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THE EFFECT OF GROWTH IRRADIANCE ON THE COUPLING OF CARBON AND NITROGEN METABOLISM IN CHAETOMORPHA LINUM (CHLOROPHYTA)
Author(s) -
McGlathery Karen J.,
Pedersen Morten Foldager
Publication year - 1999
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1046/j.1529-8817.1999.3540721.x
Subject(s) - photosynthesis , biology , algae , irradiance , thallus , botany , chlorophyta , nitrogen , carbon fixation , total inorganic carbon , photoinhibition , linum , chlorophyll , photosynthetic efficiency , carbon dioxide , ecology , photosystem ii , chemistry , physics , organic chemistry , quantum mechanics
The influence of growth irradiance on the non‐steady‐state relationship between photosynthesis and tissue carbon (C) and nitrogen (N) pools in Chaetomorpha linum (Muller) Kutzing in response to abrupt changes in external nitrogen (N) availability was determined in laboratory experiments. For a given thallus N content, algae acclimated to low irradiance consistently had a higher rate of light‐saturated photosynthesis (P max normalized to dry weight) than algae acclimated to saturating irradiance; for both treatments, P max was correlated to thallus N. Both P max and the photosynthetic efficiency (α dw ) were correlated in C. linum grown at either saturating or limiting irradiance over the range of experimental conditions, indicating that variations in electron transport were coupled to variations in C‐fixation capacity despite the large range of tissue N content from 1.1% to 4.8%. Optimizing both α and P max and thereby acclimating to an intermediate light level may be a general characteristic of thin‐structured opportunistic algae that confers a competitive advantage in estuarine environments in which both light and nutrient conditions are highly variable. Nitrogen‐saturated algae had the same photosynthesis–irradiance relationship regardless of light level. When deprived of an external N supply, photosynthetic rates did not change in C. linum acclimated to low irradiance despite a two‐fold decrease in tissue N content, suggesting that the active pools of chlorophyll and Rubisco remained constant. Both α and P max decreased immediately and continuously in algae acclimated to high irradiance on removal of the N supply even though tissue N content was relatively high during most of the N‐starvation period, indicating a diversion of energy and reductant away from C fixation to support high growth rates. Carbon and nitrogen assimilation were equally balanced in algae in both light treatments throughout the N‐saturation and ‐depletion phases, except when protein synthesis was limited by the depletion of internal N reserves in severely N‐starved high‐light algae and excess C accumulated as starch stores. This suggests that the ability for short‐term adjustment of internal allocation to acquire N andC in almost constant proportions may be especially beneficial to macroalgae living in environments characterized by high variability in light levels and nutrient supply.