Collaborative research: Nitrogen recovery in postfire lodgepole pine forests: cryptic sources, uncertain futures

合作研究：火灾后黑松林的氮恢复：来源不明，未来不确定

• 批准号: 2027263
• 负责人: Cory Cleveland
• 金额: $ 46.64万
• 依托单位: University of Montana
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-09-01 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2027263&HistoricalAwards=false
• 关键词: Collaborative; research; Nitrogen; recovery; postfire

Young conifer forests regenerating after wildfires are blanketing more of the western US each year as fire frequency and area burned increase with rising temperatures and longer fire seasons. Tree seedlings establish during the first few years after fire, and young trees reach their peak growth within the first few decades. Rapid tree growth is partly fueled by nitrogen (N), a critical plant nutrient. However, some of the N stored in forests is lost to the atmosphere via combustion during forest fires. How this lost ecosystem N is replenished after high-severity fires is not known, especially where nitrogen-fixing plants (such as legumes) that can convert atmospheric N to biologically available N, are rare. Historically, western conifer forests have recovered from fire long before they burn again. Whether more frequent high-severity fires will further reduce ecosystem N and affect forest recovery is not known. Building on long-term research since the 1988 Yellowstone Fires, this research aims to identify and quantify the sources of N recovery in young postfire lodgepole pine (Pinus contorta var. latifolia) forests and to determine how ecosystem N responds to more frequent fire. The researchers will engage journalism students to communicate their findings to broad audiences and develop new approaches for teaching students about N in forest ecosystems. Biological N fixation (BNF) is the likeliest source of the new N needed to sustain postfire stand development, and the researchers hypothesize that the new N inputs reflect the combined activity of multiple inconspicuous N sources. Using field observations and a multi-year N-fertilization experiment in Greater Yellowstone (Wyoming, USA), this study will address three questions: (1) What are the sources and rates of N inputs in aggrading lodgepole pine forests ( 40 yrs postfire), and how do sources and rates vary with stand structure and time since fire? (2) How does N availability regulate N fixation and N limitation in aggrading young ( 40 yr) lodgepole pine forests with increasing time since fire? (3) How do short-interval ( 30 yr) stand-replacing fires affect N fixation, N availability, and N stocks? This research will test expectations that total N fixation rates will increase with lodgepole pine biomass and N stocks, and that sources of biological N fixation will shift from symbiotic to cryptic, free-living N fixers as tree demand increases over time and across space. These well-integrated studies will directly address critical unknowns that constrain the ability to anticipate the future of western forests as fire activity accelerates.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.

随着气温上升和火灾季节延长，火灾频率和烧毁面积增加，野火后再生的年轻针叶林每年覆盖美国西部更多地区。树苗在火灾发生后的最初几年内生长，幼树在最初的几十年内达到生长高峰。树木快速生长的部分原因是氮 (N)，这是一种重要的植物营养素。然而，森林中储存的一些氮在森林火灾期间通过燃烧损失到大气中。在严重火灾后，这种失去的生态系统氮如何得到补充尚不清楚，特别是在能够将大气氮转化为生物可用氮的固氮植物（例如豆科植物）很少见的地方。从历史上看，西部针叶林在再次燃烧之前很久就已经从火灾中恢复过来。更频繁的高强度火灾是否会进一步减少生态系统氮并影响森林恢复尚不清楚。这项研究以 1988 年黄石火灾以来的长期研究为基础，旨在确定和量化火灾后幼年黑松 (Pinus contorta var. latifolia) 森林的氮恢复来源，并确定生态系统氮如何应对更频繁的火灾。研究人员将让新闻系学生向广大受众传达他们的发现，并开发新方法来向学生传授森林生态系统中的氮。生物固氮（BNF）是维持火后林分发展所需的新氮的最可能来源，研究人员假设新的氮输入反映了多个不显眼的氮源的综合活动。通过在大黄石国家公园（美国怀俄明州）的实地观察和多年施氮实验，本研究将解决三个问题：(1) 黑松林退化（火灾后 40 年）的氮输入来源和比率是多少？ ，来源和比率如何随林地结构和火灾发生后的时间而变化？ (2)随着火灾发生后时间的增加，氮的有效性如何调节年轻（40年）黑松林的氮固定和氮限制？ (3) 短间隔（30 年）林地更换火灾如何影响氮固定、氮可用性和氮库存？这项研究将测试总氮固定率将随着黑松生物量和氮储量的增加而增加的预期，并且随着树木需求随着时间和空间的推移而增加，生物固氮来源将从共生转变为神秘的、自由生活的固氮剂。这些综合性研究将直接解决随着火灾活动加速而限制预测西部森林未来能力的关键未知因素。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进行评估，被认为值得支持标准。

项目成果

Exploring the Role of Cryptic Nitrogen Fixers in Terrestrial Ecosystems: A Frontier in Nitrogen Cycling Research

• DOI: 10.1007/s10021-022-00804-2
• 发表时间: 2022-11-18
• 期刊: ECOSYSTEMS
• 影响因子: 3.7
• 作者: Cleveland, Cory C.;Reis, Carla R. G.;Wurzburger, Nina
• 通讯作者: Wurzburger, Nina