Differences in the vertical accretion of sediment among mangrove species with different aerial root types

Abstract

As a type of zonal vegetation along tropical and subtropical coastlines, mangrove species have developed aerial root systems to adapt to their environment. However, little is known about the differences in the surface vertical accretion (SVA) of sediment among aerial root types. In this study, three typical mangrove species with different aerial root systems (Avicennia marina with pneumatophores, Bruguiera gymnorhiza with root knees, and Kandelia candel with plank roots) were investigated in Zhenzhu Bay of the Beibu Gulf, China. Vertical accretion and the total volume of aerial roots (VM) were monitored and calculated in three communities of these species along the intertidal gradient over three growing seasons (2017–2019). The results were as follows: (1) The differences in SVA and the accretion rate among the three mangrove species were significant (p < 0.01), and the highest accretion rate was detected in plank roots (1.51 cm year−1), followed by root knees (1.05 cm year−1) and pneumatophores (0.63 cm year−1). (2) The values of VM and annual increment in VM were highest for plank roots, followed by root knees and pneumatophores, and the differences in VM and the corresponding rate of increase among mangrove species were significant (p < 0.01). (3) SVA, the surface accretion rate and VM differed among hydrogeomorphic zones, with the highest values found in the seaward fringe, followed by the interior and the landward fringe. (4) Close linear relationships between VM and SVA and between VM annual increment and SVA rate were detected regardless of root type and hydrogeomorphic zone. We conclude that significant differences in SVA and the accretion rate exist among the three mangrove species, and that SVA and VM and VM annual increment and SVA rate exhibit a linear relationship.