Importance of short‐term dynamics in carbon isotope ratios of ecosystem respiration (δ 13 C R ) in a Mediterranean oak woodland and linkage to environmental factors

Summary•  Temporal dynamics in carbon isotope ratios of ecosystem respiration (δ 13 C R ) 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 13 C R was tested. •  The relationship between δ 13 C R (determined through Keeling plots) and environmental factors was evaluated through time‐lag analysis. •  δ 13 C R exhibited high annual variation (> 7). During the transition periods, δ 13 C R 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). δ 13 C R exhibited substantial nocturnal enrichment (> 4) from dusk to dawn. •  These data indicate pronounced short‐term dynamics in δ 13 C R at hourly to daily timescales and a modulated response to environmental drivers. Substantial short‐term changes in nocturnal δ 13 C R may have important implications for the sampling protocols of nocturnal Keeling plots.