Shoots

1. Shoots

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

3. Shoot Growth • Free Growth • Concurrent initiation and elongation of new stem cells • Fixed Growth • Bud forms first year, elongation the second year • Fixed & Free Growth • Spring flush of fixed growth and summer flush of free growth under good conditions

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

5. Types of Shoots • Syllepsis • Development of a lateral shoot at the same time as the main axis • Prolepsis (fixed growth) • Lateral shoot development after a period of dormancy • Lammas (free growth) • When the terminal shoot exhibits a resumption of growth after bud set

6. Stems

7. 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.

8. What is the purpose of Secondary Growth? • Strengthens the stem • Increases transport of food & water between shoots and roots

9. Secondary Growth Includes…

10. The Cambium • Meristimatic (undifferentiated) sheath of cells surrounding stem, shoots, and roots • Vascular cambium • Contains a zone of actively dividing cells which will differentiate to become xylem and phloem • Dormant (1-10 cells wide) • Active Growth (5-40 cells wide)

11. Initiation of Cambial Growth • Started by translocation of hormones (auxins) caused by hydration, warm temperatures, photoperiod (Does this sound familiar?) • Creates the • Xylem: water- and nutrient-conducting cells • Sapwood/heartwood • Phloem: photosynthate conducting inner bark

12. Secondary Growth Includes…

13. The Bark • Purpose: • Protection • Prevention of Water Loss

14. Vasular Cambium Phloem Xylem Phellem (cork cells) Phellederm Cork Cambium (Phellogen) The Bark Ratio of Phloem : Xylem 1 : 6

15. Vasular Cambium Phloem Xylem Phellem (cork cells) Phellederm Cork Cambium (Phellogen) 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)

16. Vasular Cambium Phloem Xylem Phellem (cork cells) Phellederm Cork Cambium (Phellogen) The Bark • Outer bark (Periderm) is composed of: • Phellogen • Cork cambium (makes the phellem & phelloderm) • Phellem • Suberized – cork cells • Phelloderm • unsuberized

17. 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.)

18. Phloem Cells • Contains • Sieve elements • Connected by sieve plates to form sieve tubes • Active loading & unloading of solutes throughout the plant (requiresenergy) • Companion cells • Helps keep sieve elements viable & stores solutes • Phloem parenchyma cells • Storage & lateral transport of solutes & water • Phloem fibers • strength

19. Secondary Growth Includes…

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

21. 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

22. 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 • Xylem parenchyma • Only part of xylem which is alive • Xylem fibers • Strength

23. 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

24. 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

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

26. 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)

27. Transverse Xylem Cells • Contains • Parenchyma Cells • Living cells in xylem • Store sugars, nutrients, etc. • Transport selected minerals into/out of vessels • Ray tracheids • Found only in conifers • Allow for horizontal transport of water

28. 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

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

30. Ring Porous Diffuse Porous

31. 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 • Ring width and maximum wood density change with climate

32. 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

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

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

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

36. 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% A Effect of Drought on (A) weekly needle elongation and (B) earlywood-latewood formation in red pine B