Shoots, Stems, and Growth - Understanding Tree Structure and Development

1. Ch. 6Structure and Growth • Tree form • Shoots • Primary growth • Stems • Primary and secondary growth • Roots • Primary and secondary growth • Leaves • Primary growth

2. Shoots&Stems

3. Shoots – Primary growth

4. Lateral Primordia Bud Scales # Age Classes of Needles (function of species & environment) Different Needle Lengths (function of environment)

5. Intermittent growth is the rule! • Growth is determined by environmental constraints • cold temperatures • water stress • Buds may become • resting • dormant

6. Types of Shoots • Syllepsis • Development of a lateral shoot at the same time as the main axis • Prolepsis • Lateral shoot development after a period of dormancy • Multiple Flushing • Several flushes of growth over the growing season with resting bud set in between • Lammas • When the terminal shoot exhibits a resumption of growth after bud set

7. Syllepsis Development of a lateral shoot at the same time as the main axis Photos from G.R. Powell, University of New Brunswick http://www.unbf.ca/forestry/species/larix.htm

8. Types of Shoots • Syllepsis • Development of a lateral shoot at the same time as the main axis • Prolepsis • Lateral shoot development after a period of dormancy • Multiple Flushing • Several flushes of growth over the growing season with resting bud set in between • Lammas • When the terminal shoot exhibits a resumption of growth after bud set

9. Prolepsis Lateral shoot development after a period of dormancy Photos from G.R. Powell, University of New Brunswick http://www.unbf.ca/forestry/species/larix.htm

10. Types of Shoots • Syllepsis • Development of a lateral shoot at the same time as the main axis • Prolepsis • Lateral shoot development after a period of dormancy • Multiple Flushing • Several flushes of growth over the growing season with resting bud set in between • Lammas • When the terminal shoot exhibits a resumption of growth after bud set

11. Ch. 6Structure and Growth • Tree form • Shoots • Primary growth • Stems • Primary and secondary growth • Roots • Primary and secondary growth • Leaves • Primary growth

12. Stems

13. Stem Growth The ability to form (and add) consecutive layers of structural tissues (secondary growth) to the primary stem distinguishes woody species from all other plants.

14. What is the purpose of Secondary Growth? • Strengthensthe stem • Increases transport offood & waterbetween shoots and roots

15. Secondary Growth Includes…

16. The Cambium • Meristimatic (undifferentiated) sheath of cells surrounding stem, shoots, and roots • Vascular cambium • Dormant (1-10 cells wide) • Active Growth (5-40 cells wide) • Contains a zone of actively dividing cells which will differentiate to become • Xylem: water- and nutrient-conducting cells • Sapwood/heartwood • Phloem: photosynthate conductinginner bark

17. Secondary Growth Includes…

18. Xylem Cells • 2 Layers • Heartwood (central core) • Inactive • Serves only for support • Sapwood (outer portion) • Active transport of water • Support

19. Xylem Cells • Develop and then “die” (lose cytoplasm within a week of development) • Transport water • In a plant that is 1-m tall, 99.5% of all water is transported through the xylem • Have an added secondary cell wall (with lignin) to prevent collapse under tension & prevent water loss

20. Longitudinal Xylem Cells • Contains • Tracheids • Small, shorter than vessels • Long, angled connections • Connected by pits • Vessels • Move more water, but susceptible to cavitation • Stacked one atop the other • Connected by partially perforated walls

21. Tracheids • Found in gymnosperms & angiosperms • Water moves from one tracheid to the next through bordered pits • Aspirate & seal off for protection during freeze/thaw or drought

22. Vessels • Found in angiosperms • Water moves from one vessel to the next through perforated plates • Form long tubes (few cm to several m) • Lateral movement only occurs through bordered and half-bordered pits • Supply large amounts of water quickly • Cavitation can be a problem

23. What is Cavitation, anyway? • Water is under such greattension, it becomes unstable. • As tension increases, dissolved gases within water escape to the vapor phaseforming a bubble • Bubble expands, filling the vessel element. • Perforation plates prevent it from moving to and damaging other vessels • The bubblebreaks the continuity of the water column, stopping water transport

24. Pressure Gradients in 100-m Tall Redwoods Friction: 0.02 MPa m-1 X 100 m = 2 MPa Gravity: 1 MPa Total Pressure: 3 MPa 3 MPa *9.87 Atm = 29.6 Atmospheres 1 MPa (or 29,610 mb) Pressure at sea level = 1 Atm = 1013 mb Pressure at 3,205 ft = 0.88 Atm = 879 mb (1 MPa = 9.87 Atm)

25. Transition from Earlywood to Latewood • Why the transition? • Bud set – trees get ready for dormancy • Low temperatures • Drought • Photoperiod (length of daylight)

26. Ring Porous Diffuse Porous

27. Growth Rings • Xylem formation increases diameter of trees • Distinguishable by formation of earlywood and latewood • Extremely useful in assessing global climate change • Can even help distinguish between “natural” an “human-influenced” climate change • Dendrochonology • Ring width and maximum wood density change with climate

28. Growth Rings • Consist of • Earlywood • Large diameter • Thin cell walls • Less dense • Latewood • Small diameter • Thick cell wall • “Narrow” • Thickness & density depend upon average mean temperature

29. Growth Rings • Can be sharp…… • Ring porous • Hard pines, Douglas fir, larch, juniper Or gradual…… • Diffuse porous • Alder, beech, dogwood maple

30. Secondary Growth Includes…

31. The Bark • Purposes: • Protection • Prevention of Water Loss

32. The Bark Ratio of Phloem : Xylem 1 : 6

33. The Bark • Includes all tissues outside the vascular cambium • Inner living phloem • Not lignified • Eventually collapses and becomes part of the outer bark • Dead outer tissue (rhytidome)

34. Phloem Cells • 0.5 to 1.0 mm thick with thin walls • Retain cytoplasm (remain alive) for ~1 year; must be continually differentiated from the vascular cambium • Transport sugars & nutrients to wherever needed (roots, stems, fruits, seeds, etc.)

35. Phloem Cells • Contain • Sieve elements • Connected by sieve plates to form sieve tubes • Active loading & unloading of solutes throughout the plant (requires energy) • Companion cells • Helps keep sieve elements viable & stores solutes

36. cambium ray (xylem parenchyma) row of fibers vessel elements forming a vessel fiber tracheid ray (phloem parenchyma) xylem parenchyma cell phloem sieve tube cells with sieve plates, companion cells Stem Cross-Section

37. Play Movie

38. Leaf biomass Sapwood Cross-Area How does this relate to this class?

39. 90.78 Total Age of Cross-Section (yrs) Height (ft) 0.00 0.00 19.16 28.73 diameter (in) Stem Diameter vs. Height of a 79-year-old tree

40. Irrigated 160 23=20+3 Annual ring=6.5mm Latewood = 8% 130 30 = 25+5 Annual ring=5.9mm Latewood = 13% Drought 110 16=6+10 Annual ring=3.8mm Latewood = 8% 80 19=9+10 Annual ring=3.0mm Latewood = 13% B Effect of Drought on (A) weekly needle elongation and (B) earlywood-latewood formation in red pine A