3B Light Availability of Phytoplankton Flashcards
what are the main reasons light reaching the earth varies
latitude
season
time of day
day length
atmospheric conditions
how does latitude impact light reaching earth
poles receive less solar energy cus sun is on horizon, therefore larger impact patch
impact patch
solar rays hitting the earth
smaller impact patch means more solar energy per unit area (vice versa)
how does season impact light reaching earth
tilt of the earth causes size of impact patch to change
summer/winter solstice receives most solar energy at 23.5 degrees N/S
what is the is the tilt of the earth’s rotation axis
23.5 degrees
how does time of day impact light reaching earth
maximum solar energy occurs at noon when it is directly over head
function of time of day for the Equinox
how does day length impact light reaching earth
longer days get more sun; more solar energy
poles in summer have longer days and vice versa
what is one mole of photons called
Einstein (E)
what is photosynthesis dependent on
number of photons in the right wavelength reaching the chlorophyll
what is heating in the water column dependent on
light’s energy (short wavelength heats more)
what do we usually use to measure light
irradiance Watts (Joules/s)
watt is the conversion between Watt and Einsteins usually
1 Watt = 4.4 microE/s
what is low, optimal, and high light for a phytoplankton
< 100 microE/m^2 s
150-200 microE/m^2 s
2000 microE/m^2 s
how does atmospheric conditions affect amount of light reaching earth
clear sky lets more light in vice versa
scattering, absorption prevent light from reaching the surface
what percent of solar radiation reaches the surface on a clear day
80
what percent of solar radiation reaches the surface on a cloudy day
25
what is albedo
fraction of light reflected from a surface
average sinced different wavelengths reflect differently
large for light surfaces, vice versa
what does ocean water albedo depend on
surface roughness
sun light angle
sediment concentraion
chl concentration
do open ocean or coastal ocean have higher albedos
coastal oceans
what happens to light as it moves through water
phons scatter/ get absorbed
what is the attenuation coefficient
measure of how clear the water is
larger k is coastal water
what wavelengths does water absorb more
longer wavelengths
what kind of light is found in deeper water
blue
what is photosynthesis
fixation of CO2 into sugars
releases O2
what is respiration
suagrs being ‘burned’ with O2 to release energy (ATP) for cellular metabolism
CO2 and H2O are released
who uses respiration
all aerobic organisms
what percentage of carbon gets fixed annually by phytoplankton??
50%
how did the creation of phosynthesis change the earth’s evolution?
oxygen level increased from <1% to 20%
CO2 levels fell from >10% to 0.03%
how is phytoplankton biomass measured in the ocean?
hyperspectral radiometer- measures light reaching down the water column, temperature and salinity
clamps shut at a certain depth in the ocean
filter water to measure phytoplankton
primary production definition
stock/biomass of phytoplankton
measure of chl a or C over volume (mg chla/ml)
what is PAR
photosynthetically active radiation
400-700 nm wavelength
primary productivity definition
rate of fixation of organic carbon from inorganic carbon
photosynthesis
in mole CO2 comsumed/ml h or O2 produced/ml h or organic C produced/ml h
do phytoplankton use respiration or photosynthesis
both
respire all the time, photosynthesize in the day
Gross primary productivity definition
rate of PS without accounting for R (total C fixed)
net primary productivity
gross PP - rate of respiration
what can we determing from net PP
amount of C available for phytoplankton growth in higher trophic levels**
how can we measure net PP with a pure phytoplankton culture
bottle exposed to sunlight
how can we measure gross PP with a pure phytoplankton culture
use bottle kept in the dark to measure repiration, add that value to the value obtained from the light bottle measuring net PP
how come the light/dark bottle method doesn’t work for measuring phytoplankton net PP in situ?
because the respiration occuring is not only coming from phytoplankton, it also includes plankton respiration
how can we measure PP at sea?
adding radioactive carbon 14C to the bottle at a given ratio to C
phytoplankton become labelled with 14C
why do we let bottle sit for 24 hours when measuring net PP with 14C?
to allow for some respiration of organic 14C to occur
how can we measure net PP at sea?
radioactive carbon insert left for 24 hours
can keep at different light intensities
how can we measure gross PP at sea?
radioactive carbon insert left for 4 hours
can keep at different light intensities
why do we let bottle sit for only 4 hours when measuring gross PP with 14C?
to avoid respiration of organic 14C fixed
how do we measure phytoplankton respiration at sea
hourly gross PP - hourly net PP
what is the usual unit used when considering gross/net PP and respiration
mol C/ L h
what units does depth integrated net PP use
mol C/m^2 time
how is photosynthesis divided into two reactions?
light reaction
dark reaction
light reaction definition and formula
generates energy and O2
2H2O + light <—> H(ATP) + e-(NADPH) + O2
dark reaction definition and formula
uses energy to fix inorganic carbon into useful molecules (sugar)
CO2 + H(ATP) + e-(NADPH) <—-> CH2O +H2O
characteristics of light reaction?
light dependent
water splitting
O2 releasing
high energy electron transfer
NADPH and ATP producing
characteristics of dark reaction?
light independent
uses ATP and NADPH
fixes CO2 to form carbohydrates htrough the calvin cycle
endergonic, reduction reaction
where does photosynthesis occur in the cell?
chloroplasts
where does respiration occur in the cell?
mitochondria
where do light reactions happen in the chloroplast?
lumen of the thylakoids
what is a granum
stack of thylakoids
where do dark reactions happen in the chloroplast?
stroma
what is the stroma?
fluid inside chloroplasts but outside the thylakoids
what structures does the light reaction use in the chloroplast?
photosystem II then I
what structures does the dark reaction use in the chloroplast?
calvin cycle
RubisCO
how does the lumen facilitate light reactions?
with high [H] concentration creating electro and chemical gradient
in what order are light reaction products occuring?
oxygen (water splitting) —-> ATP (PS II) —-> NADPH (PS I)
lower to higher energy
what wavelengths do phytoplankton prefer absorbing? why?
shorter wavelengths (blue, green), means higher energy
because there is more of it that penetrates into the ocean
main photosynthetic pigments?
chlorophylls
carotenoids
what light do cartenoids absorb/transmit?
blue/green —–> yellow/orange/red
what light do chlorophylls absorb/transmit?
red/blue —-> green
how is photon energy released/transformed by phytoplankton?
fluorescence
resonance transfer
photochemistry (reduction/oxidation)
why does chl a have two absorbance peaks at blue and red?
blue photons captured are re-emitted in fluorescence as red, chla can capture these red photons again
what pigment do all phytoplankton have?
Chl a
what are accessory pigments?
allow phytoplankton to use a broader range of the light spectrum
what is a PU
photosynthetic unit
what does a photosynthetic unit do?
antenna harvests light with pigment molecules and funnels energy to the chlorophyll a (and protein complex) molecule in the reaction center
what pigment is the only one involved in electron transfer?
chla, that’s why it’s in all phytoplankton
what are some functions of accessory pigments?
allow use of broader spectral range
funnel energy to the reaction center and harvest more light
some deal with excess energy and prevent photo oxidation
how can phytoplankton adjust to low light?
increase size of antenna
increase numbe rof photosynthetic units (
what phytoplankton typically have more accesory units?
low light adjusted ones
what is a PE curve
photosynthesis as function of light intensity
AKA irradiance curve
why does net PP PE curve not pass through the origin?
since respiration is included, there is a compensation light intensity
what is a compensation ligh intensity (Ic)
intensity of light where we see equal levels of photosynthesis and respiration, therefore Net PP = 0
what ligh intensity is the compensation ligh intensity usually?
10 microE/m^2 s
what type of PP PE curve crosses through the origin? why?
gross PP, no respiration is considered, so when there’s no light, there’s no photosynthesis
how can we represent the rate of photosynthesis?
slope of the PE curve
photosynthesis change / irradiance change = alpha
how do we normalize photosynthetic efficiency to chla biomass?
divide it by amount of chla
what is the maximum rate of photosynthesis?
light intensity where rate of photosynthesis levels of (Pmax)
what is photoinhibition?
when phytoplankton get too much light and begins to damage photosystems (beta)
what is Ki
light irrandiance at 50% of max rate of photosynthesis
what is common in irradiance curves of phytoplankton adapted to low light
higher photsynthetic rate at low light (higher slope)
lower maximum rate of photosynthesis
what happens to Pmax at higher temperatures?
increases
what happens to Pmax at higher nutrient levels?
increases
what happens to photosynthetic rate (a) at higher nutrient levels?
increases
what happens to photosynthetic rate (a) at higher light levels?
decreases
what ocean do we usually see higher levels of photosynthetic rate (a)
temperate and polar regions** (check polar part)
what is the depth integrated Net Primary Productivity?
equation for finding productivity anywhere in the ocean using satellits and argo floats
what is compensation depth?
depth where we find the compensation light intensity
what can we observe happening above the compensation depth?
positive net PP, R is lower than PS
what can we observe happening below the compensation depth?
negative net PP, R is higher than PS
what allows phytoplankton to experience a range of light intensities?
movement through the mixed layer
what is Id
average light level experienced by the cells as they move in the mixed layer
what is the critical depth? (Dcr)
the depth at which the light that mixed phytoplankton are experiencing is equal to the compensation light level
zero net PP
what causes phytoplankton biomass to increase in terms of their mixing depth?
when the mixing depth is higher than the critical depth
what do we need to know in order to predict a spring bloom?
temperature
salinity and density
light levels
all in the mixed layer
what machine allows us to predict a spring bloom
argo floats, satellites
