Defensive compound concentration in boreal lichens in response to simulated nitrogen deposition

Nitrogen (N) deposition is expected to increase in northwestern Europe the next 50–100 years. The effects of higher N availability on lichens will presumably depend on their capacity to acquire carbon (C), that is, of the timing and duration of the wet and active state. If lichens respond like plants, their C and N status may affect their concentration of carbon-based secondary compounds (CBSCs), and thus their defence against herbivores, detrimental radiation, pathogens and parasites. In the present study we have manipulated N availability and timing and duration of the metabolically active state by spraying lichen transplants in an old spruce forest with rainwater or rainwater with added N corresponding to 50 kg N ha⁻¹ yr⁻¹. The spraying was applied either at night, in the morning or at noon to also investigate the effect of timing and duration of the active state. Concentrations of N, chlorophyll a (Chl a ) and CBSCs were measured before and after one summer's spraying of 10 thalli in each of four different lichen species; Alectoria sarmentosa, Lobaria scrobiculata, Platismatia glauca , and Xanthoria aureola . The added N was readily taken up by all the lichen species. A. sarmentosa, P. glauca , and X. aureola increased their Chl a concentration in response to increased N, while L. scrobiculata increased Chl a in response to increased active time. None of the studied species reduced their concentration of secondary compounds during the experimental period, but in P. glauca the concentration of all compounds were significantly lower in N-treated thalli compared with those that got only rainwater. The results are consistent with a high degree of constitutive defence in three of four species, and we conclude that all the investigated lichens seem to have rather robust chemical defence systems despite considerable manipulation of the environmental conditions.     

POPULATION CHARACTERISTICS AND FOOD RESOURCE UTILIZATION OF CONUS IN THE SEA OF CORTEZ AND WEST MEXICO

The diets and population characteristics of three abundant speciesof Conns, nux, diadema and princeps, from the Sea of Cortezare described. All were found to feed predominantly upon polychaeteworms. In addition, food notes are presented for six less abundantspecies from the same area. Comparison of the diversity of thediets of the three dominant species in the Sea of Cortez withcognate species in the Indo-West Pacific, where significantlymore congeneric species occur in any single habitat, indicatedno significant increases in diversity of prey. This lack ofecological release with respect to food in the presence of fewercompeting congeners was attributed to the presence of significantlyfewer prey species when compared to the Indo-West Pacific. (Received 23 March 1978;