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

生物膜是微生物的群落，其包括藻类、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理解相比，我们对湿地内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，泥炭地是北方纬度的一个常见景观特征。北方的泥炭地富含碳元素，而其他营养元素贫乏，部分原因是厚厚的有机土层锁住了大量的营养物质。能够耐受低养分可用性的植物（如苔藓）在泥炭地每年的生物量积累中产生很大一部分，并且分解缓慢。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物质积累为泥炭。这个小赠款（SG）项目将研究泥炭地在博南扎溪长期生态研究（LTER）网站在阿拉斯加期间，当他们被水淹没。该研究将评估植物和微生物生物膜介导的活动如何影响在潮湿阶段储存在泥炭中的碳量，以及有多少碳释放到大气中。本项目除了为生态系统科学提供新的概念基础外，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期间吸收CO2。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（包括藻类、细菌和真菌）之间的资源交换。自养生物依靠异养生物来回收营养物质，而异养生物则依靠自养生物来获得在光合作用过程中固定的碳，除非外界来源满足能量需求。在泥炭地生态系统中，高含水量，维管植物和苔藓有可能改变微生物生物膜的代谢平衡，有利于异养提供C补贴，使异养生物竞争优势的营养物质。鉴于一些植物补贴比其他植物更容易被异养生物利用，植物促进微生物活性的能力可能取决于植物群落的组成。然而，植物群落结构对泥炭地微生物生物膜的影响尚未得到广泛研究。因此，很难预测植物群落的变化，如气候变化，如何影响北方泥炭地的碳平衡。该项目将使用的富矿溪LTER网站的营养和有机物质的操作相结合，以确定在何种程度上从植物群落的有机碳补贴管理生态系统碳通量，通过调节微生物生物膜的组成在北方泥炭地。据预测，有利于不稳定的碳补贴植物组成的变化将增加二氧化碳排放量，促进异养活动和减少藻类光合作用。在这种情况下，藻类不再能够减轻异养呼吸的影响，导致系统中更大的CO2通量。或者，在不太稳定的植物补贴的存在下，异养微生物依赖于藻类来源的有机物质在生物膜内进行代谢。在这种条件下，藻类光合作用减轻了与异养呼吸相关的CO2排放。相比之下，营养丰富的植物补贴，可以减轻营养限制的生物膜导致更大的藻类生物量和CO2吸收。该项目将为两名硕士生和几名本科生提供培训机会，包括通过NSF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代表性不足的群体成员。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

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.