BIOL 4120: Principles of Ecology Lecture 6: Plant adaptations to the Environment

1. BIOL 4120: Principles of Ecology Lecture 6: Plant adaptations to the Environment Dafeng Hui Room: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

2. Topics • 6.1 Plant photosynthesis to fix carbon • 6.2 Light influences photosynthesis • 6.3 Photosynthesis is coupled with water exchange • 6.4 Water movement through plants • 6.5 Temperature influences photosynthesis • 6.6 Carbon allocation • 6.7 Other photosynthesis pathways • 6.8 Plants adaptation to different light intensity • 6.9 Plants adaptation to different temperature

3. Earth provides highly diverse environments: 1.5 million known species now

4. Three common basic functions • Assimilation: acquire energy and matter 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 require 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 (heterotrophy) • All animals are heterotrophs, secondary producers • Some organisms can be a a mixture like lichens where you have an alga and a fungus living together

5. 6.1 Photosynthesis (review) • All life on Earth is carbon based • CO2 was the major form of free carbon available in past and still is • Only photosynthesis is capable of converting CO2 into organic molecules • Only plants (some algae, bacteria) are capable of photosynthesis • All other living organisms obtain their carbon via assimilation from plants

6. Photsynthesis is a biochemical process that uses light to convert CO2 into a simple sugar such as glucose • Light of the certain wavelength (PAR) is absorbed by chlorophyll in the organelle called a chloroplast and converted via the light reactions into ATP (adenosine tri-p) and NADPH (reduced nicotinamide adenine dinucleotide phosphate) • H2O is split into oxygen and hydrogen • The oxygen is released as O2 • The hydrogen is linked to CO2 to form a three carbon organic molecule (3-PGA, phosphoglycolate; C3 photosynthesis). This is carried out by the enzyme ribulose biphosphate carboxylase- oxygenase (Rubisco) • The C3 molecules are then converted into carbonhydrates like glucose via the dark reactions • This glucose can then be used to produce energy by respiration in mitochondria or used to produce other organic compounds (proteins, fatty acids etc).

7. Photosynthesis Photosynthetic electron transport

8. 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

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

10. 6.2 Light influences photosynthesis • Obviously the amount of light received by a plant will affect the light reactions of photosynthesis • Light Compensation Point • As light declines, it eventually reaches a point where respiration is equal to photosynthesis • Light Saturation Point • As light increases, it reaches a point where all chloroplasts are working at a maximum rate • Photoinhibition • In some circumstances, excess light can result in “overloading” and even damage to chlorophyll by bleaching PAR: photosynthetically active radiation

11. 6.3 Photosynthesis involves exchanges between atmosphere and plant • Photosynthesis takes place in plants in specialized cells in the mesophyll • Needs movement of CO2 and O2 between cells and atmosphere • Diffuses via stomata in land plants (CO2, 370ppm to 150ppm) • Stomata close when photosynthesis is reduced and keeps up partial pressure of CO2 • Stomata also control transpiration • Reduces water loss • Minimizing water needs from soil (dry area) • Ratio of carbon fixed to water lost is the water-use efficiency

12. 6.4 Water moves from soil to plant to atmosphere

13. Water potential • Water moving between soil and plants flows down a water potential gradient. • Water potential ( ) is the capacity of water to do work, potential energy of water relative to pure water in reference conditions • Pure Water = 0. • in nature generally negative. • solute measures the reduction in due to dissolved substances.

14. Water moves from soil to plant to atmosphere

16. Water potential of compartment of soil-plant-atmosphere • w = p + o + m • Hydrostatic pressure or physical pressure. • Osmotic potential: tendency to attract water molecule from areas of high concentrations to low. This is the major component of total leaf and root water potentials. • Matric potential: tendency to adhere to surfaces, such as container walls. Clay soils have high matric potentials.

17. Net photosynthesis and leaf water potential Declines caused by closure of stomata

18. Water use efficiency • Trade-off • To carry out photosynthesis, plants must open up the stomata to get CO2; • Transpiration loss of water to atmosphere. • WUE: ratio of carbon fixed (photosynthesis) per unit of water lost (transpiration)

19. Photosynthesis of aquatic plants • Unique features • Lack of stomata • CO2 reacts with H2O first to produce biocarbonate. • Convert biocarbonate to CO2 • Transport HCO3- to leaf then convert to CO2 • Excretion of the enzyme into adjacent waters and subsequent uptake of converted CO2 across the membrane.

20. 6.6 Plant temperatures reflects their energy balance with the surrounding environment • Different responses of photosynthesis and respiration to temperature; • Three basic Temperature points • Min T, max T and optimal T

21. Plant leaf temperatures reflects their energy balance with the surrounding environment • Temperature is important to a plants • Photosynthesis increases as the temperature increases • Energy balance (<5% used in photosynthesis) • Radiation not used increases internal leaf temperature significantly • Some heat can be lost by convection (leaf sizes and shapes) • Some heat can be lost by radiation (leaf color) • Respiration increases as the temperature increases • Damage to enzymes etc increases with temperature • Water loss increases with temperature • Evaporation of water helps to keep the temperature lower • Thus relative humidity and available water is important Different shapes of leaves influence the convection of heat.

22. 6.7 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: reproduc.

23. Allocation and T, PPT Hui & Jackson 2006

24. Plant adaptations and trade-offs • Environmental factors are inter-dependent: light, temperature and moisture are all linked together. • In dry area: more radiation, high temperature, low relative humidity, high water demand smaller leaves, more roots • Trade-offs: more carbon allocated to below-ground.

25. 6.8 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 • Because leaf structure is limiting • High compensation and saturation lights • Changes in leaf structure evolve Red oak leaves at top and bottom of canopy

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

27. Shade tolerance and intolerance Seedling survival and growth of two tree species over a year Shade tolerance Shade intolerance

28. Shade adaptation also occurs in algae Remember that land plants are not the only plants on Earth Greed algae and diatoms also depend on sunlight for photosynthesis.

29. 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 in the bundle sheath 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 them to glucose 6.9 Other photosynthesis pathways: adaptation to water and temperature conditions

30. 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).

31. Distribution of C4 grass Spatial and seasonal gradient Number are percentage of total grass species are C4.

32. 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.

33. C3, C4 and CAM • C4 makes more effective use of CO2 • CO2 concentration in bundle cell can be 6X that of atmosphere and mesophyll cell • As rate limiting aspect of photosynthesis is usually the availability of CO2, then C4 is more efficient • Also can keep stomata closed longer and therefore better water use • But needs large amount of extra enzyme (PEP, need more energy) and there only well adapted to high photosynthesis environments • In deserts with really low water availability and high temperature • Third type – Crassulacean acid pathway – CAM • CO2 fixed converted to malate by PEP during night and stored, while stomata are open • Malate is converted back to CO2 during day and using photosynthesis, light and rubisco changed into sugar • High level of water conservation • Both processes in the mesophyll cells

34. Plants need to make serious evolutionary adaptations to water availability As water availability decreases, plants allocate more carbon to the production of roots relative to leaves. The increased allocation to roots increases the surface area of roots for the uptake of water, while the decline in leaf area decreases water losses through transpiration.

35. 6.11 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

36. Illustration of tradeoffs of C4, C3 plants with temp., CO2 concentration Increase in CO2 will influence the competition of C3 and C4

37. 6.12 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 • Micronutrients: needed in lesser quantities Zn, B • Some nutrients can be inhibitory

38. Plants exhibit adaptations to variations in nutrient availability • Uptake of a nutrient through the roots depends on its concentration • However there is a maximum • Effect of nutrient availability can also reach a maximum

39. Photosynthesis and plant growth and nutrient • Nitrogen can limit photosynthesis • Need for symbiosis • Rhizobium • Peas, beans and a few other plants • Frankia • Various woody species in southern Africa

40. Plants respond differently to extra nitrogen depending on their natural environment’s level of nitrogen or other nutrient

41. The END

42. Important set of adaptations for water conservation involve photosynthesis: • C3plants the norm in cool, moist climates • C4 plants adapted to hot, dry climates because of efficiency of CO2 uptake • CAM plants are another fundamental variation on C4 plants, also adapted to hot, dry climates

43. C3 plant anatomy and biochemistry Example: Geranium

44. C4 plant anatomy and biochemistry Examples: Sorghum vulgare (pictured), sugar cane

45. C4 photosynthesis has advantages, costs • Advantages: • CO2 in high concentration • Water loss reduced • Costs and tradeoffs: • Recovering PEP from Pyruvate expensive • Less leaf tissue devoted to photosynthesis • Not beneficial in cool climates

46. CAM photosynthesis separates cycles diurnally Example: Sedum obtusatum

47. Macronutrients

48. Micronutrients

49. Pine species are adapted to live in low nitrogen environments like sandy soils Pines retain their leaves for a long time This saves the recycling of nitrogen through the soil