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Effects of Intercropping Morel Mushrooms between Apple Tree Rows on Soil Properties and Tree Performance

  † These authors contributed equally to this work.

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07 July 2026

Posted:

08 July 2026

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Abstract
To investigate the effects of intercropping Morchella (morel mushrooms) between apple tree rows on fruit quality and orchard soil properties, a field experiment was conducted using a cultivation system combining plastic film mulching with small arched tunnels. Morchella was planted in the interrows of five-year-old apple trees, and after harvest, the spent mushroom substrate was returned to the soil via rotary tillage. Plots without Morchella cultivation served as the control. The experiment assessed the yield and quality of both apples and morels, as well as the overall impact on tree performance. In addition, soil physicochemical properties and enzyme activities were analyzed across the 0-40 cm soil profile at different depth intervals. The results demonstrated that: (1) Inter-cropping Morchella in apple interrows proved to be agronomically feasible, yielding a fresh mushroom production of 1333.737 g/m². Moreover, this cultivation system significantly enhanced the nutritional quality of the harvested morels, as evidenced by marked increases in crude fiber, total sugars, reducing sugars, and free amino acid contents. (2) In the 0-20 cm soil layer, the Morchella cultivated plots exhibited significantly higher natural water content compared to the control. The measured values for soil pH, alkali-hydrolyzable nitrogen, organic carbon, catalase activity, and sucrase activity were 5.46, 6.733 mg/kg, 38.303 g/kg, 411.859 μ mol/h/g, and 9.885 mg/d/g, respectively, all significantly greater than those in the control (p < 0.05). In the 20-40 cm layer, however, soil available potassium and organic carbon contents were 418.370 mg/kg and 28.453 g/kg, respectively, both significantly lower than the control (p < 0.05). Across both treatments, the values of soil pH, alkali -hydrolyzable nitrogen, organic carbon, available phosphorus, available potassium, and the activities of urease, amylase, catalase, and sucrase generally decreased with increasing soil depth. Notably, in the non-cultivated control plots, the contents of alkali-hydrolyzable nitrogen and organic carbon increased with depth. (3) Morchella intercropping significantly improved apple fruit quality, as reflected by marked increases in individual fresh weight, fruit shape index, reducing sugars, total sugars, and soluble solids content. (4) The treatment also substantially enhanced the photosynthetic performance of apple trees, with significant increases in transpiration rate, intercellular CO2 concentration, and stomatal conductance. Collectively, our findings demonstrate that intercropping Morchella between apple tree rows confers substantial agronomic advantages. This practice not only elevates the productivity and quality of both the mushroom crop and the apples, but also ameliorates key soil physicochemical characteristics and boosts foliar photosynthesis. The cumulative positive effects highlight its considerable promise as a viable and scalable agroecological strategy.
Keywords: 
Morchella
;  
apple
;  
yield
;  
quality
;  
soil physicochemical properties
;  
soil enzyme activities
;  
photosynthetic performance
Subject: 
Biology and Life Sciences  -   Agricultural Science and Agronomy

1. Introduction

Morchella esculenta(L.) Pers., commonly known as morel mushroom, yellow morel, or sponge mushroom, is an edible and medicinal fungus belonging to the genus Morchella within the family Morchellaceae, order Pezizales, class Pezizomycetes, and subphylum Ascomycotina [1,2]. As a prized and rare edible mushroom, esculenta is highly sought after in commercial markets. It is rich in protein, amino acids, vitamins, minerals, and bioactive compounds, including organic germanium. The species exhibits a broad spectrum of health-promoting properties, including antitumor, immunomodulatory, antibacterial, anti-fatigue, antioxidant, hypolipidemic, and hepatoprotective effects. Consequently, it holds considerable economic importance and substantial scientific research value [3,4].
In recent years, the introduction of nutrient bag technology has accelerated the expansion of Morchella cultivation. Consequently, cultivation systems have diversified considerably, evolving from the original flat shed method to include understory cultivation, facility based production, mechanized farming on plains, and temperature controlled greenhouse systems [5]. Among these, understory cultivation has emerged as one of the primary models for extension and application, owing to its efficient utilization of forest land resources, enhancement of under canopy economic returns, and reduction in production costs [6]. Currently, understory cultivation of edible fungi has been widely adopted in southern China, including Sichuan, Yunnan, and Guizhou, and has yielded substantial economic benefits. Intercropping Stropharia rugosoannulata in vineyards has been shown to increase soil organic matter, hydrolyzable nitrogen, and available potassium levels, while also significantly improving grape quality [7]. Further research on cultivating Stropharia rugosoannulata and Dictyophora echinovolvata beneath grapevines demonstrated that soil moisture, pH, organic matter, hydrolyzable nitrogen, and available potassium all exceeded control levels. At the same time, grape yield and quality were also enhanced [8]. A study on winter intercropping of Stropharia rugosoannulata in young tea plantations revealed that this practice improved soil physicochemical properties, facilitated successful overwintering of young tea plants, and increased spring tea production [9]. Studies on cultivating edible fungi beneath fruit trees have shown that this practice enhances both fungal and fruit yields and quality, while also improving the soil environment [10,11]. By ameliorating soil physicochemical properties, understory cultivation of edible fungi indirectly promotes plant growth. A study on the effects of Grifola frondosa residue returning on the growth and photosynthetic traits of chestnut seedlings revealed that this practice increased leaf area, specific leaf area, and leaf SPAD values [12]. Notably, the net photosynthetic rate (Pn) of chestnut seedlings increased by up to 25.92%, accompanied by concurrent elevations in stomatal conductance (Gs) and intercellular CO₂ concentration (Ci), indicating a marked enhancement of photosynthetic performance. Related research has demonstrated that understory cultivation significantly upregulates the expression of genes involved in the photosynthetic pathway of Coptis chinensis, while concurrently increasing chlorophyll content and plant fresh weight, thereby confirming the ameliorative effect of the understory environment on photosynthetic capacity [13]. Collectively, these findings indicate that understory edible fungus cultivation not only maximizes the utilization of forest land resources and improves fungal yield and quality, but also achieves dual harvests of fruits and mushrooms, concurrently ameliorating soil conditions and promoting the growth and development of fruit trees.
Zhaotong City in Yunnan Province is a major apple-producing area in the cool, high-altitude region of southwestern China. By the end of 2024, the apple cultivation area in Zhaotong had reached approximately 56,667 hectares, providing abundant understory space resources [14,15]. Leveraging the favorable conditions of apple orchards—such as suitable canopy closure, high air humidity, appropriate light intensity, ample oxygen availability, and relatively low diurnal temperature fluctuations—the cultivation of Morchella beneath apple trees represents a promising model for achieving synergistic gains in both ecological conservation and economic development. However, to date, research on the effects of understory Morchella cultivation in apple orchards on soil environmental conditions and on tree performance remains scarce. To address this knowledge gap, the present field experiment was conducted by intercropping Morchella between apple rows. The objective was to systematically evaluate the subsequent effects on the yield and quality of both morels and apples, as well as on soil environmental conditions and the growth and development of the fruit trees. The findings are intended to provide a scientific basis and practical guidance for the rational implementation of understory morel cultivation in apple orchards.

2. Materials and Methods

2.1. Site Description

The field experiment was conducted from December 2024 to September 2025 at the apple base of Haoran Agricultural Development Co., Ltd., located in Sujiayuan Town, Zhaoyang District, Zhaotong City, Yunnan Province (103°75″ E, 27°36″ N; elevation 1915 m). The study site is characterized by a mean annual temperature of 11 °C, an average annual precipitation of 750 mm, and a frost-free period of 230 days [16].

2.2. Test Materials

The Morchella sextelata spawn and nutrient packs were both purchased from Zhaotong Longxing Biotechnology Co., Ltd.

2.3. Experimental Design

The experiment was conducted in a five-year-old apple orchard, with Morchella planted on 24 November 2024. Ten rows of apple trees with uniform and vigorous growth were selected. The treatment group consisted of rows where Morchella was intercropped between the apple trees, while the control group received no Morchella cultivation. The cultivation system employed plastic film mulching combined with small arched tunnels. Before sowing, the soil was deeply tilled to a depth of 10-20 cm along the long axis of the orchard, with clods broken up and the surface leveled. The bed was then thoroughly irrigated. Based on the terrain, sunken planting beds were constructed with furrows measuring 10-15 cm in depth, 1 m in width, and 10 m in length to facilitate drainage and moisture retention. On each bed, three parallel sowing furrows were opened at 20 cm intervals, each approximately 5 cm deep and 10 cm wide. The Morchella spawn was crumbled, mixed with an appropriate amount of potassium dihydrogen phosphate, and evenly broadcast into the furrows. Each row received approximately five spawn bags, equivalent to 5601.7 g in total weight. After sowing, the furrows were covered with 3-5 cm of soil, followed by black plastic mulch. Small arched tunnels were then erected and covered with transparent film and shade netting to regulate temperature, humidity, and light conditions. During the subsequent growth period, mycelial development was regularly monitored. Nutrient bags were placed when mycelial (mycelial bloom) became visible, at intervals of 30 cm, with 120 bags placed per row. Following sowing, standard management practices were implemented, including appropriate water management, regulation of environmental conditions, and integrated pest and disease control, to ensure optimal morel growth.

2.4. Sample Collection and Preparation

Morchella collection: From March to April 2025, morel mushrooms were harvested, and the yield was measured. The treatment group cultivated under the apple canopy was designated as P- YDJ, while the open field cultivated control group was designated as L -YDJ. Each sampling plot measured 2 m², and each treatment was replicated three times. Fresh weight was determined immediately after harvest to calculate yield. The harvested morels were dried in an oven at 50 ℃ to constant weight, then ground to pass through a 60 mesh sieve. The resulting powder was sealed and stored for subsequent analyses.
Soil sampling: Soil samples were collected using a five-point sampling method. In the apple interrows where Morchella had been cultivated, soils were sampled from the 0-20 cm (designated A0) and 20-40 cm (designated A1) layers. The topsoil (0-20 cm) was cleared of stones and debris before physical property measurements. All collected samples were air-dried, passed through a 100 mesh sieve, sealed, and stored for later analysis. Using the same procedure, soil samples were also collected from the interrows without Morchella cultivation at 0-20 cm (designated CK0) and 20-40 cm (designated CK1) to serve as controls.
Apple sampling: Apple yield was assessed on 17 November 2025. Five apple trees from the Morchella-cultivated plots (designated PG-A) and five from the non-cultivated control plots (designated PG-CK) were selected, ensuring that all trees were of the same variety and exhibited comparable growth vigor. From each tree, ten apples of similar maturity were harvested from the four cardinal directions (east, south, west, and north) and pooled to form a composite sample. Apples from the non-cultivated plots served as the control. The harvested apples were stored at 4 °C in a refrigerator for subsequent analyses.

2.5. Measurement of Parameters

Quality assessment of Morchella and apple fruits: For morel fruiting bodies, ash content was determined following GB/T 6438-2007 [17], crude fat content following GB/T 6433-2006 [18], and crude fiber content following GB/T 5009.10-2003 [19]. while reducing sugar content was determined by the 3,5-dinitrosalicylic acid (DNS) method [20]. Crude protein content was assayed using the Coomassie Brilliant Blue G-250 staining method [21], and vitamin C content was measured by the 2,6-dichlorophenolindophenol titration method [22]. Total sugar content was measured using the anthrone colorimetric method. Free amino acid content was determined using the ninhydrin colorimetric method. For apple fruits, titratable acidity was measured by NaOH titration, soluble solids content was determined using a handheld refractometer, and fruit firmness was measured with a GY-4 digital fruit hardness tester.
Soil property measurements: Field water capacity, bulk density, total porosity, capillary porosity, and non-capillary porosity were determined following the methods described by Wang et al. [23]. Soil pH, alkali-hydrolyzable nitrogen, available phosphorus, and available potassium were measured according to the protocols outlined in Soil Agrochemistry Analysis [24]. Soil organic carbon content was determined using a Multi N/C 3100 analyzer. Soil enzyme activities—including catalase, sucrase, amylase, and urease—were assayed using commercial soil enzyme assay kits (purchased from Suzhou Grace Biotechnology Co., Ltd.).
Photosynthetic measurements: Measurements were conducted on clear days in June, July, August, and September 2025, between 10:30 and 11:30 a.m., using a Li 6800 portable photosynthesis system. Apple trees of the same variety and comparable growth vigor, located in the central area of the orchard, were selected from both the Morchella cultivated and non-cultivated plots. Functional leaves from new shoots at the same height on the southern side of the canopy were chosen for measurement. The Morchella cultivated trees were designated A6, A7, A8, and A9 (for June through September, respectively), while the corresponding control trees were designated CK6, CK7, CK8, and CK9. Li-6800-01-A red- blue light source was used, with photosynthetically active radiation (PAR) set to 1500 μmol/(m²·s), leaf chamber temperature maintained at 25 ℃, ambient CO₂ concentration at 400 μmol/mol (corrected from the original value), and relative humidity at 50%. The photosynthetic parameters measured included net photosynthetic rate [Pn, μmol/(m²·s)], transpiration rate [Tr, mmol/(m²·s)], stomatal conductance [Gs, mmol/(m²·s)], and intercellular CO₂ concentration [Ci, μmol/mol].

2.6. Data Processing

Data were organized using Microsoft Excel 2019. Statistical analyses were performed with DPS data processing software, and significant differences among treatments were determined using the least significant difference (LSD) test. Graphical representations were generated using OriginPro 2022.

3. Results

3.1. Effects of Different Cultivation Sites on Morel Yield and Quality

The yield and drying ratio of Morchella varied between cultivation sites (Table 1). Understory cultivation in the apple orchard yielded 1333.74 g/m² of fresh mushrooms, which was 16.11% higher than that of open-field cultivation, though the difference was not statistically significant. The drying ratio under the apple canopy was 9.71%, representing a significant reduction of 3.34% compared to the open-field control. These results indicate that intercropping Morchella beneath apple trees can effectively enhance fresh mushroom yield.
The nutritional composition of Morchella fruiting bodies differed significantly between cultivation sites (Table 2). Understory cultivation in the apple orchard resulted in markedly higher contents of crude fiber (14.54%), total sugars (19.38%), reducing sugars (27.65%), and free amino acids (0.78%) compared to the control, with all differences being statistically significant. Conversely, the contents of ash (7.53%), crude protein (6.26%), and vitamin C (0.16%) were significantly lower than those in the control. Crude fat content was also higher under the apple canopy, though the difference did not reach statistical significance. Collectively, these findings suggest that intercropping Morchella beneath apple trees can, to some extent, improve the nutritional quality of the harvested morels.

3.2. Effects of Morel Cultivation Between Apple Rows on the Soil Environment Under Apple

Orchards

3.2.1. Effects of Different Treatments on the Physical Properties of Soil Between Apple Rows

Intercropping Morchella between apple rows affected various soil physical properties (Table 3). Specifically, natural water content, field water capacity, total porosity, capillary porosity, and non-capillary porosity were all higher in the treated plots than in the control. Among these, natural water content (21.45%) was significantly greater than that of the control. Bulk density in the treated plots (1.51 g/cm³) was lower than in the control, though the difference was not statistically significant.

3.2.2. Effects of Different Treatments on the Chemical Properties of the Soil Between Apple Rows

Intercropping Morchella between apple rows influenced soil chemical properties (Table 4). In the 0-20 cm soil layer, the Morchella-cultivated plots exhibited significantly higher pH (5.46), alkali-hydrolyzable nitrogen (6.73 mg/kg), and organic carbon (38.30 g/kg) compared to the control (p < 0.05). Although available phosphorus and available potassium contents were lower than those in the control, the differences were not statistically significant. In the 20-40 cm layer, soil available potassium (418.37 mg/kg) and organic carbon (28.45 g/kg) were both significantly lower than those in the control (p < 0.05). Soil pH and available phosphorus were higher than in the control, while alkali-hydrolyzable nitrogen was lower; however, none of these differences reached statistical significance.

3.2.3. Effects of Different Treatments on Soil Chemical Properties across Different Soil Layers in The Apple Interrows.

The chemical properties of soils in the Morchella cultivated and non-cultivated plots differed between soil layers (Figure 1). In the Morchella-cultivated plots, the contents of pH, alkali-hydrolyzable nitrogen, available phosphorus, available potassium, and organic carbon all decreased with increasing soil depth, with reductions of 4.76%, 15.13%, 3.34%, 38.69%, and 25.72%, respectively. Among these, the decreases in pH, alkali-hydrolyzable nitrogen, available potassium, and organic carbon were statistically significant, whereas the decrease in available phosphorus was not. In the non-cultivated control plots, pH, available phosphorus, and available potassium decreased with increasing soil depth by 2.50%, 20.63%, and 16.85%, respectively. The decreases in pH and available potassium were statistically significant, while the decrease in available phosphorus was not. In contrast, alkali-hydrolyzable nitrogen and organic carbon in the control plots increased with depth by 10.89% and 12.14%, respectively, with the increase in organic carbon being statistically significant and that in alkali-hydrolyzable nitrogen being non-significant

3.2.4. Effects of Different Treatments on Soil Enzyme Activities in The Apple Interrows

Intercropping Morchella between apple rows influenced soil enzyme activities (Table 5). In the 0-20 cm soil layer, the Morchella-cultivated plots exhibited catalase and sucrase activities of 411.86 μmol/h/g and 9.89 mg/d/g, respectively, both of which were significantly higher than those in the control (p < 0.05). Urease activity was higher than in the control, while amylase activity was lower, though neither difference reached statistical significance. In the 20-40 cm layer, amylase and sucrase activities were higher than those in the control, whereas urease and catalase activities were lower. However, none of these differences were statistically significant.

3.2.5. Effects of Different Treatments on Soil Enzyme Activities across Different Soil Layers in The Apple Interrows

Soil enzyme activities in the Morchella-cultivated and non-cultivated plots differed between soil layers (Figure 2). In the Morchella-cultivated plots, the activities of urease, amylase, catalase, and sucrase all decreased with increasing soil depth, with reductions of 28.63%, 33.37%, 4.68%, and 28.91%, respectively. Among these, the decreases in amylase and sucrase activities were statistically significant, whereas those in urease and catalase activities were not. In the non-cultivated control plots, urease, amylase, catalase, and sucrase activities decreased with depth by 2.34%, 37.15%, 1.40%, and 12.14%, respectively. Among these, the decrease in sucrase activity was statistically significant, while the changes in urease, catalase, and amylase activities were not.

3.3. Effects of Different Treatments on Apple Yield and Quality

Intercropping Morchella between apple rows significantly influenced the nutritional composition of apple fruits (Table 6). In the Morchella-cultivated plots, both individual fresh weight and fruit shape index were significantly higher than those in the control (p < 0.05). Regarding internal fruit quality parameters, reducing sugars (82.53 mg/g), total sugars (101.71 mg/g), and soluble solids (15.81%) were all significantly elevated compared to the control (p < 0.05). Titratable acidity and vitamin C content were lower than those in the control, while fruit firmness was higher; however, none of these differences reached statistical significance.

3.4. Effects of Different Treatments on Photosynthetic Performance of Apple Trees

Different treatments exerted notable effects on the photosynthetic performance of apple trees (Table 7). In the Morchella-cultivated plots, the net photosynthetic rate (Pn) of apple trees increased by 4.76% and 11.84% in June and July, respectively, compared to the control (CK), whereas it decreased by 7.45% and 5.02% in August and September, respectively. However, none of these differences reached statistical significance. The transpiration rate (Tr) of apple trees was consistently higher in the Morchella-cultivated plots across all four months, with increases of 16.67%, 25.00%, 9.09%, and 16.67% in June, July, August, and September, respectively, compared to CK. The increases in July, August, and September were statistically significant. The intercellular CO₂ concentration (Ci) in apple leaves was also elevated in the treated plots, with increases of 0.42%, 4.45%, 1.51%, and 6.76% in June, July, August, and September, respectively, relative to CK. The increase observed in September reached statistical significance. Stomatal conductance (Gs) of apple trees was consistently higher in the treatment group across all months, with increases of 22.30%, 25.79%, 6.15%, and 14.33% in June, July, August, and September, respectively, compared to CK. The increase in July was statistically significant. Collectively, these results indicate that intercropping Morchella between apple rows enhanced leaf net photosynthetic rate in June and July, and consistently increased transpiration rate, intercellular CO₂ concentration, and stomatal conductance across most of the growing season, with significant promoting effects observed in multiple months.

3.5. Effects of Different Treatments on Photosynthesis in Apple Trees in Different Months

Following Morchella intercropping, the photosynthetic performance of apple trees varied significantly across months (Figure 3). The net photosynthetic rate (Pn) in both treatments exhibited a unimodal pattern, increasing initially and then declining. In the Morchella-cultivated plots, Pn peaked in July at 18.16 μmol/(m²·s), which was significantly higher than in all other months. In the control plots, Pn also reached its maximum in July at 16.01 μmol/(m²·s), significantly exceeding the values recorded in June and September, though the difference from August was not statistically significant. Transpiration rate (Tr) in both treatments followed a pattern of initial decline, followed by an increase, and then a subsequent decrease. In August, Tr reached its peak at 0.011 mmol/(m²·s) in the treated plots and 0.010 mmol/(m²·s) in the controls, with both values being significantly higher than those recorded in all other months. Intercellular CO₂ concentration (Ci) in both treatments also displayed a unimodal trend, increasing to a peak in August and then declining. In the treated plots, Ci in August (344.87 μmol/mol) was significantly higher than in all other months. In the control plots, the August value (339.68 μmol/mol) was significantly higher than those in June and July, but did not differ significantly from that in September. Stomatal conductance (Gs) in both treatments followed a similar unimodal pattern. In August, Gs values in the treated and control plots reached 0.63 and 0.60 mmol/(m²·s), respectively, both significantly higher than those in all other months. Collectively, these results indicate that, across the growing season, net photosynthetic rate peaked in July, while transpiration rate, intercellular CO₂ concentration, and stomatal conductance all reached their maximum values in August, regardless of treatment.

3.6. Correlation Analysis between Topsoil Physicochemical Properties and Soil Enzyme Activities following Morchella Cultivation

Following Morchella cultivation between apple rows, topsoil physicochemical properties and enzyme activities exhibited varying degrees of correlation (Figure 4). Specifically, soil pH showed a highly significant positive correlation with alkali-hydrolyzable nitrogen content, whereas both pH and alkali-hydrolyzable nitrogen were highly significantly negatively correlated with soil organic carbon content and catalase activity. Available phosphorus was highly significantly positively correlated with available potassium. Soil organic carbon content was highly significantly positively correlated with catalase activity. Urease activity showed a highly significant positive correlation with sucrase activity, but a highly significant negative correlation with amylase activity. Amylase activity was highly significantly negatively correlated with sucrase activity.

3.7. Correlation Analysis between Topsoil Physicochemical Properties and Photosynthetic Performance of Apple Trees following Morchella Cultivation

Following Morchella cultivation between apple rows, topsoil physicochemical properties and photosynthetic parameters of the apple trees showed varying degrees of correlation (Figure 5). Specifically, soil pH exhibited a highly significant positive correlation with transpiration rate and a highly significant negative correlation with soil organic carbon content. Alkali-hydrolyzable nitrogen content was highly significantly positively correlated with transpiration rate, and highly significantly negatively correlated with soil organic carbon content. Available phosphorus was highly significantly positively correlated with available potassium, while both available phosphorus and available potassium were highly significantly negatively correlated with intercellular CO₂ concentration. Soil organic carbon content was significantly negatively correlated with transpiration rate. Net photosynthetic rate (Pn) was highly significantly positively correlated with stomatal conductance (Gs).

4. Discussion

In this study, Morchella cultivation under apple trees yielded 1333.74 g/m² of fresh fruiting bodies, which exceeded the yield from open-field cultivation. Furthermore, the levels of crude fiber, total sugar, reducing sugar, and free amino acids in the harvested mushrooms were significantly higher than those in the control group. These results demonstrate that intercropping Morchella in apple orchards is a viable strategy for achieving both high yield and superior mushroom quality. Apple fruit quality is primarily governed by soil fertility, root system development, and nutrient uptake capacity [25,26,27]. Following Morchella intercropping, the average fresh weight per apple increased significantly. Moreover, the levels of reducing sugars, total sugars, and soluble solids in the fruit were markedly higher than those in the control group, whereas titratable acidity and vitamin C content were lower. These results indicate that intercropping Morchella between apple rows effectively enhances overall apple fruit quality.
The results of this study showed that intercropping Morchella between apple rows significantly increased the natural soil water content in the 0-20 cm layer, indicating that cultivating edible fungi can enhance soil moisture to a certain extent. This finding is consistent with previous reports on intercropping Coprinus comatus under fruit trees [11] and cultivating edible fungi under a Cupressus plantation [28]. This phenomenon can be explained by two main reasons. On the one hand, the deliberate application of large amounts of water during Morchella cultivation elevates soil moisture levels [29]. On the other hand, as the fungus decomposes the cultivation substrate for its nutritional needs, the substrate remains as a surface mulch, which effectively retards water loss from the soil and preserves moisture [30,31]. In addition, the present study revealed that Morchella cultivation significantly increased soil pH, alkali-hydrolyzable nitrogen, and organic carbon content in the 0-20 cm soil layer. This finding is consistent with a previous report on the effects of mushroom residue incorporation on nutrient dynamics in paddy soil [32]. This phenomenon can be explained by the fact that, during its growth, Morchella either releases nutrients from the decomposition of the cultivation substrate into the soil or accelerates the breakdown and transformation of existing soil nutrients. As a result, the nutrient availability in the 0-20 cm soil layer is enhanced, leading to improved soil physicochemical properties that are conducive to apple tree growth and development [33,34]. The results of this study revealed that Morchella cultivation decreased soil available potassium and organic carbon contents in the 20-40 cm layer. This decline can be attributed to two factors. First, the highly penetrative mycelia of Morchella can reach a depth of 20-40 cm and continuously take up available potassium for their nutritional needs [35]. Second, the absence of external organic matter input in this layer leads to a progressive depletion of the carbon pool, which in turn reduces both organic carbon and available potassium levels. After Morchella cultivation between apple rows, the contents of soil pH, alkali-hydrolyzable nitrogen, organic carbon, available phosphorus, and available potassium all decreased with increasing soil depth. In contrast, in the plots without Morchella cultivation, the contents of alkali-hydrolyzable nitrogen and organic carbon showed an increasing trend with depth. This may be attributed to the leaching of labile organic carbon and small-molecule nitrogen—derived from litter decomposition driven by natural precipitation—downward through the soil profile, with subsequent accumulation in the middle and lower clay-rich layers. However, the underlying mechanisms require further investigation.
Soil enzyme activity serves as a critical proxy for assessing soil biological activity and fertility [36]. A growing body of evidence indicates that the cultivation of edible fungi beneath forest canopies can markedly stimulate the soil enzyme system, facilitating nutrient turnover and energy transfer, and consequently improving soil fertility. This stimulatory effect is largely mediated by metabolites secreted by fungal mycelia, which enhance enzyme activities and shape soil microbial community dynamics [37]. In the present study, Morchella cultivation between apple rows significantly enhanced the activities of urease, catalase, and sucrase in the surface soil layer (0-20 cm). These results are in agreement with earlier findings on the impacts of mushroom residue return on soil organic carbon stability, enzymatic activity, and microbial diversity [38], as well as on the combined effects of residue and fertilizer application on paddy soil nutrients and enzyme activities [39]. This enhancement may be attributed to the incorporation of Morchella residues, which, upon decomposition, release low-molecular-weight organic substances such as phenolic acids and polysaccharides. These compounds are thought to boost enzyme activities by activating soil microorganisms and increasing microbial biomass carbon. Furthermore, the organic-carbon-rich mushroom residue can directly promote microbial metabolism, thereby contributing synergistically to enhanced soil enzyme activity. A progressive decline in enzyme activities was observed with increasing soil depth, a pattern that corroborates the commonly recognized surface-enrichment phenomenon of soil enzyme activities [40,41]. The observed decline in enzyme activity with increasing soil depth is primarily due to the fact that surface soils are subject to more intensive matter and energy exchange with the surrounding environment, creating favorable conditions for microbial colonization and growth. In contrast, in deeper soil layers, factors such as lower maturation status, reduced fertility, and limited nutrient availability tend to suppress microbial activity and reproduction, thereby leading to diminished enzyme activities.
Net photosynthetic rate (Pn) directly reflects the photosynthetic capacity of plants. Transpiration rate (Tr) serves as a key physiological indicator for assessing plant water metabolism and environmental adaptability. Stomatal conductance (Gs) is an important parameter for characterizing leaf transpiration [42,43,44]. Our results demonstrated that Morchella intercropping significantly enhanced leaf net photosynthetic rate (Pn) in June and July. Moreover, transpiration rate (Tr), intercellular CO₂ concentration (Ci), and stomatal conductance (Gs) of apple trees were all markedly increased, indicating a pronounced promotional effect. These improvements can be attributed to two main factors. First, the continuous respiratory CO₂ release from Morchella mycelia and fruiting bodies increases the availability of photosynthetic substrate, thereby directly promoting photosynthetic carbon fixation. Second, Morchella cultivation under the apple canopy improves soil structure and activates soil nutrients, which enhances the trees' water and nutrient uptake capacity, ultimately leading to increased stomatal conductance and greater light-use efficiency in apple leaves [45]. Furthermore, the fungal layer beneath the canopy can modulate the field microclimate and alleviate environmental stress-induced damage to the photosynthetic apparatus. These multiple mechanisms likely act in concert to enhance plant photosynthesis; however, the precise underlying processes require further investigation.
Soil nutrient dynamics are known to be associated with changes in enzyme activities [46]. In the present study, Morchella cultivation under apple trees modified the patterns of nutrient uptake and utilization by the root system, thereby influencing the magnitude of soil enzyme activities. In the present study, a highly significant positive correlation was observed between surface soil pH and alkali-hydrolyzable nitrogen content after Morchella intercropping, which is in agreement with the findings of a study on the impacts of long-term fertilization and straw incorporation on nitrogen fertility and productivity in reddish paddy soils [47]. This relationship is likely explained by the fact that pH modulates soil nitrogen mineralization, and given that alkali-hydrolyzable nitrogen originates predominantly from the mineralization of organic nitrogen, a process driven by microorganisms and highly responsive to pH changes. It has been demonstrated that raising soil pH in acidic environments can substantially stimulate the activity of ammonifying bacteria and related microbial populations, which facilitates the transformation of organic nitrogen into ammonium nitrogen and ultimately elevates alkali-hydrolyzable nitrogen levels [48]. The highly significant positive correlation observed between soil organic carbon and catalase activity in this study is mainly attributable to the driving effect of carbon inputs from crops on microbial metabolism. Catalase, as an extracellular enzyme secreted by soil microorganisms, serves as a direct indicator of microbial biomass and metabolic activity. Following Morchella cultivation, the input of exogenous organic carbon—such as mushroom residue—provides soil microorganisms with an abundant carbon and energy source, stimulating their proliferation and consequently enhancing the synthesis of enzyme proteins, including catalase. Furthermore, the intensification of microbial metabolism is necessarily associated with elevated respiration rates, resulting in increased production of hydrogen peroxide, which is toxic to organisms. This accumulated hydrogen peroxide serves as a substrate that induces catalase secretion, enabling the removal of excess hydrogen peroxide and safeguarding the normal physiological functions of microbial cells [49,50]. Accordingly, the elevation of soil organic carbon content represents a critical driver for boosting catalase activity and optimizing the soil metabolic environment.
Correlation analysis between surface soil physicochemical properties and leaf photosynthetic parameters following Morchella cultivation revealed a significant relationship between soil properties and apple photosynthesis. Notably, soil pH and alkali-hydrolyzable nitrogen content were highly significantly and positively correlated with transpiration rate, which can be primarily attributed to the regulatory effects of soil nitrogen supply on stomatal behavior and plant water metabolism. The magnitude of transpiration rate is directly determined by stomatal conductance, and nitrogen is a key factor regulating stomatal opening and closure. As a readily available nitrogen source that can be directly taken up by crops, soil alkali-hydrolyzable nitrogen determines leaf nitrogen content, which in turn influences the accumulation of potassium ions and osmotic regulatory substances in guard cells, thereby promoting stomatal opening. When soil nitrogen supply is adequate, plants develop a well-functioning photosynthetic apparatus and enhanced root vigor, which increases transpirational pull and significantly elevates leaf transpiration rate. Soil pH plays an indirect yet important regulatory role in this process: an optimal pH range enhances soil microbial activity and accelerates the mineralization of organic nitrogen, thereby improving the availability of alkali-hydrolyzable nitrogen [45]. In this study, soil organic carbon content was highly significantly and negatively correlated with transpiration rate. This may be because the accumulation of organic carbon is accompanied by enhanced soil microbial activity, which intensifies microbial oxygen consumption and may generate certain root-derived chemical signals—such as abscisic acid precursors—that are transported via the xylem to the leaves, where they induce partial stomatal closure and consequently reduce transpiration. In summary, soil physicochemical properties can profoundly influence the photosynthetic productivity of fruit trees through multi-pathway cascading effects.

5. Conclusions

As a novel intercropping system, cultivating Morchella between apple rows not only produces high yields of superior-quality mushrooms but also substantially improves soil physicochemical properties. Specifically, it significantly increased natural soil water content and, in the 0-20 cm layer, markedly elevated pH, alkaline-hydrolyzable nitrogen, organic carbon content, as well as catalase and sucrase activities. In contrast, in the 20-40 cm layer, available potassium and organic carbon contents were significantly reduced. Furthermore, Morchella intercropping enhanced apple fruit quality attributes, including individual fresh weight, fruit shape index, and the contents of reducing sugars, total sugars, and soluble solids. Additionally, it promoted photosynthesis in apple trees, as evidenced by significant increases in net photosynthetic rate, intercellular CO₂ concentration, and stomatal conductance. The effects of understory edible fungus cultivation are multifaceted, and the selection of suitable fungal species should be based on factors such as tree species and canopy density. The present study provides only a preliminary investigation into the cultivation effects of Morchella under apple orchards; further research is needed to evaluate its applicability in other forest types and with other edible fungus species. Moreover, the impacts of edible fungus cultivation on soil physicochemical properties, microbial community structure, and tree growth and development are long-term and dynamic processes, warranting sustained and in-depth investigation over time.

Author Contributions

Conceptualization, S.Y. and X.W.; methodology, S.Y., Y.H., L.B. and X.W.; software, X.W., L.B., C.Y. and L.D.; validation, X.W., L.B., Z.T. and J.L.; formal analysis, X.W., L.B., C.Y.; investigation, X.W., L.B., L.D., Z.T., J.L., F.X. and H.Q.; resources, X.W.; data curation, X.W., L.B. and C.Y.; writing—original draft preparation, X.W. and L.B.; writing—review and editing, supervision, X.W., S.Y. and Y.H.; project administration, S.Y.; funding acquisition, S.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work was jointly funded by Special Basic Cooperative Research Programs of Yunnan Provincial Undergraduate Universities’ Association (grant NO.202501BA070001-002); Project for Reserve Talents of Young and Middle-aged Academic and Technical Leaders. Grant number: 202305AC160057.

Data Availability Statement

The authors confirm that the data supporting the findings of this study are available within the article.

Acknowledgments

Thank you to Yang Shunqiang and He Yonghong for their meticulous guidance and valuable suggestions during the process of writing this paper.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
P-YDJ Interplanting Morchella between apple tree rows
L-YDJ Open-field cultivation of Morchella.
CK0 0-20 cm soil without Morchella cultivation
A0 0-20 cm soil with Morchella Cultivation
CK1 20-40 cm soil without Morchella cultivation
A1 20-40 cm soil with Morchella cultivation
PG-CK Apples from orchards without morel cultivation
PG-A Apples from orchards with morel cultivation
CK6 Apple trees from non-morel-cultivated plots measured in June
A6 Apple trees from morel-cultivated plots measured in June
CK7 Apple trees from non-morel-cultivated plots measured in July
A7 Apple trees from morel-cultivated plots measured in July
CK8 Apple trees from non-morel-cultivated plots measured in August
A8 Apple trees from morel-cultivated plots measured in August
CK9 Apple trees from non-morel-cultivated plots measured in September
A9 Apple trees from morel-cultivated plots measured in September.

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Figure 1. Effects of different treatments on the physicochemical properties of soil across different soil layers in the apple interrows. (a): soil pH value; (b): Alkali-hydrolyzable nitrogen; (c): Available phosphorus; (d): Available potassium; (e): Organic carbon.
Figure 1. Effects of different treatments on the physicochemical properties of soil across different soil layers in the apple interrows. (a): soil pH value; (b): Alkali-hydrolyzable nitrogen; (c): Available phosphorus; (d): Available potassium; (e): Organic carbon.
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Figure 2. Effects of different treatments on soil enzyme activities across different soil layers in the apple interrows (a): Urease; (b): Amylase; (c): Catalase; (d): Sucrase.
Figure 2. Effects of different treatments on soil enzyme activities across different soil layers in the apple interrows (a): Urease; (b): Amylase; (c): Catalase; (d): Sucrase.
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Figure 3. Effects of different treatments on apple photosynthesis in different months (a): Net photosynthetic rate ;(b): Transpiration rate ;(c): Intercellular CO₂ concentration; (d): Stomatal conductance.
Figure 3. Effects of different treatments on apple photosynthesis in different months (a): Net photosynthetic rate ;(b): Transpiration rate ;(c): Intercellular CO₂ concentration; (d): Stomatal conductance.
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Figure 4. Correlation analysis of topsoil physicochemical parameters with soil enzyme activities after planting Morchella. *，** and *** indicate significant correlations at p＜0.05,p＜0.01 and p＜0.001 level，respectively.
Figure 4. Correlation analysis of topsoil physicochemical parameters with soil enzyme activities after planting Morchella. *，** and *** indicate significant correlations at p＜0.05,p＜0.01 and p＜0.001 level，respectively.
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Figure 5. Correlation analysis between soil physicochemical properties and soil enzyme activities following Morchella cultivation.
Figure 5. Correlation analysis between soil physicochemical properties and soil enzyme activities following Morchella cultivation.
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Table 1. Comparison of yield and drying rate of Morchella across different planting sites.
Table 1. Comparison of yield and drying rate of Morchella across different planting sites.
Treatment Yield
g/m2 		Drying ratio
%
P-YDJ 1333.74±282.92 a 9.71±0.82b
L-YDJ 1118.88±57.97 a 13.05±0.19 a
Different lowercase letters within the same column indicate significant differences according to Duncan’s test (p < 0.05), and the same below. P-YDJ: interplanting Morchella between apple tree rows; L-YDJ: open-field cultivation of Morchella.
Table 2. Comparison of nutrient component contents in Morchella esculenta from different planting sites (%).
Table 2. Comparison of nutrient component contents in Morchella esculenta from different planting sites (%).
Treatment Ash
content 		Crude
fat 		Crude
fiber 		Total
sugar 		Crude
protein 		Reducing
sugar 		Vitamin C Free amino
acids
P-YDJ 7.53±0.24 b 6.58±0.55 a 14.54±0.24 a 19.38±0.47 a 6.26±0.25 b 27.65±0.65 a 0.16±0.00 b 0.78±0.06 a
L-YDJ 7.79±0.16 a 5.87±0.63 a 12.69±0.31 b 15.81±0.23 b 7.42±0.16 a 18.67±0.70 b 0.28±0.02 a 0.60±0.03 b
Table 3. Comparison of soil physical properties under different treatments.
Table 3. Comparison of soil physical properties under different treatments.
Treatment Natural water content
(%)		 Field
capacity
(%)		 Soil bulk
density（g/cm3）
 Total
porosity
（g/cm3）
 Capillary
porosity（g/cm3）
 Non-capillary
porosity（g/cm3）
CK0 13.86±1.64 b 39.88±5.70 a 1.52±0.09 a 43.82±2.93 a 0.52±0.03 a 43.31±2.89 a
A0 21.45±0.27 a 44.09±0.51 a 1.51±0.01 a 44.07±0.20 a 0.52±0.01 a 43.55±0.21 a
Different lowercase letters within the same column indicate significant differences according to Duncan’s test (p < 0.05), CK0: 0-20 cm soil without Morchella cultivation; A0: 0-20 cm soil with Morchella cultivation.
Table 4. Comparison of soil chemical properties under different treatments.
Table 4. Comparison of soil chemical properties under different treatments.
Treatment pH
value 		Alkali-hydrolyzable Nitrogen
(mg/kg)
 Available
phosphorus
(mg/kg) 		Available
potassium
(mg/kg) 		Organic
carbon
(g/kg)
CK0 5.33±0.012 b 5.55±0.49 b 6.31±1.12 a 685.63±11.52 a 30.33±0.74 b
A0 5.46±0.038 a 6.73±0.17 a 5.25±0.55 a 682.33±7.51 a 38.30±4.73 a
CK1 5.19±0.038 a 6.15±0.32 a 5.00±0.58 a 570.07±9.75 a 30.02±0.85 a
A1 5.20±0.035 a 5.71±0.15 a 5.02±1.03 a 418.37±4.37 b 28.45±0.48 b
Different lowercase letters within the same column indicate significant differences according to Duncan’s test (p < 0.05), and the same below. CK0: 0-20 cm soil without Morchella cultivation; A0: 0-20 cm soil with Morchella cultivation; CK1: 20-40 cm soil without Morchella cultivation; A1: 20-40 cm soil with Morchella cultivation.
Table 5. Comparison of soil enzyme activities under different treatments.
Table 5. Comparison of soil enzyme activities under different treatments.
Treatment Urease
（μg/d/g） 		Amylase
（μg/h/g）
 Catalase
（μmol/h/g）
 Sucrase
（mg/d/g）
CK0 177.65±55.23 a 1482.01±46.55 a 369.55±16.65 b 7.41±0.56 b
A0 204.32±77.87 a 1442.00±78.47 a 411.86±12.84 a 9.89±0.93 a
CK1 173.47±17.44 a 931.52±253.16 a 392.57±56.11 a 6.51±0.25 a
A1 145.83±29.43 a 947.49±229.33 a 364.37±32.60 a 7.03±0.45 a
Different lowercase letters within the same column indicate significant differences according to Duncan’s test (p < 0.05), and the same below. CK0: 0-20 cm soil without Morchella cultivation; A0: 0-20 cm soil with Morchella cultivation; CK1: 20-40 cm soil without Morchella cultivation; A1: 20-40 cm soil with Morchella cultivation.
Table 6. Effect of different treatments on the nutrient content in apples.
Table 6. Effect of different treatments on the nutrient content in apples.
Treatment Single fresh weight
(g)		 Fruit shape
index		 Reducing sugar
(mg/g)		 Total
sugar（mg/g)		 Soluble
Solids
（%）		 Titratable acid（mg/g) Vitamin C (mg/100g) Fruit
firmness
(N/cm2)
PG-CK 230.28±22.93b 0.81±0.20b 65.93±3.99b 94.38±1.88b 14.21±0.31 b 0.25±0.01 a 5.27±0.06a 179.41±8.68a
PG-A 262.29±12.05a 0.85±0.03a 82.53±1.73a 101.71±3.09a 15.81±0.64 a 0.21±0.02 a 5.15±0.15a 200.44±19.71a
Different lowercase letters within the same column indicate significant differences according to Duncan’s test (p < 0.05), PG-CK: apples from orchards without morel cultivation; PG-A: apples from orchards with morel cultivation.
Table 7. Effects of different treatments on photosynthesis in apple trees.
Table 7. Effects of different treatments on photosynthesis in apple trees.
month Treatment Net photosynthetic rate
（μmol/（m2.s） 		Transpiration
rate
(mmol/（m2.s） 		Intercellular CO₂ concentration
(μmol/mol) 		Stomatal
conductance
(mmol/（m2.s）
June CK6 13.30±1.90 a 0.005±0.002 a 292.62±11.65 a 0.22±0.08 a
A6 13.96±1.00 a 0.006±0.001 a 293.88±7.83 a 0.28±0.04 a
July CK7 16.01±1.95 a 0.003±0.001 b 283.79±15.16 a 0.28±0.07 b
A7 18.16±1.99 a 0.004±0.000 a 297.02±12.83 a 0.38±0.06 a
August CK8 14.31±1.60 a 0.010±0.000 b 339.68±5.21 a 0.60±0.02 a
A8 13.24±1.79 a 0.011±0.000 a 344.87±4.37 a 0.63±0.04 a
September CK9 12.35±0.29 a 0.005±0.001 b 300.60±11.66 b 0.25±0.04 a
A9 11.73±1.52 a 0.006±0.000 a 322.38±12.29 a 0.29±0.02 a
Different lowercase letters within the same column indicate significant differences according to Duncan’s test (p <0.05), CK6: apple trees from non-morel-cultivated plots measured in June; A6: apple trees from morel-cultivated plots measured in June; CK7: apple trees from non-morel-cultivated plots measured in July; A7: apple trees from morel-cultivated plots measured in July; CK8: apple trees from non-morel-cultivated plots measured in August; A8: apple trees from morel-cultivated plots measured in August;.CK9: apple trees from non-morel-cultivated plots measured in September; A9: apple trees from morel-cultivated plots measured in September.
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