Sulfur and Nitrogen Uptake by Loblolly Pine Seedlings as Influenced by Nitrogen and Sulfur Addition
The influence of increasing levels of nitrogen addition at several levels of sulfur input on nitrogen and sulfur uptake by loblolly pine seedlings was evaluated in a greenhouse study. All possible combinations of nitrogen and sulfur were incorporated into soil collected from the A horizon of a southeastern forest soil at rates of 0, 200, 500, and 1,000 g/g of N, and 0, 14, 35, and 70 g/g of S. Soil samples collected at the end of the study indicated that a similar amount of soil SO4-S had been mineralized in all treatment combinations, compared to a general pattern of increasing soil nitrogen mineralization with increasing nitrogen input. Most mineralized sulfate appeared to come from nonprotein organic compounds as there was not a significant concomitant release of nitrogen. Both shoot and root biomass responded significantly to nitrogen addition, but there was no sulfur or nitrogen-sulfur interaction response. Nitrogen treatment generally increased shoot nitrogen concentration compared to a general decrease in shoot total-, sulfate-, and organically bound-sulfur. Organically bound-sulfur concentrations were 26 to 60 percent below sulfur values calculated from an S/N ratio of 0.03 on a gram atom basis. The results show that increased nitrogen addition affected both growth and sulfur status of loblolly pine seedlings, but not entirely in the manner predicted by theoretical considerations. Forest Sci. 28:725-731.
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