Potassium, phosphorus, or nitrogen limit root allocation, tree growth, or litter production in a lowland tropical forest

Wright, S. Joseph and Yavitt, Joseph B. and Wurzburger, Nina and Turner, Benjamin L. and Tanner, Edmund V. J. and Sayer, Emma J. and Santiago, Louis S. and Kaspari, Michael and Hedin, Lars O. and Harms, Kyle E. and Garcia, Milton N. and Corre, Marife D. (2011) Potassium, phosphorus, or nitrogen limit root allocation, tree growth, or litter production in a lowland tropical forest. Ecology, 92 (8). pp. 1616-1625. ISSN 0012-9658

Abstract

We maintained a factorial nitrogen (N), phosphorus (P), and potassium (K) addition experiment for 11 years in a humid lowland forest growing on a relatively fertile soil in Panama to evaluate potential nutrient limitation of tree growth rates, fine-litter production, and fine-root biomass. We replicated the eight factorial treatments four times using 32 plots of 40 × 40 m each. The addition of K was associated with significant decreases in stand-level fine-root biomass and, in a companion study of seedlings, decreases in allocation to roots and increases in height growth rates. The addition of K and N together was associated with significant increases in growth rates of saplings and poles (1–10 cm in diameter at breast height) and a further marginally significant decrease in stand-level fine-root biomass. The addition of P was associated with a marginally significant (P = 0.058) increase in fine-litter production that was consistent across all litter fractions. Our experiment provides evidence that N, P, and K all limit forest plants growing on a relatively fertile soil in the lowland tropics, with the strongest evidence for limitation by K among seedlings, saplings, and poles.