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6 Cards in this Set
- Front
- Back
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how does snow help plants? |
with snow cover, plants are insulated, and soil may not freeze at all |
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what is the process of frost hardiness? |
2 major phases (beginning with growth cessation in autumn); 1. induction of frost hardiness; 2. exposure to near freezing temperatures deep dormancy is present 6 weeks after intial stages - buds remain dormant until they have been exposed to winter temperatures for a long period cells: membrane changes so it's easier for water to leave cell by osmosis (and freeze in intercellular area), this leaves little water in cell; sugars and other solutes accumulate to act as antifreeze |
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what is special about frost hardiness in deciduous trees? |
leaves fall off to save water (frozen soil water can't replace water lost through transpiration) leaf senescence (death) and abscission (shedding) is triggered by phytohormones (ethylene and abscisic acid among others) associated with the photoperiod getting shorter |
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how does leaf abscission occur? |
the leaf stops producing chlorophyll (colour change) - anthocyanins (red - form of sunscreen), carotenes (orange), xanthophyll (yellow) and other pigments present in leaf show proteins and fats are broken down and transported out of the leaf abscission zone forms at the base of the petiole (leaf stem) and leaf separates wound left behind is covered by waxy substance suberin |
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what do carotenes do? |
powerful antioxidants - Reactive Oxygen Species can form during photosynthesis and be very damaging |
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When are buds ready to grow again? |
chilling requirement met by Jan/Feb, but usually still too cold need cumulative sum of heat (x number of x degree days) so they know they've avoided frost HS= (number of days) x (te-to) terminal buds have higher threshold temperatures and heat sums than lateral buds |
