Resolving the limitations on plant growth and biomass

是什么限制了植物的初级生产力仍然是一个跨尺度和生物系统相关的主要问题。长期以来，农学家和农民一直在寻找支持生物量有效积累的因素，以最大限度地提高作物产量。生态学家已经确定环境条件是全球生物群系植物生产力的关键决定因素（例如Whittaker）。在天然热带森林系统中，解决这些因素尤为重要，因为热带森林具有通过在未来充当碳汇来减缓气候变化的潜力，除非生物量碳积累受到另一个因素的限制（例如，Hungate等人，2003年，《科学》）。除了气候之外，很明显，光或矿物质营养的缺乏会抑制植物的生长。然而，光和养分在多大程度上是生物量形成的实际限制因素仍不清楚。例如，在成熟的热带森林中，施肥对森林净生物量积累几乎没有明显影响（Wright et al. 2011, Ecology）。在实验温室条件下，即使在理想的生长条件下，植物也往往不能最大限度地生长（Poorter et al. 2012, Functional Plant Biology）。这一结果可能是由于根系限制、拥挤或固有的遗传限制，使植物无法充分利用可用资源。该项目旨在剖析这些因素（光、营养、拥挤和遗传）对植物生长限制的贡献。它将考虑在一系列环境系统中生长的植物，包括温室、天然热带森林和大规模实地试验，以及一系列物种，包括农作物和热带树木。我们将特别关注新的假设，即在许多条件下，根系限制对生物量积累起实际限制作用。学生将有机会发展一系列的方法来解决这个问题。我们将在受控环境中进行实验，以精确剖析根系限制（例如通过操纵盆栽大小）、养分施用和光照水平对生长和生物量形成的相对影响。我们将确定任何给定因素作为植物生长限制所需要的条件。我们还将在利兹大学实验农场使用作物试验（例如，播种率与化肥施用）来测试这些限制因素在农业环境中的影响。最后，我们将评估施肥和植物密度对巴拿马热带森林长期农田生物量形成的影响。该项目将有助于制定在农业和林业环境下提高植物生产力和生物量形成的最佳战略，并将提高我们对热带森林中营养限制对碳汇的作用的理解。

What limits primary productivity in plants remains a major question relevant across scales and biological systems. Agronomists and farmers have long sought the factors that support efficient accumulation of biomass in order to maximize crop production. Ecologists have identified environmental conditions as critical determinants of plant productivity across biomes globally (e.g., Whittaker). Within natural tropical forest systems, resolving these factors is particularly relevant since tropical forests have the potential to mitigate climate change by serving as a carbon sink in the future, unless biomass carbon accumulation becomes limited by another factor (e.g., Hungate et al. 2003, Science). In addition to climate, it is clear that deficiency in light or mineral nutrients can inhibit plant growth. However, the extent to which light and nutrients are practical limiting factors for biomass formation remains unclear. For instance, in mature tropical forests, fertiliser application has little apparent effect on net forest biomass accumulation (Wright et al. 2011, Ecology). In experimental greenhouse conditions, plants often do not maximize their growth, even under ideal growth conditions (Poorter et al. 2012, Functional Plant Biology). This result may be due to root restriction, crowding, or inherent genetic constraints that prevent the plants from taking full advantage of available resources. This project aims to dissect the contribution of these factors (light, nutrients, crowding and genetics) to the limitation of plant growth. It will consider plants grown in a range of environmental systems, including greenhouse, natural tropical forests and large-scale field experiments, and a range of species, including both agricultural crops and tropical trees. We will pay particular attention to the new hypothesis that root restriction acts as the practical limit on biomass accumulation under many conditions. The student will have the opportunity to develop a range of approaches in order to address this question. We will perform experiments in controlled environments to precisely dissect the relative effects of root restriction (e.g. through manipulating pot size), nutrient application and light levels on growth and biomass formation. We will identify what conditions are needed for any given factor to act as limitation of plant growth. We will also test the effect of these limiting factors in agricultural contexts, using crop trials (for instance, of seed drilling rate versus fertilizer application) at the University of Leeds experimental farm. Finally, we will assess the effect of fertiliser application and plant density on biomass formation in long-running field sites in the Panamanian tropical forest. This project will help to establish the best strategies for improving plant productivity and biomass formation in both agricultural and forestry contexts and will improve our understanding of the role of nutrient limitation on the carbon sink in tropical forests.