Iron nutrition of Pinus elliotii var. densa seedlings in two soils with different iron availability

Seedlings of endangered Dade County pine, Pinus elliotii var. densa, must survive long enough to form symbiotic associations with ectomycorrhizal fungi that assist uptake of mineral nutrients. Although plants need nitrogen (N), phosphorus (P), and potassium (K) in relatively large quantities, pine seedlings also may need relatively high amounts of iron (Fe). We hypothesized that iron would limit the growth of non-mycorrhizal pine seedlings in a low-Fe soil, but not in a soil with relatively abundant Fe. We grew pine seedlings in a three-factor, fully factorial experiment in pots in a greenhouse. The factors are two soils (flatwoods and sandhill) with different Fe availability from the Archbold Biological Station, three levels of weekly Fe addition (none; 37 mg; 74 mg chelated iron), and two levels of N, P, and K fertilization (none; one-time addition of 0.93, 0.28, and 1.85 g, N, P, K, respectively). At the final harvest, 18 weeks after treatments began, we measured chlorophyll a and b concentrations, dry weights of needles, stem, primary root, and fine roots. In the presence of NPK, iron had a negative effect on chlorophyll and biomass which might be the result of iron immobilizing phosphorus. In the absence of NPK, iron had a positive effect on chlorophyll and on root-to-shoot ratio which suggests that iron subtly limits seedlings in soils with little NPK, but on more fertile soils phosphorus might be the growth limiting nutrient. G. Toledo et al. 3 of 22