Mangroves are among the world's most carbon-dense ecosystems, but have suffered extensive deforestation, prompting reforestation projects. The effects of mangrove reforestation on belowground carbon dynamics are poorly understood. In particular, we do not know how fine root production develops following mangrove reforestation, despite fine root production being a major carbon sink and an important control of mangrove soil accretion.Using minirhizotrons, we investigated fine root production and its depth variation along a chronosequence of mature Vietnamese mangroves.Our results showed that fine root production decreases strongly with stand age in the uppermost 32 cm of our soil profiles. In younger mangrove stands, fine root production declines with depth, possibly due to a vertical gradient in soil nutrient availability; while root production in the oldest stand is low at all depths and exhibits no clear vertical pattern. A major fraction of fine root production occurs deeper than 30 cm, depths that are commonly omitted from calculations of mangrove carbon budgets.Younger mangroves may accrue shallow soil organic matter faster than older mangroves. Therefore, root productivity and forest stand age should be accounted for when forecasting mangrove carbon budgets and resistance to sea-level rise.

Among the various methane activation reactions, oleum-mediated (SO3–H2SO4) methane oxidation to methyl bisulfate (MBS), a methanol precursor, is one of the best methods in terms of methane conversion and product selectivity. In this report, we investigated the effect of the catalyst concentration on the MBS yield using the catalyst systems (bpym)­PtCl2, K2PtCl4, and (DMSO)2PtCl2 at 180 °C for 3 h. (bpym)­PtCl2 showed a very high stability as well as a high MBS yield of over 84%, but its catalytic activity expressed in terms of turnovers for 3 h was in the range 50–500. K2PtCl4 showed very high catalyst turnovers of over 17 000 at a low catalyst concentration; however, it deactivated rapidly to PtCl2 which prevents achieving a high MBS yield that was achieved by (bpym)­PtCl2. However, (DMSO)2PtCl2 showed an enhanced catalytic performance for both the MBS yield and the turnovers. An MBS yield of over 84% with a selectivity of 94% was obtained at a catalyst concentration of 3.0 mM, and its turnovers reached over 19 000 at a low catalyst concentration. This higher catalytic performance of (DMSO)2PtCl2 compared to the other chloride-ligated Pt compounds is due to the DMSO ligand on the Pt, which increases the solubility of the Pt species in oleum. Furthermore, as the DFT study revealed, the low dissociation energy of DMSO from the Pt center can facilitate the coordination of methane on the Pt reaction center. Although (DMSO)2PtCl2 was deactivated to PtCl2 after the reaction like the other Pt compounds with the chloride ligand, it can be reactivated to some extent by adding DMSO.

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