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Strict stoichiometric homeostasis of Cryptomonas pyrenoidifera (Cryptophyceae) in relation to N:P supply ratios

Eloísa Ramos Rodríguez, Carmen Pérez-Martínez, José María Conde-Porcuna
  • Eloísa Ramos Rodríguez
    Granada University, Spain | eloisa@ugr.es
  • Carmen Pérez-Martínez
    Granada University, Spain
  • José María Conde-Porcuna
    Granada University, Spain

Abstract

A common freshwater cryptophyte, Cryptomonas pyrenoidifera, was cultivated in batch-cultures to analyze intraspecific variation in elemental stoichiometry along a broad gradient of pulsed phosphorus (P) enrichment during the early acclimation period and to determine the immediate homeostatic capacity of the nitrogen-to-phosphorus (N:P) ratio of this alga when nutrients are at saturating levels. Experimental results revealed that nitrogen (N) and P cell quotas significantly increased with increasing P concentration. However, despite the wide range of N:P ratios in the medium, Cryptomonas N:P ratios were highly stable at higher P-level treatments, indicating a highly conservative behavior and suggesting strict elemental homeostasis when nutrients are at saturating levels. The strictly homeostatic N:P ratio appears to be attributable to their high potential for a fast luxury consumption of both N and P after a brief and intense episode of increased resource availability and to physiological limits on their nutrient storage capacity. Most importantly, the N:P biomass ratio at nutrient saturating levels converged around 11:1, which was the observed ratio of maximum internal cell quotas for N and P (i.e. Qmax,N:Qmax,P) under the prevailing experimental conditions. This value is particularly informative for C. pyrenoidifera because it represents cell storage quotients and may be a taxon-specific evolutionary optimum, providing a reference point to infer the grade of nutrient-limitation. The experimental data give ranges of variation in C. pyrenoidifera elemental composition permitting, among others, proper parameterization of cryptophyte stoichiometry models.

Keywords

Cryptomonas pyrenoidifera; ecological stoichiometry; elemental homeostasis; optimal N:P ratio; luxury storage capacity

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Submitted: 2016-04-13 13:08:57
Published: 2016-11-15 00:00:00
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Copyright (c) 2016 Eloísa Ramos Rodríguez, Carmen Pérez-Martínez, José María Conde-Porcuna

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