DISSERTATION RESEARCH: Woody plant encroachment into grasslands: Impacts on landscape-scale patterns of soil carbon, nitrogen, and phosphorus storage and dynamics

接受少量降雨或降雪的土地约占地球陆地面积的40%。这些地区的大部分地区正在经历植物的替代，主要是草与树木和灌木的数量增加。这种变化通常会增加植物和土壤中的碳含量，并影响对植物生长重要的其他元素（如氮和磷）的使用;碳积累也可能影响气候。 氮和磷是通常限制植物生长速率的营养素，其中一种的供应会影响其他元素。尽管碳、氮和磷在植物和土壤中很重要，但很少有研究将这三种元素同时考虑到干旱景观中，树木和灌木的数量正在增加。该项目将测量树木和灌木大量取代草地的地区土壤中碳、氮和磷的储存模式。研究结果将提供有关树木和灌木取代草的原因以及这些变化对这些环境意味着什么的知识。这项研究获得的信息将用于改进数学模型，这些模型描述了气候和养分循环的相互作用，从而可以为这些旱地的保护和管理提供信息。有关这项研究的教育材料将与德克萨斯州A M农业生命推广计划合作为公众准备。草地、稀树草原和沙漠生态学家长期以来一直对木本植物繁殖后土壤养分库大小的改变感兴趣。然而，大多数以前的研究养分动态后，木本入侵已被限制在小的空间尺度，仅限于土壤剖面的最上部，并主要集中在C和/或N。 本研究将量化土壤有机碳，全氮，全磷在整个土壤剖面，以使第一次评估的规模C：N：P土壤化学计量学木本植物入侵草地。具体目标是：（1）检查植被覆盖变化是否改变了三维空间格局的土壤C，N和P存储在景观尺度;（2）测试是否土壤P尺度相对于C和N的等距，以及这些等距模式是否随土壤深度的变化在N-固定剂侵蚀系统。养分储存将被量化的空间特定的土壤芯采取的深度为1.2米的亚热带稀树草原景观，其中N固定木本植物在过去的世纪已侵入草地。 结果将提供新的看法，木本侵占的影响，在干旱和半干旱生态系统的C，N和P循环之间的相互作用在整个地球仪，并提高我们的能力，代表这些相互作用的联系地球化学-气候模型。

Lands that receive small amounts of rain or snow occupy approximately 40% of the Earth's land surface. Large portions of these areas are experiencing a replacement of plants that are mostly grasses with increased numbers of trees and shrubs. This change generally increases the amount of carbon found in both plants and soils, and impacts how other elements that are important for plant growth, such as nitrogen and phosphorus, are used; carbon accumulation may also impact climate. Nitrogen and phosphorus are nutrients that often limit the rates at which plants grow, and the supply of one or the other can affect other elements. Despite the importance of carbon, nitrogen and phosphorus in plants and soils, very few studies have been conducted that consider all three elements together in dry landscapes, where the numbers of trees and shrubs are increasing. This project will measure patterns of storage of carbon, nitrogen, and phosphorus within the soils in areas where trees and shrubs have largely replaced grasses. The results will provide knowledge on why trees and shrubs are replacing grasses and what these changes mean for those environments. The information gained by this research will be used to improve mathematical models that describe the interactions of climate and nutrient cycles that in turn can inform the conservation and management of these dry lands. Educational materials about the research will be prepared for the general public in cooperation with the Texas A&M AgriLife Extension program.Modification of soil nutrient pool sizes following woody proliferation has long been of interest to grassland, savanna, and desert ecologists. However, most previous studies examining nutrient dynamics following woody encroachment have been confined to small spatial scales, limited to the uppermost portions of the soil profile, and focused primarily on C and/or N. This research will quantify soil organic C, total N, and total P throughout the entire soil profile in order to make the first assessment of landscape-scale C:N:P soil stoichiometry following woody plant encroachment into grassland. Specific objectives are: (1) Examine whether vegetation cover change alters the 3-dimensional spatial patterns of soil C, N, and P storage at the landscape scale; and (2) Test whether soil P scales isometrically with respect to C and N, and whether these isometric patterns change with soil depth in N-fixer encroached systems. Nutrient stores will be quantified in spatially-specific soil cores taken to a depth of 1.2 meters in a subtropical savanna landscape where N-fixing woody plants have encroached into grasslands during the past century. Results will offer new perceptions on the effects of woody encroachment on interactions between C, N, and P cycles in arid and semi-arid ecosystems across the globe, and enhance our ability to represent these interactions in linked biogeochemistry-climate models.