Forest Bio PDF
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This document discusses photosynthesis, respiration, and water relations in plants. It covers topics like photorespiration, light compensation point, light saturation point, and the effects of water and temperature on photosynthesis.
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Photorespiration ○ Happens in the light ○ RuBisCO binds to oxygen instead of carbon ○ RuBP + O2 → 3C + 2C. 2C gets split into CO2, and the steps for that is photorespiration ○ No ATP Su...
Photorespiration ○ Happens in the light ○ RuBisCO binds to oxygen instead of carbon ○ RuBP + O2 → 3C + 2C. 2C gets split into CO2, and the steps for that is photorespiration ○ No ATP Summary ○ NDPH2 = The Reducing power Reduces CO2 Is used to get hydrogens to make a carbohydrate END OF MATERIAL FOR EXAM 2 Environmental effects on photosynthesis Light compensation point: the minimum light level where you break even No gain or loss in carbon Around 20-40 microM/m^2 s Little to now growth in the plant Below this point, more respiration occurs than photosynthesis Dark respiration: completely in the dark When the plant breathes out carbon dioxide Light saturation point: point that anymore light cannot increase photosynthesis Where the curve plateaus Maximum photosynthetic rate a plant can achieve The slope on the linear portion of the line: known as light use efficiency ○ ○ ○ Graph with shade curve and sun curve Point 1: Sun plants have greater respiration than shade plants near origin Point 2: Shade plants have greater light use efficiency on linear part of line This is because they put more chlorophyll into light harvesting chlorophyll They saturate so low because they have fewer photosystems Point 3: Higher saturation at plateau of sun curve Point 4: Sun has greater max photosynthetic rate at plateau Light Some leaves can change shape based on whether they are in the shade or the sun ○ Shade leaves can become thinner between parts and more spread out Will have positive photosynthesis at lower levels, but will saturate at lower light levels ○ Sun leaves can be thicker and have less surface area ○ Water R ate of photosynthesis is high when water intake is good and vice versa Plants open their stomata to let CO2 in, but water vapor rushes out leading trees to experience water deficits Stomatal effects refer to the fact that during a drought, trees often respond by closing their stomata. This reduces water loss but decreases CO2 intake. Non stomatal effects: refers to general internal problems which occur during water stress which limit photosynthesis. (Ex. Chloroplast disruption) Temperature ○ 20-30 degrees celsius is a good area CO2 Studies find an increase in photosynthesis and growth when there is an increase in CO2 lants have both photosynthesis and respiration P Respiration Glycolysis ○ Breaking down of large carbohydrates into smaller carbon units ○ Units then get sent to the Krebs Cycle Krebs Cycle ○ Units are broken down into CO2 ○ Get NADH and FADH Electrontransport with NADH and FADH, but it flows the opposite way ○ Makes ATP and water is generated Essentially it is photosynthesis backwards by using the sugar first The oxidation of carbohydrates which results in the release of energy in the form of ATP Used formaintenanceandgrowth Growth Photosynthesis Respiration rate ○ Maintenance and growth Maintenance typically occurs more in older trees Seasonal pattern of photosynthesis and respiration ○ Some trees perform photosynthesis for 6 months vs some for 9 months Leaf area ○ Generally the higher the leaf area index, the faster the plant grows CHAPTER 4 Water Leaves are 80-90% water 50% water in wood Is the solvent for all reactions Is the reactant for photosynthesis Maintains turgor (pressure) in plant tissue Cellular water relations (movement) Water potential ○ Water flows freely from high to low potentials ○ To go from low to high, a pump may be needed ○ Pure water has water potential = 0 ○ Pure water has an osmotic potential also equal to 0 ○ The osmotic potential is due to the addition of solutes to water (goes down) ○ If things are dissolved in water, the potential becomes negative Osmotic Potential - READ TEXTBOOK CHAPTER FOR EXAMPLES Water potential =osmotic potential + pressure potential ○ Plants can hold more pressure due to their cell wall Osmometer Water moves from higher water potential to lower ○ Reverse osmosis ○ ○ A piston is used to apply pressure Water Uptake The taller the tree, the more water “pressure” it has ○ When cut, water does not spill out everywhere Cohesion Tension Theory ○ Water in the trees are undertensionrather than pressurebecause they are beingpulledrather than pushed to the top ○ Driving Force: an ever decreasing water potential out in the air 100% Relative Humidity → water potential of 0 90% → -143 bars ○ Hydration: Pathway has to stay hydrated for system, to work ○ Cohesion: For everything to hold together, water has to be cohesive Caused by water’s hydrogen bond Chain doesn’t snap, water is pulled to the top Transpiration Measuring Water Potential ○ Need a pressure chamber (bomb) How does the mesophyll cell get water from a tube (xylem) if it has positive pressure and the tube has negative pressure? Drought Resistance (determinants) ○ Root systems Deeper root systems can have better drought resistance ○ Leaf adaptations between species Pine needle vs broadleaf Most pines can withstand drier conditions ○ Metabolic adaptations Some plants have tight stomatal control ○ Water storage Trunks can store water ○ Osmotic adjustment Trees are capable of adjusting osmotic potential -15 wp=-15op+0p ○ Will be wilted -15 wp=-18op+3p ○ Not wilted Can adjust 3-5 bars Growth Regulators -CHAPTER 5 ○ Auxin Helps to maintain the trees (apical dominance) Stimulates rooting (main growth regulator in the powder for rooted cuttings) Is involved with phototropism (plant’s movement toward light) Stimulates elongation at the tip Causes epicormic branches ○ Gibberellins (GA) Is the signal that tells cells to start elongating (stem) Flower/fruit production Anti-GA’s Inhibits the production of GA ○ Plants don’t elongate ○ Cytokinins Stimulates cell division Can be sprayed on trees and numerous new buds start to form ○ Ethylene “Aging” hormone Helps with the ripening of fruit ○ Abscisic Acid (AbA) Causes seed and stem dormancy Dormancy ○ Imposed Dormancy Perennial plants Goes dormant because of unfavorable dormancy conditions External factors cause dormancy Grass that stops growing because of cold weather ○ Innate Dormancy What trees have ○ Pre dormancy Ex. Dry conditions then lots of rain causes blooming Is reversible Premature blooming ○ True dormancy Prevents germination despite proper conditions ○ Post dormancy Capable of breaking bud and growing Still held back by bad weather Dormancy development (true dormancy) ○ Daylength Turning lights off or using a black sheet to act as shorter days ○ Temperature Lowering temp can make trees go dormant ○ Water supply Dormancy needs dryer conditions ○ Nutrient supply Having a surplus of nutrients (just fertilizing the lawn) delays dormancy Release from dormancy ○ To release a tree from true dormancy to post dormancy, they need 6-8 weeks if chilling ○ Warm soil and cytokinin in the soil signals bud breaking (has to be in post dormancy) Soil takes a long time to get warm, which helps to not become active too early Seed source differences ○ Northern seed sources require longer photoperiods (daylength) for active growth to continue. If they are moved south, they will set bud much sooner. If southern seed sources are moved north, they require shorter photoperiods, which keeps them growing for longer up north Cold tolerance ○ Trees have no heat source Winter burn ○ Red belt disease Sort of like a belt on the mountains where the soil above freezes and the soil below is warm enough Frost cracks ○ When trunk expands and splits due to water freezing in the xylem Chilling Injury ○ When plants are exposed to low temperatures, but not below freezing Membranes above freezing temperatures go solid Strawberries Saturated fatty acids are solid at higher temperatures (fewer to no double bonds) ○ Stay liquid all the way down into very cold temperatures Supercooling ○ Lowering a liquid’s temperature below its freezing point without it solidifying Oaks, elms, walnut, apple Intracellular Dehydration ○ Not supercooling ○ Pushes water out of the cells and into the spaces between them so that it can freeze and not cause damage ○ Simply just frozen because it’s dehydrated Homogeneous Nucleation Point ○ -39 C
