Effect of traffic stress on component traits and physiological metabolism of Euphorbia thymifolia

Euphorbia thymifolia is a wild native turfgrass germplasm resource. To explore its trampling tolerance and response mode to different traffic frequencies, namely mild (3 times per month), moderate (5 times per month), and severe (10 times per month), trampling simulation experiments were performed on potted E. thymifolia for 20 feet each time. After a month of treatment, the parameters including component traits, antioxidant enzyme activity, osmotic substance content, and chlorophyll content were determined to analyze the effects of traffic on the growth and physiology of E. thymifolia. 1) The response sequence of leaf traits to traffic was as follows: leaf number > leaf length > leaf area > leaf width > leaf thickness; the response sequence of stem traits to traffic was as follows: secondary branch number > longest length > total length > first-level branch number > internode length; and the response sequence of root traits to traffic was as follows: main root length > adventitious root length > main root diameter > lateral root number > adventitious root number. 2) Mild traffic increased leaf area and secondary branch number, while moderate and severe traffic limited the growth and regeneration of roots, stems, and leaves. 3) Trampling significantly affected the activities of peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and soluble protein (SP) content in stems and leaves (P < 0.05), but the physiological response and resistance of stems to traffic were stronger than those of leaves. Evaluated together, stems and leaves showed traffic tolerance. 4) By significantly increasing chlorophyll (Chl) content (P < 0.05), E. thymifolia reduced the influence of leaf number reduction caused by traffic on photosynthesis. Under traffic stress, the ratio of Chla/Chlb was relatively maintained, thus providing support for survival, growth, and resistance. In summary, the morphological and physiological metabolism of E. thymifolia adapted to different traffic frequencies to form traffic resistance, even at severe frequencies, leading to survival and growth. Therefore, E. thymifolia is suitable as a turfgrass for planting in steppingstone gaps.