ROW: Nutrient Uptake and Growth in Eastern Deciduous Tree Seedlings

本研究将研究一组相对生长率和林隙定殖能力差异很大的森林树种的离子吸收率、相对生长率和土壤养分依赖性之间的关系。假设：1)相对生长速度快的定殖种比生长速度慢的定殖种具有更高的最大离子吸收能力；2)相对生长率较低的耐阴树种在低养分浓度下的根系吸收能力高于生长快的缝隙定殖树种；3) NO3、K等土壤流动离子差异最大，PO4、NH4等土壤固定离子差异较小；4)适应低营养条件的幼苗的养分吸收率大于适应高营养条件的幼苗，相对生长率高的物种的这种可塑性更大；5)在田间，林隙定植的幼苗比生长缓慢、耐阴的物种不仅对林隙地增加的光效更敏感，而且对施肥地增加的养分效也更敏感。东部落叶林的6种树种将由种子生长。其中3种是相对生长率较高的林隙定殖种（李、尾树栎和白桦），3种是相对生长率较低的耐阴种（美洲黄曲霉、山核桃和北方栎）。将进行三个独立的实验来检验这些假设。

This study will examine the relationship between ion absorption rate, relative growth rate, and the soil nutrient dependence of a suite of forest tree species that vary widely in both relative growth rate and canopy gap colonization ability. It is hypothesized that: 1) Gap colonizing species with high relative growth rates will have higher maximum ion absorption capacities than slowly growing species; 2) Shade tolerant species with low relative growth rates will have higher root absorption capacities at low nutrient concentrations than fast growing, gap colonizing species; 3) These differences will be greatest for soil mobile ions such as NO3 and K and less for soil immobile ions such as PO4 and NH4; 4) Nutrient uptake rates will be greater for seedlings acclimated to low nutrient conditions than to high nutrient conditions, and that this plasticity will be greater for species with high relative growth rates; 5) In the field, gap colonizing seedlings will be more responsive than slowly growing, shade tolerant species not only to increased light availability in gap sites but also to increased nutrient availability in fertilized sites. Six tree species of the eastern deciduous forest will be grown from seed. Three of these species represent gap colonizing species with high relative growth rates (Prunus serotina, Quercus coccinea, and Betula populifolia), and three represent shade tolerant species with low relative growth rates (Fraxinus americana, Carya ovata, and Quercus borealis). Three separate experiments will be performed to test the hypotheses.