Sensitivity of Trichodesmium erythraeum and Crocosphaera watsonii abundance and N2 fixation rates to varying NO3− and PO43− concentrations in batch cultures

Aquatic Microbial Ecology

Douglas G. Capone¹  Jill A. Sohm¹  Julien Dekaezemacker¹  Angela N. Knapp¹  Sophie Bonnet¹ 

关键词: N2 fixation;    Trichodesmium;    Crocosphaera;    Inhibition;    C:N:P ratio;   

DOI  :  10.3354/ame01577

学科分类：生物科学（综合）

来源: Inter-Research

【 摘 要 】

ABSTRACT: Batch cultures of Trichodesmium erythraeum, strain IMS101, and Crocosphaera watsonii, strain WH8501, were grown under metal- and vitamin-replete conditions to evaluate differences in diazotroph abundance and N₂ fixation rates as well as biomass C:N:P ratios resulting from changes in the concentrations of nitrate (NO₃⁻) and phosphate (PO₄³⁻) in culture media. Holding light levels and temperature constant, variations in culture NO₃⁻ and PO₄³⁻ concentrations included (N:P ratios in µM) 0:0.5, 5:1, 8:0.5, and 16:1. The abundance of both diazotrophs was greatest in the 16:1 and 5:1 N:P ratio treatments (i.e. those grown with 1 µM PO₄³⁻) while the highest N₂ fixation rates for both diazotrophs were observed in the 0:0.5 treatment (i.e. those grown in NO₃⁻-free media). Measurable but reduced (~25 to 50% of the rates in cultures grown with no NO₃⁻) N₂ fixation rates were evident in both T. erythraeum and C. watsonii cultures grown with up to 16 µM NO₃⁻. These results indicate that while diazotrophs grown in the presence of NO₃⁻ have significantly lower N₂ fixation rates than those not chronically exposed to NO₃⁻, these lower per cell N₂ fixation rates are compensated for by a greater abundance of diazotrophs in treatments with 1 µM PO₄³⁻ and result in comparable volume-integrated rates of N₂ fixation. Additionally, N₂ fixation rates for T. erythraeum and C. watsonii were comparable when normalized to carbon (biomass). Finally, the exponential-phase C:N:P biomass ratios of both diazotrophs were similar to each other as well as to previous studies and varied little among the treatments but increased, often significantly, between exponential and stationary growth phases.

【 授权许可】

Unknown