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.

与世界各地的许多半干旱生态系统一样，南加州也受到越来越频繁和强烈的野火和干旱的影响。这些极端事件可能会导致入侵杂草取代本地灌木，扰乱土壤的物理结构以及生活在土壤中的细菌和真菌等微生物(微生物)的群落，从而导致生态系统的长期变化。植物、微生物和土壤的这些变化可能会影响整个生态系统的工作方式，包括生态系统如何有效地从大气中吸收二氧化碳(CO2)，并将碳作为有机物长期储存。土地吸收和储存碳的能力非常重要，因为它可以减缓二氧化碳在大气中的积累，减缓其对气候的影响。计算机模型预测未来生态系统的变化将如何影响大气二氧化碳。然而，没有足够的信息来对野火和干旱将如何改变南加州灌木丛等半干旱生态系统做出自信的预测。研究野火和干旱的综合影响需要进行实验，在这些实验中，景观中其他类似的部分要么被烧毁，要么未被烧毁，而且落在试验田上的雨量可以控制。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，可能代表了真正的野火将如何影响生态系统。另一方面，野火是不可预测的。这使得很难计划一项实验，要求有可比较的烧毁和未烧毁的景观，进入地点，火灾前区域的初步信息，以及在季节性降雨开始之前建立避雨场所的时间。NSF的这个快速项目利用了这样一个机会，野火烧毁了一个研究得很好的自然保护区的一部分，如果立即采取行动，可以在主雨季之前建立一个降雨实验。这个项目利用了一个难得的和时间敏感的机会，将自然野火和受控降雨实验结合在析因设计中，并将数据纳入一个改进的模型，用于预测半干旱生态系统对气候变化的间歇性和渐进性方面的反应。这一快速合同允许在季节性降雨开始之前，在被烧毁和未被烧毁的地区建造降雨避难所。该项目测试了以下假设：火和干旱将相互作用，促进草本植物和其他草本植物的入侵，并导致1)生态系统C增加的物候以及更短的生长季节，2)通过土壤结构和微生物群落的变化，增加生态系统对C和N损失的脆弱性。因此，火灾和干旱将协同作用，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响应(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共同体地球系统模型(CESM)，从而能够对美国西南部和世界其他半干旱生态系统进行预测。C和N将在土壤物理组分(不同大小类别的团聚体、颗粒有机质、微生物生物量等)中进行测量，微生物群落结构将使用鸟枪式元基因组测序来表征。植物测量将包括树冠和树叶水平的群落组成、物候和生态生理测量，以及景观水平的遥感图像。生态系统建模活动将把这些数据放入生态系统级别的框架中。这个为期一年的项目将为更长期的研究奠定基础。这一奖项反映了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。