Physiological Ecology 2

1. Physiological Ecology 2 Plant adaptation

2. Plant Adaptations to the Physical Environment: • Thermal, Moisture, and Nutrient Environments • Thermal Environment • Plants live in a thermal environment which is changable in both time and space. • At any given location, temperatures vary both diurnally (through the day) and seasonallyas a function of the input of solar (short-wave) radiation. • The ultimate source of heat is solar radiation. • However, plants are also continually absorbing short- and long-wave radiation from the surrounding environment as well (e.g. conduction, reflection etc)

3. The heat budget: heat energy gained must = the heat energy lost + energy stored. • Heat energy gained is the total of heat inputs from the sun + heat from surrounding environment + heat from metabolism. • Heat loss is the sum of infrared radiation (reradiation) + convection + transpiration (evaporation) from the plant. • The ability to dissipate heat by evaporation is influenced by stomatal conductance and diffusion gradient (vapor pressure deficit)

4. Convective heat loss is a function of the temperature difference between the plant and the surrounding air; • for heat to be lost by convection, the leaf temperature must be higher than that of the surrounding air. • It is also influenced by the conductance or thermal exchange across the boundary layer(the layer of air adjacent to the leaf surface) • e.g. as an organism looses heat the boundary layer warms – the higher difference in temp between the boundary layer & air – the greater the heat loss

5. Influence of leaf shape and size on dissipation of heat by conductance Smaller, more lobed leaves – greater surface area (for unit mass) for heat exchange

6. Net carbon gain the difference between: • rate of carbon uptake by photosynthesis and • rate of carbon loss by respiration • is influenced by temperature, as both processes respond directly to variations in temperature.

7. Plants typically display a photosynthetic response to temperature • with a lower minimum at which net photosynthesis becomes positive, • an optimum temperature at which the net rate of photosynthesis is maximum, and • a maximum temperature, above which net photosynthesis declines.

8. Species found in cooler environments tend to have lower minimum, optimum, and maximum temperatures - than species found in warmer climates. • C4 plants typically have a higher range of optimal temperatures than C3 plants.

9. Generalized relationship between leaf temperature and the processes of photosynthesis and respiration. (b) (a)

10. Temperature sensitivities of the maximum rates of net photosynthesis for C3 and C4 photosynthesis.

11. Plants also tend to acclimate to their temperature environment • - i.e. the range of temperatures over which net photosynthesis is at its maximum shifts in to match the thermal conditions under which the plant is grown.

12. Relationship between net photosynthesis and temperature for a variety of terrestrial plants from dissimilar thermal habitats. (Arctic lichen) (cool, coastal dune plant) (summer active, desert perennial) (evergreen desert shrub)

13. Temperatures affect: • - survival, • - growth, • - reproduction, and • - germination of seeds. • E.g. temperature thresholds can induce flower formation. • Other temperatures can bring about flower development. • Some plants have a “chilling” requirement • - certain number of days of low temperature to induce growth or germination.

14. Moisture Environment • The growth of plant cells and the efficiency of their physiological processes are highest when the cells are at maximum turgor—they are fully hydrated. • - When turgor pressure drops, water stress occurs, ranging from wilting to dehydration and mechanical stress.

15. For the leaves to maintain maximum turgor, the water lost to the atmosphere in transpiration must be replaced • by water taken up from the soil through the root system and transported through the stem and branches to the leaves. • The movement of water through the soil-plant-atmosphere continuum is passive (no energy required) • i.e. movement is due to pressure gradients set up by leaf losses of water through transpiration.

17. The movement of water from soil to root and from cell to cell through the plant is described by an equation based on the movement of electricity: • Ohm’s Law • This law describes the [electrical] energy movement in response to a current (~pressure) differential and subject to resistance. • For water to move, there must be a continuous water concentration gradient from soil, to the roots to the leaves etc.

18. For water to move or diffuse from soil solution into the roots and through the supporting tissues to the leaves, it must pass through plant cell membranes. • Plant membranes are differentially permeable or semi-permeable • i.e. some substances can pass through the membranes, others cannot • Plant membranes are fairly permeable to water and permeable for other substances can vary.

19. A Solute is a dissolved substance. • A Solvent is the liquid in which the solute is dissolved (e.g. water) • Osmosis is the movement (diffusion) of solvent (water) molecules from and area of high concentration, to an area of low concentration through a semipermeable membrane. • This movement or diffusion, • and whether or not the solute can pass though the semi-permeable membrane, • accounts for the spread of a solute throughout the solvent.

20. Osmotic potential is the tendency of water molecule to move from areas of high to low concentration • e.g. a solution with high concentration of water molecules (and possibly a lower concentration of solutes) • has a higher osmotic potential than a solution with a lower concentration of water molecules (and possibly higher concentration of solutes) • The OP is a also function of the concentration of a solution. • - the higher the concentration of a solution, the lower the osmotic potential and the greater the tendency to gain water.

21. The gradient of osmotic potential from the soil -where water potential / concentration is the highest- • is maintained by the continual loss of water to the atmosphere through transpiration -where the water potential is the lowest. • The loss of water through transpiration continues as long as: • (a) the amount of energy striking the leaf is enough to supply the necessary latent heat of evaporation, • (b) moisture is available for roots in the soil, and • (c) the roots are capable of removing water from the soil.

22. The value of leaf water potential at which the stomata close • and transpiration and net photosynthesis ceases • varies among plant species and reflects basic differences in their • - biochemistry, • - physiology and • - morphology.

23. Species are arranged in declining general moisture conditions

24. Plants respond to short-term moisture stress by: • - reduction of net photosynthesis; • - increased internal temperatures; • - effects on protein synthesis; • - wilting and leaf curling (reduces leaf area); • - premature autumn coloration and leaf drop; • - accumulation of inorganic ions, amino acids, sugars and sugar alcohols in leaves (alters OP)

25. Plants respond to long-term moisture stress by: • -change in leaf size and morphology and • - a decline in carbon allocation for leaf production - • with an increase of carbon for the production of roots.

26. Relationship between plant water availability and the ratio of root mass (mg) to leaf area (cm2) for broadleaved peppermint. As available water increases, the plant responds by producing more foliage at the expense of roots.

27. Plants adapted to wet environments= mesic • Plants adapted to dry environments= xeric • Wet environment plants may have a higher rate of photosynthesis and higher rate of transpiration – as water loss is not a problem • but transpiration may be limited due to high water levels outside the plant • High rates of transpiration would be an obvious a problem for dry environment plants – so photosynthesis is limited • but these plants have higher water efficiency =carbon uptake per unit of water transpired • NB – C4 plants have higher values of water efficiency

28. Interspecific variation in adaptations to mesic and xeric environments • Diurnal changes in: • stomatal conductance, • transpiration, • assimilation, and • water use efficiency (ratio of carbon uptake per unit water transpired) • for two species of Eucalyptus from contrasting environments grown under the same conditions in the greenhouse. • E. dives is a xeric species • E. saligna is a mesic species (a) (b) (c) (d)

29. The amount of carbon allocated to root mass, as opposed to leaf mass increases • as the amount of available water decreases Less water – greater root biomass

30. One way plants can loose heat is via transpiration (heat input into water vapor) • But as water level declines ability to loose heat this way declines • Heat loss via convection is another method for heat loss • Smaller leaves increase the surface area to volume ratio – so such leaves increase convection heat loss • As precipitation decreases – average leaf size decreases. • Small leaves = adaptation to loose heat in xeric conditions

31. As rainfall decreases – size of leaf decreases

32. ADAPTATIONS TO FLOODING • Too much water can be as bad as too little • Excess water around the roots can result in lack of oxygen (soil air pores filled)– causing death of root tips • The roots are less able to take up water - wilting • Also dead plant material can travel up & clog the xylem (water transporting vessels) • To adapt – plants in poorly drained soils have shallow horizontal roots systems (to maximize oxygen) • BUT - makes these plants vulnerable to drought & winds

33. Nutrient Environment • Plants require 16 elements classified as macro- and micronutrients on the basis of the quantities of the element required for plant growth. • Micronutrients (tiny amounts needed) are only limiting on: • - unusual geological formations, • - very old and weathered soils, or • - areas of extreme human disturbance.

34. Of the macronutrients (large quantities needed) Carbon, Hydrogen and Oxygen are derived from carbon dioxide and water. • They are made available to the plant as simple sugars through photosynthesis. • The remaining six— • nitrogen • phosphorus • potassium • calcium • magnesium • sulfur • —exist in a variety of states in the soil

35. Plants require nutrients in inorganic or mineral form. • So nutrients that have been incorporated into living tissues as organic nutrients and returned to the soil must be transformed to inorganic form • - through decomposition - • before they are available for uptake by plants. • The cycling of nutrients from the soil or water to the plant • and back to the soil, where it is transformed into inorganic form through decomposition is called nutrient cycling.

36. The rate of nutrient uptake by plants is influenced by availability and demand and is described by the Michaelis-Menten equation (rate of nutrient uptake as a function of the external concentration of the nutrient). • The rate of uptake of a nutrient largely controls the content of that nutrient in plant tissues. • Nutrient content of plant tissues, especially the leaves, affects important plant processes, such as photosynthesis. • e.g. 50 % of the total nitrogen in leaf tissues is associated with the maintenance of photosynthesis.

37. Plant uptake rate (V) of potassium as a function of availability (Cext) Uptake Conc. Of Nutrient • As the external nutrient concentrationincreases above some minimum, the rate of uptake by the plant increases. • As the nutrient concentration continues to rise, the rate of increase in uptake per unit increase in concentration declines. • Eventually, the plant reaches a maximum uptake rate, at which point any further increases in nutrient concentration does not result in increased rates of uptake.

38. One way that plants respond to low availability of nutrients • and the associated reductions in root uptake rates • is an increased allocation of carbon to the production of root tissue. • An additional adaptation is increased leaf longevity. • Studies show a significant inverse relationship between nitrogen concentration and leaf life span (e.g. nitrogen decreases – leaf longevity increases)

39. Relationship between (a) leaf longevity and leaf nitrogen concentration and (b) leaf longevity and net photosynthetic rate for a wide variety of plants from different habitats. low nitrogen = greater leaf longevity low nitrogen = lower rate of photosynthesis

40. Before leaf senescence(goes brown & drops off) • plants transport a significant percentage of nutrients from the leaves to the perennial parts (year round – eg stem/trunk & branches) of the plant • prior to leaf fall. • The process of reabsorption of nutrients from senescent plant parts to other plant tissues is called nutrient retranslocation.

41. Nutrient retranslocation Green Litter leaf (dropped leaves) Species %N %N %N Reabsorption White oak 2.08 0.82 60.58 Scarlet oak 2.14 0.85 60.28 Southern red oak 1.88 0.60 68.09 Red maple 1.96 0.76 61.22 Tulip poplar 2.55 0.90 64.71 Virginia pine 1.62 0.54 66.67 American hornbeam 2.20 1.16 47.27 Sweetgum 1.90 0.59 68.95 Sycamore 2.10 0.90 57.14

42. Mutualism (an interaction between two species that is beneficial to both) • is another adaptation to low nutrient conditions. • Two examples are: • nitrogen fixation – symbiotic bacteria transform atmospheric nitrogen into a form useable by plants. • This occurs in terrestrial (rhizobium bacteria) and aquatic (cyanobacteria) environments. • Legumes and red alder are examples.

43. 2) mycorrhizal fungi associated with the root systems of terrestrial plants. • They are attached to the roots and extend out into the soil. • These fungi gain energy from the roots and assist in the uptake of nitrogen and phosphorus by the roots.

44. Physiological Ecology 2 Animal adaptation

45. Animal Adaptations to the Environment • Nutritional Environment • The need for animals to derive their energy from organic carbon compounds presents them with a potentially wide range of food items. • The ultimate source of these organic compounds is plants. • However, animals differ by the means they use to acquire these compounds.

46. Herbivores utilize plant material and are primary consumers. • Food is generally plentiful, but the diet is constrained by low protein levels (plants are low in proteins and high in carbohydrates, much of which is in the form of cellulose and lignin in cell walls) and the relative indigestibility of cellulose in plant materials. • Adaptations in herbivores are aimed at increasing the digestion and assimilation of plant materials and often involve complex digestive systems with a multi-part stomach inhabited by anaerobic bacteria and protozoans that function as fermentation vats.

47. e.g. ruminants - plant matter is chewed and then swallowed the food enters the rumen where bacteria ferments plant material the fermented plant material is regurgitated (cud) and re-chewed and re-swllowed - The fermenting bacteria break down carbohydrates and also produce B vitamins, the enzyme cellulase, and amino-acids e.g. coprophagy – animals such as rabbits produce green feces (after processing by microorganisms in the caecum) These pellets are high in protein and lower fiber These are re-digested and dry, high fiber, low protein pellets are produced.

48. Omnivores utilize both plant and animal tissues. Food habits of many omnivores vary with the seasons, stages in the life cycle, and their size and growth rate. • Carnivores feed on animal tissue and are secondary consumers. • Carnivores are not usually constrained by diet quality (animal tissue is high in fat and proteins which they use as structural building blocks); • rather, their major constraint is related to obtaining sufficient amounts of food through capture of elusive prey. • Adaptations in carnivores, therefore, are related to increasing the success of prey capture.

49. Detrivores are detrital feeders, that is, they feed on dead plant and animal matter. • Like herbivores, they depend heavily on mutualistic relations with microorganisms to aid in the breakdown of cellulose and lignin.

50. Animals require mineral elements and 20 amino acids, of which 14 are essential. • These needs differ little among vertebrates and invertebrates. • The ultimate source of most of these nutrients is plants; for this reason, the quantity and quality of plants affect the nutrition of 1ary consumers. • When the amount of food is insufficient, consumers may suffer from acute malnutrition, leave the area or starve. • When food is of low quality, it reduces reproductive success, health and longevity.