Effects of grass intercropping on root physiology and morphology of olive seedlings under varying water conditions

In the present study, the effects of intercropping grasses on the physiology and morphology of olive roots were examined under different water conditions to provide scientific and feasible guidance for optimizing the grass pattern and strengthening the ecological management of olive orchards. The experiment used the 2-year-old Olea europaea variety "Arbequina" as the test material and divided the material into three groups, including planted Paspalum notatum and Trifolium repens and no grass treatment as the control. Different amounts of irrigation were used each time, including 300, 350, 400, 450, and 500 mL. After sampling, the physiological and morphological indexes of olive roots were measured. The results demonstrated that 1) intercropping with grass improved the root vigor, the active absorbing surface area, the ratio of the active absorbing surface area to the total absorbing surface area of the olive roots, and intercropping grasses reduced the superoxide anion production rate and malondialdehyde (MDA) content of olive root, increased the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and the content of proline, soluble protein, and soluble sugar in the olive root, thus enhancing the root osmotic adjustment function; 2) intercropping grasses significantly improved the total root length, surface area, root volume, and root tip number of the olive roots, and the root average diameter indicated an increasing tendency when the two species of grasses were intercropped. Intercropping grasses could also increase root dry weight, shoot dry weight, and root-to-shoot ratio. Based on a comparison of these treatments, intercropping P. notatum with 450 mL of irrigation each time demonstrated the best growth and development of the olive roots.