Hydrologic-induced concentrated soil nutrients and improved plant growth increased carbon storage in a floodplain wetland over wet-dry alternating zones

Hydrological gradient variations in wetlands have a vital impact on wetland carbon storage. However, the mechanisms by which hydrological gradient variations affect biomass and carbon storage by regulating the soil nutrient contents and plant diversity remain unclear. This study attempted to explore these influencing mechanisms by studying the relationships between hydrological gradient variations and carbon storage in wetlands. The results showed that the average nutrient content, plant biomass and soil carbon content values in the high-frequency wet-dry alternating zones (HFWA, zones where the frequency of water level occurs between -25 cm and 25 cm greater than 0.5) were 1.4 times, 2.3 times and 0.43 higher, respectively, than those in the low-frequency wet-dry alternating zones (LFWA, zones where the frequency of water level occurs between -25 cm and 25 cm less than 0.3). These results indicated that the HFWA zones had higher soil nutrients, higher plant dominance, higher biomass and higher soil carbon contents than the LFWA zones. The structural equation model revealed a significant positive correlation between wet-dry alternations and the soil nutrient-plant biomass-soil carbon relation in wetlands. Moreover, there was also a significant positive correlation between wet-dry alternations and the plant dominance-plant biomass-soil carbon relation in wetlands. This implied that the concentrated effect of HFWA on soil nutrients promotes plant growth, enhances plant dominance, promotes plant productivity, and enhances the capacities of plants to input carbon to the soil, thereby increasing the soil carbon content. This study closely linked wetland hydrological gradients, plant biodiversity and wetland carbon sequestration and profoundly revealed the mechanisms by which hydrological gradients in wetlands regulate the concentrations of nutrient elements, thereby affecting vegetation growth and carbon sequestration; these results could provide a new cognitive basis for understanding the coupling of carbon and water.