Spartina alterniflora invasion decouples multiple elements in coastal wetland soils

From bedrock to life activity and atmospheric deposition: Drivers of soil element coupling across horizons

Unraveling the intricate coupling of multiple elements and their underlying drivers in natural soils is crucial for comprehending ecosystem functions, yet this knowledge has remained elusive. Using a comprehensive dataset of 900 soil samples collected from 116 sites across 26 mountains, this study dissected the coupling relationship of 23 elements within three soil development horizons, spanning five climate zones in China. Our findings revealed a robust continental-scale coupling of soil elements, influenced by plants and environmental factors including spatial distance, climate, soil properties, and atmospheric nitrogen deposition, accounting for 36% of the observed variance in element coupling. Notably, our study unveiled the horizon-specific nature of element coupling mechanisms. In the parent horizon, rock type exerted the primary control on the dynamics of element coupling. However, as soil developed, life activities and atmospheric deposition of anthropogenic trace metals concurrently reshaped the element coupling patterns, particularly in the organic and surficial mineral horizons. Elements were divided into two distinct elemental groups, exhibiting opposite fitting trends with atomic mass and crustal abundance, and the effect of these properties on coupling diminished with soil depth. Heavy metals enriched by human activity deviated from property-based predictions with lower coupling. This study represents the first continental-scale quantification of multi-element coupling across soil horizons, underscoring the paramount importance of life activity and atmospheric deposition in modulating the initial lithological-mediated multi-element coupling. Our insights advance understanding of terrestrial ecosystem biogeochemistry and urge further research on the impacts of anthropogenic activities and environmental changes on these delicate elemental interactions.

Context dependence masks the long-term harm of Spartina alterniflora invasion on macrobenthos in China

The invasion of Spartina alterniflora poses a significant threat to the biodiversity of tidal wetlands, including mangroves, native saltmarshes, and mudflats. However, its impact on macrobenthos, a key group within these ecosystems, remains a subject of debate. In a meta-analysis of 2411 data points from 105 studies on macrobenthos in China's tidal wetlands, we found that at the coastal scale of mainland China, S. alterniflora invasion did not significantly affect the abundance or diversity of macrobenthos. However, single-factor analysis showed strong spatiotemporal variation in the invasion's effects on macrobenthos, which obscured the negative effects of S. alterniflora in specific local areas. Key factors such as habitat type, temperature, tidal strength, seawater chemistry, and invasion duration play a critical role in shaping the extent of the invasion's impact. Our predictive model, which integrates these factors, suggests that 19.63% of China's tidal wetlands could experience dual losses in macrobenthos abundance and diversity within just one year of S. alterniflora invasion. This proportion increases to 34.03% after 10 years, and rises to as high as 61.85% after 20 years. These findings suggest that the negative effects of S. alterniflora on macrobenthos are often masked by context dependence. Therefore, it is crucial to identify and prioritize the protection of tidal wetlands at higher risk of invasion to safeguard macrobenthos communities and maintain their essential ecosystem services.

Spartina alterniflora invasion altered phosphorus retention and microbial phosphate solubilization of the Minjiang estuary wetland in southeastern China

Spartina alterniflora invasion is considered a critical event affecting sediment phosphorus (P) availability and stock. However, P retention and microbial phosphate solubilization in the sediments invaded with or without S. alterniflora have not been fully investigated. In this study, a sequential fractionation method and high-throughput sequencing were used to analyze P transformation and the underlying microbial mechanisms in the sediments of no plant (NP) zone, transition (T) zone, and plant (P) zone. Results showed that except for organic phosphate (OP), total phosphate (TP), inorganic phosphate (IP), and available phosphate (AP) all followed a significant decrease trend from the NP site to the T site, and to the P site. The vertical decrease of TP, IP, and AP was also observed with an increase in soil depth. Among the six IP fractions, Fe-P, Oc-P, and Ca10-P were the predominant forms, while the presence of S. alterniflora resulted in an obvious P depletion except for Ca8-P and Al-P. Although S. alterniflora invasion did not significantly alter the alpha diversity of phosphate-solubilizing bacteria (PSB) harboring phoD gene, several PSB belonging to p_Proteobacteria, p_Planctomycetes, and p_Cyanobacteriota showed close correlations with P speciation and IP fractions. Further correlation analysis revealed that the reduced soil pH, soil TN and soil EC, and the increased soil TOC mediated by the invasion of S. alterniflora also significantly correlated to these PSB. Overall, this study elucidates the linkage between PSB and P speciation and provides new insights into understanding P retention and microbial P transformation in the coastal sediment invaded by S. alterniflora.