查看更多>>摘要：Photosynthesis is the most important biochemical reaction on Earth.It has co-evolved and developed with the Earth,driving the biogeochemical cycle of all elements on the planet and serving as the only chemical process in nature that can convert light energy into chemical energy.Some heavy oxygen isotopic(18O)labeling experiments have"conclusively"demonstrated that the oxygen released by photosynthesis comes only from water and are written into textbooks.However,it is not difficult to find that bicarbonate has never been excluded from the direct substrate of pho-tosynthesis from beginning to end during the history of photosynthesis research.No convincing mechanism can be used to explain photosynthetic oxygen evolution solely from water photolysis.The bicarbonate effect,the Dole effect,the thermodynamic convenience of bicarbonate photolysis,the crystal structure characteristics of photosystem Ⅱ,and the reinterpretation of heavy oxygen isotopic labeling(18O)experiments all indicate that the photosynthetic oxygen evolution does not exclude the important role and contri-bution of bicarbonate photolysis.The recently proposed view that bicarbonate photolysis is the premise of water photolysis,bicarbonate photolysis and water photolysis work together with a 1∶1(mol/mol)stoichiometric rela-tionship,and the stoichiometric relationship between oxy-gen and carbon dioxide released during photosynthetic oxygen evolution is also 1∶1,has excellent applicability and objectivity,which can logically and reasonably explain the precise coordination between light and dark reactions during photosynthesis,the bicarbonate effect,the Dole effect,the Kok cycle and the neutrality of water and carbon in nature.This is of great significance for constructing the bionic artificial photosynthetic reactors and scientifically answer-ing the question of the source of elemental stoichiometric relationships in nature.
查看更多>>摘要：The Lichi volcanics are a suite of mafic-inter-mediate-felsic rocks and are considered coeval with the Abor volcanics(～132 Ma)of the Siang window in the Eastern Himalaya.Here,we present the first report of tra-chytic rocks from the Lichi volcanics,which are exposed in the Ranga valley,along the Kimin-Yazali road section in the Eastern Himalayan Region,Northeast India.The tra-chytes occur in close association with sandstones of the Gondwana Group of rocks and are characterised based on field,petrographical,and geochemical investigations.These fine-grained trachytes are composed of alkali feld-spar,biotite,plagioclase,sodic-amphibole,apatite,ill-menite,and titanite.The REE profiles of the evolved trachytic rocks(higher SiO2 content)display fractionated trends.The fractionation of accessory mineral phases,like apatite and titanite,was possibly responsible for the strongly fractionated REE patterns of the evolved samples.The trachytic rocks demonstrate high apatite saturation temperatures of 988±14 ℃(1σ,n=8).The Aluminium Saturation Index(＜1.1)and binary discrimination dia-grams of these peralkaline trachytes define their affinity with A-type granitoids.Elemental ratios like Y/Nb,Nb/U,and Ce/Pb signify that the Lichi trachytes are differentiated products of mantle-derived ocean island basalts.Trace elemental discrimination diagrams Th/Yb versus Nb/Yb,Y versus Nb,and Y+Nb versus Rb reflect a within-plate tectonic regime for the trachytes.From the results pre-sented in this work,we infer that the development of rifting events during the breakup of eastern Gondwana due to the onset of Kerguelen plume activity further led to under-plating of basic magma in lower crustal levels.These parental basaltic magmas underwent fractionation pro-cesses forming differentiated trachyandesites and trachytes.Taking into consideration the similarities recorded between the Lichi volcanics and Abor volcanics,this study supports the idea that Kerguelen plume activities resulted in the emplacement of these volcanics in the Eastern Himalayas.
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