Controlling factors on the global distribution of a representative marine non-cyanobacterial diazotroph phylotype (Gamma A)

[摘要] Non-cyanobacterial diazotrophs may be contributors to globalmarine N 2 fixation, although the factors controlling their distributionare unclear. Here, we explored what controls the distribution of the mostsampled non-cyanobacterial diazotroph phylotype, Gamma A, in the globalocean. First, we represented Gamma A abundance by its nifH quantitative polymerase chain reaction (qPCR) copies reportedin the literature and analyzed its relationship to climatological biologicaland environmental conditions. There was a positive correlation between theGamma A abundance and local net primary production (NPP), and the maximalobserved Gamma A abundance increased with NPP and became saturated when NPPreached ∼  400 mg C m −2  d −1 . Additionally, ananalysis using a multivariate generalized additive model (GAM) revealed thatthe Gamma A abundance increased with light intensity but decreased withincreasing iron concentration. The GAM also showed a weak but significantpositive relationship between Gamma A abundance and silicate concentration,as well as a substantial elevation of Gamma A abundance when the nitrateconcentration was very high ( ≳  10  µ M). Usingthe GAM, these climatological factors together explained 43 % of thevariance in the Gamma A abundance. Second, in addition to the climatologicalbackground, we found that Gamma A abundance was elevated in mesoscalecyclonic eddies in high-productivity (climatological NPP  >  400 mg m −2  d −1 ) regions, implying that Gamma A can respond to mesoscalefeatures and benefit from nutrient inputs. Overall, our results suggest thatGamma A tends to inhabit ocean environments with high productivity and lowiron concentrations and therefore provide insight into the nichedifferentiation of Gamma A from cyanobacterial diazotrophs, which aregenerally most active in oligotrophic ocean regions and need a sufficientiron supply, although both groups prefer well-lit surface waters. Moresampling on Gamma A and other non-cyanobacterial diazotroph phylotypes isneeded to reveal the controlling mechanisms of heterotrophic N 2 fixation in the ocean.

[学科分类] 大气科学