Development and Structure
Salvi, Amanda M , Smith, Selena .
Effect of canopy shading on morphology, anatomy, and self-shading in spiral gingers (Costus).
The avoidance of self-shading is a common adaptation in plants to increase the light capture efficiency of leaves. While most plants orient leaves as far away as possible from each other (most often, 120°–180°), the genus Costus (Costaceae, Zingiberales), which are tropical angiosperms known as spiral gingers, has a spiromonostichous phyllotaxy with divergence angles as low as 30°–50°. One hypothesis for why this unique morphology evolved is that the leaf arrangement is an adaptation to increase light availability through a decrease in self-shading. In order to better understand Costus vegetative morphology and the relationship between light availability, two Costus species—C. malortieanus and C. pulverulentus—were studied. Research was conducted in two wet tropical forests of northern Costa Rica: Bijagual Ecological Reserve and La Selva Biological Station. Whole plant morphology of individual Costus, including percent self-shading, internode length (IL), and leaf divergence angle (LDA), was compared to canopy openness overhead (range: 0.2–20.6% open). Leaf anatomical traits, including thickness of total leaf, spongy mesophyll, and hypodermis; stomatal density; and vein length per area (VLA), were compared to both canopy openness and location of leaf along the stem. The spiromonostichous phyllotaxy was confirmed to be a successful adaptation to limit self-shading, but self-shading did not decrease in shadier conditions, nor did morphological traits (self-shading, IL, and LDA) correlate strongly with light availability. Both canopy openness and self-shading were greatest in C. pulverulentus, which may reflect its habit (tall with narrow leaves, allowing apical leaves to reach direct sunlight when the plant grows taller than nearby competing plants ). In C. malortieanus, spongy mesophyll thickness and VLA increased with increased light availability (R2 > 0.7), suggesting a higher photosynthetic ability with more light availability. Although all traits increased statistically with increased canopy openness, no other traits were strongly correlated with light availability. In contrast, in C. pulverulentus leaf anatomy changed little, suggesting an evolutionary restriction to their shadier habitat. In both species, apical leaves experiencing little self-shading only differed in VLA and stomatal density from basal leaves with the greatest amount of self-shading, suggesting leaves along the stem do not differ in photosynthetic ability. These results suggest that Costus experiences little whole plant morphological response to light availability, but can show some anatomical response, and that the spiromonostichous leaf arrangement helps to maximize photosynthetic ability in different light levels for the lifespan of the plant.
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1 - University of Michigan , Earth & Environmental Sciences, 2534 CC Little Bldg, 1100 North University Ave., Ann Arbor, Michigan, 48109-1005, United States
spiromonostichous leaf arrangement
Presentation Type: Oral Paper
Session: 29, Development and Structure I
Location: 202/Savannah International Trade and Convention Center
Date: Tuesday, August 2nd, 2016
Time: 2:00 PM
Candidate for Awards:Maynard F. Moseley Award