Regulation of climate, soil and hydrological factors on macrophyte biomass allocation for coastal and inland wetlands in China

Knowledge of root: shoot ratio (R/S) is fundamental for our understanding of carbon allocation and storage in terrestrial ecosystems. Due to the periodic variation of water table and the difficulty of measuring belowground biomass (BGB), macrophyte biomass allocation in both coastal and inland wetlands remains unclear, especially at regional scale. In this study, 131 records of biomass allocation in wetlands were collected to examine general pattern of macrophyte R/S in relation to climate, soil, and hydrological factors in China using model selection and variance decomposition analysis. Our results showed that coastal wetlands supported higher aboveground biomass (AGB, 3.1 kg m⁻²) but a lower R/S (1.2) than inland ones (1.47 kg m⁻² and 3.1, respectively). The positive relationships between AGB and BGB and between BGB and R/S in coastal wetlands were significantly different from those in inland wetlands, while only inland wetlands exhibited a significant negative correlation between R/S and AGB (R² = 0.19, p < 0.001). Among climate (i.e., mean annual temperature and precipitation), soil (e.g., pH, salinity, soil organic carbon, soil nitrogen and phosphorus concentration), and hydrological (water level and depth for coastal and inland wetlands, respectively) properties, the latter two groups explained 64% and 31% of spatial variation for inland and coastal R/S, respectively, compared with climate (2.7% and 1.5%, respectively). Specifically, soil salinity was the most important factor in regulating R/S for coastal wetlands, while, for inland wetlands, it was soil phosphorus. This study highlights the importance of hydrology, soil salinity and nutrients on wetland R/S and BGB estimation, which could be incorporated into wetland ecosystem models to improve prediction performance for carbon dynamics and their feedbacks to climate change in the future.