Satellite-derived primary productivity and its spatial and temporal variability in the China seas

The spatial and temporal variability of primary productivity in the China seas from 2003 to 2005 was estimated using a size-fractionated primary productivity model. Primary productivity estimated from satellite-derived data showed spatial and temporal variability. Annual averaged primary productivity levels were 564.39, 363.08, 536.47, 413.88, 195.77, and 100.09 gCm2a1 in the Bohai Sea, northern Yellow Sea （YS）, southern YS, northern East China Sea （ECS）, southern ECS, and South China Sea （SCS）, respectively. Peaks of primary productivity appeared in spring （April-June） and fall （October and November） in the northern YS, southern YS, and southern ECS, while a single peak （June） appeared in the Bohai Sea and northem ECS. The SCS had two peaks in primary productivity, but these peaks occurred in winter （January） and summer （August）, with the winter peak far higher than the summer peak. Monthly averaged primary productivity values from 2003 to 2005 in the Bohai Sea and southern YS were higher than those in the other four seas during most months, while those in the southem ECS and SCS were the lowest. Primary productivity in spring （March-June in the southern ECS and April-July in the other five areas） contributed approximately 41% on average to the annual primary productivity in all the study seas except the SCS. The largest interannual variability also occurred in spring （average standard deviation = 6.68）, according to the satellite-derived estimates. The contribution during fall （October-January in the southern ECS and August-November in the other five areas） was approximately 33% on average; the primary productivity during this period also showed interannual variability. However, in the SCS, the winter （December-March） contribution was the highest （about 42%）, while the spring （April-July） contribution was the lowest （28%）. The SCS did share a feature with the other five areas： the larger the contribution, the larger the interarmual variability. Spatial and temporal variability of satellite-derived ocean primary productivity may be influenced by physicochemical environmental conditions, such as the chlorophyll-a concentration, sea surface temperature, photosynthetically available radiation, the seasonally reversed monsoon, river discharge, upwelling, and the Kuroshio and coastal currents.

The diversity and ecological significance of microbial traits potentially involved in B_(12) biosynthesis in the global ocean

Cobalamin(B_(12)),an essential nutrient and growth cofactor for many living organisms on Earth,can be fully synthesized only by selected prokaryotes in nature.Therefore,microbial communities related to B_(12) biosynthesis could serve as an example subsystem to disentangle the underlying ecological mechanisms balancing the function and taxonomic make-up of complex functional assemblages.By anchoring microbial traits potentially involved in B_(12) biosynthesis,we depict the biogeographic patterns of B_(12) biosynthesis genes and the taxa harboring them in the global ocean,despite the limitations of detecting de novo B_(12) synthesizers via metagenomes alone.Both the taxonomic and functional composition of B_(12) biosynthesis genes were strongly shaped by depth,differentiating the epipelagic zones from the mesopelagic layers.Functional genes related to B_(12) biosynthesis were relatively stably distributed across different oceans,but the taxa harboring them varied considerably,showing clear functional redundancy among microbial systems.Microbial taxa carrying B_(12) biosynthesis genes in the surface water were influenced by environmental factors such as temperature,oxygen,and nitrate.However,the composition of functional genes was only weakly associated with these environmental factors.Null model analyses demonstrated that determinism governed the variations in B_(12) biosynthesis genes,whereas a higher degree of stochasticity was associated with taxonomic variations.Significant associations were observed between the chlorophyll a concentration and B_(12) biosynthesis,confirming its importance in primary production in the global ocean.The results of this study reveal an essential ecological mechanism governing the assembly of microbes in nature:the environment selects for function rather than taxonomy;functional redundancy underlies stochastic community assembly.