3.2. Effect of variable nutrient levels on culture physiology
The maximum quantum efficiency (F v/Fm ) of reaction centers in
PS-II of chlorophyll represents the physiological state of the culture
and the nutrient stresses (White et al., 2011). A Fv/F m value of less
than 0.5 implies the culture is in a stressed state; and this value
declines with increasing stress level of the culture (Ramanna
et al., 2014). These quantum efficiencies were calculated for all five
nutrient levels throughout the course of the experiments ( Fig. 4a).
Since all experiments were conducted with nutrient-starved cells
to avoid the effect of internally stored nutrients on growth and
uptake of nutrients, these cells were in a stressed condition based
on the evidence of the initial Fv/F m value for each experiment being
less than 0.3. With the addition of nutrients in each experiment,
the nutrient stress in the culture was reduced as evident by the
increasing quantum efficiencies in the early light periods. Increase
in Fv/F m values was observed for 2 days only in cultures with the
lowest initial nitrogen input (experiment N l -Ph ), after which these
efficiencies declined to very low levels. This indicates that as the
nitrogen became limiting, the culture became nutrient stressed.
Nutrient stress affected the culture physiology and effects were
visible in terms of low growth of C. sorokiniana (Fig. 1a). At other
nutrient levels, quantum efficiencies increased for 3 days. For med-ium nitrogen levels (Nm -Ph ), nutrient stress was evident after
3 days whereby Fv/F m started to decline appreciably. At higher
3.2. Effect of variable nutrient levels on culture physiologyThe maximum quantum efficiency (F v/Fm ) of reaction centers inPS-II of chlorophyll represents the physiological state of the cultureand the nutrient stresses (White et al., 2011). A Fv/F m value of lessthan 0.5 implies the culture is in a stressed state; and this valuedeclines with increasing stress level of the culture (Ramannaet al., 2014). These quantum efficiencies were calculated for all fivenutrient levels throughout the course of the experiments ( Fig. 4a).Since all experiments were conducted with nutrient-starved cellsto avoid the effect of internally stored nutrients on growth anduptake of nutrients, these cells were in a stressed condition basedon the evidence of the initial Fv/F m value for each experiment beingless than 0.3. With the addition of nutrients in each experiment,the nutrient stress in the culture was reduced as evident by theincreasing quantum efficiencies in the early light periods. Increasein Fv/F m values was observed for 2 days only in cultures with thelowest initial nitrogen input (experiment N l -Ph ), after which theseefficiencies declined to very low levels. This indicates that as thenitrogen became limiting, the culture became nutrient stressed.Nutrient stress affected the culture physiology and effects werevisible in terms of low growth of C. sorokiniana (Fig. 1a). At othernutrient levels, quantum efficiencies increased for 3 days. For med-ium nitrogen levels (Nm -Ph ), nutrient stress was evident after3 days whereby Fv/F m started to decline appreciably. At higher
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