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

生态系统通过光合作用固定大气中的碳，然后将其分配到地上植物结构，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理解明显弱于地上碳分配。然而，在草原上，每年进入地下的碳量远远大于分配到地上的碳量。我们对地下碳分配的控制和地上与地下碳的比例的初步理解是一个重大的知识差距，因为根是有机物质和养分进入土壤的主要输入。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：降水如何影响上述/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，或者根部受到的影响小于叶子和树枝？ 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而有所不同？ 该项目将在新墨西哥州、科罗拉多和堪萨斯进行实验，以了解降水对地上和地下碳分配的影响及其潜在机制。（1）植物响应机制，表明地下水分配随着水资源可用性的增加而减少，（2）营养级联机制，表明相反的模式来自不同的敏感性的根饲养者和他们的捕食者对水的可用性。最后一个假设（3）表明，从干旱到潮湿的草原，植物反应的幅度降低，而营养级联现象的幅度增加。营养级联机制可能受到地下捕食者在干旱草原，这是在潮湿的生态系统中更大的丰度。实验设计包括位于三种不同生态系统类型的补充领域和微观实验：奇瓦瓦沙漠草原，NM，短草草原，CO，和高草草原，KS。现场实验包括在每个站点增加和减少降水。微宇宙实验是基于进行4个土壤动物处理x5个水处理的整料。土壤动物处理包括（1）无动物（仅原生细菌和真菌）的土壤，（2）接种线虫根食动物的去动物区系土壤，（3）接种线虫根食动物和线虫捕食者的去动物区系土壤，以及（4）对照。 微宇宙管将位于每一个水操纵地块使用每个生态系统类型的优势草种的个人。该项目将培训一名博士后研究员以及研究生和本科生，包括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察窗示范项目，该研究所是一个非营利组织，每年向新墨西哥州南部和得克萨斯州西部的12 000多名儿童和4 500多名成年人提供获奖的科学教育。与"问一个生物学家"计划的伙伴关系将导致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通过水的可用性来调节的文章。该项目将在夏季可持续发展计划期间举办与气候对地下过程影响相关的特别活动，吸引当地教师和学生的参与，以及针对公众的“管理地球”系列活动。

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.