| Soil nutrient heterogeneity at spatial scales that allow individual plants to experience multiple belowground environments is potentially an important influence on the competitive dynamics of plant communities. I investigated three topics related to soil heterogeneity in a Nicaraguan rainforest: spatial and temporal soil heterogeneity, morphological root foraging by plants, and the interaction between nutrient heterogeneity and root foraging on belowground competition.; In the field, I examined soil properties to quantify their heterogeneity, and to determine the influence of aboveground plant inputs and natural wildfires on soil nutrients. Both univariate and geostatistical methods were used to quantify the forests heterogeneity. Variability as measured by the coefficient of variation ranged between 12% and 92%. While N and K variability tended to be low, leaf litter and P tended to be on the high end of this range. The range over which soil components were autocorrelated (patch size) for the majority of soil properties in the forest was ≤20 meters. Burning altered the spatial variability by decreasing average patch size (12m vs. 7m). However, it had a variable effect on soil nutrient availability. Burning increased P, left K unchanged, and increased N at one site but decreased it in a second. It appears that site differences in N values were due to variable fire temperatures at the two locations.; Overall, plants in this forest forage morphologically for nutrients by growing roots prolifically into nutrient-rich substrates though a greenhouse study showed this to be a species-specific response. In addition, evidence was found that roots of some species are finer when growing into nutrient-rich substrates and that growing in a heterogeneous soil environment may be advantageous to some species.; In greenhouse experiments, I examined how soil heterogeneity and root foraging may interact to influence competition within plant populations through an effect on the size-symmetry of belowground competition. This work found that when combined with morphological root foraging, soil heterogeneity increases the symmetry of competition. This result goes in a direction contrary to traditional theory and suggests the nature of belowground competition is more complicated than previously thought. |
