The Relationship of Biomass Allocation and Nutrient Dynamics in Loblolly and Slash Pine Forests.

Aboveground biomass allocation and its effect on various aspects of N and P dynamics were investigated in loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Engelm.) stands planted at different spacings. Further, the relationship of nutrient demand and root production was investigated to validate the functional balance hypothesis in forest stands. N mineralization was greater in loblolly pine stands than slash pine, corresponding with greater needle litter N concentration. Both N and P mineralization increased in loblolly pine stands with increasing stand density, the result of greater nutrient input through increased litterfall. There were no species differences in total standing N at wider spacings, but slash pine had greater standing N at narrower spacings. There were no species differences in total standing P at any spacing. With increasing stand density in loblolly pine, total N and P increased then decreased. The majority of standing N and P was located in the crown. Loblolly pine had more standing N and P in the crown than slash pine. With increasing stand density, the fraction of total standing biomass, N, and P in the crown decreased. There were no species differences in apparent N and P demand (total N and P in annual aboveground production minus retranslocation). Apparent N and P demand in loblolly pine stands increased with stand density then decreased. Retranslocation minimized variation in apparent N and P demand between species and densities. Conflicting with apparent N and P demand, actual N and P uptake were greater in loblolly pine, and actual N uptake was positively and linearly related to stand density. Fine root production did not differ between species. The proportion of total net primary production allocated to fine roots was lower than reported in other studies and may be related to a drought that forced roots below the maximum sampling depth. For loblolly pine, stand density appears to have influenced annual aboveground biomass allocation and subsequent N demand and uptake which was positively and linearly related to fine root production, thus supporting the functional balance hypothesis. However, there was no evidence for the functional balance hypothesis in slash pine