The above and the belowground nitrogen allocation strategy of Scirpus mariqueter based on 15N isotope tracing along an elevation gradient and its significance for coastal wetlands restoration

Background Ecological restoration of coastal wetlands has become particularly urgent worldwide as wetland areas have declined dramatically over the past two decades. Aims To understand the nitrogen allocation strategy of Scirpus mariqueter (S. mariqueter) and provide theory support for future wetland management and restoration. Methods The study investigated the response mechanism of S. mariqueter to altitude spatial changes in Nanhui Dongtan from 2017 to 2019 using remote sensing imagery and field surveys. The ecological adaptability of S. mariqueter at different elevations (denoted as A, B, and C for elevations 2.40, 3.15, and 3.49 m, respectively) was analyzed through 15N stable isotope tracing technology. In July and September 2020, 15N‐enriched urea solution was uniformly sprayed onto the leaf surfaces of S. mariqueter at different sites. Plant samples were collected at the end of July and September, and the aboveground, belowground, seed, and rhizome biomass were measured, followed by 15N isotope tests. Results (1) From 2017 to 2019, the biomass of S. mariqueter significantly increased in the elevation change of 0.44–0.48 m, with the maximum aboveground biomass increase of 488.70 g dm−2. The density also increased significantly in the elevation change of 0.13–0.43 m, peaking at 674.02 plants m−2; (2) during the growing period, the biomass of A, B, and C increased. The aboveground portion of the 15N allocation rate accounted for 74%–84%. The belowground portion of the 15N allocation rate positively correlated with elevation; (3) during the reproductive period, elevation positively correlated with the 15N distribution rate of seeds and corms, as well as the biomass allocation rate of seeds and aboveground portions. The 15N allocation rate of the corms was higher than that of seeds. Additionally, elevation exhibited a negative correlation with belowground biomass allocation rate. (4) Point A has the highest difference of above and belowground biomass proportion, and 15N isotope allocation. Area of point A is the critical area affecting vegetation expansion and should be paid more attention in the future work of coastal management and restoration. Conclusion There is an adaption strategy of S. mariqueter that affects the plant‐soil interaction and the biogeomorphological development process along the elevation gradient.