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Applying the dual-isotope conceptual model to interpret physiological trends under uncontrolled conditions
Citation:
Barnard, H. R., RENEEJ BROOKS, AND B. J. Bond. Applying the dual-isotope conceptual model to interpret physiological trends under uncontrolled conditions. TREE PHYSIOLOGY. Heron Publishing, Victoria, B.C, Canada, 32:1183-1198, (2012).
Impact/Purpose:
Forest growth is a major component in the nation's carbon budget and our ability to predict how forest growth varies spatially and temporally will be critical for developing realistic carbon budget models for the USA. Our predictive abilities are directly linked to understanding the long-term responses of controlling physiological mechanisms behind carbon gain. The inter-relationships among ring width and δ13C and δ18O in tree ring cellulose have the potential to illuminate valuable long-term physiological and environmental information on forest growth controls. We apply a dual isotope approach to infer physiological response of trees in differing crown dominance classes to changing environmental conditions using a qualitative conceptual model of the 13C-18O relationship. We found that dominant trees are more responsive to environmental controls compared to other crown classes within the same stand. The correlation of stable isotopes with environmental variables is useful for assessing the impacts of environmental change over long time series. This isotope tool could be quite useful for extrapolating forest growth responses to the environment spatially and temporally for understanding the dynamics of forest growth as part of the nation's carbon budget.
Description:
The inter-relationships among δ13C and δ18O in tree ring cellulose and ring width have the potential to illuminate long-term physiological and environmental information in forest stands that have not been monitored. We examine how within-stand competition and environmental gradients affect ring widths and the stable isotopes of cellulose. We utilize a natural climate gradient across a catchment dominated by Douglas-fir and temporal changes in climate over an 8-year period. We apply a dual-isotope approach to infer physiological response of trees in differing crown dominance classes to temporal and spatial changes in environmental conditions using a qualitative conceptual model of the 13C–18O relationship and by normalizing the data to minimize other variance. The δ13C and δ18O of cellulose were correlated with year-to-year variation in relative humidity and consistent with current isotope theory. Using a qualitative conceptual model of the 13C–18O relationship and physiological knowledge about the species, we interpreted these changes as stomatal conductance responses to evaporative demand. Spatial variance between plots was not strong and seemed related to leaf nitrogen rather than any other environmental variable. Dominant trees responded to environmental gradients more consistently with current isotope theory as compared with other classes within the same stand. We found a correlation of stable isotopes with environmental variables is useful for assessing the impacts of environmental change over short time series and where growth varies only minimally with climate.
