BIOL 4120 Principles of Ecology Lecture 3 Adaptation
BIOL 4120: Principles of Ecology Lecture 3: Adaptation to Physical Environment: Light, Energy and Heat Dafeng Hui Office: Harned Hall 320 Phone: 963 -5777 Email: dhui@tnstate. edu
Topics (Chapter 3) n n n n 3. 1 Light is primary source of energy for the biosphere 3. 2 Plants capture the energy of sunlight by photosynthesis 3. 3 Plants modify photosynthesis in high water stress environments 3. 4 Diffusion limits uptakes of dissolved gases from water 3. 5 Temperature limits occurrence of life 3. 6 Each organism functions best under certain temperature 3. 7 Homeothermy increases metabolic rate and efficiency
Earth provides highly diverse environments: 1. 7 million known species now
All species have three common basic functions n n Assimilation: acquire energy from external environment Reproduction: to produce new individuals Response to external stimuli: able to respond to both physical (light, temperature etc) and biotic (predator etc). All organisms acquire energy • Energy obtained directly from an energy source by a living organism is called autotrophy (autotroph) n n Plants are autotrophs, primary producers So are certain bacteria like Thiobacullus ferrooxidans • Energy obtained indirectly from organic molecules by a living organism is called heterotrophy (heterotroph) n n All animals are heterotrophs, secondary producers Some organisms can be a mixture like lichens where you have an alga and a fungus living together Autotrophs obtain solar energy through photosynthesis.
3. 1 Light is the primary source of energy for the biosphere n n n All life requires energy to sustain itself With very few exceptions, all life on earth is dependent on solar energy Life on Earth exists because it’s fitness is optimal for the environment created by solar energy Shortwave longwave radiation Earth is a balanced ecosystem in term of solar energy inputs and outputs
Light is the primary source of energy for the biosphere PAR: photosynthetically active radiation 400 -700 nm
Light absorption spectra of plants
Light absorption spectra of algae Ulva: sea lettuce, shallow water Porphyra: red alga, deep-water
3. 2 Plants capture energy of sunlight by photosynthesis Photosynthesis (review) n n n All life is built on a framework of carbon atoms The ultimate source of carbon for organic molecules is CO 2 is transformed into organic molecules by plants (photosynthesis).
n n Photosynthesis is the process by which the Sun’s energy (shortwave radiation) is used to fix CO 2 into carbohydrates (simple sugars) and release O 2 Photosynthesis begins with light reactions • Absorption of light energy by chlorophyll (a pigment molecule) • Conversion of the light energy into ATP (adenosine tri-Phosphate) and NADPH (Reduced form of nicotinamide adenine dinucleotide phosphate) Photosynthesis continues with the dark reactions • Incorporation of CO 2 into simple (organic) sugars using the energy provided by ATP and NADPH • Carboxylation is catalyzed by the enzyme rubisco (ribulose biphosphate (Ru. BP) carboxylaseoxygenase)
C 3 n The Calvin cycle (C 3 cycle) initially fixes CO 2 into 3 -PGA (phosphoglycerate) This cycle is called Calvin-Bensen cycle, or C 3 cycle. Plants employing it are known as C 3 plants
Ru. BP: Ribulose biphosphate Rubisco: ribulose biphosphate (Ru. BP) carboxylase-oxygenase 3 -PGA: phosphoglycerate G 3 P: glyceraldehyde 3 -phosphate
C 3 cycle (Calvin cycle) One major drawback of C 3 pathway: Rubisco can catalyze both carbonxylation And Ru. BP oxygenation Reduce the efficiency of photosynthesis. C 3 plant: trees, forbs, some grasses
Photosynthesis Cellular respiration Net photosynthesis = (Gross) Photosynthesis - Respiration
BIOL 4120: Principles of Ecology Lecture 3: Adaptation to Physical Environment: Light, Energy and Heat Dafeng Hui Office: Harned Hall 320 Phone: 963 -5777 Email: dhui@tnstate. edu
Recap n n Water and salt balance by plants and animals Solar radiation is the energy source for life, PAR, water absorption Photosynthesis C 3 photosynthetic pathway
3. 3 Other photosynthesis pathways: adaptation to water and temperature conditions n n n To increase water use efficiency in a warm dry environment, plants have modified process of photosynthesis C 3 • Normal in mesophyll with rubisco C 4 • Warm dry environment • Additional step in fixation of CO 2 • Phosphoenolpyruvate synthase (PEP) does initial fixation into Malate and aspartate • Malate and aspartate are transported to bundle sheath as an intermediate molecule • Rubisco and CO 2 convert there to sucrose
C 4 pathway Advantages over C 3 pathway 1. PEP does not interact with O 2 (Ru. BP react with O 2 and reduce the photosynthesis efficiency) 2. Conversion of malic and aspartic acids into CO 2 within bundle sheath cell acts to concentrate CO 2, create a much higher CO 2 concentration. C 4 plants have a much higher photosynthetic rate and greater water-use efficiency. C 4 plants are mostly grasses native to tropical and subtropical regions and some shrubs of arid and saline environments (Crop: corn, sorghum, sugar cane).
CAM pathway CAM (Crassulacean acid metabolism) pathway Hot desert area Mostly succulents in the family of Cactaceae (cacti), Euphorbiaceae and Crassulaceae) Similar to C 4 pathway Different times: Night: open stomata, convert CO 2 to malic acid using PEP Day: close stomata, reconvert malic acid to CO 2, C 3 cycle.
Comparison of three photosynthetic pathways C 3: Dovefoot geranium, C 4: sorghum, CAM: Sierra sedium
3. 4 Plant adaptation to control water loss In addition to photosynthetic pathway differences, heat and drought-adapted plants have anatomic and physiological modifications that reduce transpiration, heat load and enable plants to tolerate high temperature.
3. 5 Photosynthesis of aquatic plants n Unique features • Lack of stomata • Direct diffusion of CO 2 across cell membrane n Slow in water than in air (10^4 times slower) • Some plants: CO 2 reacts with H 2 O first to produce biocarbonate, and Convert biocarbonate to CO 2 n Transport HCO 3 - into leaf then convert to CO 2 Excretion of the enzyme into adjacent waters and subsequent uptake of converted CO 2 across the membrane. n CO 2 could be a constraint in dense sea-grass beds n
Oxygen concentration in aquatic environment High O 2 in the surface due to diffusion O 2 is dissolved in water O 2 concentration in water is determined by solubility and diffusion. Anaerobic conditions in the deep water
3. 6 Carbon gained in photosynthesis is allocated to production of plant tissues Carbon allocation is an important issue and has not been well studied. Difficult to measure, especially below ground. Allocation to different parts has major influences on survival, growth, and reproduction. Leaf: photosynthesis Stem: support Root: uptake of nutrient and water Flower and seed: reproduction.
In dry grassland ecosystems, plants have long roots
Allocation and environmental factors (such as temperature and precipitation) Hui & Jackson 2006
Constraints Imposed by the Physical Environment Have Resulted in a Wide Array of Plant Adaptations n n Plants must maintain a positive carbon balance to survive, grow, and reproduce Essential plant resources and conditions are interdependent • Light (PAR) • CO 2 • H 2 O and Minerals • Temperature
3. 7 Species of Plants are adapted to light conditions n Plants adapted to a shady environment • Lower levels of rubisco • Higher levels of chlorophyll (increase ability to capture light, as light is limiting) • low light compensation and saturation lights n Light intensity Red oak leaves at top and bottom of canopy Plants adapted to a full sun environment • Higher levels of rubisco • Lower levels of chlorophyll • High compensation and saturation lights n Changes in leaf structure evolve
Light affects photosynthesis and respiration Stuart Davies of Harvard University studied the photosynthesis and respiration of seedlings of nine tree species under different light
Light also affects whether a plant allocates to leaves or to roots Change of allocation to leaf of broadleaved peppermint (Reich et al. ). n Shade tolerant (shadeadapted) species • Plant species adapted to low-light environments n Shade intolerant (sunadapted) species • Plant species adapted to high-light environments
Shade tolerance and intolerance Shade tolerance Seedling survival and growth of two tree species over a year Augspurger (1982) Shade intolerance
BIOL 4120: Principles of Ecology Lecture 3: Adaptation to Physical Environment: Light, Energy and Heat Dafeng Hui Office: Harned Hall 320 Phone: 963 -5777 Email: dhui@tnstate. edu
Recap n n n C 4 and CAM pathways Aquatic plants Photosynthesis and environmental factors • Light, response curve, adaptation
3. 9 Temperatures influence photosynthesis and respiration n n Different responses of photosynthesis and respiration to temperature; Three basic Temperature points • Min T, max T and optimal T
Plants need to make serious evolutionary adaptations to temperature C 4 C 3 Neuropogon: Arctic lichen (C 3) Ambrosia: cool coastal dune plant (C 3) Tidestromia: summer-active desert C 4 perennial Photosyn. rate and Topt Atriplx: everygreen desert C 4 plant n Topt: C 3: <30 o. C; C 4: 30 o. C to 40 o. C; CAM, >40 o. C
Plants Vary in Their Response to Environmental Temperatures n n n Temperature responses are not fixed When individuals of the same species are grown under different thermal conditions, a divergence in temperature response of net photosynthesis is often observed • The Topt shifts in the direction of thermal conditions under which the plant is grown A similar pattern is seen in individual plants in response to seasonal shifts in temperature (acclimation)
Big saltbush, C 4
Affinity is a good measure of enzyme function. Produce different forms of enzyme.
3. 12 Plants exhibit adaptations to variations in nutrient availability n n Plants need nutrient for metabolic processes and synthesize new tissues According to amount of nutrient required: • Macronutrients: needed in large amount N, P, K, Ca, Mg, S • Micronutrients: needed in lesser quantities Zn, B, Cu, Ni, Fe n Some nutrients can be inhibitory
Plants exhibit adaptations to variations in nutrient availability n n n Uptake of a nutrient through the roots depends on its concentration However there is a maximum uptake rate Effect of nutrient availability can also reach a maximum
Photosynthesis and nutrient n n Nitrogen can limit photosynthesis N in enzyme rubisco and pigment chlorophyll.
n Plants respond differently to extra nitrogen depending on their natural environment’s level of nitrogen or other nutrient Two grass species, carpet bent grass (A. stolonifera) in high N and velent bent grass (A. canina) in low N conditions.
Other factors: Impact of CO 2 on photosynthesis Illustration of tradeoffs of C 4, C 3 plants with CO 2 concentration Increase in CO 2 will influence the competition of C 3 and C 4
3. 13 Regulation of internal conditions involves homeostasis and feedback Homeostasis: The maintenance of a relatively constant internal environment in a varying external environment. Homeostasis depends on negative feedback Negative feedback: when a system deviates from the normal or desired state, mechanisms function to restore the system back to that state. Example: room temperature setting
Homeostasis n n n To stay alive, animals need to keep their body within certain limits • Temperature • Water balance • p. H • Salt balance Feedback systems to help to keep within specific limits Outside limits – • Dehydration • Heat shock • Salt imbalance • Death
Negative feedback (thermoregulation)
Animals exchange energy with their surrounding environment n Body structure influences the T exchange Temperature (Tb, Ts, Ta) n Tb<->Ts conduction n • Core temperature Tb • Surface temperature Ts n n Ts<->Ta: convection, radiation, evaporation n n Ears Fingers Toes Boundary layer (a thin layer of air surround the body) Insulation (air, body covering) influences energy exchanges
3. 14 Animals have different methods of maintaining their body temperatures Three groups of animals n Endothermy resulting in homeothermy • Use of internal heat source (metabolically) n n n Mammals and birds Maintain a fairly constant temperature (warm-blooded) Ectothermy resulting in poikilothermy • Use of external heat sources n n n Reptiles, amphibians, fish, insects and invertebrates Results in a variable body temperature (cold-blooded) Heterothermy • Uses both endothermy and ectothermy n Bats, bees and hummingbirds
Poikilotherms depend on environmental temperatures • As the temperature increases, so does the metabolic rate • Therefore these animals are more active during the day • Every 10 o. C doubles metabolic rate (Q 10) • Natural condition: low metabolic rate and high conductivity • Activities also controlled by temperature • Upper and lower limits vary n n Lizards and snakes have a 5 o C Amphibians have a 10 o. C Operative T range: range of body T at which poikilotherms can carry out their daily activities.
n n During the day, the snake can maintain a fairly constant temperature by adjusting it’s environment (bask in sun to raise T, seek shade to cool, submerge in water etc) During the night, it has few options • Temperature drops 1015 degrees • Become torpid (slow moving) • Restricted by environment • Maximum size due to need for surface area to gather heat • No minimum size
3. 15 Homeotherms escape thermal restraints of the environment n n n Homeotherms can escape thermal restraints of the environments, thus can exploit a wide range of thermal environments But needs energy to maintain relative constant T Therefore homeotherms use large amounts of glucose etc to maintain temperature (aerobic respiration) O 2 is consumed during respiration Rate of O 2 consumption is used to measure metabolic rate Basal metabolic rate is considered as proportional to their body mass (body mass 0. 75) (debate? See Hui & Jackson 2007 and others)
Metabolic rate and body mass
Resting metabolic rate and ambient temperature Thermoneutral zone: a range of environmental temperatures within which the metabolic rates are minimal. Critical T: lower and upper critical T
BIOL 4120: Principles of Ecology Lecture 3: Adaptation to Physical Environment: Light, Energy and Heat Dafeng Hui Office: Harned Hall 320 Phone: 963 -5777 Email: dhui@tnstate. edu
Recap n Photosynthesis and environmental factors • (Light) Temperature • Nutrients (and Water) • CO 2 Homeostasis and negative feedback Endothermy and ecotothermy
Homeotherms can escape thermal constraints of the environments Ways to keep body warm: 1. Insulation to reduce the convection: fur, feather, or body fat Mammals: fur, change fur in the winter Fur can keep body heat in and the heat out Birds: feather Insects: a dense fur-like coat (moths, bees) 2. When insulation fails: shivering (a form of involuntary muscular activity that increase heat production. 3. Small mammals: burn brown fat (bats) without shivering. Ways to keep body Cool: 1. birds and mammals: evaporation of moisture from skin 2. mammals: sweat glands (horse, human), panting 3. birds: gular fluttering
3. 16 Endothermy and Ectothermy involve trade-offs Endotherms can survive in large range of T, why not all animals are endotherms? Trade-offs: Endothermy Activity: under all environments Energy: high Food: most for respiration, less to growth Limits on size: limit on minimum size Ectotherms limited to environmental T low less for respiration more to growth limit on maximum size
Limited in size Warm-blooded animals: body mass (volume) produce heat, lost through surface area, the ratio of surface to volume is key factor too. • Small animals have larger ratio and greater relative heat loss to environment, require higher mass-specific metabolic rate to maintain and consume more food energy per unit body weight. • Too small n Need too much energy to keep temperature stable Cold-blooded animals absorb heat through n 2 gm limit surface, thus the surface area to volume is n Shrew (Solex spp) key factor. Large animals limited to warm eats own body weight in food every areas. day to maintain S/V=6*1/L temperature
3. 17 Torpor and hibernation help some animals conserve energy Torpor Small homeothemic animals become heterothermic Body temperature drops to ambient at night Inactive Bats, Some mice, kangaroos
Torpor and hibernation help some animals conserve energy n Hibernation • Many poikilotherms and some mammals have winter torpor to save energy • Selective advantage when resources are few • Mammals n Heart rate, respiration fall n Temperature drops to ambient n Groundhogs, chipmonks n Not all bears • No temperature change • Just long sleep with no eating, drinking, defecating or urinating • Females give birth and feed young in this period • Can wake up easily • Do not visit a bear cave in winter!
3. 18 Some animals use unique physiological means for thermal balance Storing body heat: Camel, oryx and some gazelles Body T change from 34 oc to 41 o. C for camel Reduce need for evaporative cooling and save water and energy Supercooling: many ectothermic animals of temperate and Arctic regions When the body T below freezing points without actually freezing The presence of certain solute (glycerol) in the body lower the freezing points Wood frog, grey tree frog, spring peeper Countercurrent heat exchange: to conserve heat in a cold environment and to cool vital part of body during heat stress.
n Countcurrent heat exchange happens in homeotherms (porpoise, whale) as well as in certain poikilotherms (tuna, mackerel shark) To preserve heat in cold water, and get ride of heat in warm water
To cool brain, reduce T by 2 -3 o. C
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