Journal of Conference Abstracts

Implications of Stratospheric Ozone Reduction for Terrestrial Ecosystems

Martyn M. Caldwell (mmc@cc.usu.edu)

Ecology Centre, Utah State University, Logan, Utah, U.S.A.

Stratospheric ozone depletion has elicited substantial interest in the significance of solar UV-B for the biosphere including biogeochemical processes. Solar UV-B increases that result from stratospheric ozone reduction must, however, be taken in context with other global environmental changes such as elevated CO₂ and temperature. Rather than direct damaging effects of UV-B, the more significant effects of solar UV-B in terrestrial ecosystems, both historically and in the future, is likely to involve indirect processes mediated by UV-B action on vegetation, microbes and abiotic photochemistry. Several, potentially far-reaching effects of solar UV-B that might be mediated by vegetation involve changes in secondary plant chemistry and, specifically the shikimic acid pathway. Solar UV-B can stimulate regulatory enzymes early in this pathway and change the composition of secondary products. A variety of phenylpropanoid products can influence many interactions between vegetation, microbes and herbivores. Plant antimicrobial compounds induced by stress (including UV-B), commonly termed, phytoalexins, include isoflavanoids, stilbenes, psoralens, coumarins and some flavonols. Many of these compounds and others such tannins, lignin and suberin can play a role in defense against insect and vertebrate herbivores. Additionally, some flavonoids are important regulatory compounds, in Rhizobium infection of roots with resulting nitrogen fixing activity. Thus, if increased solar UV-B elicits increases in these phenylpropanoid products, changes in plant-herbivore relations, plant pathogen resistance, etc. might be expected. Plant litter decomposition has been shown to be affected both by changes in the secondary chemistry of the plant tissues and due to direct photochemical effects on the litter itself and effects on microbes decomposing the litter. Changes in solar UV-B can also affect the competitive ability of plants and, thus, might lead to changes in species composition of some ecosystems.

Historical Variations in Lead Fluxes in the Pyrenees
(NE Spain) from a Dated Lake Sediment Core

Lluís Camarero¹ (camarero@porthos.bio.ub.es), Pere Masqué² (iffr6@cc.uab.es),
Ioan Ani-Ragolta² (iani@pie.xtec.es), Jordi Catalan¹ (catalan@porthos.bio.ub.es),
Sergi Pla¹ (sergipla@porthos.bio.ub.es) & Joan Albert Sanchez-Cabeza² (ja.sanchez@cc.uab.es)

¹ Departament d'Ecologia - Centre de Recerca d'Alta Muntanya,
Universitat de Barcelona, Diagonal 645, E-08028, Barcelona, Spain.

² Departament de Física, Universitat Autònoma de Barcelona, E-08193, Bellaterra, Spain.

Variations in lead concentration in lake sediments reflect changes in the fluxes of this element in the past. We have studied a sediment core from a lake in the Pyrenees (Lake Redó at 2240 m a.s.l., NE Spain), with the aim of reconstructing the past environmental and climatic conditions in the lake and its catchment. The core was dated using ²¹⁰Pb (for recent sediments) and ¹⁴C (for older strata). The lake is far from pollution sources (such as the highly industrialised and densely populated area of Barcelona), so the lead content in its recent sediments is interpreted as a record of the atmospheric lead deposition at regional and global scales. We found a surface peak of lead concentration which was ca. four times higher than the background level. We attribute this peak to the deposition of lead released to the atmosphere during the burning of fossil fuels this century. A second peak appeared in a deeper layer, with a maximum lead concentration of ca. six times higher than the background level. The origin of this peak is unclear. We discuss the validity of several hypotheses to explain it (mining and smelting activities in Roman times, extensive forest fires, changes in vegetation associated with environmental variations), on the basis of complementary measurements, such as isotopic composition of lead, microfossil analysis, and mineralogical and chemical composition of sediments, including the content of other heavy metals.