with F4 showing the smallest value of 0.98 (Figure 4d).

‘Diaoganxing’ had an increase in fruit volume and single fruit weight. The fruit volume entered a rapid expansion phase at 68 d post-anthesis, which lasted until 86 d post-anthesis. By 95 d post-anthesis, F4 had the largest fruit volume (24.2 cm³), representing an increase of 39.66%, and was significantly different from other treatments (p ≤ 0.05). In contrast, F1 had the smallest fruit volume (17.5 cm³), representing a decrease of 22.91% (Figure 4e). Fruit fresh weight did not show significant differences (p ≤ 0.05) until 59 d post-anthesis, after which it began to increase significantly at 68 days post-anthesis. By 95 d post-anthesis, the F4 treatment reached the maximum fresh weight (22.41 g), while F1 had the minimum fresh weight (15.1 g) (Figure 4f). Fruit firmness decreased during fruit development, with a rapid decline beginning at 68 d post-anthesis. By 95 d post-anthesis, the control (CK) reached the minimum firmness (0.91 kg/cm²) (Figure 4g). Fruit density did not vary significantly (p ≤ 0.05) during the early fruit development period. By 95 days post-anthesis, the highest fruit density was observed in F2 (1.35 g/cm³), while the lowest was in F4 (0.91 g/cm³) (Figure 4h).

Different mulching materials had significant effects on the color of apricot fruits. The CCI value can be used to indicate color changes (Figure 5): when the value is greater than 1, it indicates that the fruits exhibit a reddish hue, while a value less than 1 indicates a greenish hue. As shown in Figure 5, the color transition period began at 68 d post-anthesis. By 86 d post-anthesis, the CCI values of the fruit skin for F3, F4, and F5 were greater than 0, indicating that these treatments initiated the transition from green to orange earlier than others. This also suggested that these treatments had a better color transition effect, showing significant differences compared to the control (CK) (p ≤ 0.05). By 95 d post-anthesis, the CCI value of the F5 treatment reached the highest value (6.23) among all treatments, with significant differences compared to other treatments (p ≤ 0.05), followed by F4 (5.82).

As shown in

Table 2. Effects of Different Film Covering on Fruit Chromatic Values.

Chromatic Values	Treatment	Days After Anthesis
		41 d	50 d	59 d	68 d	77 d	86 d	95 d
L*	CK	21.71 ± 1.81 a	23.84 ± 3.7 a	26.19 ± 4.65 a	36.74 ± 5.59 b	51.12 ± 7.62 c	65.41 ± 5.21 ab	72.66 ± 8.36 a
	F1	17.44 ± 2.33 bc	20.07 ± 2.71 b	26.86 ± 2.27 a	30.67 ± 4.62 c	54.21 ± 10.51 bc	58.52 ± 5.42 c	63.94 ± 13.48 b
	F2	19.62 ± 3.72 ab	21.26 ± 2.81 b	26.79 ± 3.44 a	28.83 ± 5.42 c	54.24 ± 8.81 bc	60.17 ± 3.08 bc	69.25 ± 5.41 ab
	F3	16.71 ± 2.13 c	22.3 ± 2.06 ab	27.63 ± 5.17 a	42.6 ± 4.44 a	59.83 ± 9.99 b	66.76 ± 6.28 a	64.26 ± 4.69 b
	F4	19.72 ± 3.18 ab	22.13 ± 1.83 ab	24.95 ± 2.62 a	39.52 ± 3.09 ab	57.09 ± 12.86 bc	64.48 ± 6.05 ab	65.54 ± 3.14 ab
	F5	18.69 ± 2.63 bc	21.39 ± 1.66 ab	27.75 ± 4.38 a	40.37 ± 4.9 ab	69.23 ± 4.46 a	66.16 ± 8.05 a	66.83 ± 7.1 ab
a*	CK	−18.53 ± 0.97 b	−20.24 ± 2.26 b	−21.46 ± 2.58 a	−24.67 ± 1.43 a	−30.86 ± 2.81 c	−9.36 ± 10.84 b	36.7 ± 4.9 ab
	F1	−15.94 ± 1.52 a	−17.77 ± 1.98 a	−22.26 ± 1.21 a	−22.56 ± 0.78 a	−27.81 ± 3.96 bc	1.57 ± 14.84 b	33.03 ± 3.21 b
	F2	−17.08 ± 1.63 ab	−18.88 ± 1.72 ab	−22.06 ± 1.7 a	−22.08 ± 2.09 a	−30.19 ± 2.62 bc	−6.74 ± 15.99 b	37.92 ± 6.84 ab
	F3	−15.6 ± 1.72 a	−19.63 ± 1.46 b	−22.36 ± 2.95 a	−25.76 ± 0.83 a	−24.12 ± 9.61 b	18 ± 10.73 a	34.45 ± 6.08 b
	F4	−17.64 ± 2.16 b	−19.37 ± 1.29 ab	−20.88 ± 1.56 a	−19.86 ± 16.57 a	−24.75 ± 8.57 bc	16.14 ± 16.29 a	38.32 ± 6.4 ab
	F5	−17 ± 2.04 ab	−19.32 ± 1.1 ab	−22.41 ± 1.81 a	−19.65 ± 15.42 a	−14.43 ± 12.11 a	23.8 ± 11.76 a	41.74 ± 6.58 a
b*	CK	31 ± 2.52 a	33.26 ± 5.39 a	37.82 ± 6.84 a	52.45 ± 7.13 b	67.93 ± 7.85 c	94.21 ± 7.75 ab	115.1 ± 13.71 a
	F1	24.58 ± 3.4 c	28.51 ± 3.99 a	38.96 ± 3.28 a	42.69 ± 3.26 c	71.92 ± 14.56 bc	89.13 ± 8.8 b	112.38 ± 6.69 ab
	F2	26.65 ± 3.28 bc	24.27 ± 19.86 a	38.81 ± 5.05 a	41.64 ± 7.6 c	74.5 ± 6.02 bc	88.56 ± 9.32 b	113.39 ± 8.15 a
	F3	23.5 ± 3.56 c	31.25 ± 4.65 a	40.22 ± 7.66 a	60.39 ± 5.75 a	81.65 ± 10.35 b	107.89 ± 12.89 a	103.92 ± 4.12 bc
	F4	28.32 ± 4.91 ab	31.86 ± 2.79 a	36.13 ± 3.86 a	57 ± 5.36 ab	81.54 ± 9.23 b	92.04 ± 27.49 b	100.73 ± 11.61 c
	F5	26.65 ± 4 bc	31.32 ± 2.6 a	39.29 ± 4.46 a	53.97 ± 9.9 ab	97.77 ± 10.33 a	106.19 ± 13.39 a	101.02 ± 10.28 c

Data of L* represents brightness, (dark and bright), a* (red and green) and b* (yellow and blue) represent chromatic values on the color difference of fruit. In the table, lowercase letters represent significance analysis (p ≤ 0.05).

, the L* of all treatments generally showed an increase as fruit development progressed. At 95 d post-anthesis, the L* of CK and F3 were significantly different (p ≤ 0.05). Additionally, the a* of F5 was significantly higher than that of F1 and F3, with the difference being statistically significant (p ≤ 0.05).

During the experimental period, the a* were mostly negative in the early stages until 85 d post-anthesis, when the a* of F1, F3, F4, and F5 began to show positive values. Among them, F5 had the largest a* (23.8). By 95 d post-anthesis, the a* of F5 remained the highest among all treatments, reaching 41.74. The b* represents the yellow-blue spectrum, where a smaller value indicates a more bluish hue, while a larger value indicates a more yellowish hue. At 95 d post-anthesis, the b* of the control (CK) reached the maximum value of 115.1, while the minimum value was observed in F4, with a b* of 100.73.

3.3. The Effects of Mulching on the Internal Quality of Fruits

Titratable acidity, carotenoids, soluble sugars, and vitamin C content are important indicators of the intrinsic nutritional quality of apricot fruit. In this study, the titratable acid content showed a gradual decline during fruit development: from 59 to 95 d post-anthesis, the content decreased rapidly from an average of 44.22% to 21.99%. By 95 d post-anthesis, F5 had the lowest titratable acid content (18.31%), which was 0.3 times lower and significantly different from the other treatments, while the control (CK) had the highest titratable acid content (24.56%) (Figure 6a).

The carotenoid content exhibited a trend of initial decrease followed by an increase, reaching the lowest value at 77 d post-anthesis when F4 had the lowest content (0.97 mg/g). By 95 d post-anthesis, the carotenoid content of F4 (4.27 mg/g) and F5 (4.34 mg/g) was significantly higher than that of the other treatments (p ≤ 0.05), representing increases of 13.60% and 14.71%, respectively, compared to the control (CK) (3.76 mg/g) (Figure 6b).

The soluble sugar content showed an increase during fruit development, with a rapid rise after 68 days post-anthesis. By 95 days post-anthesis, F4 had the highest soluble sugar content (15.39 mg/g), representing an increase of 30.77%, while the lowest content was observed in the CK treatment (11.77 mg/g) (Figure 6c).

The vitamin C content followed a similar trend to soluble sugar content, showing an increase. By 95 d post-anthesis, F4 reached the maximum value (17.08 mg/g) among all treatments, representing an increase of 3.22 mg/g (23.26%). Additionally, F4 showed significant differences (p ≤ 0.05) compared to other treatments during this period (Figure 6d).

The soluble solids content exhibited a slow increase, with significant differences (p ≤ 0.05) among treatments at 77 d post-anthesis. F3, F4, and F5 were significantly higher than CK, F1, and F2. By 95 d post-anthesis, F4 had the highest soluble solids content (24.43%), followed by F5 (24.4%), while the lowest was observed in F1 (21.13%). The soluble solids content in F4 and F5 increased by 12.76% and 12.61%, respectively, and both were significantly different from the other treatments (p ≤ 0.05) (Figure 6e).

3.4. Correlation Analysis Among Fruit Quality Indicators of Covering with Different Materials

According to the correlation analysis results (Figure 7), among the appearance characteristics indicators, the longitudinal diameter, transverse diameter, and lateral diameter showed highly significant positive correlations with volume and single fruit fresh weight. The fruit shape index exhibited a highly significant negative correlation with the transverse and lateral diameters while showing a highly significant positive correlation with firmness. Firmness demonstrated a highly significant negative correlation with the transverse diameter, lateral diameter, volume, and single fruit fresh weight. Density showed a significant negative correlation with the transverse diameter, lateral diameter, and single fruit fresh weight but a significant positive correlation with the fruit shape index and firmness.

In terms of functional components, the contents of soluble sugars, soluble solids, and vitamin C all exhibited highly significant positive correlations with the transverse diameter, lateral diameter, volume, and single fruit fresh weight while showing highly significant negative correlations with the fruit shape index and firmness. Specifically, soluble sugars showed a highly significant negative correlation with titratable acid content and a significant positive correlation with carotenoid content. Soluble solids exhibited a highly significant negative correlation with titratable acid but highly significant positive correlations with soluble sugars and vitamin C. Vitamin C showed a highly significant negative correlation with titratable acid and significant positive correlations with carotenoids, soluble sugars, and soluble solids.

Among the color indicators, a*, b*, L*, and CCI all displayed highly significant positive correlations with the transverse diameter, lateral diameter, and single fruit fresh weight while showing highly significant negative correlations with the fruit shape index and firmness. Specifically, a* exhibited a highly significant negative correlation with titratable acid and significant positive correlations with soluble sugars, soluble solids, and vitamin C. b* showed a highly significant positive correlation with carotenoid content, along with significant positive correlations with soluble sugars, soluble solids, and vitamin C. L* demonstrated a highly significant negative correlation with titratable acid and significant positive correlations with vitamin C and soluble solids.

In summary, the expansion of appearance characteristics morphology (e.g., increases in transverse diameter, lateral diameter, and single fruit fresh weight) is often accompanied by improvements in functional components (such as soluble sugars and vitamin C) and enhanced coloration, while also being associated with a reduction in the fruit shape index, decreased firmness, and lower titratable acid content.

4. Discussion

4.1. Influenced by Plastic Film Mulching on Orchard Microenvironment

During the growth and development of plants, the light intensity in the middle and lower canopy decreases significantly as the leaf area gradually increases [27]. In this study, we found that F5 significantly increased the light intensity in the middle and lower canopy. Specifically, F5 increased the average light intensity by 1034.04 lux at 50 cm above the ground and by 31,697.07 lux at 100 cm above the ground, with the light intensity of F5 being significantly higher than that of the other treatments (p ≤ 0.05). F5 exhibited a stronger light-reflecting ability, with reflectance increasing by 2.6 to 3.3 times. Hemming [28] found that using reflective mulch in greenhouses resulted in more uniform light distribution, a significant increase in light intensity received by the middle and lower leaves of plants, and an increase in photosynthetically active radiation (PAR) by 4.39% compared to conventional plastic mulch. Yuan [6] demonstrated that covering the ground of facilities with reflective mulch enhanced the reflected light under the grape canopy to twice the original level.

The regulatory effects of mulch films with different materials on soil temperature vary. F4 and F5 effectively reduced soil temperature and attenuated temperature fluctuations, maintaining a more stable soil temperature. Among them, F5 exhibited the strongest ability to reduce soil temperature, with a decrease of 1.95–2.26 °C. Yin [29] demonstrated that mulching significantly improves soil temperature regulation. Wang [12] found that laying reflective insulation film on the ground effectively reduced the temperature of different soil layers by 1.84 °C under protected cultivation conditions and by 1.89 °C in an open-field environment. This finding was also confirmed in our study. F1–3 significantly increased soil temperature, and Liu’s [30] study on mulch film coverage concluded that mulch films could enhance soil temperature. However, during the high-temperature periods of May and June, the mulching treatment effectively reduced soil temperature, thereby mitigating the adverse effects of thermal stress on apricot trees and ensuring normal growth patterns [31]. This thermoregulatory function highlights the potential of mulching as a climate resilience strategy in apricot cultivation. Nevertheless, the optimal temperature range for apricot tree growth remains undefined, and the mechanisms underlying temperature-mediated physiological responses are yet to be fully elucidated. Future studies should prioritize quantifying species-specific thermal thresholds and validating these findings across diverse agroecological contexts to refine adaptive management protocols.

Soil moisture is a critical factor influencing the growth of fruit trees [32]. In this experiment, the soil moisture content of all treatments showed varying degrees of improvement. Among them, F4 exhibited the highest average soil moisture content across all soil layers, which was significantly different from other treatments (p ≤ 0.05). Previous studies have shown that ground mulching can increase soil moisture content by 5.66% in the 0–40 cm soil layer. Additionally, it can block vertical evaporation and turbulent flow of soil moisture, forcing lateral water movement under the mulch to reduce ineffective evapotranspiration, thereby significantly improving soil moisture use efficiency [33].

4.2. Influenced by Plastic Film Mulching on Fruit Quality

In actual production, mulching is often used to improve the tree growth environment, thereby enhancing fruit quality [34]. In this study, F5 had the most significant effect (p ≤ 0.05) on improving fruit coloration and was the fastest treatment for color transition, with fruit coloration occurring 10 d earlier. By 95 d post-anthesis, the CCI value of F5 reached the maximum value of 6.23, representing an increase of 39% across all treatments. Similarly, Zeng [35] demonstrated that the CCI value of the fruit skin in mulching treatments was consistently higher than that of the control group. Zhang [36] found that laying reflective insulation film promoted fruit surface coloration in cherries, resulting in lower brightness and chroma values. At the same time, F4 significantly improved fruit dimensions, fresh weight, and volume, with increases of 4.46%, 4.22%, 2.20%, 19.65%, and 39.66%, respectively, by 95 d post-anthesis. Liu [37] studied the effect of reflective ground mulch on grapes and concluded that the longitudinal and transverse diameters of the fruit, as well as the fruit grain quality, increased compared to the control.

Additionally, mulching significantly reduced titratable acid content while improving intrinsic fruit quality indicators such as carotenoids, soluble sugars, vitamin C and soluble solids content. In this study, F4 increased vitamin C content by 23.26%, followed by F3 with an increase of 17.99%. F4 and F5 showed the most significant enhancement (p ≤ 0.05) in soluble solids content, with increases of 12.76% and 12.61%, respectively, by 95 d post-anthesis. These findings align with previous studies on ‘Jvfeng’ grapes [37] and ‘Zijinghong 1’ and ‘Hujingmilu’ peaches [38]. In this study, the titratable acid content was reduced by 1.81%, 6.36%, 11.81%, 17.27%, and 25.45% for different treatments. Zhang [34] found that mulching with black plastic mulch and white plastic mulch between rows of ‘Qiuji’ plum trees effectively reduced titratable acid content by 16% and 18%, respectively. The carotenoid content began to increase rapidly after 77 d post-anthesis, with F5 reaching the highest value (4.36 mg/g) by 95 d post-anthesis. The results of this study showed that ground mulching increased the soluble sugar content in fruits, with F4 having the best enhancement effect, increasing soluble sugar content by 33.77%, which is consistent with the findings of Zeng [35] on citrus. Wang [39] conducted a study on the effect of reflective insulation film on ‘Gongchuan’ mandarin oranges and also concluded that mulching increased the vitamin C content of the fruit.

5. Conclusions

It was found that mulching significantly optimized the microenvironment for apricot tree growth. Among the treatments, F4 had the most significant effect (p ≤ 0.05) on regulating soil temperature and moisture, reducing soil temperature by 4.60% and increasing soil moisture by 17.09%. F5 showed the most significant improvement (p ≤ 0.05) in the light environment, increasing light intensity by 161.04–208.71% and reflectance by 2.6–3.3 times (p ≤ 0.05). In conclusion, this study identified two high-performing mulch films based on their distinct functional effects. The F4 treatment demonstrated the ability to stabilize and reduce soil temperature, enhance water retention and moisture conservation, and promote fruit expansion and intrinsic quality improvement. Meanwhile, the F5 treatment created an optimized light environment for apricot trees, thereby facilitating the early maturation of the fruit. In the future, further research will explore the long-term ecological effects of mulching materials and supporting agronomic measures to refine the precision management system for apricot orchards in arid zones.