RUI: SG: Source or Sink? Do Plant-Microbial Interactions Determine the Direction of Carbon Flux During the Wet Phase of Northern Peatlands?

生物膜是微生物群落，包括藻类、真菌和细菌——在水生环境中紧密结合生长的生物体。与我们对大多数其他环境中生物膜生态学的了解相比，我们对湿地中微生物相互作用的了解还很缺乏。这种知识差距在泥炭地尤其明显，泥炭地是北纬地区常见的景观特征。部分原因是由于厚厚的有机土层锁住了大量的营养物质，北部泥炭地富含碳而缺乏其他营养物质。在泥炭地，能够忍受低养分利用率的植物，如苔藓，产生了很大一部分年生物量积累，而且分解缓慢。随着时间的推移，植物生长（初级生产）和微生物分解之间的不平衡导致有机质以泥炭的形式积累。这个小型拨款（SG）项目将在阿拉斯加的Bonanza Creek长期生态研究（LTER）地点研究泥炭地被水淹没的时期。这项研究将评估植物和微生物生物膜介导的活动如何影响在这个潮湿阶段储存在泥炭中的碳量，以及有多少碳被释放到大气中。除了绘制生态系统科学的新概念基础外，该项目还将为来自代表性不足群体的本科生提供研究经验，并培养两名研究生。微生物生物膜由自养（藻类）和异养（细菌和真菌）微生物组成，在水生生态系统功能中起着关键作用。异养生物膜负责将二氧化碳（CO2）释放到大气中，而自养生物膜在光合作用过程中吸收二氧化碳。生物膜组成对生态系统碳(C)排放的总体影响是由微生物（包括藻类、细菌和真菌）之间的资源交换决定的。自养生物依靠异养生物来循环养分，而异养生物依靠自养生物来获取在光合作用过程中固定的C，除非外界能满足能量需求。在高含水量的泥炭地生态系统中，维管植物和苔藓有可能通过提供C补贴来改变微生物生物膜的代谢平衡，使其有利于异养生物，从而使异养生物能够与自养生物竞争有效养分。鉴于一些植物补贴比其他植物补贴更容易被异养生物利用，植物促进微生物活动的能力可能取决于植物群落组成。然而，泥炭地植物群落结构对微生物生物膜的影响尚未得到广泛的研究。因此，很难预测植物群落的变化，比如随着气候变化而发生的变化，如何影响北部泥炭地的碳平衡。该项目将在Bonanza Creek LTER站点使用营养物质和有机物的组合操作，以确定植物群落的有机碳补贴通过调节北部泥炭地微生物生物膜的组成来控制生态系统碳通量的程度。据预测，有利于稳定碳补贴的植物组成变化将通过促进异养活动和减少藻类光合作用来增加二氧化碳排放。在这种情况下，藻类不再能够减轻异养呼吸的影响，从而导致系统产生更大的二氧化碳通量。或者，在不太稳定的植物补贴存在的情况下，异养微生物依靠藻类来源的有机物在生物膜内进行代谢。在这种情况下，藻类光合作用减轻了与异养呼吸有关的二氧化碳排放。相比之下，富含营养的植物补贴可以缓解生物膜的营养限制，从而增加藻类生物量和二氧化碳吸收率。该项目将为两名硕士生和几名本科生提供培训机会，其中包括通过美国国家科学基金会资助的印第安纳州路易斯斯托克斯少数民族参与联盟招募的科学领域代表性不足群体的成员。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Biofilms are communities of microorganisms, which include algae, fungi, and bacteria - organisms that grow in close association in aquatic environments. Compared to our understanding of biofilm ecology in most other environments, our knowledge of microbial interactions within wetlands is lacking. This knowledge gap is particularly evident in peatlands, a common landscape feature at northern latitudes. In part because of thick organic soil layers that lock up significant amounts of nutrients, northern peatlands are rich in carbon and poor in other nutrients. Plants such as mosses that can tolerate low nutrient availability produce a large fraction of annual biomass accumulation in peatlands, and this decomposes slowly. Over time, an imbalance between plant growth (primary production) and microbial decomposition leads to the accumulation of organic matter as peat. This small grant (SG) project will study peatlands at the Bonanza Creek Long-Term Ecological Research (LTER) site in Alaska during periods when they are inundated with water. The research will assess how between plant- and microbial biofilm-mediated activities impact the amount of carbon that gets stored in peat under this wet phase, and how much carbon is released into the atmosphere. In addition to charting new conceptual ground in ecosystem science, this project will provide research experiences for undergraduate students from under-represented groups and train two graduate students.Microbial biofilms are comprised of autotrophic (algae) and heterotrophic (bacteria and fungi) microorganisms that play a key role in aquatic ecosystem function. Heterotrophic biofilms are responsible for releasing carbon dioxide (CO2) to the atmosphere, whereas autotrophic biofilms take up CO2 during photosynthesis. The overall influence of biofilm composition on ecosystem carbon (C) emissions is determined by the exchange of resources among microorganisms, including algae, bacteria, and fungi. Autotrophs rely on heterotrophs to recycle nutrients, and heterotrophs rely on autotrophs for C that is fixed during photosynthesis, unless energetic requirements are met by outside sources. In peatland ecosystems with high water content, vascular plants and mosses have the potential to shift the metabolic balance of the microbial biofilm in favor of heterotrophy by providing C subsidies that allow heterotrophs to outcompete autotrophs for available nutrients. Given that some plant subsidies are more easily used by heterotrophs than others, the ability for plants to facilitate microbial activity may depend on plant community composition. However, the impact of plant community structure on microbial biofilms has not been widely studied in peatlands. As a result, it is difficult to predict how shifts in plant communities, such as those occurring with climate change, influence the C balance of northern peatlands. This project will use a combination of nutrient and organic matter manipulations at the Bonanza Creek LTER site to determine the extent to which organic C subsidies from plant communities govern ecosystem C flux by regulating the composition of microbial biofilms in northern peatlands. It is predicted that shifts in plant composition that favor labile C subsidies will increase CO2 emissions by promoting heterotrophic activity and reducing algal photosynthesis. In this condition, algae are no longer able to mitigate the effects of heterotrophic respiration leading to greater CO2 flux from the system. Alternatively, in the presence of less labile plant subsidies, heterotrophic microorganisms rely on algal sources of organic matter for metabolism within the biofilm. In this condition, algal photosynthesis mitigates CO2 emissions associated with heterotrophic respiration. Nutrient-rich plant subsidies, by contrast, could alleviate nutrient limitation of the biofilm resulting in greater algal biomass and CO2 uptake. The project will provide training opportunities for two masters students and several undergraduates, including members of underrepresented groups in science recruited through the NSF-funded Louis Stokes Alliance for Minority Participation Consortium in Indiana.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.