Below- and aboveground N and P use by Abies amabilis stands

Annual N and P requirements and internal redistributions were determined for above- and belowground vegetation component of young (23-yr-old) and mature (180-yr-old) subalpine Abies amabilis stands in the Washington Cascades Mountains. The primary objective was to evaluate the importance of fine-root production in determining total vegetation N and P uptakes from soil nutrient pools. In the young stand, N and P requirements for aboveground plant components were, respectively, 42.7 and 5.54 kg@?ha^-^1^@?yr^-^1, while for belowground plant components, requirements were 75.5 and 10.94 kg@?ha^-^1@?yr^-^1. Aboveground N and P requirements in the mature stand totalled 27.7 and 4.11 kg@?ha^-^1@?yr^-^1, respectively, with belowground components totalling 74.5 and 14.61 kg@?ha^-^1^.yr^-^1^. Requirements were met by both nutrient uptake from the soil and internal nutrient redistribution. Total uptakes of N and P for aboveground components were 26.9 and 2.86 kg@?ha^-^1^.yr^-^1 in the young stand; uptake for belowground components were 44.0 and 5.64 kg@?ha^-^1^.yr^-^1. In the mature stand, N and P uptakes for aboveground plant components totalled 11.7 and 1.68 kg@?ha^-^1^.yr^-^1, while those of belowground components were 34.4 and 4.58 kg@?ha^-^1@?yr^-^1. In the young stand 41% of N and 48% of P requirements were provided by internal redistribution. Internal redistribution provided 55% of N and 66% of P requirements in the mature stand. The ratio of below- to aboveground total production was 1.8 in the young stand, and 2.8 in the mature stand. Below- to aboveground nutrient requirement and uptake ratios were from 1.6 to 2.0 in the young stand, while those for the mature stand were from 2.7 to 3.6. Within-stand patterns of nutrient uptake were not fundamentally different from those of nutrient requirements. Ratios of uptake for above- and belowground components were generally within 10% of corresponding requirement ratios.