Impacts of physiological response and species composition on ecosystem respiration
Abstract
Stable isotope analyses have provided insights into physiological controls of ecosystem carbon balance. Here we present measurement updates of a nation-wide network of carbon-13 ratios of ecosystem respiration (δ13CR) observed in 10 ecosystems, many of which are part of AmeriFlux. Systematic variations in δ13CR have been reported with an average intra-seasonal variation of 2.3 ± 0.5‰ in the Wind River Experimental Forest in southern Washington, USA over the period of 2001 - 2007. This seasonal pattern of δ13CR was consistently observed in all three coniferous forests of relatively uniform lifeform in the Pacific Northwest USA (Wind River Canopy Crane, Mary-Fir, and Metolius). In contrast, we observed no apparent seasonal differences in the δ13CR value at Harvard Forest, a mixed deciduous forest, during the same period. Two possible mechanisms have been suggested to explain inter- and intra-annual variations in δ13CR: 1) canopy physiological response (stomatal closure) to drought and 2) shifts in species composition within an ecosystem. The former is most tractable for the observed δ13CR variation in stands with a uniform lifeform, such as seen at the Wind River Canopy Crane location. The Harvard Forest is a mixed deciduous forest where shifts are occurring in the proportion of major species, Red Oak (ring-porous) and Red Maple (diffuse-porous). Shifts in species dominance within an ecosystem may result in δ13CR values where species effects and environmental response effects offset each other. Alternatively, ring-porous species may exhibit much less dynamic δ13CR patterns than diffuse-porous or tracheid-dominated forest species. On a seasonal basis, the relationships between δ13CR variations and environmental conditions are in general consistent with leaf-level physiological response, regardless of ecosystem types. Relative impacts resulting from physiological response and changes in species dominance on δ13CR variation may be used as constraints to characterize ecosystem respiration, which can cascade to result in detectable patterns in the atmosphere at continental scales. A canopy-process model will be developed and tested against these ideas using multi-year δ13CR measurements from a variety of ecosystems.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.B23C0458L
- Keywords:
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- 0315 Biosphere/atmosphere interactions (0426;
- 1610);
- 0428 Carbon cycling (4806);
- 0439 Ecosystems;
- structure and dynamics (4815);
- 0454 Isotopic composition and chemistry (1041;
- 4870);
- 1600 GLOBAL CHANGE