CO2 increase responses

Question 1

CO2 of the past

Answer 1

400mya when early plants began to diversify, 20x CO2 conc of now.
first angiosperms evolved in high CO2.
since industrial revolution has almost doubled.

Question 2

what is the fertilisation effect

Answer 2

Long et al 2006
growing crops at increased CO2 is associated with increased yields. (550 ppm compared to 380ppm)
Crops respond directly to rising [CO2] through photosynthesis and stomatal conductance.

Question 3

what enzyme is the calvin cycle reliant on

Answer 3

RuBisCO

at 25 degrees C, rate of carboxylation is 4x that of oxidation (wasteful).

Question 4

how does the fertilization effect work concerning rubisco?

Answer 4

C3 species such as wheat and rice RuBisCO is not CO2-saturated by current levels of [CO2] so photosynthesis increases at increased [CO2].

also, photorespiration, is inhibited by increased [CO2].
results in increased photosynthesis at higher CO2 = higher biomass and yields.

Question 5

what did the FACE experiment test?

Answer 5

Free Air Carbon dioxide Enrichment - used towers in natural environment to bleed CO2 into exp area.
Theoretically, growing wheat at 550ppm co2 should give 38% ph increase.
tested in FACE exp, and increase in ph was not observed.

Question 6

why did FACE exp not match results of lab exp?

Answer 6

Long et al (2006) concluded that a series of feedbacks existed in the field that constrain realization of the potential benefits of elevated [CO2].

Question 7

what did myers et al 2015 find?

Answer 7

crops grown at elevated [CO2] produce grain that has significantly reduced levels of the key human micronutrients iron and zinc.

Question 8

why is there a need to increase iron and zinc content in grain?

Answer 8

iron and zinc def is public health problem in the UK.
25% of 19-64 yo have Zn def, and 20% women 11-64 have Fe def.
luckily, clear variation btw crop varieties so maybe selective breeding can improve the situation.

Question 9

Why does growth at elevated [CO2] impact negatively on grain micronutrients?

Answer 9

heatherington - 1998
neg impacts on transpiration and nutrient aquisition.
reduced no. stomata per leaf.
reductions in stom aperture.

Question 10

Why is stom density inversely correlated to atmospheric CO2 conc?

Answer 10

CO2 specific steps feed into pathway in which ABA controls stom development.

1. A CO2-specific step is mediated by the Arabidopsis HIC gene
2. HIC encodes a β-ketoacyl CoA synthase responsible for the synthesis of very long chain fatty acids (VLCFAs) - components of plant cuticle
3. Perhaps altered cuticular wax composition affects the diffusion of an endogenous inhibitor of stomatal development?

Question 11

what controls stom development?

Answer 11

signalling pathway involving EPF2 peptide - neg regulator.
to be activated, must be cleaved by protease CRSP.
CRSP induced at high CO2.

Question 12

what else in involved in controlof stomatal development by elevated CO2?

Answer 12

beta carbonic anhydrase
maybe this is the CO2 sensor?
unknown link between bicarbonate and CRSP/EPF2.

Question 13

what does removing ABA receptors/biosynthesis show?

Answer 13

no more effect of elevated CO2, so ABa receptors must be involved.

Question 14

describe an experiment showing how CO2 controls stomatal density in a systemic manner

Answer 14

Lake et al2010
sealed mature leaved in a gas tight cuvette, and exposed to ambient or elevated CO2.
Stomatal density measured in new leaves that develop outside the cuvette.
Found: new leaves grown at ambient CO2 have the same no. stomata as mature leaves at elevated CO2. (this is not expected for new leaves in normal conditions.)
Concluded the mature leaves control the number of stom on new leaves via long distance signalling.

Question 15

how does light influence stomatal development?

Answer 15

Casson et al 2009
increased stom density in response to high light.
process dependent on phy B and PIF4.

Question 16

describe an experiment showing that old leaves control stom density and that phyB is involved in light regulated density.

Answer 16

arabidopsis grown under high light.
existing leaves over 5mm shaded except for one leaf left in high light. control - unshaded plant.
stom index of leaf that developed at high light is typical of shaded plant.
shows old leaves control stomatal dev.
PhyB mutant had stom index same as control.

Question 17

overall what controls stomatal density and what does this tell us?

Answer 17

light and CO2 conc signals.
signals operate using systemic signalling systems. responses to drought are likely to be influenced by aditional signals from the environment.

Question 18

what are the direct effects of elevated CO2 on stomatal aperture?

experiment?

Answer 18

heatherington 1998
stom aperture decreases
less CO2 uptake for ph and less transpiration. may be beneficial in drought but also may reduce mineral uptake.

incubated isolated epidermis in buffer and then exposed to increasing co2 conc. repeated with EGTA present - no reduction in aperture in response to co2.
EGTA is a Ca2+ chelator, suggesting that increase in Ca2+ is needed for response to co2.
also needed for ABA induced closure.

Question 19

how do CO2 and ABA signalling pathways relate?

Answer 19

both need Ca2+ involved.
Accepted that ABA pathway is evolutionarily older than CO2 pathway.
and possible that the CO2 pathway starts upstream of OST1 and joins onto the ABA pathway here, to induce stom closure. - Engineer et al 2015
unsure is ABA is required for this response

Question 20

who demonstrated that ABA receptors were needed for CO2 induced guard cell closure

Answer 20

Chater et al 2015
elevated CO2 induced stom closure in WT arabidopsis, but not in PYR/PYL triple and quadruple mutants. shows ABA receptors are needed for this response

Also, used nced3nced5 double mutant (NCED is enzyme needed for ABA biosynthesis) and saw no response to elevated CO2. shows ABA is also needed.

Question 21

Where does the ABA come from involved in the CO2 signalling pathway?

Answer 21

Transcriptomic analysis shows that guard cells express all the genes involved in the ABA biosynthesis pathway .
they are upregulated in response to a drop in RH.
unsure whether CO2 has same effect or if CO2 stimulates ABA deconjugation

Question 22

How did Grey et al disprove the fertilisation effect?

Answer 22

in cooler wetter years:
High CO2 increases yield by about 22%.
High CO2 decreases stomatal aperture (transpiration) so conserves soil water
in hot dry conditions:
high co2 increases sensitivity to drought, causing stomata to close so reducing ph and increasing leaf temp, increasing transpiration offsetting the co2 effect.
net effect yield decreased by 1% due to N2 def and smaller leaves due to drought.