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Lecture 6

Biology Lecture 6 Article 4.docx

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University of Toronto St. George
Scott Browning

BIOLOGY LECTURE #6 Glorious, Golden, Gigantic Quaking Aspen - Populus tremuloides - Sister species (Eurasian aspen) occupy broadest range of any tree species in world - Alaska to Mex, Vancouver to Maine - NC part: occur @ any elevation - S part: only @ high elevations - Bark is living tissue + carries out photosynthesis, which contributes to impressive geographic range - Aspen drops its leave in winter but stay alive SO needs metabolic energy - Tan to greenish hue in bark = photosynthetic capability given by differing levels of chloroplasts - Stem photosynthesis gives aspen’s over-wintering survivor capabilities - BAD: LOWER FIRE RESISTANCE + FOOD SOURCE - Form RAMETS: individual patches of many stems, with own trunk, branches, leaves AND SHARED ROOT SYSTEM!!!! - Ramets all from single aspen seed, so make a single clone - Root system severed = separate entities but technically part of same clone because same genetically identical patches - Boundaries: seen in early spring when flowering + leafing-out occur - M + F separately (DIOECIOUS) - Early Spring: make small strings of reproductive parts, AKA CATKINS, either male (pollen) or female (eggs) - Lots of seeds mature + float off from F on cotton like hairs on air currents - After shedding pollen + sends, make leaves at same time in stem of given clone *BOUNDARIES SEEN* - Late fall prior to dropping leave =gold, yellow, rose, red leaf colors - Color patches don’t mark clonal boundaries because chemical processes make colors (sensitive to local micro-climate conditions... aspect/soil moisture) - All pigments can be found in leaf from spring to fall but when temperatures drop aspect break down green chlorophyll that dominates spring color and other pigments become more visible - Many though aspen reproduction by seeds RARE, but actually frequent - Ability of aspen to produce whole strands of “trees” provides another key element in explaining species ability to occupy huge geographic ranges - Benefits of asexual expansion: SPREADING THRU ROOTS THEN SEND UP SHOOTS - - one part of clones might be near water/vital soil nutrients “S
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