Nutrient and water acquisition and
anchorage: Roots (including
architecture, cluster, gas exchange,
contractile)
Questions
• Discussions:
– Dilys: posting paper and questions for this week
– Tatiana: will be picking a paper to post for next
week
• Paper due in 2 weeks
• Any questions?
Paper
•
Short paper: You will also be expected to write a short paper due on 8 March (3-5 pages) on
a particular evolutionary innovation in structural design. The topic can, but does not have to
be, the same as your discussion paper theme. Your paper should:
– Briefly and generally introduce your topic;
– Describe where in the phylogeny your innovation occurred;
– Describe what the evolutionary innovation in structural design is, comparing this design
to closely related taxa who lack these evolutionary shifts;
– Explain how the shift in design allowed the taxa to function differently (or perhaps in
the same way but via different means);
– End with your assessment, explaining in what scenarios taxa having the evolutionary
innovation are better off than taxa that lack this innovation (Are taxa with that
innovation more competitive in certain settings? Or might it just be a different way to do
the same thing?);
– You should include at least 8 references. You will need to include both inline citations
and a bibliography section formatted for a standard journal in ecology and evolution. I
strongly encourage you to add inline references and build your bibliography using a
reference manager. Last semester we used Zotero (http://www.zotero.org/) and it
worked very well. If anyone wants to schedule time to see how this works, let me know.
Roots
• Function?
Ferns
Gymnosperms
Angiosperms
Rooting architecture
• Primary and secondary (lateral) roots
• Diffuse root (all fibrous)
Root types
• Coarse vs fine
• Lots of specialized types. Such as?
Root distribtuion
• Rooting depth: up to ~68 m
• But, bulk of roots are in the top soil surface.
Why?
Pericycle
Endodermis
Secondary growth
Primary vs Secondary
Evolution of Cluster (Proteoid)
Question
• Most Proteaceae (~1600 spp), as well as at
least ~ 30 genera within a subclade of the
Rosid I, form cluster (Proteoid) roots.
• Associated with species growing in nutrient poor
soils (especially P, but also Fe, K, and N)
• Can their structure and function be pulled
together into a cohesive whole?
Evolution of Cluster (Proteoid)
Ferns
Gymnosperms
Angiosperms
What defines a cluster root
• Morphology
• Exudation
• Metabolism
Morphology
• Intense growth of determinate branch roots
(=rootlets) with associated hairs clustered
along root
– Simple or compound forms
– Cluster root: 1-3 cm long with 10-100
rootlets/mm, Rootlets: 0.5-35 mm, Root hairs:
800/mm2
– Originating from percicycle
– Function?
Simple
Compound
Phenology
• Production is sensitive to P (and/or Fe, N, K
levels)
– Rootlets are produced during the rainy seasons (24 months)
– Individual root may be active for only 1-3 weeks
Exudation
• P has poor solubility and is generally fairly
inaccessible
• Cluster roots have many exudates, including
large quantities of carboxylates, such as citrate
and malate, released just after rootlets are
fully formed at ~ 3-4 days (= exudative burst
that lasts ~ 2 days)
• Carboxylates bind P or displace it from the soil
Metabolism
• Citrate/malate are thought to be pulled out of
mitochondria away from the respiration
pathway
– ~20 - 30% of a plants fixed carbon can be exudates
Question
• Can cluster root structure and function be
pulled together into a cohesive whole?
– Appears to be linked in morphology, use of
exudates, and use of metabolic products
– And, …
Dauciform roots too