期刊
NEW PHYTOLOGIST
卷 172, 期 2, 页码 330-346出版社
WILEY
DOI: 10.1111/j.1469-8137.2006.01836.x
关键词
carbon isotope discrimination; carbon isotope ratio (delta C-13); ecosystem respiration; Keeling plot; Mediterranean woodland; stable isotope; time-lag; vapour pressure deficit (VPD)
Temporal dynamics in carbon isotope ratios of ecosystem respiration (delta C-13(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 delta C-13(R) was tested. The relationship between delta C-13(R) (determined through Keeling plots) and environmental factors was evaluated through time-lag analysis. delta C-13(R) exhibited high annual variation (> 7). During the transition periods, delta C-13(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). delta C-13(R) exhibited substantial nocturnal enrichment (> 4) from dusk to dawn. These data indicate pronounced short-term dynamics in delta C-13(R) at hourly to daily timescales and a modulated response to environmental drivers. Substantial short-term changes in nocturnal delta C-13(R) may have important implications for the sampling protocols of nocturnal Keeling plots.
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