Importance of short-term dynamics in carbon isotope ratios of ecosystem respiration (δ13CR) in a Mediterranean oak woodland and linkage to environmental factors

Abstract

• Temporal dynamics in carbon isotope ratios of ecosystem respiration (δ13CR) were evaluated on hourly, daily and annual timescales in a Mediterranean woodland. Emphasis was given to the periods of transition from wet to dry season and vice versa, when the system turns from a net carbon sink to a source. The constancy of nocturnal δ 13CR was tested. • The relationship between δ13CR (determined through Keeling plots) and environmental factors was evaluated through time-lag analysis. • δ13CR exhibited high annual variation (> 7). During the transition periods, δ13CR correlated significantly with factors influencing photosynthetic discrimination, soil respiration, and whole-canopy conductance. Time-lags differed between below- and above-ground variables, and between seasons. A shift in regression parameters with environmental factors indicated seasonal differences in ecosystem responsiveness (e.g. temperature acclimation). δ13CR exhibited substantial nocturnal enrichment (> 4) from dusk to dawn. • These data indicate pronounced short-term dynamics in δ13C R at hourly to daily timescales and a modulated response to environmental drivers. Substantial short-term changes in nocturnal δ13CR may have important implications for the sampling protocols of nocturnal Keeling plots. © The Authors (2006).