Premium
EFFECTS OF FLOWING WATER ON NITROGEN‐ AND PHOSPHORUS‐LIMITED PHOTOSYNTHESIS AND OPTIMUM N:P RATIOS BY SPIROGYRA FLUVIATILIS (CHAROPHYCEAE) 1, 2
Author(s) -
Borchardt Mark A.
Publication year - 1994
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 - 10.1111/j.0022-3646.1994.00418.x
Subject(s) - photosynthesis , respiration , spirogyra , nitrogen , biology , phosphorus , zoology , algae , nutrient , botany , water flow , ecology , chemistry , soil science , organic chemistry , environmental science
The effects of flowing water on net photosynthesis, dark respiration, specific growth rate, and optimum N:P ratios by Spirogyra fluviatilis Hilse were assessed. The alga was cultivated under nitrogen or phosphorus limitation in laboratory streams at three flow velocities: 3, 12, and 30 cm·s −1 . The Droop equation adequately described respiration and photosynthesis (PS net ) as a function of N or P cell quota (Q N or Q p ). The data show that for N‐ or P‐limited Spirogyra fluviatilis , flowing water is physiologically costly. Generally, flowing water had little effect on respiration rates; however, the proportion of gross photosynthesis devoted to dark respiration did increase with flow velocity. For photosynthesis, the minimum N and P cell quotas increased with velocity, and the theoretical PS net maxima for N and P both appeared greatest at 12 cm·s −1 . The Droop models showed that for any given Q N or Q p , PS net , was reduced by the 30‐cm·s −1 treatment. Consistent with this finding, independent estimates of specific growth rates for P‐limited S. fluviatilis in the laboratory streams were inversely related to flow velocity when ambient PO 4 −3 was undetectable. However, growth was not diminished at the fastest velocity when PO 4 −3 was available for uptake. Thus, the increase in cellular phosphorus demand can be offset by flow‐enhanced P uptake when conditions permit; otherwise, growth will be impaired. The optimum N:P ratios for S. fluviatilis at 3, 12, and 30 cm·s −1 were 50, 58, and 52 by atoms, respectively, when calculated for PS net = 0. The optimum ratios were inversely related to PS net and decreased to approximately 20 when PS net was near maximum. The potential for flowing water to mediate nutrient partitioning among lotic algae by altering growth rates and optimum nutrient ratios is discussed.