Effects of phosphorus fertilization and liming on growth, mineral nutrition, and gas exchange of Alnus rubra seedlings grown in soils from mature alluvial Alnus stands
In southern coastal British Columbia, red alder (Alnus rubra Bong.) is recommended for reforestation on some low-elevation, fertile, and moist sites (e.g., alluvial sites). Correlative data indicate that P deficiencies limit the growth of alder in low-pH soils; deficiencies of P and other elements may also develop in the presence of an alder stand. Because alder may be grown in repeated rotations on alluvial sites, we sought to determine whether elemental deficiencies were likely in soils from mature stands. We examined the effects of P additions (as triple super phosphate) and liming (as dolomitic limestone) on potted red alder seedlings grown in soils from mature alluvial alder stands. Four soils were "low-pH" (mean = 4.5) and two were "high-pH" (mean = 5.5); all were classified as very rich. Growth of unfertilized seedlings was greatest in the soil with the highest soil Bray-P levels. Growth rates increased with P supply, but the response decreased with increasing Bray-P and was less in the high-pH soils. Liming increased soil pH and uptake of Mg, but did not increase growth. Phosphorus additions increased growth mainly by increasing P uptake, leaf size, and biomass allocation to branches. Photosynthetic rates were highest in the intermediate P treatment, but instantaneous water use efficiency increased with P rate. Phosphorus deficiencies may limit the growth of alder seedlings in alluvial soils previously containing mature alder stands.