Mangrove forest degradation indicated by mangrove-derived organic matter in the Qinzhou Bay,Guangxi,China,and its response to the Asian monsoon during the Holocene climatic optimum

The response of mangrove ecosystems to the Asian monsoon in the future global warming can be understood by reconstructing the development of mangrove forests during the Holocene climatic optimum（HCO）, using proxies preserved in coastal sediments. The total organic matter in sediments of a segmented core, with calibrated age ranges between 5.6 and 7.7 cal. ka BP and corresponding to the HCO, from the Qinzhou Bay in Guangxi, China, is quantitatively partitioned into three end-members according to their sources： mangrove-derived, terrigenous,and marine phytoplanktonic, using a three-end-member model depicted by organic carbon isotope（δ13Corg） and the molar ratio of total organic carbon to total nitrogen（C/N）. The percentage of mangrove-derived organic matter（MOM） contribution is used as a proxy for mangrove development. Three visible drops in MOM contribution occurred at ca. 7.3, ca. 6.9, and ca. 6.2 cal. ka BP, respectively, are recognized against a relatively stable and higher MOM contribution level, indicating that three distinct mangrove forest degradations occurred in the Qinzhou Bay during the HCO. The three mangrove forest degradations approximately correspond to the time of the strengthened/weakened Asian winter/summer monsoon. This indicates that even during a period favorable for the mangrove development, such as the HCO, climatic extremes, such as cold and dry events driven by the strengthened/weakened Asian winter/summer monsoon, can trigger the degradation of mangrove forests.

The potential of contribution of mangrove-derived organic matter in intertidal sediments as a proxy of mangrove development in the northern Beibu Gulf

Located between terrestrial and marine ecosystems,mangrove forests are sensitive to changes in climate.The responses of mangrove ecosystems to climate change in the future can be understood by reconstructing past mangrove dynamics using proxies preserved in the intertidal sediments.Considering the complexity of the proxies commonly used,it is necessary to develop a relatively simple,inexpensive proxy.In this study,available chemical tracers(δ13Corg and C:N)of the four cores(YLW02,YLW03,O18,and Q37)from the intertidal zone of the northern Beibu Gulf(NBG)and a three-end-member(mangrove,sea grass,and suspended particulate matter)model was utilized to determine the contribution of mangrove-derived organic matter(CMOM)in carbonate-free sediments.Compared with the summed concentration of mangrove pollen(SCMP),a significant positive correlation between CMOM and SCMP is displayed.The calculated CMOM for an additional 210Pb-dated sediment core from the Yingluo Bay,NBG(YLW01)clearly indicates a mangrove development going through degradation,flourishing,relative degradation,and relative flourishing,which are separately in correspondence with the lowest,highest,lower,and higher air temperature and rainfall in the time intervals of 1890–1918 AD,1919–1956 AD,1957–1990 AD,and 1991–2010 AD.This suggests that CMOM preserved in intertidal sediments has a potential to reconstruct historical mangrove development in high resolution,at the very least,along the coasts of the NBG.

Polyoxygenated dihydropyrano[2,3-c]pyrrole-4,5-dione derivatives from the marine mangrove-derived endophytic fungus Penicillium brocae MA-231 and their antimicrobial activity

A new polyoxygenated dihydropyrano[2,3-c]pyrrole-4,5-dione derivative, pyranonigrin F （1）, together with a related known compound, pyranonigrin A （2）, were isolated and identified from Penicillium brocae MA-231, an endophytic fungus obtained from the fresh tissue of the marine mangrove plant Avicennia marina. The structures of these metabolites were determined based on comprehensive spectral interpretation and the absolute configuration of compound 1 was established by X-ray crystallographic analysis. Compounds 1 and 2 showed potent activity against a broad spectrum of human-, aqua-, and plant-pathogens.

Polyketides with potential bioactivities from the mangrove‑derived fungus Talaromyces sp.WHUF0362

Metabolites of microorganisms have long been considered as potential sources for drug discovery.In this study,fve new depsidone derivatives,talaronins A-E(1-5)and three new xanthone derivatives,talaronins F-H(6-8),together with 16 known compounds(9-24),were isolated from the ethyl acetate extract of the mangrove-derived fungus Talaromyces species WHUF0362.The structures were elucidated by analysis of spectroscopic data and chemical methods including alkaline hydrolysis and Mosher’s method.Compounds 1 and 2 each attached a dimethyl acetal group at the aromatic ring.A putative biogenetic relationship of the isolated metabolites was presented and suggested that the depsidones and the xanthones probably had the same biosynthetic precursors such as chrysophanol or rheochrysidin.The antimicrobial activity assay indicated that compounds 5,9,10,and 14 showed potent activity against Helicobacter pylori with minimum inhibitory concentration(MIC)values in the range of 2.42-36.04μmol/L.While secalonic acid D(19)demonstrated signifcant antimicrobial activity against four strains of H.pylori with MIC values in the range of 0.20 to 1.57μmol/L.Furthermore,secalonic acid D(19)exhibited cytotoxicity against cancer cell lines Bel-7402 and HCT-116 with IC_(50) values of 0.15 and 0.19μmol/L,respectively.The structure–activity relationship of depsidone derivatives revealed that the presence of the lactone ring and the hydroxyl at C-10 was crucial to the antimicrobial activity against H.pylori.The depsidone derivatives are promising leads to inhibit H.pylori and provide an avenue for further development of novel antibiotics.