Abstract: 【Objective】The effects of straw mat and other mulching materials on apple roots and leaves in different seasons were revealed, which provided a basis for the reasonable mulching in the orchard.【Method】In the spring (April 18), the materials of straw mat, agricultural carpet, horticultural fabric and transparent plastic film were mulched on the ground of 3-year-old Starkrimson apple tree (Malus domestica Borkh), respectively, the clean tillage was used as control. It was measured that the changes of root activity, nitric oxide (NO) production rate, nitrate reductase (NR) activity, nitric oxide synthase (NOS) activity in roots, net photosynthetic rate and other physiological parameters in the next mid-spring, late summer, mid-autumn and early winter. The plant growth root architecture were analyzed in autumn and winter.【Result】The changes of root activity, root NO production rate, leaf Pn and other physiological parameters were significantly different among the four mulchings in different seasons. In spring, the root activity, root NR and NOS activity, and NO production were increased after the mulching treatment, especially the transparent plastic film and agricultural carpet increased them more. In summer, they were also increased under the straw mat and agricultural carpets treatments, but were significantly reduced under transparent plastic film treatment. In the autumn, the activities of NR and NOS were increased under the four mulching treatments. In the early winter, the values of above root physiological parameters all increased significantly under the mulching of straw mat, agricultural carpet and horticultural fabric. Straw mat had more significant effects on root physiological characteristic than other mulching materials in the year except spring. The four treatments reduced the coefficient of variation of all the root physiological parameters, among which the agricultural carpet was the smallest, while transparent plastic film was the largest. The four mulching enhanced the leaf Pn in late summer, mid-autumn and early winter, improved leaf water use efficiency (WUE) in the autumn, increased the total length, diameter, volume and fractal dimension of the roots in the early winter, and promoted shoot growth and trunk thickening. The effects of straw mat and agricultural carpet mulching were more significant than other two materials. The straw mat had the most significant effects on the improvement of root physiological characteristics, and morphological structure, the increase of leaf photosynthetic characteristics and the promotion of plant growth. The effect of agricultural carpets on root fractal dimension is similar to that of straw mat, which is higher than that of horticultural fabric and transparent plastic films in autumn, and the stability of agricultural carpets on the changes of root physiology is most prominent. The effects of horticultural fabric on leaf Pn were less than that of straw mat in late summer and mid-autumn, and its effect on root physiological parameters was less stable than that of agricultural carpet. The transparent plastic film reduced the root activity in the late summer and mid-autumn. In the four treatments, transparent plastic film had the least effect on leaf WUE as well as on plant growth in autumn, and the stability on root physiological changes was also minimal.【Conclusion】From the beneficial effects of the four mulching materials on root activity, root architecture, photosynthesis, water use efficiency, plant growth and root physiological changes, straw mat is the best.

Key words: young apple tree, straw mat, mulching, photosynthesis, root architecture, nitric oxide