Root productivity contributes to carbon storage and surface elevation adjustments in coastal wetlands

Abstract

Background and aims: Additions of organic matter in coastal wetlands contributes to blue carbon sequestration and adjustment to sea-level rise through vertical growth of substrates. To improve models of carbon sequestration and adaptation to sea-level rise, data of root mass and volume additions across tidal gradients are required. This study aims to characterise the influence of vegetation zonation and tidal position on root mass and volume dynamics within substrates. Methods: The root ingrowth technique was coupled with sediment cores to quantify below-ground root mass and volume production, standing stocks and turnover across two years to 90 cm depth at Kooweerup, Victoria, Australia. Measurements of vertical accretion quantified mineral sediment additions at the surface. Results: The results indicate a complex non-linear relationship between root production and tidal position, which is driven by variation in vegetation structure across mangrove (442–3427 g fine root mass m-2 yr-1), saltmarsh (540–860 g m-2 yr-1) and supratidal forest (599 g m-2 yr-1) zones. Fine root volume additions ranged from 274 to 4055 cm3 m-2 yr-1 across sampling locations. Root production was greatest for older mangroves and tidally defined optimal zones of production were evident for mangrove and saltmarsh. The live rooting zone extended beyond depths typically measured in studies, and for forested sampling locations, live roots were found as deep as 1.0 m. Conclusion: These data can be used to improve highly parameterised models accounting for carbon sequestration and substrate vertical adjustment across an intertidal gradient by quantifying both root mass and volume additions across the live rooting zone.