Abstract
Due to the close linking between the biosphere and atmosphere, there are clear impacts of changes in climate, atmospheric deposition of nutrients/pollutants and land use (Global Changes) on the terrestrial biosphere. Lichens, with a direct dependence on atmospheric conditions, are much more affected by their immediate microclimate than by the ecosystem’s prevailing macroclimate. In contrast to higher plants, poikilohydric organisms have different mechanisms of water and CO2 exchange. The application of stable isotopes to the understanding of the mechanisms that are fundamental to lichen gas exchange and water uptake is a promising tool for the evaluation of lichen response to environmental changes. Indeed, lichens have been shown to be influenced by a large number of natural and anthropogenic environmental factors, serving as ecological indicators. Thus, we may use these organisms to model the impact of key global change drivers, such as nitrogen deposition and biodiversity changes, at local scale. Particularly useful is the application of the Lichen Diversity Value (LDV) in order to evaluate the impact of global drivers. Moreover, it has been shown that these indices, associated with main photobiont types, green-algae (LDVch) or cyanobacteria (LDVcyh), and/or nitrophilous versus oligotrophic species, were good candidates as ecological indicators. Besides mapping with high spatial resolution the effects of climate alterations, lichen functional groups could also be used as an early-warning system in order to detect the first effects of climate change in ecosystems before sudden shifts occur on other components that may be less sensitive. Clearly, lichens possess the adequate traits to be used as powerful indicators of complex interactions between atmosphere and biosphere, and thus can generate potentially interesting models for global change drivers.
Highlights
Useful is the application of the Lichen Diversity Value (LDV) in order to evaluate the impact of global drivers
Since lichens are directly influenced by microclimatic conditions, such as light, water, temperature and CO2 concentration, the isotopic composition of their organic matter (OM) integrates environmental factors acting on their specific microhabitat over a range of weather conditions, as well as a variety of land-uses over long periods of time
The isotopic composition of OM is determined by an economic equilibration between carbon source and sink, which are mainly photosynthesis and respiration
Summary
Studying lichens as a globally important ground cover component and a physiological model of poikilohydric organisms may provide the scientific community with new insights of pedosphere-atmosphere exchange processes. Carbon and oxygen isotopic composition are of major importance in evaluating physiological processes driving CO2 and water exchange because they provide information on fractionation processes as well as characterize plant metabolism and interactions with the ecosystem (i.e. Dawson et al 2002).
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