Fate of intercepted light? n Reflect n Transmit n Absorb
Fate of leaf intercepted light? n Reflect - (6-12% PAR, 70% infrared, 3% UV) Degree of reflection varies with type of leaf surface n Transmit - average 10-20% (primarily green and far red) n What would influence this? thickness and structure of leaf n Absorb – What does this depend upon?
Leaf Area Index LAI Interpretation of LAI see fig 5.5 (d) pg 47 (m 2 leaf area/m 2 ground area) LAI 3 means 3m 2 leaf area over each m 2 of ground
LAIs of different canopy types Summer Temperate Deciduous Forest: LAI 3-5 (1-5% light hitting canopy reaches floor) Summer Pine Forest LAI 2-4 (10-15% light hitting canopy reaches floor) Tropical Rain Forest LAI 6-10 (.25 – 2% light reaches floor)
Light levels and LAI n Why is the amount of light reaching the forest floor of the pine forest greater than that of the deciduous forest? n Does the LAI of an area change throughout the year? n What are the consequences of this for plants of the forest floor?
Light Levels n Are there other factors other than LAI and leaf angle that would influence the amount of light a forest floor organism might receive? See Fig. 5.7 page 49
Photosynthetic Terms n PAR – photosynthetically active radiation n Light compensation point (LCP) n Light saturation point (LSP) n photoinhibition
PS terms expanded n Light compensation point: rate of C0 2 uptake in PS = rate of C0 2 loss in Respiration n Short version rate of PS = rate of respiration n Light Saturation Point – Point at which increasing light does not increase PS n Photoinhibition - High light levels inhibit PS
Apply your Smarts n How does the concentration of Rubisco relate to photosynthesis rate? n What does the production of Rubisco have to do with respiration? n What do respiration rates have to do with tolerance to shade?
Apply your Smarts Apply your Smarts n What do respiration rates have to do with the light compensation point? n What does the light compensation point have to do with shade tolerance or intolerance? n In general what types of plants would you expect to have a lower light saturation point: shade inotlerant or shade tolerant Why?
Apply your Smarts Apply your Smarts n What would you change in a plant that would increase or lower the light compensation point? n Plant a shade intolerant plant in the shade. What would the plant do to compensate for being in low light?
Leafs and Light n How does the amount of light a leaf receives influence its shape and sizE? n See page 52 n And what does surface area and volume have to do with it?
Plants and Temperature n Heat gain and loss – What are the parameters? n Reflectivity of leaf and bark n Orientation of leaves to sun and wind? n Size and shape of leaves Frost hardiness – n Transpiration cooooooling………
Plants and Temperature n Frost hardiness – mostly genetic n Addition of protective compounds (antifreeze type) allows super cooling n Ice forms in the cell wall???? n Transpiration cooooooling………
Photosynthesis 6CO 2 + 12 H 2 0 ---> C 6 H 12 O 6 + 6H 2 0 + 60 2 OR 6CO 2 + 6 H 2 0 ---> C 6 H 12 O 6 + 60 2
PS Problem n If you put a plant in a closed container with an atmosphere of 14 C0 2, and H 2 18 0 where would you find the radioactive carbon and the heavy oxygen ( 18 0) in the container and/or plant?
Fates of reactants C0 2 H20H20 C 6 H 12 0 6 0202 H20H20 H20H20