| I examined fine ({dollar}<{dollar}2 mm diameter) root growth, root turnover rates, root decomposition rates, and root competition to address how these belowground processes are related to soil nutrient availability in tropical forests. These dynamics are often inferred from observations of aboveground forest dynamics.; In a lowland wet forest in Costa Rica, I compared root processes in canopy gaps and in undisturbed understory areas on two soil types (fertile and infertile). Fine root biomass and length were reduced under canopy openings, especially on the infertile soil. This reduction was unrelated to aboveground gap size or percent canopy openness in 1- to 18-month-old gaps. Exposure to root competition did not affect growth of seedlings of the pioneer tree species Hampea appendiculata on either soil type. Creation of nutrient-rich patches had little effect on root growth, except in canopy gaps on the infertile soil, where fertilization caused root proliferation. In this forest, the belowground consequences of gap formation depend on soil type, but cannot be predicted from aboveground gap characteristics.; Belowground net primary productivity, root turnover rates, and root decomposition rates were measured in three montane wet forests in Hawaii that differed in nutrient availability but were dominated by the same tree species (Metrosideros polymorpha). Belowground net primary productivity, root turnover rates, and root decomposition rates were lowest in a forest where aboveground growth was limited by phosphorus (P). These rates were similar in a forest where aboveground growth was limited by nitrogen (N) and a forest with relatively higher levels of available N and P. Fertilization with N or P had no effect on these belowground processes at the N-limited site, but P-fertilization at the P-limited site increased the rates of these processes. At these three sites, the dynamics of root growth, turnover, and decomposition were not necessarily similar to aboveground growth, leaf turnover rates, or leaf decomposition rates. Root dynamics were strongly influenced by P-availability but not by N-availability. In both the Costa Rican and Hawaiian forests, belowground plant characteristics could not be predicted from aboveground characteristics. |
