Foliar responses of tamarack and black spruce to drainage and fertilization of a minerotrophic peatland

Abstract

A drainage and fertilization experiment was established in 1989 in a tamarack (Larixlaricina (Du Roi) K. Koch) and black spruce (Piceamariana (Mill.) B.S.P.) mixed natural stand growing on a minerotrophic peatland. The drained site was ditched in fall 1987. Fertilization treatments of N–P–K at 0:0:0, 0:80:120, 200:80:120, and 400:80:120 kg•ha−1 (N as urea) were applied in late May 1989 Tamarack short-shoot needles and black spruce current-year needles, sampled on 31 August 1989 and 2 September 1990, were analysed for unit needle mass and N, P, and K. Drainage without fertilization increased foliar N, P, and K concentration of tamarack and black spruce, with larger responses occurring in tamarack. However, drainage decreased needle mass of unfertilized black spruce, although net assimilation rate increased, suggesting that an increased proportion of photosynthate was allocated to root development. Needle mass of tamarack was not affected in 1989 but was increased in 1990 by drainage, indicating different acclimation mechanisms to drainage by the two species. Responses in unit needle mass and foliar N and P concentration of both species to P–K alone, and (or) N–P–K fertilization, were higher on the drained than on the undrained site. Increased availability and uptake of N and P with a lowered water table were a likely consequence of increased near-surface soil temperature, improved soil water–soil aeration relations, and accelerated N and P mineralization and uptake rates. Foliar N, P, and K of tamarack were more responsive to fertilization than those of black spruce. N–P–K elevated foliar N concentrations of tamarack and black spruce and resulted in concomitant increases in needle mass, suggesting that N was limiting both species. Addition of P–K alone increased foliar P concentration and foliar mass of tamarack, indicating a P limitation to tamarack growth.