Tree ring proxies show physiological responses of eastern red cedar to increased CO2 and SO4 concentrations over the 20th century
Abstract
We examined the relationships between tree growth during the past century and the ratio of internal carbon dioxide concentration to atmospheric CO2 concentration (ci/ca) and instantaneous water-use efficiency (iWUE) by analyzing δ13C in tree rings of Juniperus virginiana growing on a limestone outcrop in West Virginia, US. Tree rings from years 1909 to 2008 from five Juniperus virginiana trees that ranged from 116 years to over 300 years in age were measured for basal area growth and used for isotopic analysis. Instantaneous WUE increased from approximately 75 to 112μmol mmol-1 over the past century, representing a 49% increase. In addition, we found a positive relationship between iWUE and the basal area increase over this time period, suggesting the increase in WUE translated into greater growth of the Juniperus trees. Typically, we might expect that increased growth of these trees reflects increased photosynthetic rates and decreased stomatal conductance rates resulting from increased atmospheric CO2 concentrations. However, this area of the central Appalachian Mountains has historically received some of the highest rates of acid deposition in the nation resulting from being downwind from an abundance of coal-fired power plants in the Ohio River valley. Our results show that ci/ca declined 14% between 1909 and 1980, but increased 9.6% between 1980 and 2009. We hypothesize that the directional change in ci/ca that occurred around 1980 was due to a reduction in sulfur emissions imposed by the Clean Air Act, environmental legislation enacted in 1970 and amended in 1990. Sulfur deposition measured by the National Atmospheric Deposition Program (NADP) in West Virginia near our Juniperus site shows a 53% decline between 1979 and 2009 and these NADP data show a highly significant negative correlation with ci/ca of Juniperus over this time period. Previously, experimental studies have shown that acidic sulfur mist leaches calcium from leaves causing a reduction in stomatal control and lowering internal leaf CO2 concentrations. Thus, these tree-ring data show proxy evidence for physiological responses to increased CO2 over the previous century, but also provide a biotic signature illustrating the role of environmental legislation to alleviate environmental pollution at large spatial and temporal scales.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B21E0290T
- Keywords:
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- 0414 BIOGEOSCIENCES / Biogeochemical cycles;
- processes;
- and modeling;
- 0439 BIOGEOSCIENCES / Ecosystems;
- structure and dynamics;
- 0478 BIOGEOSCIENCES / Pollution: urban;
- regional and global;
- 0488 BIOGEOSCIENCES / Sulfur cycling