Aspen Secondary Chemistry
Phenolic Glycosides and Tannins
USDA Forest Service Proceedings RMRS-..P-..18.2001.
Results:
- Among clones in a common field habitat, levels of total phenolic glycosides vary from <1 to 16%.
- Levels of condensed tannins vary from 3 to nearly 30%.
- Measurements of chemical variation among clones in the field do not indicate true genotypic variation, because they may be confounded with differences among local (clone) environments.
- Clonal variation in herbivore preference or performance may be more strongly determined by secondary than primary chemical composition.
E.A. Erwin, M.G. Turner, R.L. Lindroth, and W.H. Romme. 2001. Secondary plant compounds in seedling and mature aspen (Populus tremuloides) in Yellowstone National Park, Wyoming. American Midland Naturalist 145:299-308.
Background: Widespread establishment of seedling aspen occurred in Yellowstone National Park following the extensive 1988 fires. Aspen stands occupy 2% of YNP and aspen stems are intensively browsed by native ungulates.
Results:
- Phenolic glycosides were higher in seedlings than in mature stands.
- Condensed tannin and leaf nitrogen were higher in mature stands than in seedlings.
- Leaf nitrogen and all secondary compounds were greater in unbrowsed seedlings than in seedlings subjected to simulated browsing.
- Secondary compounds did not differ between mature aspen stands that were unburned whether or not they were browsed.
- Burned stands (all of which were browsed) had greater concentrations of secondary compounds and leaf nitrogen than the unburned stands.
- Browsing did not effect concentrations of secondary compounds in mature aspen.
- Burning increased secondary compounds and leaf nitrogen.
- Leaf phenolic glycosides and tannins are not active defenses by browsing by herbivores
- Variation in levels between juvenile and mature ramets represents ontogenetic shifts in expression of defense.
- Variation between clipped and unclipped seedlings results from shifts in carbon/nutrient availability.
Conclusion: Results from this research suggest that foliar phenolic glycosides and tannins are not active defenses induced in response to browsing by large mammals. Browsing decreased leaf nitrogen and all secondary compounds in seedlings.
Osier, T.L., S.Y. Hwang, and R.L. Lindroth. 2000. Within-and Between-Year Variation in Early Season Phytochemistry of Quaking Aspen (Populus Tremuloides Michx.) Clones. Biochemical Systematics and Ecology 28:197–208.
Objective: To quantify changes in the chemistry of ten aspen clones from leaf-out to mid-summer.
Results:
- Nitrogen and water concentrations of leaves of clones were similar and declined as the season progressed.
- Condensed tannins increased over time and variation between clones was substantial.
- Phenolic glycosides were more complex: depending upon clone, concentrations were highest in the beginning, middle or end of the period monitored.
- Concentrations of plant chemistry were highly correlated between years, suggesting that the chemistry of aspen clones are predictable year-to-year.
Carbon-Nutrient Balance
Hemming J.D.C. and R.L. Lindroth. 1999. Effects of light and nutrient availability on aspen: growth, phytochemistry, and insect performance. J. Chem. Ecol. 25:1687-1714.
Objective: To explored the effect of resource availability on plant phytochemical composition within the framework of carbon-nutrient balance (CNB) theory.
Methods: Treatments were two levels of light and three levels of nutrient availability. We measured photosynthesis, productivity, and foliar chemistry [water, total nonstructural carbohydrates (TNC), condensed tannins, and phenolic glycosides], Gypsy moths and forest tent caterpillars were reared on foliage from each treatment to determine effects on insect performance.
Results Aspen:
- Photosynthetic rates increased with high light, but not nutrient availability.
- Tree growth increased to direct and interactive effects of light and nutrient availability.
- Increasing light reduced foliar nitrogen
- Increasing nutrient availability increased foliar nitrogen.
- TNC levels were elevated under high light conditions, but not by nutrient availability.
- Starch and condensed tannins responded to changes in resource availability in a manner consistent with CNB theory; levels were highest under conditions where tree growth was limited by nutrients (high light and low nutrient availability).
- Phenolic glycosides were only moderately influenced by resource availability.
Results Insects:
- Insect performance varied relatively little among treatments.
- They performed most poorly on the high light-low nutrient availability treatment.
- Since PGs are the primary factor determining aspen quality for these insects, and these compounds were minimally affected by the treatments, the limited response of the insects was not surprising.
Conclusions:
- The ability of CNB theory to predict allocation to defense compounds depends on the response of specific allelochemicals to changes in resource availability.
- Whether allelochemicals defend a plant depends on the response of insects to specific allelochemicals.
- We found substantial allocation to storage and defense compounds under conditions in which growth was carbon-limited (low light), suggesting a cost to defense in terms of reduced growth.
Aspen Defense
T.P. Clausen, P.B. Reichardt, J.P. Bryant, R.A. Werner, K. Post and K. Frisby. 1989. Chemical model for short-term induction in quaking aspen (Populus tremuloides) foliage against herbivores. J. Chem. Ecol. 15:2335-2346.
Results:
- Simulated herbivory of quaking aspen leaves induced increases in concentrations of two phenol glycosides, salicortin and tremulacin, in leaves within 24 hr.
- Crushing leaves resulted in conversion of salicortin and tremulacin to 6-hydroxy-2.cyclohexenone (6-HCH).
- Salicortin, tremulacin, 6-HCH, and its degradation product, catechol, are toxic to the large aspen tortrix fed an artificial diet.
S.B. St. Clair, S.D. Monson, E.A. Smith, D.G. Cahill and W.J. Calder. 2009. Altered leaf morphology, leaf resource dilution and defense chemistry induction in frost-defoliated aspen (Populus tremuloides). Tree Physiol. 29:1259–1268.
Background: In May 2007, a frost event defoliated much of Utah’s high elevation aspen. About 5 weeks later, the frost-defoliated aspen produced a second leaf flush.
Results:
- Severe frost damage was characterized by patchy canopy re-flushing with leaves that were four times larger than the first flush leaves.
- Moderate frost damage produced full canopy flushes with second flush leaves that were typically smaller than the first flush leaves.
- The second flush leaves tended to be thicker, and had lower nutrient and sucrose concentrations, but had equal or higher rates of photosynthesis.
- These leaves showed a general pattern of defense chemistry induction with phenolic glycosides and condensed tannins increasing two-to threefold.
- Some of the changes in leaf morphology and defense chemistry observed in second flush leaves in 2007 persisted in leaves produced in the following year.
M. Harutaa, J.A. Pedersenb and C.P. Constabela. 2001. Polyphenol oxidase and herbivore defense in trembling aspen (Populus tremuloides): cDNA cloning, expression, and potential substrates. Physiologia Plantarium 112:552–558.
- We cloned and sequenced a trembling aspen PPO cDNA. PPO gene expression is induced systemically by wounding, by forest tent caterpillar feeding, and by MeJa.
- We propose that the major in vivo PPO substrate is catechol released from the phenolic glycoside salicortin.
- Release of catechol and subsequent PPO oxidation is a possible mechanism of toxicity of trembling aspen phenolic glycosides.
- Plant defense in trembling aspen therefore involves both protein- and phytochemical-based components.
- Such complexity as a result of an interaction of phytochemicals and plant proteins in a defense context is becoming increasingly apparent in many plant-herbivore interactions.
Aspen Toxicology
B.R. Taylor, J. S. Goudy and N.B. Carmichael. 1996. Toxicity of Aspen Wood Leachate to aquatic life: Laboratory Studies. Environ. Toxicol. Chem. 15:150–159.
Results:
- Aspen logs produce a dark, watery, acutely toxic leachate.
- Leaching from aspen chips was rapid, with 1% mass loss in the first 24 h. After 2 weeks in water, all remaining leachable material (3% total) was removed.
- Fresh aspen leachate from a 1:9 wood-water mixture (35 d immersion) was amber, pH 4, extremely high BOD (2,600 mg/L), and high conductivity (1140 mS/cm).
- Leachate was rich in phenols (30 mg/L), organic carbon (2,480 mg/L), and organic nitrogen (13 mg/L).
- Median acutely toxic concentrations of leachate were consistently 1 to 2% of full strength for trout and Daphnia.
- Inhibition of bacterial metabolism began at concentrations below 0.3%.
- Leachate was less toxic to plant life but inhibited algal growth at concentrations of 12 to 16%.
- Toxicity of fresh aspen leachate persisted for more than 2 months unless artificially aerated.
- Oxygen depletion, low pH, and phenolic compounds contribute to the toxicity of aspen leachate, but much of the toxic effect must be attributed to other, unidentified constituents.
Methodology Preserving Leaves
C.M. Orians. 1995. Preserving leaves for tannin and phenolic glycoside analyses: A comparison of methods using three willow taxa. J. Chem. Ecol. 21:1235-1243.
Freeze-dried leaves in external flasks without temperature control contain lower concentrations of phenolic glycosides,
Air-dried leaves had lower concentrations of condensed tannins vacuum-dried fresh leaves have high concentrations of both phenolic glycosides and condensed tannins. Salicin, a product of salicortin and 2.cinnamoyl salicortin degradation, is absent in vacuum-dried leaves, but present in air-dried leaves and very high in freeze-dried leaves. Thus, the presence of salicin in this system is an artifact of the preservation technique.