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，其中包括藻类、真菌和细菌--这些生物在水环境中密切相关地生长。与我们对大多数其他环境中的生物膜生态的了解相比，我们对湿地内微生物相互作用的知识是缺乏的。这种认识差距在泥炭地尤为明显，泥炭地是北纬地区的一种常见景观特征。在一定程度上，由于厚厚的有机土层锁定了大量的养分，北部泥炭地富含碳，而缺乏其他养分。能够耐受低养分供应的植物，如苔藓，在泥炭地每年积累的生物量中，有很大一部分是由苔藓等植物产生的，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的积累，如泥炭。这个小额赠款(SG)项目将研究阿拉斯加Bonanza Creek长期生态研究(LTER)遗址的泥炭地，研究它们被水淹没的时期。这项研究将评估植物和微生物生物膜介导的活动之间的关系如何影响在湿相下储存在泥炭中的碳量，以及有多少碳释放到大气中。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，它们在水生生态系统功能中发挥关键作用。异养生物膜负责向大气中释放二氧化碳(CO2)，而自养生物膜在光合作用中吸收二氧化碳。生物膜组成对生态系统碳(C)排放的总体影响取决于微生物之间的资源交换，包括藻类、细菌和真菌。自养生物依赖异养生物循环营养物质，异养生物依赖自养生物获取在光合作用过程中固定的碳，除非外部来源满足能量需求。在高含水率的泥炭地生态系统中，维管植物和苔藓有可能通过提供碳补贴来改变微生物生物膜的代谢平衡，有利于异养生物获得可用养分。考虑到一些植物补贴比其他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的组成。然而，在泥炭地，植物群落结构对微生物生物膜的影响还没有得到广泛的研究。因此，很难预测植物群落的变化，例如那些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。该项目将结合Bonanza Creek LTER现场的营养和有机质操作，通过调节北部泥炭地微生物生物膜的组成，确定植物群落的有机碳补贴在多大程度上管理生态系统的碳通量。据预测，有利于不稳定碳补贴的植物成分的变化将通过促进异养活动和降低藻类光合作用来增加二氧化碳排放。在这种情况下，藻类不再能够缓解异养呼吸的影响，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新陈代谢。在这种情况下，藻类光合作用减轻了与异养呼吸相关的二氧化碳排放。相比之下，营养丰富的植物补贴可以缓解生物膜的营养限制，导致更大的藻类生物量和二氧化碳吸收。该项目将为两名硕士学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路易斯·斯托克斯少数群体参与联盟在印第安纳州招募的科学中代表性不足的群体的成员。该奖项反映了国家科学基金会的法定使命，并通过使用基金会的智力优势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.