More Than One Limiting Nutrient - P and N Limitation
51
-.. 2
Bacteria
- ,
"0
--~
~
~ 1
Algae
(,)
t.+::
.....
(,)
0
c..
U':)
O~------~------~~------+--------r------~
o
1
2
3
4
5
Dissolved inorganic P ([~g P] liter-i)
Fig. 3.7. Monod curves describing phosphorus limited growth in algae and bacteria according
to the parameter sets given in Table 3.3
Table 3.3 summarizes typical phosphorus uptake and utilization
parameters for bacteria compared to corresponding parameters for algae,
taken from Table 3.1. The resulting Monod half-saturation parameters for
typical algae and bacteria [given by Eq. (3.11)] differ by more than an order
of magnitude, making phosphorus-limited bacteria competitively superior
to algae (Fig. 3.7). This competitive advantage of bacteria would be maintained even if we had chosen the most favorable algal parameter combination from Table 3.1 [that is, using the high values of j.l' and a', and the low
value of Q' in Table 3.1 gives K' = 0.25 (J.lg P) r\ which is still higher by a
factor of 5 than the bacterial half-saturation parameter in Table 3.3].
3.7 More Than One Limiting Nutrient - P and N
Lilllitation
Although some authors have advocated the idea that multiple limiting
factors affect phytoplankton growth in a multiplicative fashion (Rodhe
1978; Bader 1982), it seems now generally accepted that a threshold model
is more appropriate for describing situations where more than one
essential element can become limiting to phytoplankton growth (Tilman 1982;