Effects of mowing frequency on the growth performance of Spartina alterniflora and its competitive intensity with native plants

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Spartina alterniflora (S. alterniflora) is one of the most aggressive invasive alien plant species in China's coastal wetlands, posing serious threats to wetland ecosystem structure, functioning, and biodiversity. In this study, S. alterniflora collected from the coastal wetlands of Tangshan, Hebei Province, China, was grown in a controlled pot experiment. Four mowing treatments (0, 1, 2, and 3 mowing events) were applied at 30-day intervals. The growth performance of different reproductive types of S. alterniflora (Ramets, Seedlings, and Mixture) was evaluated under competition with the native dominant species Phragmites australis and Suaeda salsa. Basal diameter, Number of blades, Height, Fresh weight, and Dry weight were measured, and the absolute growth rate (r), relative neighbor effect (RNE), and interaction strength (I) were calculated to assess the effects of mowing frequency on plant growth and competitive interactions. The results showed that: (1) Mowing significantly suppressed the growth of S. alterniflora, and the inhibitory effect increased with mowing frequency. Fresh weight (p = 0.001–0.008) and Dry weight (p < 0.001–0.012) were the most sensitive indicators of mowing disturbance. A single mowing event significantly reduced biomass accumulation, whereas repeated mowing (two or three events) further suppressed plant growth. (2) Competitive intensity differed among competitive scenarios. Under the same mowing frequency, Phragmites australis exerted stronger competitive suppression on S. alterniflora than Suaeda salsa. (3) The three reproductive types also responded differently to mowing and competition. Ramets consistently maintained higher growth performance and stability than the other reproductive types, Mixture showed intermediate performance, whereas Seedlings were the most sensitive to frequent mowing and competitive stress, suggesting that clonal reproduction enhances the tolerance of S. alterniflora to mowing disturbance. These findings provide a theoretical basis for optimizing mowing-based management strategies for S. alterniflora and promoting ecological restoration of invaded coastal wetlands.

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