RAPID: Do wildfire effects on roots and rhizosphere activity control both short- and long- term soil C stabilization?

RAPID：野火对根系和根际活动的影响是否会控制短期和长期土壤碳稳定？

• 批准号: 2102833
• 负责人: Kate Lajtha
• 金额: $ 15.2万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-02-01 至 2023-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2102833&HistoricalAwards=false
• 关键词: RAPID; Do; wildfire; effects; roots

This RAPID proposal is to examine soil carbon dynamics in forest stands affected by a large and catastrophic wildfire that burned three watersheds and surrounding forest in the H.J. Andrews Experimental Forest, OR. Old-growth forests in the USA hold significant amounts of carbon (C) in both tree biomass and in soils. Because of this, disturbances such as forest harvest or fire that might release C into the air from vegetation or soil have the potential to impact the atmosphere. Both the number and the sizes of wildfires in the Pacific Northwest have been increasing in the last several decades, and increases in temperature are projected to lengthen fire seasons. Because so many Western U.S. ecosystems are expected to experience increasingly large and severe fires in the near future, understanding how wildfire impacts ecosystem C cycling is increasingly critical to future projections of global temperatures. While fire effects on the C budgets of above ground vegetation are relatively easy to observe and measure, fire effects on soil organic matter C below the surface is less easy to measure or predict. Given that the soil C pool is over 3 times greater than the atmospheric C pool, it is critical to understand the mechanisms of soil response to extreme fire disturbance in order to have accurate models of global C concentrations under different scenarios of environmental change. Results from this research will not only inform global earth system science models, but will also help inform ecosystem managers about potential benefits and costs of different fire management scenarios.This research will test novel hypotheses about the influences of root/rhizosphere activity and above and belowground detrital inputs on soil C stabilization and destabilization after catastrophic disturbance. Hypotheses are based on a new model of soil C dynamics that starts with the argument that soil C in undisturbed ecosystems is a balance between rhizosphere-derived priming losses and root-derived soil C gains. Priming of soil C occurs when inputs of labile C sources, usually from live root exudation, fuels increased respiration (= C loss) of stable soil organic matter (SOM) pools such as mineral-associated organic matter (MAOM); however, efficient microbial use of high-quality detrital inputs such as fine root litter are retained (= C gain) in soil as MAOM. These two competing processes keep MAOM levels both stable and below true mineral saturation. However, when tree-mortality disturbance occurs, not only is there a significant influx of dead fine root material (aiding soil C stabilization through microbial use and microbial turnover), but rhizosphere priming ceases as root exudation of labile dissolved organic carbon ceases (removing soil C destabilization). This model predicts that change to soil C pools and C dynamics after significant disruption to detrital inputs is remarkably rapid due to immediate reduction in rhizosphere activity coupled with continued influx of detrital root materials. This is contrary to current models of soil C after harvest or fire in which the most stable pools of soil C could increase until the forest regenerates. A sampling grid will be established based on tree mortality, burn severity, pre-fire aboveground biomass and LiDAR-derived geophysical variables throughout the region burned in the Holiday Farm fire at the Andrews Forest. Soil cores will be taken along transects within identified sampling sites and density fractionated to separate out roots, particulate soil carbon, and MAOM. SOM in whole soils and soil physical fractions will be characterized using solid-state 13C nuclear magnetic resonance also allowing us to examine any movement of pyrogenic C into either POM or MAOM pools.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.

这一快速建议是为了研究受一场巨大而灾难性的野火影响的林木中的土壤碳动态，这场大火烧毁了H.J.安德鲁斯实验森林的三个流域和周围的森林。美国的古老森林在树木生物量和土壤中都含有大量的碳(C)。正因为如此，森林收获或火灾等干扰可能会从植被或土壤中释放碳到空气中，这可能会影响大气。在过去的几十年里，太平洋西北部的野火数量和规模都在增加，气温的上升预计会延长火灾季节。由于预计在不久的将来，美国西部的许多生态系统将经历越来越大和严重的火灾，了解野火如何影响生态系统C循环对未来全球气温的预测越来越重要。火对地上植被碳收支的影响相对容易观察和测量，而火对地表以下土壤有机质C的影响则不太容易测量或预测。考虑到土壤碳库是大气碳库的3倍以上，了解土壤对极端火扰动的响应机制，以获得不同环境变化情景下全球碳浓度的准确模型是至关重要的。这项研究的结果不仅将为全球地球系统科学模型提供信息，还将有助于生态系统管理者了解不同火灾管理情景的潜在收益和成本。本研究将检验关于灾难性干扰后根/根际活动以及地上和地下碎屑输入对土壤C稳定和不稳定的影响的新假说。假设基于一个新的土壤碳动态模型，该模型认为在未受干扰的生态系统中，土壤碳是根际启动损失和根源土壤碳增量之间的平衡点。当不稳定的碳源(通常来自活的根分泌物)的输入增加了稳定的土壤有机质(SOM)库的呼吸(=C损失)时，土壤C的启动发生；然而，高效的微生物利用高质量的碎屑输入，例如细根凋落物，作为MAOM保留在土壤中(=C增益)。这两个相互竞争的过程使MAOM水平保持稳定，并低于真正的矿物饱和度。然而，当树木死亡扰动发生时，不仅有大量的死细根物质流入(通过微生物利用和微生物周转来帮助土壤碳稳定)，而且根际引发也停止了，因为根中不稳定的溶解有机碳的分泌停止(消除土壤碳的不稳定)。该模型预测，在碎屑输入显著中断后，土壤碳库和碳动态的变化非常迅速，这是由于根际活动立即减少，加上碎屑根物质的持续流入。这与目前的收获或火灾后土壤碳的模型相反，在这种模型中，最稳定的土壤碳库可能会增加，直到森林再生。将根据在安德鲁斯森林假日农场火灾中烧毁的整个区域的树木死亡率、烧伤严重程度、火灾前地上生物量和激光雷达得出的地球物理变量建立采样网格。将沿着确定的采样点内的横断面采集土芯，并对密度进行分级，以分离出根部、土壤颗粒碳和MAOM。整个土壤和土壤物理部分中的SOM将使用固态13C核磁共振进行表征，这也使我们能够检查任何进入POM或MAOM池的热源C的移动。该奖项反映了NSF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。