Response of heterotrophic and autotrophic microbial plankton to inorganic and organic inputs along a latitudinal transect in the Atlantic Ocean

[摘要] The effects of inorganic and/or organic nutrient inputs on phytoplankton andheterotrophic bacteria have never been concurrently assessed in open oceanoligotrophic communities over a wide spatial gradient. We studied theeffects of potentially limiting inorganic (nitrate, ammonium, phosphate,silica) and organic nutrient (glucose, aminoacids) inputs added separatelyas well as jointly, on microbial plankton biomass, community structure andmetabolism in five microcosm experiments conducted along a latitudinaltransect in the Atlantic Ocean (from 26° N to 29° S).

Primary production rates increased up to 1.8-fold. Bacterial respiration andmicrobial community respiration increased up to 14.3 and 12.7-foldrespectively. Bacterial production and bacterial growth efficiency increasedup to 58.8-fold and 2.5-fold respectively. The largest increases weremeasured after mixed inorganic-organic nutrients additions. Changes inmicrobial plankton biomass were small as compared with those in metabolicrates. A north to south increase in the response of heterotrophic bacteriawas observed, which could be related to a latitudinal gradient in phosphorusavailability. Our results suggest that organic matter inputs will result ina predominantly heterotrophic versus autotrophic response and in increasesin bacterial growth efficiency, particularly in the southern hemisphere.Subtle differences in the initial environmental and biological conditionsare likely to result in differential microbial responses to inorganic andorganic matter inputs.

[学科分类] 地球化学与岩石