Calcium and pH interaction on root nodulation of nursfry-grown red alder ( Alnus rubra bong.) seedlings by Frankia

Abstract

Growing interest in red alder ( Alnus rubra Bong.) for land-reclamation and commercial use has led to investigations of nursery production methods. Pure culture Frankia inoculum has been used to enhance red alder seedling growth, resulting in better cost efficiency and production quality. The effects of altered pH from applied calcium amendments on inoculum effectiveness at a Washington state nursery site were examined. Calcium oxide was used to increase pH from 5.6 to 7, and CaCl 2 was used as a calcium control. A randomized complete-block design was used in a factorial experiment, with nine treatments: control, CaCl 2 and CaO (equimolar calcium concentrations for calcium treatments); each soil treatment at 0, 20 and 200 μl packed cell volume m −2 Frankia inoculum rates. Soil samples were collected throughout the year for pH measurements. Seedling numbers, height, root and shoot weights, and percentage of nodulated plants were determined at mid-season and at lifting. A companion study on the effects of pH adjustment with HCl was done at an Oregon nursery. Greater seedling nodulation at mid-season paralleled increased height differences at lifting. A significant ( P < 0.01) interaction between inoculum rate and soil treatment on the number of plants nodulated was found at the Washington site. The CaCl 2 soil amendment temporarily lowered pH to 4.5 when the plots were inoculated and seeded. This treatment also had the greatest proportion of seedlings nodulated at mid-season and at lifting, indicating a possible interaction between calcium and low soil pH, within the pH range studied. To our knowledge, this is the first report of increased nodulation for red alder at pH 4.5, relative to that seen at pH 5.6 or 7.2. We found that the numbers of packable seedlings were greatest at the highest inoculum rate and that the CaCl 2 treatment had on average 20 more packable seedlings per plot ( P < 0.05) and nearly twice as many nodules per plant as control or CaO treatments.