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的植物结构，如叶子和树枝，或者分配到地下的结构，如根。我们目前对控制地下碳分配的因素的认识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以及地上碳与地下碳的比例的基本了解是一个重大的知识缺口，因为根是土壤中有机物质和营养物质的主要输入。对这些生态系统中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。本研究解决了以下问题：降水如何影响碳的地上/地下分配？在干旱期间，地上和地下结构受到的影响是相同的，还是根系受到的影响比树叶和树枝小？最后，降水对碳分配的影响是恒定的，还是在沙漠和湿润草原之间有所不同？该项目将在新墨西哥州、科罗拉多州和堪萨斯州进行实验，以了解降水对地上与地下碳分配的影响及其潜在机制。本文提出了三个新的假设：(1)植物响应机制，表明地下分配随着水分有效性的增加而减少；(2)营养级联机制，表明根食动物和它们的捕食者对水分有效性的不同敏感性得出相反的模式。最后的假设(3)表明，从干旱草原到湿润草原，植物的响应强度降低，而营养级联现象的强度增加。营养级联机制可能受到干旱草原地下捕食者丰度的限制，而湿润生态系统的地下捕食者丰度更高。实验设计包括三个不同生态系统类型的互补田间和微观实验：奇瓦瓦沙漠草原，NM，短草草原，CO和高草草原，KS。田间试验包括每个站点降水的增加和减少。微观世界实验是基于单体石经受4种土壤动物处理x 5种水处理。土壤动物处理包括：(1)无动物（只有原生细菌和真菌）的土壤，(2)接种线虫根食用菌的土壤，(3)接种线虫根食用菌和线虫捕食者的土壤，以及(4)控制。利用每种生态系统类型的优势草种个体，在每个水处理地块上设置微型管。该项目将培养一名博士后、研究生和本科生，包括来自弱势群体的学生。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示范项目。Asombro科学教育研究所是一个非营利组织，每年向新墨西哥州南部和德克萨斯州西部的12,000多名儿童和4,500多名成年人提供获奖的科学教育。与“问生物学家”计划的合作将产生一篇关于植物和地下生物之间相互作用以及这些相互作用如何被水的可用性调节的文章。该项目将在夏季可持续发展项目中举办与气候对地下过程的影响有关的特别活动，该项目将吸引当地教师和学生参加，并举办面向公众的“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.