Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate

1. 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

2. Topics (Chapter 3) • 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

3. Earth provides highly diverse environments: 1.7 million known species now

4. All species have three common basic functions • 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) • 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) • 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.

5. 3.1 Light is the primary source of energy for the biosphere • 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

6. Light is the primary source of energy for the biosphere PAR: photosynthetically active radiation 400-700 nm

7. Light absorption spectra of plants

8. Light absorption spectra of algae Ulva: sea lettuce, shallow water Porphyra: red alga, deep-water

9. 3.2 Plants capture energy of sunlight by photosynthesisPhotosynthesis (review) • All life is built on a framework of carbon atoms • The ultimate source of carbon for organic molecules is CO2 • CO2 is transformed into organic molecules by plants (photosynthesis).

10. Photosynthesis is the process by which the Sun’s energy (shortwave radiation) is used to fix CO2 into carbohydrates (simple sugars) and release O2 • 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 CO2 into simple (organic) sugars using the energy provided by ATP and NADPH • Carboxylation is catalyzed by the enzyme rubisco (ribulose biphosphate (RuBP) carboxylase-oxygenase)

11. C3 • The Calvin cycle (C3 cycle) initially fixes CO2 into 3-PGA (phosphoglycerate) This cycle is called Calvin-Bensen cycle, or C3 cycle. Plants employing it are known as C3 plants

12. RuBP: Ribulose biphosphate Rubisco: ribulose biphosphate (RuBP) carboxylase-oxygenase 3-PGA: phosphoglycerate G3P: glyceraldehyde 3-phosphate

13. C3 cycle (Calvin cycle) One major drawback of C3 pathway: Rubisco can catalyze both carbonxylation And RuBP oxygenation Reduce the efficiency of photosynthesis. C3 plant: trees, forbs, some grasses

14. Cellular respiration Photosynthesis Net photosynthesis = (Gross) Photosynthesis - Respiration

15. 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

16. Recap Water and salt balance by plants and animals Solar radiation is the energy source for life, PAR, water absorption Photosynthesis C3 photosynthetic pathway

17. To increase water use efficiency in a warm dry environment, plants have modified process of photosynthesis C3 Normal in mesophyll with rubisco C4 Warm dry environment Additional step in fixation of CO2 Phosphoenolpyruvate synthase (PEP) does initial fixation into Malate and aspartate Malate and aspartate are transported to bundle sheath as an intermediate molecule Rubisco and CO2 convert there to sucrose 3.3 Other photosynthesis pathways: adaptation to water and temperature conditions

18. C4 pathway • Advantages over C3 pathway • PEP does not interact with O2 (RuBP react with O2 and reduce the photosynthesis efficiency) • Conversion of malic and aspartic acids into CO2 within bundle sheath cell acts to concentrate CO2, create a much higher CO2 concentration. • C4 plants have a much higher photosynthetic rate and greater water-use efficiency. • C4 plants are mostly grasses native to tropical and subtropical regions and some shrubs of arid and saline environments (Crop: corn, sorghum, sugar cane).

19. CAM pathway CAM (Crassulacean acid metabolism) pathway Hot desert area Mostly succulents in the family of Cactaceae (cacti), Euphorbiaceae and Crassulaceae) Similar to C4 pathway Different times: Night: open stomata, convert CO2 to malic acid using PEP Day:close stomata, re-convert malic acid to CO2, C3 cycle.

20. Comparison of three photosynthetic pathways C3: Dovefoot geranium, C4: sorghum, CAM: Sierra sedium

22. 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.

23. 3.5 Photosynthesis of aquatic plants • Unique features • Lack of stomata • Direct diffusion of CO2 across cell membrane • Slow in water than in air (10^4 times slower) • Some plants: CO2 reacts with H2O first to produce biocarbonate, and Convert biocarbonate to CO2 • Transport HCO3- into leaf then convert to CO2 • Excretion of the enzyme into adjacent waters and subsequent uptake of converted CO2 across the membrane. • CO2 could be a constraint in dense sea-grass beds

27. Oxygen concentration in aquatic environment O2 is dissolved in water O2 concentration in water is determined by solubility and diffusion. Anaerobic conditions in the deep water High O2 in the surface due to diffusion

28. 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.

29. In dry grassland ecosystems, plants have long roots

30. Allocation and environmental factors (such as temperature and precipitation) Hui & Jackson 2006

31. Constraints Imposed by the Physical Environment Have Resulted in a Wide Array of Plant Adaptations • Plants must maintain a positive carbon balance to survive, grow, and reproduce • Essential plant resources and conditions are interdependent • Light (PAR) • CO2 • H2O and Minerals • Temperature

32. 3.7 Species of Plants are adapted to light conditions • 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 • Plants adapted to a full sun environment • Higher levels of rubisco • Lower levels of chlorophyll • High compensation and saturation lights • Changes in leaf structure evolve Light intensity Red oak leaves at top and bottom of canopy

33. Light affects photosynthesis and respiration Stuart Davies of Harvard University studied the photosynthesis and respiration of seedlings of nine tree species under different light

34. Light also affects whether a plant allocates to leaves or to roots Change of allocation to leaf of broadleaved peppermint (Reich et al.). • Shade tolerant (shade-adapted) species • Plant species adapted to low-light environments • Shade intolerant (sun-adapted) species • Plant species adapted to high-light environments

35. Shade tolerance and intolerance Seedling survival and growth of two tree species over a year Augspurger (1982) Shade tolerance Shade intolerance

36. 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

37. Recap • C4 and CAM pathways • Aquatic plants • Photosynthesis and environmental factors • Light, response curve, adaptation

38. 3.9 Temperatures influence photosynthesis and respiration • Different responses of photosynthesis and respiration to temperature; • Three basic Temperature points • Min T, max T and optimal T

39. Plants need to make serious evolutionary adaptations to temperature C4 C4 C3 Neuropogon: Arctic lichen (C3) Ambrosia: cool coastal dune plant (C3) Tidestromia: summer-active desert C4 perennial Atriplx: everygreen desert C4 plant Photosyn. rate and Topt • Topt: C3: <30oC; C4: 30oC to 40oC; CAM, >40oC

40. Plants Vary in Their Response to Environmental Temperatures • 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 the thermal conditions under which the plant is grown • A similar pattern is seen in individual plants in response to seasonal shifts in temperature (acclimation)

41. Big saltbush, C4

43. Affinity is a good measure of enzyme function. Produce different forms of enzyme.

44. 3.12 Plants exhibit adaptations to variations in nutrient availability • 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 • Some nutrients can be inhibitory

45. Plants exhibit adaptations to variations in nutrient availability • 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

46. Photosynthesis and nutrient • Nitrogen can limit photosynthesis • N in enzyme rubisco and pigment chlorophyll.

47. 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.

48. Illustration of tradeoffs of C4, C3 plants with CO2 concentration Other factors: Impact of CO2 on photosynthesis Increase in CO2 will influence the competition of C3 and C4

49. 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

50. Homeostasis • To stay alive, animals need to keep their body within certain limits • Temperature • Water balance • pH • Salt balance • Feedback systems to help to keep within specific limits • Outside limits – • Dehydration • Heat shock • Salt imbalance • Death