Collaborative Research: Water Availability Controls on Above-Belowground Productivity Partitioning: Herbivory versus Plant Response

合作研究：水资源可用性对地上地下生产力分配的控制：食草动物与植物的反应

• 批准号: 1456631
• 负责人: Diana Wall
• 金额: $ 16.05万
• 依托单位: Colorado State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-06-15 至 2020-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1456631&HistoricalAwards=false
• 关键词: Collaborative; Research; Water; Availability; Controls

Ecosystems fix carbon from the atmosphere through photosynthesis, which is then allocated to aboveground plant structures, such as leaves and branches, or to belowground structures, such as roots. Our current understanding of the factors that control belowground carbon allocation is significantly weaker than aboveground allocation. Yet, in grasslands the amount of carbon that goes belowground each year is much larger than the amount of carbon allocated aboveground. Our rudimentary understanding of the controls of belowground carbon allocation and the ratio of aboveground to belowground carbon is a significant knowledge gap, as roots are a major input of organic material and nutrients into soil. Predictions of future carbon storage in these ecosystems hinge on our understanding of the effects of environmental availability on allocation of carbon belowground. This study addresses the questions: How does precipitation affect the above/belowground partitioning of carbon? During drought periods, are above and belowground structures equally affected, or are roots affected less than leaves and branches? Finally, is the effect of precipitation on carbon allocation constant or does it vary from deserts to humid grasslands? This project will install experiments in New Mexico, Colorado and Kansas to understand the effect of precipitation on the partitioning of carbon above versus belowground and the underlying mechanisms.This proposal presents three novel hypotheses based on: (1) a plant-response mechanism, suggesting decreased belowground allocation with increasing water availability, and (2) a trophic-cascade mechanism, suggesting the opposite pattern derived from the differential sensitivity of root feeders and their predators to water availability. A final hypothesis (3) suggests that the magnitude of plant responses decreases from arid to humid grasslands while the magnitude of the trophic-cascade phenomenon increases. The trophic-cascade mechanism may be constrained by the abundance of belowground predators in arid grasslands, which is greater in humid ecosystems. The experimental design includes complementary field and microcosm experiments located in three different ecosystem types: Chihuahuan Desert Grassland, NM, Shortgrass Steppe, CO, and Tallgrass Prairie, KS. The field experiment includes additions and reductions of precipitation at each site. The microcosm experiment is based on monoliths subjected to 4 soil fauna treatments x 5 water manipulations. Soil fauna treatments consist of (1) soil devoid of fauna (just native bacteria and fungi), (2) defaunated soil inoculated with nematode root feeders, (3) defaunated soil inoculated with nematode root feeders and nematode predators, and (4) control. Microcosm tubes will be located in each of the water manipulation plots using individuals of the dominant grass species of each ecosystem type. This project will train a post-doctoral fellow and graduate and undergraduate students, including students from underrepresented groups. Collaboration with the Asombro Institute for Science Education, a non-profit organization that provides award-winning science education to more than 12,000 children and 4,500 adults annually in southern New Mexico and western Texas, will include establishing a demonstration project of a soil-observation window at the Chihuahuan Desert Nature Park. Partnerships with the "Ask A Biologist" program will result in an article on the interactions between plants and belowground organisms and how these interactions are modulated by water availability. The project will contribute special events associated with the effects of climate on belowground processes during a summer sustainability program that engages local teachers and students, and the "Managing the Planet" series aimed at the general public.

生态系统通过光合作用固定大气中的碳，然后将碳分配给地上植物结构，如叶子和树枝，或地下结构，如根。我们目前对控制地下碳分配的因素的了解明显弱于地上分配。然而，在草原上，每年地下的碳量远远大于地上分配的碳量。我们对地下碳分配的控制以及地上和地下碳的比率的基本了解是一个重大的知识鸿沟，因为根是有机物质和养分进入土壤的主要输入。对这些生态系统未来碳储量的预测取决于我们对环境可用性对地下碳分配的影响的理解。这项研究解决的问题是：降水如何影响地上/地下的碳分配？在干旱期间，地上和地下结构是否同样受到影响，或者根受到的影响比叶和枝条受到的影响要小？最后，降水对碳分配的影响是恒定的，还是从沙漠到潮湿的草原不同？该项目将在新墨西哥州、科罗拉多州和堪萨斯州进行实验，以了解降水对地上和地下碳分配的影响及其潜在的机制。这项提议提出了三个新的假设：(1)植物反应机制，表明地下分配的减少随着水的可获得性的增加；(2)营养-级联机制，提出相反的模式，来自根食性动物及其捕食者对水可获得性的差异化敏感性。最后一个假设(3)表明，从干旱草原到湿润草原，植物反应的幅度减小，而营养级联现象的幅度增加。干旱草原地下捕食者的丰富程度可能制约了营养级联机制的发挥，在湿润的生态系统中，这种限制更为明显。实验设计包括位于三个不同生态系统类型：奇瓦瓦沙漠草原(NM)、短草草原(CO)和塔尔格拉斯草原(KS)的补充性田间和微观世界实验。田间试验包括每个地点降水的增加和减少。微宇宙实验是基于4个土壤动物处理×5个水处理的整体。土壤动物处理包括(1)没有动物的土壤(只有本地细菌和真菌)，(2)接种线虫食根者的默认土壤，(3)接种线虫食根者和线虫捕食者的默认土壤，以及(4)对照。微宇宙管将设置在每个水处理地块中，使用每个生态系统类型的优势草种的个体。该项目将培养一名博士后研究员以及研究生和本科生，包括来自代表性不足群体的学生。与Asombro科学教育研究所的合作将包括在奇瓦瓦沙漠自然公园建立一个土壤观测窗口的示范项目。Asombro科学教育研究所是一个非营利性组织，每年在新墨西哥州南部和德克萨斯州西部为12000多名儿童和4500多名成年人提供获奖的科学教育。与“问生物学家”计划的伙伴关系将产生一篇关于植物和地下生物之间的相互作用以及这些相互作用如何受到水的可获得性调节的文章。该项目将在吸引当地教师和学生参与的夏季可持续发展计划期间，以及针对普通公众的“管理地球”系列活动期间，举办与气候对地下过程的影响有关的特别活动。