Long-term partitioning of biomass and nitrogen following application of nitrogen fertilizer to Corsican pine

Abstract

The effects of N fertilizer on Corsican pine (Pinusnigra var. maritima (Ait.) Melv.) were studied for 22 years. Basal area increment significantly (p < 0.05) increased in response to N fertilizer for 3, 6, 11, and 13 years after applications ceased, in treatments that received 252, 504, 1008, and 1512 kg N•ha−1, respectively. Volume increment changed from a quadratic to a linear response to N level during the study period. Overall, the highest rate of N fertilizer increased the aboveground standing biomass by 42%, four-fifths of which occurred in stems. The response of crown components was variable, but there was evidence of a prolonged increase in foliage biomass due to N fertilizer. Initial retention of N within stands was sustained in the longer term, although N distribution altered. These results supported earlier predictions that the growth response to N fertilizer could be sustained through internal cycling, without increasing demands for N uptake from the soil. Increase of N within stands (over and above fertilizer inputs) was similar to estimated rates of atmospheric input, with indirect evidence of a positive feedback between increased foliage biomass and increased levels of N interception by crowns.