Growth, foliar nutrition and δ 13C responses of red alder ( Alnus rubra) to phosphorus additions soon after planting on moist sites

Abstract

In south-coastal British Columbia, a low availability of phosphorus (P) may limit the early growth of young red alder ( Alnus rubra Bong.), even on sites classified as productive for red alder. However, it remains unclear as to what P addition rates best alleviate P deficiencies on such sites and how long effects of P additions on growth persist. We applied P 1–3 months after planting at rates up to 60 g P tree −1 and assessed growth and foliar elemental contents over three growing seasons at three sites with site productivity classed as good for red alder. Foliar δ 13C was also determined in year 1 in the two sites on Vancouver Island and in year 2 in the site on the British Columbia mainland coast in order to better understand the relationships among foliar nutritional status, leaf water use efficiency (WUE), and growth. P additions at planting significantly increased height (11–15%), diameter (26%) and stem volume (62–64%) through 3 years. Maximum growth rates were achieved at P addition rates of 30 g tree −1 and at foliar P concentrations of 2.2–2.5 g kg −1. Growth did not increase further at addition rates of 60 g P tree −1. Stem growth increases were accompanied by increased individual leaf mass, first-year foliar concentrations of N, P, Ca, Mg, and S, and foliar δ 13C, the latter suggesting that WUE increased with P additions. Foliar concentrations of P in unfertilized trees were at deficient levels, based on earlier studies, and increases in first-year foliar P concentrations and stem growth through year 3 were consistent with responses in earlier single-tree plot experiments. Longer-term measurements are required to define the duration of growth response to P additions in these otherwise-productive sites.