Patterns and drivers of local and species contributions to β-diversity of phytoplankton assemblages in the Changjiang River Estuary

The Changjiang River Estuary (CRE) and its offshore plumes host a diverse phytoplankton community; however, the spatiotemporal dynamics of these microorganisms and their environmental drivers remain poorly understood. This study aims to elucidate the spatiotemporal variations and environmental heterogeneity of phytoplankton communities in the CRE, as well as to understand the factors driving their assemblage. Utilizing ecological survey data collected from the CRE and adjacent waters during spring and summer from 2018 to 2020, we conducted a spatiotemporal analysis of phytoplankton β-diversity in the region. We decomposed β-diversity into species contributions to β-diversity (SCBD) and local contributions to β-diversity (LCBD) to examine spatial differences in phytoplankton diversity and the contributions of individual species within the community. Our findings reveal that spatial differences, primarily driven by water salinity and distance from the coastline, are key factors influencing the heterogeneity of phytoplankton community composition. Key species such as Skeletonema costatum, Melosira granulata, and M. granulata var. angustissima significantly affected β-diversity. Further, β-diversity decomposition reveals that community assembly is driven by interactive biogeochemical forces: salinity gradients shape spatial heterogeneity through runoff-seawater mixing, eutrophic conditions promote the dominance of nutrient-dependent taxa, and silica availability regulates diatom-to-flagellate succession. This study provides a methodological paradigm for analyzing phytoplankton community assembly mechanisms in estuaries, thereby offering scientific support for biogeography-based ecosystem management in the CRE.