Biomass and nutrient allocation in Douglas-fir and amabilis fir seedlings: influence of growth rate and temperature.

Allocation of biomass and nutrients to current-year and one-year-old shoots and roots of two-year-old conifer seedlings with differing rates of growth was studied. Differences in growth rate were achieved by selecting fast- and slow-growing populations of the relatively fast- and slow-growing conifer species, Pseudotsuga menziesii (Mirb.) Franco and Abies amabilis Dougl. ex Loud, respectively. Environmentally controlled differences in growth rate were induced by placing half of the seedlings in a 10 degrees C growth chamber and half in a 20 degrees C growth chamber in their second growing season. Seedling samples were harvested in May, before the temperature treatment, and in July and November of the second growing season, and biomass and nutrient concentrations of current-year and one-year-old shoots and roots were determined. Seedling biomass and nutrient allocation differed among the high-growth treatments. Seedlings exhibiting high growth in response to the 20 degrees C treatment and faster growing populations within species both showed increased allocation to new shoots, whereas seedlings of the fast-growing species showed greater allocation to old shoots than to new shoots. Increased growth increased nutrient uptake, but nutrient concentration decreased with growth rate as a result of dilution, so that faster-growing seedlings had greater nutrient-use efficiency than slower-growing seedlings. Retranslocation of P and K was seen in the second year only in slow-growing populations at 10 degrees C. Nutrient concentrations of one-year-old plant parts decreased in the second year, indicating new growth was a stronger sink for nutrients than second-year growth.