Otto L. Lange

Toxicity and antifeedant activity of lichen compounds against the polyphagous herbivorous insect Spodoptera littoralis

Abstract Four frequently occurring lichen compounds, (−)- and (+)-usnic acid, vulpinic acid, and stictic acid were studied for toxicity and antifeedant activity against larvae of the polyphagous insect herbivore Spodoptera littoralis . Both enantiomers of usnic acid as well as vulpinic acid provoked strong mortality as well as significant growth retardation and a pronounced increase of the larval period in chronic feeding experiments with neonate larvae at concentrations comparable to or even significantly below their natural concentrations in various lichens. In these experiments the LD 50 of the most active compound (−)-usnic acid was observed at 8.6,μmol g −1 dry wt whereas the LD 50 of the (+)-enantiomer, or of vulpinic acid amounted to 90.8 and 111.0,μmol g −1 dry wt, respectively. Stictic acid caused no larval mortality. The deleterious efrects of the usnic acid enantiomers and of vulpinic acid are probably due to the antifeedant properties, as well as to acute toxicity as demonstrated by injection into the larval haemolymph. In all experiments, (−)-usnic acid was always the most active compound indicating a remarkable correlation of antifeedant activity and acute toxicity.

SEQUESTRATION OF LICHEN COMPOUNDS BY LICHEN-FEEDING MEMBERS OF THE ARCTIIDAE (LEPIDOPTERA)

A survey for the presence of sequestered lichen compounds in 103 wild-caught imagines representing eight different genera and 16 different species of the Arctiidae was conducted. Known lichen compounds were detected for the first time in 24 of the analyzed specimens (representing five different genera and 11 different species) based on their HPLC retention times and on their UV-absorption spectra. The anthraquinone parietin, the depside atranorin, as well as a hydrolytic cleavage product of the latter were among the lichen compounds most frequently detected in wild-caught imagines. The observed variation of sequestered lichen compounds in wild-caught imagines with unknown feeding history may be due to several reasons. Lack of lichen compounds in imagines may have been caused, for example, by larvae feeding on lichens with no or only minute amounts of phenolic products. The age of the specimens analyzed may also influence the results obtained. Avoidance of lichen compounds by selective feeding on those parts of lichen thalli that have no or little lichen products may be another reason for the lack of lichen compounds in imagines. Preliminary feeding experiments conducted with larvae ofEilema complana, for example, indicated that the larvae fed exclusively on the algal layer and cortex of the lichenCladonia pyxidata, whereas the medulla, which is rich in fumarprotocetrarie acid, was avoided. As expected, imagines hatching from the larvae were free of this lichen compound. Any ecological role of the sequestered lichen compounds for the herbivores is unknown. It is possible, however, that sequestered lichen compounds may be utilized for the chemical defense of arctiid moths or against microbial pathogens.

Photoprotection of reaction centres in photosynthetic organisms: mechanisms of thermal energy dissipation in desiccated thalli of the lichen Lobaria pulmonaria

*The photobionts of lichens have previously been shown to reversibly inactivate their photosystem II (PSII) upon desiccation, presumably as a photoprotective mechanism. The mechanism and the consequences of this process have been investigated in the green algal lichen Lobaria pulmonaria. *Lichen thalli were collected from a shaded and a sun-exposed site. The activation of PSII was followed by chlorophyll fluorescence measurements. *Inactivation of PSII, as indicated by the total loss of variable fluorescence, was accompanied by a strong decrease of basal fluorescence (F(0)). Sun-grown thalli, as well as thalli exposed to low irradiance during drying, showed a larger reduction of F(0) than shade-grown thalli or thalli desiccated in the dark. Desiccation increased phototolerance, which was positively correlated to enhanced quenching of F(0). Quenching of F(0) could be reversed by heating, and could be inhibited by glutaraldehyde but not by the uncoupler nigericin. *Activation of energy dissipation, apparent as F(0) quenching, is proposed to be based on an alteration in the conformation of a pigment protein complex. This permits thermal energy dissipation and gives considerable flexibility to photoprotection. Zeaxanthin formation apparently did not contribute to the enhancement of photoprotection by desiccation in the light. Light-induced absorbance changes indicated the involvement of chlorophyll and carotenoid cation radicals.

Upland tundra in the foothills of the Brooks Range, Alaska, U.S.A.: lichen long-term photosynthetic CO2 uptake and net carbon gain

Estimates of carbon gain were obtained based upon integration of previously published measurements of diel courses of CO2 exchange of seven lichen species in their natural tundra habitat. Total net photosynthetic CO2 uptake, CO, loss by dark respiration, and the balance between these were calculated. The field measurements (146 observations of lichen sample diel courses on 26 d distributed over the growth periods from July through September in 1988 and 1989) were classed with respect to 5 types of weather conditions. The occurrence of these weather types during the growing season was established according to meteorological data. Combination of these data sets permits an estimate of seasonal carbon gain. Integrated photosynthetic carbon uptake was highest for the cyanobacterial Peltigera malacea, 1.5 times higher than for Dactylina arctica and 5 times higher than for the least productive Masonhalea richardsonii, both being green algal species. There was an essentially linear correlation across species between the sum of carbon uptake and short-term maximal rates of net photosynthesis, stressing the importance of photosynthetic capacity for carbon gain. Mean respiratory carbon loss for all of the species was ca. 33%. Three groups of species were determined with respect to estimated seasonal carbon balance: high productivity (carbon gain of 24.0-21.5% of thallus carbon content) which included D. arctica, P. malacea, P. aphthosa, and Thamnolia vermicularis, lowest productivity (6.8%) for M. richardsonii, and intermediate for Cetraria cucullata (15.9%) and Stereocaulon alpinum (14.6%). Seasonal carbon gain is related to the maximal possible thallus growth. Estimates of annual lichen biomass increase in typical tundra communities ranged from 47.2 gDW m-2 for

Lichen species dominance and the resulting photosynthetic behavior of Sonoran Desert soil crust types (Baja California, Mexico)

IntroductionLichen dominated biological soil crusts (BSCs) occur over large areas in the Sonoran Desert of the southwestern USA and northwest Mexico. In Baja California BSCs show a distinct patchiness and several types can be distinguished. Two chlorolichen- and two cyanolichen-dominated BSCs were selected. We hypothesize that patchiness and the resulting domination of certain functional lichen groups will result in patchiness of photosynthetic CO2-uptake related to environmental factors as well.MethodsFour different soil crust samples were placed in cuvettes and their CO2 exchange was recorded in an open system with an infrared gas analyzer. Air blown over the BSCs had a controlled CO2 content of 350 ppm. Four cuvettes were operated in parallel. Photosynthetic CO2 exchange was continually recorded throughout the experiment.ResultsBesides the dominating chlorolichens Psora decipiens and Placidium squamulosum and the cyanolichens Peltula patellata and P. richardsii, several other lichen species and 12 cyanobacterial species were found in the biological soil crusts sampled. The chlorolichen BSCs already gained positive net photosynthesis with high air humidity alone, while the cyanolichen types did not, but showed smaller CO2-uptake depression after water suprasaturation. Such specific net photosynthesis responses to mode of hydration and to crust water content seem to correlate with precipitation characteristics of their habitat.ConclusionsSpecies specific photosynthetic performance related to activation of respiration and net photosynthesis as well as to crust water content help to explain niche occupation and species composition of BSCs. Different functional types have to be considered when they have a patchy distribution.

How to minimize the sampling effort for obtaining reliable estimates of diel and annual CO 2 budgets in lichens

Estimating carbon budgets for poikilohydric organisms, such as lichens and bryophytes, requires methods other than those for homoiohydric plants due to a strong dependency of carbon gain on fluctuating hydration. This paper provides guidance with respect to optimal sampling strategies for estimating annual carbon budgets of lichens and bryophytes, based on a one-year dataset of half-hourly CO 2 -exchange readings on the epilithic placodioid lichen Lecanora muralis (syn. Protoparmeliopsis muralis ) and tests the effects of reduced sampling frequencies and different temporal sampling schemes on carbon budget estimates. Both fine-scale sampling (measurements within a day) and large-scale sampling (selection of days within a year) are addressed. Lowering the sampling frequency within a day caused large deviations for 24-h (diel) budget estimates. Averaged over a larger number of days, these errors did not necessarily cause a large deviation in the annual budget estimate. However, the occurrence of extreme deviations in diel budgets could strongly offset the annual budget estimate. To avoid this problem, frequent sampling ( c . every 1·5 hours) is necessary for estimating annual budgets. For estimating diel budgets and patterns a more frequent sampling (every c . 0·5 hours, balancing data resolution and disturbance) is often needed. Sampling fewer than 365 days in a given year inevitably caused estimates to deviate from the ‘true’ carbon budget, i.e. the annual budget based on half-hourly measurements during 365 days. Accuracy increased with total sample frequency, and blocking days caused larger deviations than sampling randomly or regularly spaced single days. Restricting sampling to only one season led to strongly biased estimates. The sampling effort required for a reliable estimate of the annual carbon balance of lichens based on simple extrapolations of diel carbon budgets is impracticably large. For example, a relatively large sample of 52 random days yielded an estimate within 25% of the true annual budget with only 60% certainty. Supporting approaches are therefore suggested, in particular extrapolating diel budgets using ‘weather response types’, possibly aided by diel activity patterns from chlorophyll fluorescence, or modelling CO 2 exchange as a function of climatic conditions.

Chlorophyll fluorescence, photosynthetic capacity, and chlorophyll and nutrient contents of the leaves of 'undamaged' and 'damaged' beech in the Würzburg region.

ZusammenfassungIm Zusammenhang mit der Frage nach den Ursachen der «neuartigen Baumschäden» wurden im Verlaufe der Vegetationsperiode 1986 an verschiedenen Standorten im Umkreis von Würzburg in zeitlichen Abständen Chlorophyllfluorezsenz-Messungen an ungeschädigten und an als geschädigt eingestuften Buchen (Fagus sylvatica) durchgeführt. Ergänzend wurden an den Blättern Photosynthesekapazitäts-Messungen, Bestimmungen des Chlorophyllgehaltes und des Verhältnisses Chlorophyll a zu b, sowie Analysen der Konzentration an wasserlöslichen Ionen (Ca2+, K+, Mg2+, SO42−, PO43−, NO3− Cl−, Malat und Oxalat) durchgeführt.Für keines der verwendeten Kriterien konnten Unterschiede zwischen den geschädigten und ungeschädigten Bäumen gefunden werden. Die Photosynthese der Blätter der geschädigten Bäume war im Vergleich zu den ungeschädigten Kontrollen unbeeinträchtigt. Eine direkte Einwirkung atmosphärischer Schadstoffe auf die Assimilationsorgane als differenzierende Primärursache für die in der Morphologie zum Ausdruck kommenden Schäden kann also mit allergrößter Wahrscheinlichkeit ausgeschlossen werden. Es Konnte auch keine Störung des Nährstoffhaushaltes der Blätter bei den untersuchen Bäumen nachgewiesen werden. Die Frage nach den Primärursachen der «neuartigen Baumschäden» bei der Buche bleibt daher-zumindest für unser Untersuchungsgebit—unbeantwortet. Die weitere Kausalanalyse wird sich sowohl in konzeptioneller als auch in technisch-methdischer Hinsicht kompliziert gestalten.SummaryDuring the course of the 1986 growing season chlorophyll fluorescence measurements were obtained from leaves of beech trees (Fagus sylvatica L.) which had been classified as damaged and undamaged, both of which were examined at different sites in the area of Würzburg. In addition, photosynthetic capacity, chlorophyll content, the ratio of chlorophyll a to b, and the concentration of water-soluble ions (Ca2+, K+, Mg2+, SO42−, PO43−, NO3−, Cl−, malate and oxalate) of leaves were determined.No differences between undamaged and damaged trees were found with respect to the investigated criteria. In comparison with the visually undamaged control trees, the photosynthetic apparatus of leaves from injured trees proved to be unaffected. It can probably be excluded that the damage expressed in tree morphology results primarily from a direct impact of atmospheric pollutants on the assimilatory organs. Moreover no disturbances in leaf mineral content were found. Therefore, the question of the primary causes of beech damage—at least for our study sites—can not be answered. Further investigations into the causes of forest decline will be very complicated methodologically as well as conceptually.