Plant Adaptations

Photosynthesis:

Light Reaction: light energy into electrical energy

Chlorophyl excited :

thermal dissipation, fluorescence, electron transfer

Dark Reaction: into chemical energy

Reduction of carbon

6CO₂+12H₂O Þ C₆H₁₂O₆ +O₂ +6H₂O

Getting CO₂: Evapotranspiration

Stomata must open to allow evaporation

But balanced by soil water availability

Aquatics: no stomata: can use bicarbonate

Both can be CO2 limited

CO₂ Capture

Rubisco: carboxylation of ribulose biphosphate

Yields two 3-PGA (C3 plants)

Photorespiration: Ribisco oxygenating ribulose biphosphate,

releases CO₂, limits efficiency by 30-50%, only in the light

Dark Respiration: mitochondria: maintenance and growth

C4 Photosynthesis (fig. 6.3)

PEP carboxylase: CO2 capture in mesophyl- malate and aspartate

Bundle sheath cells CO2 is removed and re-fixed by Rubisco

High CO2 concentration in BSC

PEP higher affinity for CO2 than Rubisco,

Reduces CO2 concentration in mesophyl

Reduces photorespiration in mesophyl and bundle cells

High CO2 environment

C4’s grasses, some shrubs, herbaceous plants in arid and saline

CAM photosynthesis: similar, but lack bundle sheath cells

Allows stomates to open at night when cool, moist, accumulate malate

Stable Carbon Isotope analysis and C3, C4

C3: algae, wheat, rice, veggies, Trees, less efficient, discriminate against 13C

C4: Sugarcane, Corn, Spartina- high efficiency, little discrimination

PAR: Engleman’s experiment

Light Response curve (Figure 6.6)

Compensation Point, Saturation Point, Photoinhibition

Adaption to light levels: morphology and biochemistry

shade tolerance as species adaptation

leaf morphology

root mass to leaf area (fig 6.8)

Ribisco Concentration and Light repsonse curve (Fig.6.7)

Periodicity in Plants

Photoperiod: critical daylength

Day neutral, short-day or long-day plants

Seasonality: temperature or rainfall

Phenology:

causes of the timing of plant response,

Hopkin’s Law:

4 days for each: degree of Lat. N: 17 mph

5 degrees of longitude east

400 ft. of elevation

interrelations between plants and herbivores

Phenology and migration: http://www.learner.org/jnorth/

Temperature Effects

Energy balance for plants:

Rn=M+S+(C+lE)

Where:

Rn=radiation balance

M=light converted to chemical energy

S=Light converted to heat energy

C= convection

E= evaporation includes transpiration (dominates) and evaporation from surfaces

l=latenet heat of vaporization

M=”intake” respiration vs new biomass+ nutrients

Dissipation of heat keeps leaves from reaching critical temperatures

Thermal effects on photosynthesis and respiration

Heat content controls the rate of chemical reactions

Affects Rubisco and PEP-carboxylase (Fig 7.2)

Increased temp favors photorespiration over carbon dioxide fixation by Rubisco,

Affects Dark Respiration (fig 7.3)

Balance of Respiration and Photosynthesis

NPP=GPP-plant respiration

Effect of temperature: (fig 7.4)

Fig 7.5: Species differences: adaptations to different temp regimes:

Arctic Lichen (Neuopogon), temp dune plant (Ambrosia), desert plants

C4 tolerates heat better than C3 (Fig 7.6)

Lack of photorespiration by Rubisco in C4 mesophyl,

higher temp opitmum for PEP carboxylase

Effect of temperature on growth: degree-days, heat sums, cold sums

Ususally some minimum:

Fig. 7-9, by season

Fig. 7.10 geographically

Fig. 7.11 by type- Evergreeness

0-10°C chill sensistive evergreen broadleafs die

-15°C lowest temp for broadleaf evergreens

-15°C to -40°C, broadleaf deciduous dominates: supercooliing, lack of ice nucleation

below -40°C, ice formation without nucleation: conifers

Water

Evapotranspiration covered earlier

Osmotic pressure also important, Fig 7.13

Accounts for turgor pressure that keeps the stomates open and non-wilted state

Salt adaptation in Spartina: malate used to balance osmolarity

Juncus

Xeric Adaptations:

Small Waxy leaves

Heavy cuticle

Succulent

Deep roots

Response to Hydric:

Shallow root systems

Kness and pneumatophores

Aerenchymous tissue

Hollow stems/roots

Nutrients

C, H, O

N, P, K, Ca, Mg, S

Nutrient uptake

Availability affects uptake rate but saturatable (fig 7.24, 7.25)

Adaptations to nutrient stress:

Greater affinity

Greater root mass/above ground tissue (Fig 7.26)

Cost of adaption; fig 7.27

Facilitated nutrient transfer: mutualisms:

extracting nutrients with sugars

N₂ fixation

Resorption of nutrients table 7.1