Increased Availability of Nitrogen and Phosphorus in the Root Zone of Conifers

The N and P contents of herbaceous vegetation and soil across the interface between pine or larch plantations and the open, abandoned fields in which they were planted were investigated. Herbaceous plants growing beneath or near the conifers had significantly higher N and P concentrations as well as greater dry weight. NO 3 ‐N, NH 3 ‐N, and readily soluble P were also significantly higher beneath or near the conifers. Although the total N of the forested and open soils was not different, significantly higher percentages of the organic N could be extracted with hydrofluoric acid from the soil beneath 10‐ to 14‐year‐old plantations. However, the proportion extracted from soils beneath 32‐ to 33‐year‐old plantations was not different from that extracted from adjacent old‐field soils. All lines of evidence are consistent with a hypothesis that the conifer rhizosphere mineralizes or otherwise extracts some fraction of the soil nitrogen that had been resistant to microbial action under the previous vegetation.