Leaf Chemistry (leaf + chemistry)

Distribution by Scientific Domains

Selected Abstracts

Effects of variable phytochemistry and budbreak phenology on defoliation of aspen during a forest tent caterpillar outbreak

Jack R. Donaldson
Abstract 1,The present study assessed the relationship between clonally variable rates of defoliation in trembling aspen (Populus tremuloides Michx.) and two potential resistance traits: defensive chemistry and leaf phenology. 2,In 2001, coincident with a major outbreak of the forest tent caterpillar (Malacosoma disstria Hubner) in the northcentral U.S.A., we monitored defoliation rates, phytochemical composition, and foliar development in 30 clones of trembling aspen. Leaf chemistry was also assessed in re-flushed leaves and 2 years post-outbreak. 3,Early in the season, differences in defoliation among clones were substantial but, by mid-June, all clones were completely defoliated. Leaf nitrogen, condensed tannins, and phenolic glycosides varied among clones but did not relate to defoliation levels. Budbreak phenology differed by 3 weeks among clones and clones that broke bud early or late relative to forest tent caterpillar eclosion experienced reduced rates of defoliation. 4,Defoliation led to increased tannins and slight decreases in phenolic glycoside concentrations in damaged leaf remnants, but to moderately decreased tannins and a six-fold increase in phenolic glycosides in reflushed leaves. This shift in chemical composition may significantly affect late season herbivores. 5,These results suggest that aspen chemical resistance mechanisms are ineffective during intense episodic eruptions of outbreak folivores such as the forest tent caterpillar. Variable budbreak phenology may lead to differential susceptibility during less intense outbreak years and, at peak forest tent caterpillar population densities, mechanisms affording tolerance are probably more important than chemical defences. [source]

Shift in birch leaf metabolome and carbon allocation during long-term open-field ozone exposure

Abstract Current and future ozone concentrations have the potential to reduce plant growth and increase carbon demand for defence and repair processes, which may result in reduced carbon sink strength of forest trees in long-term. Still, there is limited understanding regarding the alterations in plant metabolism and variation in ozone tolerance among tree species and genotypes. Therefore, this paper aims to study changes in birch leaf metabolome due to long-term realistic ozone stress and to relate these shifts in the metabolism with growth responses. Two European white birch (Betula pendula Roth) genotypes showing different ozone sensitivity were growing under 1.4,1.7 ambient ozone in open-field conditions in Central Finland. After seven growing seasons, the trees were analysed for changes in leaf metabolite profiling, based on 339 low molecular weight compounds (including phenolics, polar and lipophilic compounds, and pigments) and related whole-tree growth responses. Genotype caused most of the variance of metabolite concentrations, while ozone concentration was the second principal component explaining the metabolome profiling. The main ozone caused changes included increases in quercetin-phenolic compounds and compounds related to leaf cuticular wax layer, whereas several compounds related to carbohydrate metabolism and function of chloroplast membranes and pigments (such as chlorophyll-related phytol derivatives) were decreasing. Some candidate compounds such as surface wax-related squalene, 1-dotriacontanol, and dotriacontane, providing growth-related tolerance against ozone were demonstrated. This study indicated that current growth-based ozone risk assessment methods are inadequate, because they ignore ecophysiological impacts due to alterations in leaf chemistry. [source]

Effects of Elevated Carbon Dioxide on the Growth and Foliar Chemistry of Transgenic Bt Cotton

Gang Wu
Abstract A field study was carried out to quantify plant growth and the foliar chemistry of transgenic Bacillus thuringiensis (Bt) cotton (cv. GK-12) exposed to ambient CO2 and elevated (double-ambient) CO2 for different lengths of time (1, 2 and 3 months) in 2004 and 2005. The results indicated that CO2 levels significantly affected plant height, leaf area per plant and leaf chemistry of transgenic Bt cotton. Significantly, higher plant height and leaf area per plant were observed after cotton plants that were grown in elevated CO2 were compared with plants grown in ambient CO2 for 1, 2 and 3 months in the investigation. Simultaneously, significant interaction between CO2 level investigating year was observed in leaf area per plant.Moreover, foliar total amino acids were increased by 14%, 13%, 11% and 12%, 14%, 10% in transgenic Bt cotton after exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 in 2004 and 2005, respectively. Condensed tannin occurrence increased by 17%, 11%, 9% in 2004 and 12%, 11%, 9% in 2005 in transgenic Bt cotton after being exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 for the same time. However, Bt toxin decreased by 3.0%, 2.9%, 3.1% and 2.4%, 2.5%, 2.9% in transgenic Bt cotton after exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 for same time in 2004 and 2005, respectively. Furthermore, there was prominent interaction on the foliar total amino acids between the CO2 level and the time of cotton plant being exposed to elevated CO2. It is presumed that elevated CO2 can alter the plant growth and hence ultimately the phenotype allocation to foliar chemistical components of transgenic Bt cotton, which may in turn, affect the plant-herbivore interactions. [source]

Insect herbivores and their frass affect Quercus rubra leaf quality and initial stages of subsequent litter decomposition

OIKOS, Issue 1 2008
Christopher J. Frost
Defoliation-induced changes in plant foliage are ubiquitous, though factors mediating induction and the extent of their influence on ecosystem processes such as leaf litter decomposition are poorly understood. Soil nitrogen (N) availability, which can be affected by insect herbivore frass (feces), influences phytochemical induction. We conducted experiments to test the hypotheses that insect frass deposition would (1) reduce phytochemical induction following herbivory and (2) increase the decomposition and nutrient release of the subsequent leaf litter. During the 2002 growing season, 80 Quercus rubra saplings were subjected to a factorial experiment with herbivore and frass manipulations. Leaf samples were collected throughout the growing season to measure the effects of frass deposition on phytochemical induction. In live foliage, herbivore damage increased tannin concentrations early, reduced foliar N concentrations throughout the growing season, and lowered lignin concentrations in the late season. Frass deposition apparently reduced leaf lignin concentrations, but otherwise did not influence leaf chemistry. Following natural senescence, litter samples from the treatment groups were decomposed in replicated litterbags for 18 months at the Coweeta Hydrologic Laboratory, NC. In the dead litter samples, initial tannin concentrations were lower in the herbivore damage group and higher in the frass addition group relative to their respective controls. Tannin and N release rates in the first nine months of decomposition were also affected by both damage and frass. However, decomposition rates did not differ among treatment groups. Thus, nutrient dynamics important for some ecosystem processes may be independent from the physical loss of litter mass. Overall, while lingering effects of damage and even frass deposition can therefore carry over and affect ecosystem processes during decomposition, their effects appear short lived relative to abiotic forces that tend to homogenize the decomposition process. [source]

Early ontogenetic trajectories vary among defence chemicals in seedlings of a fast-growing eucalypt

Abstract Ontogenetic changes in leaf chemistry can affect plant,herbivore interactions profoundly. Various theoretical models predict different ontogenetic trajectories of defence chemicals. Empirical tests do not consistently support one model. In Eucalyptus nitens, a fast-growing tree, we assessed early developmental changes to seedlings, in foliage concentrations of nitrogen and the full suite of known secondary (defence) chemicals. This included the terpene, ,-pinene, whose impact on marsupial herbivory is unknown. To test for the influence of abiotic conditions on the ontogenetic trajectories we overlaid a nutrient treatment. Ontogenetic trajectories varied among compounds. Sideroxylonals and cineole were barely detected in very young seedlings, but increased substantially over the first 200 days. Total phenolic concentration increased fourfold over this time. In contrast, ,-pinene concentration peaked within the first 60 days and again between 150 and 200 days. Nutrients altered the degree but not the direction of change of most chemicals. A shorter trial run at a different season showed qualitatively similar patterns, although ,-pinene concentration started very high. We investigated the effect of detected levels of ,-pinene and cineole on food intake by two mammalian herbivores, common brushtail possums (Trichosurus vulpecula) and red-bellied pademelons (Thylogale billardierii). Under no-choice conditions neither terpene reduced intake; but with a choice, possums preferred ,-pinene to cineole. The ontogenetic trajectories of most compounds were therefore consistent with models that predict an increase as plants develop. Published data from later developmental stages in E. nitens also confirm this pattern. ,-Pinene, however, was the only secondary compound found at significant levels in very young seedlings; but it did not constrain feeding by marsupial herbivores. Models must allow for different roles of defensive secondary chemicals, presumably associated with different selective pressures as plants age, which result in different ontogenetic trajectories. [source]