Effects of Long-Term Nutrient Input on Progeny Seed Nutrient Contents, Germination and Early Growth Characteristics of Typical Coastal Wetland Plants

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Seed reproduction is a vital stage in the life cycle of plants. In coastal wetlands, where nutrient regimes are increasingly altered by climate change and anthropogenic inputs, understanding how long-term nutrient enrichment affects progeny seed germination and early seedling establishment is essential for predicting vegetation shifts. In this study, we conducted a long-term nutrient addition experiment (2015–2024) in the Yellow River Delta with three nitrogen (N) and phosphorus (P) supply levels (Low, Medium, and High) and three N:P ratios (5:1, 15:1, and 45:1) to examine the effects of nutrient enrichment on seed nutrient contents, germination, and early seedling growth characteristics of Suaeda salsa and Phragmites australis measured in late 2024. Results showed that long-term fertilization increased the P content in S. salsa seeds by 17.1% to 146.0%, whereas N content was less influenced. In contrast, both N and P contents of P. australis seeds remained relatively stable across treatments. The seed germination and early seedling growth of the two species responded differently to various fertilization treatments. S. salsa seeds showed higher sensitivity to long-term fertilization, with improved behaviors under high nutrient level or 5:1 supply ratio. In contrast, P. australis performed better under medium nutrient level or higher N:P ratios (15:1 or 45:1). Correlation analysis indicated that P content in S. salsa seeds was significantly positively correlated with germination percentage, germination rate, germination index, and early seedling biomass, while N content was significantly correlated only with biomass. No significant correlations were observed between seed nutrients and germination or early seedling growth in P. australis. These findings underscore species-specific strategies in response to long-term nutrient enrichment and may ultimately influence species coexistence, community succession, and the resilience of coastal wetlands under ongoing global change.

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