Photosynthetic performance associated with phosphorus availability in mats of Didymosphenia geminata (Bacillariophyceae) from Patagonia (Argentina and Chile)

Abstract:

Recently reported blooms of Didymosphenia geminata from rivers in Argentinean and Chilean Patagonia, together with non-typical blooms reported from lake systems, have the potential to alter community and ecosystem dynamics of aquatic environments in the region. In an effort to quantify key aspects of ecosystem function of D. geminata mats in Patagonia, we describe for the first time photosynthesis–irradiance (P-E) curves of this species, associated P-E parameters (R, P_max and α) and their relationship to other functional (alkaline phosphatase activity [APA] enzyme activity and chlorophyll a) and environmental variables (soluble reactive and organic phosphorous, electrical conductivity). Mats of D. geminata from lakes and rivers representing east and west sides of the Andes from 40°S to 46°S (i.e. much of current known distribution) varied mostly in the α and P_max parameters of P-E curves. Southern systems showed a higher α and lower P_max parameters than more northern sites on the east slope of the cordillera. None of the P-E curves showed photoinhibition. P-E parameters for the two lakes fell within the range of values for riverine mats; although, soluble reactive P was notably higher in the lakes. We used two different statistical approaches to evaluate associations across environmental, functional or P-E parameters, finding a strong relation between APA and P_max and a weak one between soluble reactive phosphorus, pH, dissolved organic phosphorus and functional parameters. Our results do not contradict previous observations on the importance of P availability in communities of D. geminata; although the variability in response across P-E parameters suggests a more complex mechanism of regulation than implied in the existing literature.

Key Words::

• Diatoms
• Invasive species
• Phosphorus
• Photosynthesis–irradiance curves

ACKNOWLEDGEMENTS

This study received financial support from: Universidad Nacional del Comahue (Program 04/B166), Cooperation Project Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina) – Comisión Nacional de Investigación Científica y Tecnológica (CONICYT, Chile) (CH 12/02 – PCCI 12034). The authors would like to thank Luis Uribe and Emilio Alarcon for help with field sampling and analysis in Chile.