Effects of Spartina alterniflora invasion on carbon, nitrogen, phosphorus and silicon stoichiometry in coastal saltmarsh wetlands

Spartina alterniflora is one of the most widespread invasive plants globally, with particularly rapid expansion in coastal wetlands of China, posing a severe threat to the structure and function of native ecosystems. Ecological stoichiometry serves as a fundamental theoretical framework for understanding its invasion mechanisms and informing ecological restoration, especially regarding its demand for silicon (Si) and interactions with carbon (C), nitrogen (N), and phosphorus (P). In the present study, sediment samples were collected from S. alterniflora habitats (SA), Phragmites australis habitats (PA), and mudflat habitats (MF) to quantify the concentrations and stoichiometric characteristics of various Si, C, N, and P fractions. The results demonstrated that compared to MF and PA, the invasion of S. alterniflora significantly increased the contents of bioavailable silicon (ASi) by 1.3–1.4 times, reaching up to 347.5 mg/kg in 0–40 cm surface sediments. Similarly, total carbon (TC) and total nitrogen (TN) increased by 1.2–1.4 times and 1.5–2.1 times, respectively, while total organic carbon (TOC) and dissolved organic carbon (DOC) were elevated by 1.7–3.0 times and 1.7–2.2 times in the 0–40 cm sediment layer. In contrast, bioavailable phosphorus (AP) markedly declined, with SA sediments containing only 15%–64% of the AP levels observed in PA and MF habitats across the 0–100 cm sediment. In SA sediments, ASi exhibited a significant positive correlation with C, N, P, and their stoichiometric ratios (C/N, C/P, N/P). These findings indicated that the invasion of S. alterniflora modified sediment physicochemical properties by enhancing Si availability and restructuring the C, N, and P stoichiometric characteristics, thereby creating a sediment condition favorable for its proliferation, and amplifying its ecological invasiveness.