Relative Influence Of Salinity In The Flow And Accumulation Of Organic Carbon In Open-water Karstic Mangroves

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Abstract
Carbonate - open-water mangroves have high OC content, apparently due to sediments’ biophysical characteristics. However, the role of key regulators such as salinity and hydroperiod, which modulate the forest structure and therefore carbon dynamics, has been little explored. This study evaluates the influence of salinity on the accumulation of aerial and underground OC (production of litter and roots), in open-water karstic forests. For this purpose, an experimental design was implemented on San Andrés Island, where there is an edaphic salinity gradient because of the water regime. Three physiographic types of mangroves characterized by different saline regimes were selected. Two inland forests of mesohaline regime (9.63 ± 6.26 and 11.54 ± 7.46 PSU), a euhaline fringe forest (37.47 ± 5.76 PSU), and a hyperhaline regime basin forest (62.36 ± 10.54 PSU). The working hypothesis was the existence of an inverse relationship between salinity and litter production, and a direct relationship between salinity and root production. Root production was evaluated using the growth core implantation technique (108 soil cores), selecting live roots according to diameter (<2, 2-5 and 5-20 mm). The mean (±SD) OC content in dry litter (Mg C ha-1 y-1) was 8.96 ± 0.28; 5.57 ± 0.15; 6.31 ± 0.27; and 4.54 ± 0.8; while the production of dry roots was 0.41 ± 0.08; 1.19 ± 0.46; 1.30 ± 0.5 and 0.24 ± 0.20, for the mesohaline forests, the euhaline forest and the hyperhaline forest, respectively. The proposed hypothesis was sustained among forests with marked salinity ranges. Leaf litter production was not very high in forests with intermediate salinity, and root production was very low in high salinity, suggesting that salinity acts in synergy with other variables influencing the species composition and their functioning. These results affirm the high productivity of carbonate environments and the contribution of autochthonous production.

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