RAPID: Interactive effects of wildfire and severe drought on plants, soil microbes and C storage in a semiarid shrubland ecosystem

RAPID：半干旱灌木丛生态系统中野火和严重干旱对植物、土壤微生物和碳储存的相互作用

• 批准号: 2154746
• 负责人: David Lipson
• 金额: $ 19.9万
• 依托单位: San Diego State University Foundation
• 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: 2021-12-01 至 2024-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2154746&HistoricalAwards=false
• 关键词: RAPID; Interactive; effects; wildfire; severe

Like many semiarid ecosystems around the world, southern California is subject to increasingly frequent and intense wildfires and droughts. These extreme events can cause long-term changes in the ecosystem by allowing invasive weeds to replace native shrubs and disrupting the physical structure of soil and the communities of microscopic organisms (microbes) like bacteria and fungi that live in the soil. These changes to plants, microbes and soils can affect how the whole ecosystem works, including how effectively the ecosystem can absorb carbon dioxide (CO2) from the atmosphere and store carbon for a long time as organic matter. The ability of land to absorb and store carbon is very important because it can slow down the accumulation of CO2 in the atmosphere, slowing down its effects on the climate. Computer models predict how future changes in ecosystems will influence atmospheric CO2. However, there is not enough information to make confident predictions of how wildfire and drought will change semiarid ecosystems like southern California shrublands. Studying the combined effects of wildfire and drought requires experiments where otherwise similar parts of the landscape are either burned or unburned, and the amount of rain falling on an experimental plot can be controlled. For safety reasons, prescribed burns are carried out under conditions that are very different from natural wildfires, and might represent how real wildfires will affect ecosystems. On the other hand, wildfires are unpredictable. This makes it hard to plan an experiment that requires comparable burned and unburned landscape, access to the location, preliminary information about the area before the fire, and the time to establish rain shelters before the onset of seasonal rains. This NSF RAPID project takes advantage of such an opportunity, in which a wildfire burned part of a well-studied nature preserve, and a rainfall experiment could be established before the main rainy season, given immediate action.This project takes advantage of a rare and time-sensitive opportunity to combine a natural wildfire with a controlled rainfall experiment in a factorial design and incorporate the data into an improved model for predicting the response of semiarid ecosystems to episodic and gradual aspects of climate change. This RAPID award allows rainfall shelters to be constructed in burned and unburned areas prior to the onset of seasonal rains. The project tests the hypotheses that fire and drought will interact to promote invasion by grasses and other herbaceous species, and cause 1) earlier phenology of ecosystem C gain as well as a shorter growing season, and 2) an increase in the vulnerability of the ecosystem to loss of C and N via changes in soil structure and microbial communities. Thus, together fire and drought will synergistically contribute to lower ecosystem C stocks. This project will (1) establish a factorial drought × wild fire experiment, (2) measure ecosystem responses (including plant and soil components) to the factorial treatments, and (3) organize these data for incorporation into the Millennial Model and the Community Earth System Model (CESM), enabling predictions for both the U.S. Southwest, and other semiarid ecosystems around the world. C and N will be measured in soil physical fractions (various size classes of aggregates, particulate organic matter, microbial biomass, etc.), and the microbial community structure will be characterized using shotgun metagenomic sequencing. Plant measurements will include community composition, phenology, and ecophysiological measurements at the canopy and leaf level, and remotely sensed imagery at the landscape level. The ecosystem modeling activities will place these data into an ecosystem-level framework. This one-year project will lay the groundwork for longer-term studies.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.

与世界上许多半干旱生态系统一样，南加州也遭受日益频繁和严重的野火和干旱，这些极端事件可能导致入侵杂草取代原生灌木并破坏土壤和土壤的物理结构，从而导致生态系统发生长期变化。生活在土壤中的微生物（微生物）群落，如细菌和真菌。植物、微生物和土壤的这些变化会影响整个生态系统的运作方式，包括生态系统从大气中吸收二氧化碳 (CO2) 的效率。土地吸收和储存碳的能力非常重要，因为它可以减缓大气中二氧化碳的积累，从而减缓其对气候的影响。计算机模型可以预测未来的变化。然而，没有足够的信息来准确预测野火和干旱将如何改变南加州灌木丛等半干旱生态系统，需要在景观的其他类似部分进行实验。要么被烧毁要么出于安全原因，规定的燃烧是在与自然野火非常不同的条件下进行的，并且可能代表真正的野火将如何影响生态系统。野火是不可预测的，因此很难计划一项需要可比较的烧毁和未烧毁景观、地点、火灾发生前区域的初步信息以及在季节性降雨开始之前建立避雨所的时间的实验。迅速的该项目利用了这样的机会，其中一场野火烧毁了经过充分研究的自然保护区的一部分，如果立即采取行动，可以在主要雨季之前进行降雨实验。该项目利用了罕见且时间敏感的机会该 RAPID 奖项提供了将自然野火与因子设计中的受控降雨实验相结合的机会，并将数据纳入改进的模型中，以预测半干旱生态系统对气候变化的偶发性和渐进性方面的反应。和该项目测试了以下假设：火灾和干旱会相互作用，促进草类和其他草本物种的入侵，并导致 1) 生态系统碳增加物候提前以及生长季节缩短，以及2) 由于土壤结构和微生物群落的变化，生态系统对碳和氮损失的脆弱性增加。因此，火灾和干旱将协同降低生态系统碳储量。该项目将 (1) 建立因子干旱。 × 野火实验，(2) 测量生态系统对因子处理的反应（包括植物和土壤成分），以及 (3) 组织这些数据以纳入千禧年模型和社区地球系统模型 (CESM)，从而能够预测两者美国西南部和世界各地的其他半干旱生态系统将通过土壤物理部分（各种尺寸类别的团聚体、颗粒有机物、微生物生物量等）来测量碳和氮，并且微生物群落结构将被测量。植物测量将包括冠层和叶片水平的群落组成、物候学和生态生理学测量，以及景观水平的遥感图像，将这些数据放入生态系统水平框架中。这个为期一年的项目将为长期研究奠定基础。该奖项反映了 NSF 的法定使命，并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，被认为值得支持。