Adaptations of strangler figs to life in the rainforest canopy

Schmidt, Susanne and Tracey, Dieter P. (2006) Adaptations of strangler figs to life in the rainforest canopy. Functional Plant Biology, 33 5: 465-475.


Author Schmidt, Susanne
Tracey, Dieter P.
Title Adaptations of strangler figs to life in the rainforest canopy
Journal name Functional Plant Biology   Check publisher's open access policy
ISSN 1445-4408
Publication date 2006
Sub-type Article (original research)
DOI 10.1071/FP06014
Volume 33
Issue 5
Start page 465
End page 475
Total pages 11
Editor Jennifer Henry
Place of publication Collingwood
Publisher Csiro Publishing
Collection year 2006
Language eng
Subject C1
270402 Plant Physiology
620301 Native forests
Abstract Figs are rainforest keystone species. Non-strangler figs establish on the forest floor; strangler figs establish epiphytically, followed by a dramatic transition from epiphyte to free-standing tree that kills its hosts. Free-standing figs display vigorous growth and resource demand suggesting that epiphytic strangler figs require special adaptations to deal with resource limitations imposed by the epiphytic environment. We studied epiphytic and free-standing strangler figs, and non-strangler figs in tropical rainforest and in cultivation, as well as strangler figs in controlled conditions. We investigated whether the transition from epiphyte to free-standing tree is characterised by morphological and physiological plasticity. Epiphyte substrate had higher levels of plant-available ammonium and phosphate, and similar levels of nitrate compared with rainforest soil, suggesting that N and P are initially not limiting resources. A relationship was found between taxonomic groups and plant N physiology; strangler figs, all members of subgenus Urostigma, had mostly low foliar nitrate assimilation rates whereas non-strangler figs, in subgenera Pharmacocycea, Sycidium, Sycomorus or Synoecia, had moderate to high rates. Nitrate is an energetically expensive N source, and low nitrate use may be an adaptation of strangler figs for conserving energy during epiphytic growth. Interestingly, significant amounts of nitrate were stored in fleshy taproot tubers of epiphytic stranglers. Supporting the concept of plasticity, leaves of epiphytic Ficus benjamina L. had lower N and C content per unit leaf area, lower stomatal density and 80% greater specific leaf area than leaves of conspecific free-standing trees. Similarly, glasshouse-grown stranglers strongly increased biomass allocation to roots under water limitation. Epiphytic and free-standing F. benjamina had similar average foliar delta C-13, but epiphytes had more extreme values; this indicates that both groups of plants use the C-3 pathway of CO2 fixation but that water availability is highly variable for epiphytes. We hypothesise that epiphytic figs use fleshy stem tubers to avoid water stress, and that nitrate acts as an osmotic compound in tubers. We conclude that strangler figs are a unique experimental system for studying the transition from rainforest epiphyte to tree, and the genetic and environmental triggers involved.
Keyword Biomass Allocation
Carbon-13
Epiphyte
Ficus
Hemiepiphyte
Nitrate
Nitrogen-15
Rainforest
Resource Use
Stomatal Density
Tuber
Water Stress
Plant Sciences
Urostigma Sect. Malvanthera
Venezuelan Palm Savanna
N-15 Natural-abundance
Plant-responses
Water Relations
Nitrogen-source
Cloud Forest
Tree
Clusia
Q-Index Code C1

 
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Created: Wed, 15 Aug 2007, 08:19:58 EST