Top-down control on major groups of global marine diazotrophs  

作　　者：Hua Wang Ya-Wei Luo 

机构地区：[1]State Key Laboratory of Marine Environmental Science,Xiamen University,Xiamen 361102,China [2]College of Ocean and Earth Sciences,Xiamen University,Xiamen 361102,China

出　　处：《Acta Oceanologica Sinica》2022年第8期111-119,共9页海洋学报（英文版）

基　　金：The National Natural Science Foundation of China under contract Nos 41890802 and 42076153。

摘　　要：Dinitrogen(N_(2))fixed by a group of prokaryotes(diazotrophs)is the dominant process adding bioavailable nitrogen into the ocean.Although it has been intensively studied how N_(2) fixation is controlled by resources(bottom-up factors),it is unclear whether the grazing(top-down control)effectively impacts growth and distribution of different diazotroph groups.In this study,we evaluate this question by conducting log-log regression of diazotroph biomass onto corresponding N_(2) fixation rates in the global ocean.The slope of the regression for Trichodesmium is~0.8,indicating that a small portion of the increase in N_(2) fixation does not accumulate as its biomass.This leads to a conclusion that Trichodesmium is under a substantial top-down control,although bottom-up control still dominates.We also analyze the residuals of the regression in the North Atlantic,concluding that free trichomes of Trichodesmium are subject to stronger top-down control than its colonies.The weak correlation between the biomass and N_(2) fixation of unicellular cyanobacterial diazotrophs indicates that the degree of top-down control on this type of diazotrophs varies greatly.The analyses obtain unrealistic results for diatom-diazotroph assemblages due to complicated nitrogen sources of these symbioses.Our study reveals the variability of top-down control among different diazotroph groups across time and space,suggesting its importance in improving our understandings of ecology of diazotrophs and predictions of N_(2) fixation in biogeochemical models.Measurements of size-specific N_(2) fixation rates and growth rates of different diazotroph groups can be useful to more reliably analyze the top-down control on these key organisms in the global ocean.

关 键 词：marine diazotrophs nitrogen fixation top-down control bottom-up control TRICHODESMIUM diatom-diazotroph assemblages 

分 类 号：Q938.8[生物学—微生物学]