Below Ground Control of Ecosystem Carbon Sequestration under Elevated CO2

二氧化碳浓度升高下生态系统碳封存的地下控制

• 批准号: NE/X000273/1
• 负责人: Gareth Phoenix
• 金额: $ 77.92万
• 依托单位: University of Sheffield
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX000273%2F1
• 关键词: Below; Ground; Control; Ecosystem; Carbon

As atmospheric CO2 concentrations rise, plants can photosynthesise more and take more CO2 out of the atmosphere. This carbon (C) can then be stored in plants and soils, reducing atmospheric CO2 and global warming. However, our ability to predict global increases in C uptake are severely constrained because there are so few studies on the effects of elevated CO2 (eCO2) on ecosystems where the availability of the nutrient phosphorus (P) restricts plant growth (P-limited ecosystems) - yet more than 40% of the world's ecosystems are P-limited. Furthermore, it is below ground processes, including interactions between plants, soil microbes and soil chemistry, that will control the ability of these ecosystem to store more C, yet we have very little understanding of how these processes respond to eCO2 in P-limited ecosystems. Understanding below ground responses is essential because soils are the largest store of C in terrestrial ecosystems so we must understand how elevated CO2 changes stores of C in soils as well as in plants. Furthermore, soil C inputs influence the cycling of P and so can determine whether plants can gain the extra P needed for increased growth and C gain, while the fate of C in soil will determine whether it contributes to long-term C stocks or is released. This project will address these knowledge needs using our unique experiment that exposes two contrasting grassland ecosystems (a limestone and an acidic grassland) to elevated CO2 in a natural outdoor setting using Free Air CO2 Enrichment technology (FACE). The grasslands are both P-limited but, critically, plants have responded to eCO2 in directly opposing ways with the limestone grassland increasing biomass, and the acidic grassland reducing biomass. Significantly, the grasslands have contrasting soils linked to developmental age that makes them well suited to gaining mechanistic insights that can be applied broadly across P-limited soils, and may explain the opposing responses. The CO2 enrichment is in combination with P and N nutrient manipulations that allow us to investigate the importance of P-limitation and the influence of globally important atmospheric N deposition that can also influence P cycling. There is a strong theoretical basis for hypothesising that it is the differences in soil biogeochemistry that explains the contrasting plant biomass responses to eCO2: in developmentally young soils (such as our limestone soil), increased C inputs may enhance weathering of primary P-minerals like calcium phosphates and stimulate enzymatic mineralization of organic P, leading to greater plant P availability for growth and C sequestration. In contrast, in soils at later stages of pedogenesis (such as our acidic soil), P is locked up in secondary minerals that are difficult for soil microbes and plants to access. While elevated CO2 may provide the C for enzymes to increase mineralisation of organic P, this is predominantly done by soil microbes which will have reduced efficacy in acidic soil, leading to strong competition for P between plants and microbes, limiting the plant growth benefit of elevated CO2. Critically, these theories remain untested.Using a combination of stable- and radioisotope C tracers, we will trace the short and long-term fate of C and its pathway through plants, microbes and soil. We will determine how the fate of new plant C inputs controls P dynamics by using P isotope tracers to determine how CO2 influences P availability, plant uptake, and competition for P with soil microbes and the soil matrix. Finally, we will use advanced molecular approaches to understand how soil microbes respond to the C inputs and how this influences their cycling of P and its availability to plants. This work aims to determine mechanistically the reasons for the contrasting plant productivity responses in the two grasslands and, in so doing, develop the broad understanding needed to predict future rates of C uptake in P-limited ecosystems.

随着大气中二氧化碳浓度的上升，植物可以进行更多的光合作用，并从大气中吸收更多的二氧化碳。这些碳(C)可以储存在植物和土壤中，减少大气中的二氧化碳和全球变暖。然而，我们预测全球碳吸收增加的能力受到严重限制，因为关于二氧化碳（eCO2）升高对营养磷(P)可用性限制植物生长的生态系统（限磷生态系统）的影响的研究很少，而世界上超过40%的生态系统是限磷的。此外，它是地下过程，包括植物、土壤微生物和土壤化学之间的相互作用，将控制这些生态系统储存更多C的能力，但我们对这些过程如何在磷限制的生态系统中响应eCO2知之甚少。了解地下的反应是至关重要的，因为土壤是陆地生态系统中最大的碳储存地，所以我们必须了解二氧化碳的升高是如何改变土壤和植物中碳储存的。此外，土壤C的输入影响P的循环，因此可以决定植物是否能够获得额外的P，以促进生长和C的增加，而土壤中C的命运将决定它是否有助于长期的C储备或被释放。该项目将通过我们独特的实验来解决这些知识需求，该实验使用自由空气二氧化碳富集技术（FACE），将两个截然不同的草地生态系统（石灰石和酸性草地）暴露在自然室外环境中升高的二氧化碳中。两种草地都是磷有限的，但重要的是，植物对eCO2的响应方式直接相反，石灰岩草地增加了生物量，酸性草地减少了生物量。值得注意的是，草原具有与发育年龄相关的对比土壤，这使得它们非常适合获得可以广泛应用于磷限制土壤的机制见解，并可能解释相反的反应。CO2富集与P和N养分操纵相结合，使我们能够研究P限制的重要性以及全球重要的大气N沉降的影响，这也可以影响P循环。有一个强有力的理论基础假设，土壤生物地球化学的差异解释了植物生物量对eCO2的不同反应：在发育中的年轻土壤（如我们的石灰石土壤）中，增加的C输入可能会增强磷酸钙等初级磷矿物的风化作用，并刺激有机磷的酶矿化，从而提高植物生长和碳封存的P可利用性。相反，在土壤形成后期的土壤中（比如我们的酸性土壤），磷被锁在次生矿物质中，土壤微生物和植物难以接近。虽然升高的CO2可能为酶提供C来增加有机磷的矿化，但这主要是由土壤微生物完成的，这在酸性土壤中会降低效率，导致植物和微生物之间对P的激烈竞争，限制了植物从升高的CO2中获得的生长益处。关键的是，这些理论仍未经检验。利用稳定和放射性同位素C示踪剂的组合，我们将追踪C的短期和长期命运及其通过植物、微生物和土壤的途径。我们将通过使用磷同位素示踪剂来确定二氧化碳如何影响磷有效性、植物吸收以及与土壤微生物和土壤基质对磷的竞争，从而确定新植物C输入的命运如何控制磷动力学。最后，我们将使用先进的分子方法来了解土壤微生物如何响应C输入，以及这如何影响它们的P循环及其对植物的可用性。这项工作旨在从机制上确定两个草原上植物生产力响应差异的原因，并在此过程中，发展预测未来磷限制生态系统中碳吸收速率所需的广泛理解。