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Lecture 23: "Predicting Tree Responses To Climate Change"

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Biology 2601A/B
Brown Jason

Organismal Physiology Lecture No. 23: Predicting Tree Responses To Climate Change Thursday November 29 , 2012 Introduction – Trees & Forests & The Importance Of Increasing Temperatures: -Trees and forests are important for: carbon storage and sequestration, being major biodiversity hotspots and altering regional albedo and hotspot patterns. Temperature is an important control on tree distribution and its present increase will greatly affect tree populations. Tree Growth Trends: -Determining if trees vary in their response to temperature in predictable ways can be done by examining different functional groups (i.e. deciduous vs. evergreen species, conifers vs. broad-leaved species). Researchers synthesized 63 studies spanning 58 species grown in varying environments (growth chambers, greenhouses, open-top chambers and field studies) and looked at their biomass, anatomy and physiological changes. They found that elevated growth temperatures generally increase tree growth and this response is stronger in deciduous trees (evergreens often don’t grow better at warmer temperatures). Leaf and canopy growth are more stimulated than root biomass. -It appears that the reason for enhanced growth in deciduous species at higher temperatures is due to increased biomass requiring more carbon accumulation. This can be achieved through greater carbon gain (in photosynthesis), reduced carbon losses (in respiration) or a combination of both. Changes in photosynthetic capacity such as V cmax(Calvin cycle) and Jmax(electron transport) as well as the dark respiration rate were also examined. They looked at parameters measured at: 25°C (baseline rate) to observe differences that indicate acclimation and growth temperature to observe differences that indicate a combination of the direct, acute temperature effect and acclimation. -Dark respiration rates acclimate with growth temperature (trees from warmer conditions have lower basal respiration rates). There is no acclimation of photosynthetic capacity (V cmaxand Jmax). The cause of difference between evergreens and deciduous species is unclear. Black Spruce Growth: -Black spruce seeds were grown at 22/16°C (cool) and 30/22°C (warm), looking for an ability to acclimate to high temperatures. Warm-grown black spruce have: 25-30% shorter shoots, 60% less biomass, 60% lower root to shoot ratios, and could increase drought stress. Warm-grown seedlings develop drought stress more quickly than cool-grown seedlings. The same response was observed in tree rings and the greenhouse. Photosynthesis (carbon gain) is suppressed in warm-grown spruce since the thermal optimum is higher in warm-grown trees. Photosynthesis at growth temperature is 10% lower in warm- grown spruce. -Photosynthetic rates are 4.5-fold greater than respiration rates at 10-15°C, but only 2-fold higher at 35°C. Wha
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