Increased dark respiration and calcium deficiency of red spruce in relation to acidic deposition at high-elevation southern Appalachian Mountain sites

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Abstract
Rates of net photosynthesis and dark respiration of red spruce (Picearubens Sarg.) foliage were examined in relationship to soil and foliar nutrient status at three elevations across each of three mountains in the southern Appalachians. These studies tested our previously stated hypothesis that increased dark respiration and reduced growth were associated with natural or induced nutrient deficiency at higher elevation sites. A consistent and highly significant reduction in the ratio of net photosynthesis to dark respiration was found at the highest sites on each mountain compared with lower sites, as had been previously reported for the initial two test sites. This response was produced by significant increases in dark respiration that were associated with low foliar calcium levels and high foliar aluminum levels found at the higher elevation sites in this region. Net photosynthesis was generally comparable between sites. A consistently inverse relationship between dark respiration and foliar calcium was found across highest and lowest elevation sites, while the midelevation sites, where calcium:aluminum ratios were highest, showed less evidence of respiratory response to calcium. Calcium in shoots was significantly reduced in association with increasing levels of soil aluminum in the rooting zone across all sites. Collectively, these studies suggest that reduced calcium supply, occurring in association with competitive inhibition of calcium uptake by high concentrations of aluminum found in soil, may have reduced the availability of carbon for red spruce growth at higher elevation sites. Inferential evidence examined, including atmospheric deposition levels, soil solution chemistry, and historical tree-ring chemistry, suggests that acidic deposition would have been a contributing factor in inducing or amplifying calcium deficiency.

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