Carbon partitioning and allometric relationships between stem diameter and Total Organic Carbon (TOC) in plant components of Bruguiera gymnorrhiza (L.) Lamk. and Lumnitzera racemosa willd in a microtidal basin estuary in Sri Lanka

Abstract

The capacity of plants to sequester carbon depends on net primary productivity and pattern of biomass/carbon partitioning within the plant which is not well understood for mangroves. Above (A) to below (B)-ground carbon ratio (A/B) of both Bruguiera gymnorrhiza (L.) Lamk. and Lumnitzera racemosa Willd. from where micro-tidal conditions prevail, Negombo estuary, Sri Lanka (7°11′42.18″N- 79°50′47.50″E) was approximately 3, and more closely resembles that of terrestrial plants than mangroves in macro-tidal environments. Relatively low inundation frequency, duration and depth apparently promote aerial growth than root production. Wet oxidation without external heating, followed by colorimetric method was adopted to determine total organic carbon (TOC) of plant components. Except for leaves of L. racemosa, nearly half the biomass of all other components of the two species was composed of TOC. Statistically significant allometric relationships exist among TOC and dbh (diameter at breast height) of trees. It was found that 96.5% of TOC in L. racemosa was in sequestered form (in the wood) compared to B. gymnorrhiza which only accumulated 78.7% in sequestered form. Profuse branching of L. racemosa contributes to the higher carbon sequestration capacity