Abstract
Nitrogen source effects on rhizosphere pH were evaluated for Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], Sitka spruce [Picea sitchensis (Bong.) Carr.] and western hemlock [Tsuga heterophylla (Raf.) Sarg.] seedlings and a 40-year-old second growth Douglas-fir stand. Nitrogen additions of 400 mg kg−1 decreased rhizosphere pH up to 0.7 units in ammonium treatments and increased pHr by up to 1.2 units in nitrate treatments. Both N sources increased foliar N but did not increase foliar P. Rhizosphere pH effects differed between the two soils used in the seedling study. Ovall soil with higher native ammonium levels had less pH increase with added nitrate. All three conifer seedlings reacted similarly to nitrogen source. Changes in rhizosphere pH of Douglas-fir seedlings were evident one week after nitrogen application and these changes were statistically significant after two weeks. Nitrogen induced pH changes were related to N added but the relation was not linear, and followed the buffering capacity curves of both soils. As pH decreased foliar Mn levels increased dramatically. Rhizosphere pH of a 40-year-old Douglas-fir stand followed the same trends as seedlings. Ammonium decreased pH in the soil surface only, while nitrate increased rhizosphere pH to a depth of 20 to 30 cm. Changes were evident one year after application.
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Rollwagen, B.A., Zasoski, R.J. Nitrogen source effects on rhizosphere pH and nutrient accumulation by Pacific Northwest conifers. Plant Soil 105, 79–86 (1988). https://doi.org/10.1007/BF02371145
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DOI: https://doi.org/10.1007/BF02371145