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SU FOR 232 - Adaptation to Light

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FOR 232 1st Edition Lecture 6Outline of Last Lecture I. AdaptationII. Liebig’s Law of Minimum: (1840)III. Blackman’s Law of Limiting Factors (1905):IV. Shelford’s Law of Tolerance (1913): V. FitnessVI. Compensating factorsVII. HomeostasisOutline of Current Lecture: Adaptation to Light I. Why are plants green?II. LightIII. PhotosynthesisIV. Shade ToleranceV. Competition of lightVI. Morphological AdaptationsVII. PhotoperiodismVIII. ProvenanceIX. Flowering timesX. Spring phenologyCurrent LectureI. Why are plants green?a. Because they reflect mostly green wavelength to our eyesb. Plants absorb primarily blue and red wavelength for photosynthesisII. Lighta. Visible light represents a tiny fraction of all types of energyb. PAR (Photosynthetically Active Radiation) (in previous lecture notes)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.c. Action Spectrum: is response of photosynthetic pigments to light wavelengthsIII. Photosynthesisa. Light reactions: capture of solar energy, uptake of CO2, release of O2 and water vapori. Gas exchange through stomataii. O2 is waste productb. Dark reactions: C fixation in carbohydrate using energy from light reactionsi. Do not require darkness.. they just do not require lightii. C from CO2 used to build backbone of sugars such as glucose iii. Multiple pathways:1. C3- common, efficient but can be limited by intense sunlight, high temps2. C4- grasses and tropical plants, good at high temps, drought-vulnerable3. CAM succulents and desert species, capture CO2 only at night, store in organic acids, use the C photosynthesis during daytimec. Light response curve: rate of photosynthesis over time, after light strikes chloroplastsd. Compensation point- level of light needed to achieve no net yield of energy i. Costs of chemical reaction are offset by energy produced from ite. Induction rate- rate of change in Ps as light increases (shape of reaction curve)f. Saturation point- light level at which the maximum photosynthesis rate is reachedIV. Shade Tolerance: species vary in their ability to grow and survive in deep shade. Adaption involves different responses to light.a. Shade-intolerant species have higher max Ps rate and saturation pointb. Shade-tolerant species have lower compensation point.c. Shade tolerant trees depend on sunflecks as source of direct light.V. Competition for lighta. Example: Beech can tolerate deeper shade ad can advance to canopy without much light. So infrequent and small gaps favor beechb. Sugar maple elongates upward into gaps more quickly than beech, but needs more light to do so. So sugar maple favor frequent and large gaps of light.c. These difference in shade tolerance, along with variable disturbances, allow species to coexist.VI. Morphological Adaptationsa. Dimorphism: two or more formsb. Sun vs shade leavesi. Leaves in full sun tend to be smaller, simpler, numerousii. Leaves in shade are larger, often more complex in shape, fewerc. Early season vs late seasoni. Seasonal changes in leaf morphology can adapt to changing light conditions (angle, intensity, cloud cover)d. Phototropism: adjusting leaf angle with sunlight, either to capture more lighte. Or to avoid photoinhibition (too much light can interfere with photosynthesis)VII. Photoperiodism:a. Response of plants to timing and length of light and dark periods (which change in predictable patterns during each year)b. Biological clock- allows plants to adjust growth and metabolism to seasonal fluctuationsc. Photoperiod (day length) controls:i. Entrance into dormancy for the most temperate/ boreal speciesii. Flowering timesiii. Total productivityiv. Plant nutritionVIII. Provenance:a. Local populations are adapted to photoperiod at a given latitudei. As days lengthen, it likely will get warmer soon, and this occurs later at high latitudesii. As days shorten, it likely will get colder soon, and this occurs earlier at high latitudesiii. In colder climates, shorter dark periods needed to induce winter dormancyb. Individuals will typically exhibit this photoperiod response when transplanted t other locations = provenanceIX. Flowering timesa. Many plant species reproduce based on photoperiod cuesb. Short-day plants reproduce during short photoperiods (either spring or fall)c. Long-day plants reproduce during long photoperiods or interrupted, irregular photoperiodsd. Timing of reproduction is an adaptation that coincides with recruitment strategiesX. Spring Phenologya. Spring flush (bud burst, leaf out) requires a minimum photoperiod (and an earlierfreezing period) but can be highly temperature dependent b. Warm temps. In late winter can initiate growth many weeks before risk of frost endsc. Some species are precious growers, requiring less light if temperatures warm earlier than usuald. Thaw-freeze cyclesi. Crop damage (apple orchards in 2010 in NY)ii. Sugar


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