Can Interspecific Variation in Whole-Plant Resource Economies and Underlying Physiological and Morphological Traits Provide a Mechanistic Basis for Forest Composition?

人类活动在很大程度上影响着北温带森林中氮、钙和水的有效性。这些变化可能会严重影响森林的组成和动态，因为水、氮和钙以物种特有的方式限制了北方温带森林中树木的生长和存活。通过描述不同树种在土壤资源梯度上的生长和存活差异的作用机制，以及这些树种特征如何与光照条件相互作用来确定物种竞争能力，将有助于预测森林响应的能力。我们假设，在低土壤资源环境中生长和存活较大的树种的苗木具有提高有限土壤资源的整株利用效率和获得途径的特性，这些特性是适应低土壤资源的基础，这些特性发生在高土壤资源环境中的耐荫性和/或高光生长率之间的权衡。这两个实验都将使用北方温带森林中常见的9种阔叶落叶植物，但它们的丰度在光和土壤资源环境中有所不同。在田间试验中，苗木被移植到施肥(钙、氮、钙+氮)和未施肥的地块中，这些地块分布在下密歇根州下部冰川地区的不同光照和独立的景观水平的水分和养分梯度上。在三年的实验期间，我们将监测幼苗的生长和存活，并测量我们假设的物种表现差异背后的全植物形态和生理特征。室外塑料盆栽试验将使我们能够比田间试验更深入地研究细根的生理和动态。综合这些数据，我们将能够确定：1)物种对氮、钙、水和光的自然梯度的特定生长和存活反应；2)在施肥的小区中，N和Ca限制生长和存活的程度及其在景观梯度上的变化；3)氮、钙和水的获取和利用效率的种间差异；4)与物种在土壤资源的获取和利用效率上的差异有关的全植物资源经济的生理和形态成分；5)在土壤资源利用率低的情况下，全植物资源经济和相关性状的种间差异是否导致生长和存活的差异；6)基于资源的生长和存活的种间权衡以及物种差异所特有的形态/生理性状。

Human activities are substantially influencing the availability of nitrogen, calciumand water in north temperate forests. These changes may strongly affect forest composition and dynamics because water, nitrogen and calcium limit - in a species-specific manner -the growth and survival of trees in northern temperate forests. The ability to predict forest responses will be aided by characterizing the functional mechanisms that underlie tree species differences in growth and survival across soil resource gradients and how these species traits interact with light availability in determining species competitive abilities. We hypothesize that seedlings of tree species with greater growth and survival in low soil resource environments have collections of traits that enhance whole-plant use efficiency of and access to limiting soil resources, that these traits underlie adaptation to low soil resources, and that these traits occur at a tradeoff with shade tolerance and/or high light growth rates in high soil resource environments.A seedling transplant experiment to field plots and a closely linked potted seedling experiment are proposed to address these hypotheses. Both experiments will use the same nine broad-leaved deciduous species that are common in northern temperate forests, but that vary in abundance across light and soil resource environments. For the field experiment, seedlings have been transplanted into fertilized (Ca, nitrogen, Ca + nitrogen) and unfertilized plots distributed across variation in light and independent landscape-level gradients of water and nutrients in glaciated northwestern lower Michigan. Over the three-year duration of the experiment, we will monitor seedling growth and survival and measure whole-plant morphological and physiological traits that we hypothesize underlie species differences in performance. The outdoor plastic pot experiment will allow us to more thoroughly examine fine root physiology and dynamics than could be accomplished in the field experiment.Collectively these data will allow us to determine: 1) species specific growth and survival responses to natural gradients of nitrogen, calcium, water and light; 2) with fertilized plots, the degree to which N and Ca limit growth and survival and how it varies over the landscape gradient; 3) interspecific variation in access to, and use efficiency of nitrogen, calcium and water; 4) the physiological and morphological components of whole-plant resource economies that are associated with species differences in access to, and use efficiency of soil resources; 5) whether interspecific variation in whole-plant resource economies and related traits underlie variation in growth and survival at low soil resource availability; 6) interspecific trade-offs in resource-based growth and survival and the particular morphological / physiological traits underlying species differences.