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Free keywords:
ecosystem functioning; net ecosystem exchange
Water-vapor exchange; gap filling strategies; net ecosystem
exchange; ponderosa pine forests; soil respiration; eddy
covariance; carbon-dioxide; terrestrial ecosystems; deciduous
forest; climate-change
Abstract:
There are many ways of studying forest responses to global change. Most current national and international programs focus on net gas exchange of the terrestrial biosphere and are typically interdisciplinary, multi-scale projects. Key objectives of these programs are surprisingly similar to those of classical plant ecophysiology studies, i.e., to explore functional relationships of plant or plant community responses to environmental change. Thus, common research questions that link plant ecophysiology to ecosystem functioning can be identified for both research communities, promising complementarity and synergism for joint research projects. Although some well-established ecophysiological relationships, such as light responses or stomatal limitations of photosynthetic gas exchange, are currently employed in many ecosystem-scale net flux studies for gap-filling or modeling, only 14% (n = 27) of all eddy covariance flux studies in forests (n = 196; published between 1992 and April 2002) include plant ecophysiological measurements (n = 24) or biomass and growth estimates (n = 8). Generally, emphasis is on CO2 exchange measurements at various scales (foliage, shoots, branches; n = 14) and water relations measurements (n = 11). These measurements do not fully support the typical parameterization of stand and regional models, which often need information on canopy architecture and nitrogen nutrition. By means of a complementary research approach, valuable information can be acquired that is unobtainable by means of a single approach. This additional information is important for the identification of underlying biotic and environmental drivers, for the regulation of net ecosystem fluxes and their partitioning, and the independent validation of measured net ecosystem fluxes. Thus, combining micrometeorology and ecophysiology at flux sites is strongly recommended for ecosystem functioning studies.
