History of Earth’s Climate презентация

energy output only 70% of present
Liquid water present ~4.3 billion years

billion years ago
Produced oxygen and removed carbon dioxide and methane (greenhouse gases)
Earth went through periods of cooling (“Snowball Earth”) and warming
Earth began cycles of glacial and interglacial periods ~3 million years ago

energy input from the Sun. Some of the Sun’s energy is reflected by clouds. Other is reflected by ice. The remainder is absorbed by the earth.

equal to the amount radiated back into space, the earth remains at a constant temperature.

amount radiated, then the earth heats up.

the amount radiated, then the earth cools down.

greenhouse. Energy from the Sun penetrates the glass of a greenhouse and warms the air and objects within the greenhouse. The same glass slows the heat from escaping, resulting in much higher temperatures within the greenhouse than outside it.

in the stroma.

The Dark Cycle (Calvin Cycle), or more descriptively, the carbon reactions of photosynthesis

~200 billion tons of CO2 are converted to biomass each year

The enzyme ribulose biphosphate carboxylase/oxygenase, Rubisco, that incorporates CO2 is 40% of the protein in most leaves.

of the CO2 acceptor, ribulose-1, 5-biphosphate, forming two molecules of 3-phosphoglcerate.

Reduction of 3-phosphoglycerate to form glyceraldehyde-3-phosphate which can be used in formation of carbon compounds that are translocated.

Regeneration of the CO2 acceptor ribulose-1, 5-biphosphate from glyceraldehyde-3-phosphate

rapid carboxylation at the low concentration of CO2 found in photosynthesizing cells

The negative change in free energy associated with carboxylation of RuBP is large so the forward reaction is favored.

RuBP

Rubisco will also take O2 rather than CO2 and oxygenate RuBP – called photorespiration.

The rate of operation of the Calvin Cycle can be enhanced by increases in the concentration of its intermediates. That is the cycle is autocatalytic.

Also, if there are insufficient intermediates available, for example when a plant is transferred from dark to light, then there is a lag, or induction period, before photosynthesis reaches the level that the light can sustain. (There can also be enzyme induction.)

Rubisco is notoriously inefficient as a catalyst for the carboxylation of RuBP and is subject to competitive inhibition by O2, inactivation by loss of carbamylation, and dead-end inhibition by RuBP. These inadequacies make Rubisco rate limiting for photosynthesis and an obvious target for increasing agricultural productivity. Really?

increase the maximum rate of photosynthesis in the short term

time due to increasing atmospheric O2 concentration -the product of photosynthetic organisms themselves.

In the presence of higher O2 levels, photosynthesis rates are lower.

The inhibition of photosynthesis by O2 was first noticed by the German plant physiologist, Otto Warburg, in 1920, and called the "Warburg effect".

in bundle sheath cells than found in photosynthetic cells of C3 plants.

The first product of CO2 fixation is malate (C4) in mesophyll cells, not PGA as it is in C3 plants. This is transported to bundle sheath cells

CO2 is released from malate in bundle sheath cells, where it is fixed again by Rubisco and the Calvin cycle proceeds. PEP is recycled back to mesophyll cells.

This enables C4 plants to sustain higher rates of photosynthesis. And, because the concentration of CO2 relative to O2 in bundle sheath cells is higher, photorespiration rates are lower.

C4 Photosynthesis

Calvin cycle between day and night

CAM plants open their stomates at night. This conserves H2O. CO2 is assimilated into malic acid and stored in high concentrations in cell vacuoles

During the day, stomates close, and the stored malic acid is gradually recycled to release CO2 to the Calvin cycle

First discovered in succulents of the Crassulacea: e.g.,sedums

al. 97
Nature

δ13C

Ca (low rate of photosynthesis, open stomata), then εp ≈ εf. Large fractionation, low plant δ13C values.

When Ci << Ca (high rate of photosynthesis, closed stomata), then εp ≈ εt. Small fractionation, high plant δ13C values.

+4.4‰

εp = εf = +27‰

εf

0

0.5

1.0

Fraction C leaked (φ3/φ1 ∝ Ci/Ca)

δi

δf

δ1

εp = δa - δf = εt + (Ci/Ca)(εf-εt)

Ci/Ca, typically with values less than those for εta.

εp = εta+[εPEP-7.9+L(εf-εtw)-εta](Ci/Ca)

Under arid conditions, succulent CAM plants use PEP to fix CO2 to malate at night and then use RUBISCO for final C fixation during the daytime. The L value for this is typically higher than 0.38. Under more humid conditions, they will directly fix CO2 during the day using RUBISCO. As a consequence, they have higher, and more variable, εp values.

εp = 4.4+[-10.1+L(26.3)](Ci/Ca)

efficiency because of Photorespiration

is plentiful, temperature and light levels are moderate (temperate climates)

C4 plants are favoured in environments where water is limiting and light and temperatures are high (tropical / subtropical habitats)

bisphosphate (RuBP, Rubisco) most abundant protein on Earth; enzyme captures CO2 but also has high affinity for O2.
Phosphoglyceric acid (PGA) is 3-C sugar formed during CO2 uptake.
Photorespiration makes photosynthesis less efficient but also protects cells from excess light energy.
At high CO2:O2 ratios, Rubisco is more efficient, thus C3 plants respond more to elevated CO2 than do C4 plants
Most trees, shrubs, cool-season grasses

favored by high O2, low CO2 and warm temperatures

carboxylase, with much higher affinity for CO2.
Oxaloacetate (OAA) is 4-C sugar formed during CO2 uptake.
Rubisco concentrated in bundle sheath cells, where OAA delivers CO2.
Photorespiration limited because CO2:O2 is much higher inside bundle sheath cells than in C3’s.
Less Rubisco needed for psn means higher N-use efficiency.

High water use efficiency (C gained per H2O lost) because stomates can be partly closed.
Lower response to elevated CO2
Cost of C4: additional ATP is needed for PEP cycle, which may limit C4 growth at low light levels
2000 species in 18 families; half of all grass (Poaceae) species (warm-season grasses)

CO2 released to the atmosphere and the increase in atmospheric CO2 concentration during last decades.
• Atmospheric oxygen is declining proportionately to CO2 increase and fossil fuel combustion.
• For the last half century, the CO2 airborne fraction (AF) parameter remained consistent and averaged at 0.55 (the AF parameter is the ratio of the increase in atmospheric CO2 concentration to fossil fuel-derived CO2 emissions). AF has been introduced to assess short- and long-term changes in the atmospheric carbon content; in particular, AF of 0.55 indicates that the oceans and terrestrial ecosystems have cumulatively removed about 45 % of anthropogenic CO2 from the atmosphere over the last half century [6].
• The isotopic signature of fossil fuels (e.g., the lack of 14C and the depleted level of 13C carbon isotopes) is detected in atmospheric CO2.
• There exists an interhemispheric gradient in the atmospheric CO2 concentrations in the Northern and Southern Hemispheres. In particular, the predominance of fossil-derived CO2 emissions in more industrially developed Northern Hemisphere (compared to the Southern Hemisphere) causes the occurrence of the atmospheric CO2 gradient in the amount of about 0.5 ppm per GtC per year [6].
• There have been dramatic changes in RFCO2 values over the last decades. For example, during 1995–2005, the RFCO2 increased by about 0.28 W/m2 (or about 20 % increase), which represents the largest increase in RFCO2 for any decade since the beginning of the industrial era. RFCO2 in 2005 was estimated at RFCO2=1.66±0.17 W/m2 (corresponding to the atmospheric CO2 concentration of 379±0.65 ppm), which is the largest RF among all major forcing factors (The concept of radiative forcing (RF))
• The data show that the changes in the land use greatly contributed to the RFCO2 value in the amount of about 0.4 W/m2 (since the beginning of the industrial era). This implies that the remaining three quarters of RFCO2 can be attributed to burning fossil fuels, cement manufacturing, and other industrial CO2 emitters [6].