Effects of Intercropping Morchella Between Apple Tree Rows on Soil Physicochemical Properties and Tree Performance

To investigate the effects of interplanting Morchella (morel mushrooms) between rows of apple trees on orchard soil properties and apple tree performance, a field experiment was conducted using a cultivation system combining small-arch tunnels with plastic film covering. The Morchella was interplanted in a five-year-old apple orchard, with plots without Morchella cultivation serving as the control. Measurements included Morchella yield and quality, apple fruit quality, and leaf photosynthetic performance. Additionally, soil physicochemical properties and enzyme activities were analyzed across the 0–40 cm soil layer at different depths. The results demonstrated that: (1) Intercropping Morchella in apple interrows proved to be agronomically feasible, yielding a fresh mushroom production of 1333.74 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, 6.73 mg/kg, 38.30 g/kg, 411.86 μ mol/h/g, and 9.89 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 418.37 mg/kg and 28.45 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) Interplanting Morchella improved apple fruit quality to a certain extent, significantly increasing individual fruit fresh weight, fruit shape index, and the contents of reducing sugars, total sugars, and soluble solids. (4) Interplanting Morchella also enhanced the photosynthetic rate of apple trees to some degree, significantly increasing transpiration rate, intercellular CO2 concentration, and stomatal conductance. Collectively, interplanting Morchella in apple orchards can produce a reasonably high yield of high-quality mushrooms, increase individual apple fruit fresh weight, improve the physicochemical properties of the 0–20 cm soil layer, and enhance the photosynthetic performance of the apple trees. These combined benefits demonstrate clear practical potential and support the promotion and application of this intercropping system in orchard production.