Interspecific variations in mangrove stem biomass: A potential storehouse of sequestered carbon

Abstract

Variations in stem biomass and carbon density in 12 mangrove species were studied to understand the potential of carbon storage in the live biomass of Bhitarkanika mangrove ecosystems, South-East Coast of India. The results highlighted significant inter-species variations (p<0.01; ANOVA) in the stem wood density and carbon content and could be attributed to the spatial variations in soil fertility, adaptation, freshwater supply, genus identity as well as properties of the fibre lumen and wall. Among the studied species, Avicennia officinalis showed the highest carbon density and Corg/Ntot ratios followed by Heritiera fomes. Further, the higher carbon sequestration capacity of these two mangrove species was confirmed through Principal Component Analysis (PCA). Corg, Corg/Ntot and cellulose/protein ratio were strongly associated with the wood density of the studied mangrove species. Mangrove stem diameter (at breast height; DBH), wood density and tree height were used to estimate the above-ground biomass of all the species, which showed remarkably higher biomass for Avicennia officinalis. Possible adaptation of these species under extreme environmental conditions in addition to variations in vessel wall thickness caused by differential carbon fixation and storage in the form of biomass could explain the variability in elemental properties of mangrove stem wood. Heritiera littoralis and Kandelia candel with relatively higher lignin to cellulose content showed greater potentials to sustain biotic and abiotic stresses and indicated higher carbon sequestration as recalcitrant biomass. The lowest carbon density and highest ratio of cellulose/lignin in the Sonneratia apetala and Sonneratia caseolaris species indicated faster plant growth compared to the other studied species. FTIR analysis evidenced that the increase in the 1728–1733 cm −1 band height assigned to cellulose and decrease in the 1517–1519 cm −1 band height assigned to lignin.