Title: Alders increase soil phosphorus availability in a Douglas-fir plantation
Abstract: The effect of red alder (Alnusrubra Bong.) on soil phosphorus (P) availability in conifer forests of the Pacific Northwest has been the focus of several recent studies. One study at the Thompson Research Center in Washington State, found Bray No. 2 extractable P to be lower in soils under pure alder than in soils under adjacent stands of pure conifer. The Thompson study, and others in forests of the Northwest, have also found that the quantity of P in aboveground litter fall is greater for conifer stands mixed with alder than in adjacent pure conifer stands, suggesting equal or greater soil P availability under the influence of alder. We assessed the effect of low densities of red alder on soil P, using a modified Hedley sequential P fractionation scheme, in a Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) plantation in coastal Oregon. We determined that soils under plots with 190 alder stems/ha and 740 Douglas-fir stems/ha had greater inorganic P availability than pure Douglas-fir plots (740 stems/ha). Inorganic P fractions, sequentially extracted from soils at 0–0.15 m depths by anion exchange resins, by sodium hydroxide, and by hydrochloric acid, were 65–225% greater in plots with alder. Soil phosphatase activity was nearly three times greater in plots mixed with alder. No significant pH differences between the treatments were found. We conclude that red alder appears to increase the availability of soil P at our site, but note that increased P supplies may not prevent a P limitation on productivity for either alder or conifers.
Publication Year: 1995
Publication Date: 1995-10-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 119
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