Mangroves are recognized as one of the richest carbon storage systems. However, the factors regulating carbon sinks in mangrove ecosystems are still unclear, particularly in the subtropical mangroves. The biomass, production, litterfall, detrital export and decomposition of the dominant mangrove vegetation in subtropical (Kandelia obovata) and tropical (Avicennia marina) Taiwan were quantified from October 2011 to July 2014 to construct the carbon budgets. Despite the different tree species, a principal component analysis revealed the site or environmental conditions had a greater influence than the tree species on the carbon processes. For both species, the net production (NP) rates ranged from 10.86 to 27.64 Mg C ha year and were higher than the global average rate due to the high tree density. While most of the litterfall remained on the ground, a high percentage (72%-91%) of the ground litter decomposed within 1 year and fluxed out of the mangroves. However, human activities might cause a carbon flux into the mangroves and a lower NP rate. The rates of the organic carbon export and soil heterotrophic respiration were greater than the global mean values and those at other locations. Only a small percentage (3%-12%) of the NP was stored in the sediment. The carbon burial rates were much lower than the global average rate due to their faster decomposition, indicating that decomposition played a critical role in determining the burial rate in the sediment. The summation of the organic and inorganic carbon fluxes and soil heterotrophic respiration well exceeded the amount of litter decomposition, indicating an additional source of organic carbon that was unaccounted for by decomposition in the sediment. Sediment-stable isotope analyses further suggest that the trapping of organic matter from upstream rivers or adjacent waters contributed more to the mangrove carbon sinks than the actual production of the mangrove trees.

The effect of a ligand on the electron deficiency and Lewis acidity of the Cp*-substituted boron dication has been investigated experimentally and theoretically. In addition to the reported IMes- and N-heterocyclic olefin (NHO)-stabilized boron dications, the related cyclic alkylamino carbene (CAAC)-coordinated boron mono- and dications have also been synthesized and structurally characterized. An electrochemical study of dications [3a-3c] confirms the higher electron deficiency of the dicationic system than the related boron monocations. Moreover, the presence of a π-acidic CAAC ligand is critical for realizing stable radical species generated from the chemical reduction of boron cations. The nature of the axial ligand also significantly affects the selectivity of the hydride addition reaction of boron dications. While bulky superhydride reacts with [3a-3c] in the same manner to give the cyclic boreniums, [BH] attacks three different electrophilic sites of boron dications: the sp carbon of Cp* of the IMes-coordinated system ([3a]), the central boron atom of the NHO-stabilized analogue ([3b]), and the ylidene carbon of the CAAC-containing boron dication ([3c]).

Mangrove overgrowth could decrease biodiversity and increase flooding risk. Thinning has been proposed as a managerial action, which would decrease the capacity of mangroves for carbon sequestration. The aim of the present study was to examine the relationship between differences in mangrove tree density and carbon sequestration capacity. Three sampling sites were established in the Fangyuan mangroves of Taiwan, including seaward and landward sites with Avicennia marina and a site with Kandelia obovata, with control (C; no thinning), medium thinning (MT; 50% thinning) and high thinning (HT; only one tree left at the centre) treatments. The HT treatment significantly reduced the areal carbon sequestration rates (66–84%), but the reductions in the MT treatment were much lower (3–30%). Considering the carbon sequestration per tree, the HT treatment resulted in the significantly highest rates (two- to fivefold higher) than those under the MT and C treatments. Medium thinning appears to be the optimal strategy to meet the demand of reducing the loss of carbon sequestration capacity for mangrove management. Together, the data from in the present study and the relevant literature suggest a maximum level of carbon sequestration by managing the density to 30600treesha–1 for K. obovata and 10500treesha–1 for A. marina.

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