Phosphorus budget of a 70-year-old northern hardwood forest

Recent measurements have made it possible to revise and improve the phosphorus budget of the Hubbard Brook Experimental Forest, including partitioning P uptake by vegetation from the forest floor and mineral soil and estimating net P mineralization in the forest floor. Both living biomass and forest floor are accumlating P (at rates of 1.3 and 0.16 kg P ha^-1 yr^-1 respectively) in this 70-yr old northern hardwood forest. About 61% of the P taken up by the vegetation each year comes from the forest floor (5.9 kg P ha^-1 yr^-1 of a total 9.6 kg P ha^-1 yr^-1), even though the P content of this pool is just 5% of that in mineral soil. The turnover rate of P in the forest floor is 7% yr^-1, while that of the mineral soil is 0.3% yr^-1. Recycling of P in the forest floor is very efficient; of the 5.6 kg P ha^-1 yr^-1 net mineralization in the forest floor, only 0.3 kg P ha^-1 leaches into the mineral soil; the rest is taken up by plants. This tight recycling of P is important because P is less readily available in the mineral soil than in the forest floor.