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

• Main Authors: Eloísa Ramos Rodríguez, Carmen Pérez-Martínez, José María Conde-Porcuna
• Format: Article
• Language: English
• Published: PAGEPress Publications 2016-11-01
• Series: Journal of Limnology
• Subjects: Cryptomonas pyrenoidifera; ecological stoichiometry; elemental homeostasis; optimal N:P ratio; luxury storage capacity
• Online Access: http://www.jlimnol.it/index.php/jlimnol/article/view/1487

<p>A common freshwater cryptophyte, <em>Cryptomonas pyrenoidifera</em>, 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, <em>Cryptomonas</em> 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. <em>Q</em>_max,_N:<em>Q</em>_max,_P) under the prevailing experimental conditions. This value is particularly informative for <em>C. pyrenoidifera</em> 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 <em>C. pyrenoidifera </em>elemental composition permitting, among others, proper parameterization of cryptophyte stoichiometry models.</p>