PLANKTON IN NITROGEN AND PHOSPHORUS CYCLES
127
Deep-tank culture (14.5"C)
0.9 pg-atoms NH:-N/I
greatly dependent on either the level or the nature of the nitrogen
aupply that was utilized (Table V). Moreover, laboratory-cultured cells
of Ditylum brightwellii contained less nitrogen and phosphorus than did
those from the deep-tank cultures.
Laboratory culture (2OOC)
260 pgatoms NO;-N/l
TABLE V. THE CELLULAR NITROGEN AND PHOSPHORUS CONTENTS AND N : P
RATIOS OF Two PHYTOPLANKTONIC SPECIES IN RELATION TO THE NUTRIENT
SUPPLY. (Data from Strickland et d., 1969.)
__
Nitrogen (pgleell)
Phosphorus (pglcell)
N: P (atoms)
Ditylum brightwellii
NH -grown cells
. . -
-. - -. -
300
65
10.2 : 1
Nutrient-starved
cells
NH: -grown cells
I
NO -grown cells
- - -
-~
NO J -grown cells
320
80
8.8: 1
120
23
1143:l
Caehonina tiiei
~- - _ _ _
_
~
_.__ -
-
-
-
Deep-tank culture (2OOC)
Nitrogen (pglcell)
Phosphorus (pgleell)
N: P (atoms)
I
24.5
6.7
8-1 :I
' 34.0
7.2
9 4 : l
10*6:1
The relationship, if there be one, between the nitrogen and phosphorus contents of marine phytoplankton and their nutrient supply
remains obscure.
A. Release of organic forms of nitrogen and phosphorw
by phytoplanktm
A considerable proportion of the organic matter produced during
photosynthesis by phytoplankton may be released in a soluble form by