Spartina alterniflora invasion enhances sediment nitrification processes in coastal wetland

Abstract

Aims

Spartina alterniflora (S. alterniflora) invasion notably impacts sediment nitrogen (N) biogeochemical processes in coastal wetlands. However, its effects on different nitrification processes and their mechanisms in both surface (0–10 cm) and subsurface (10–20 cm) sediments remain unclear.

Methods

Potential nitrification rates mediated by ammonia-oxidizing archaea (AOA), bacteria (AOB), and comammox Nitrospira (PAR_AOA, PAR_AOB, and comammox rates), their relative contributions, functional genes (AOA, AOB, and Ntsp-aomA), and controlling factors were investigated in both surface and subsurface sediments of native Cyperus malacensis and adjacent S. alterniflora-invaded habitats with varying years (6, 10, and 14 years) in the Minjiang River Estuary, China.

Results

These three nitrification rates varied both spatially and seasonally. Summer nitrification rates (5.57 ± 2.28 μg N g^–1 d^–1) in both surface (0–10 cm) and subsurface (10–20 cm) sediments of these ecosystems were substantially higher than winter levels (3.78 ± 1.76 μg N g^–1 d^–1). S. alterniflora invasion increased nitrification rates (39.54–68.13%) and associated functional gene abundances (28.08–52.92%) in both seasons, with surface sediments (118.40–153.85%) markedly showing higher values than subsurface layers (32.80–73.17%). Additionally, the relative contribution of PAR_AOA in nitrification exhibited a marked enhancement with the S. alterniflora invasion. PLS-PM results further indicated that the spatiotemporal fluctuations in sediment nitrification rates were predominantly driven by organic matter accumulation and ambient temperature.

Conclusions

These findings highlight the substantial influence of S. alterniflora invasion on sediment nitrification dynamics, providing fundamental data for estimating N budgets and turnover in the estuarine wetlands.