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; 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.

野火后，年轻的针叶树森林每年都在覆盖更多的美国西部，因为随着温度的上升和更长的火灾季节，火灾频率和面积燃烧增加。大火后的头几年建立了树幼苗，在头几十年中，幼树达到了高峰生长。快速树的生长部分由氮（N）（一种关键的植物营养素）促进。但是，在森林大火期间，通过燃烧在森林中存储的一些n丢失。在高温大火之后，如何补充该丢失的生态系统N，尤其是在很少有大气n转换为生物学上的N氮的固氮植物（例如豆类）很少见。从历史上看，西方针叶树森林在再次燃烧之前就已经从火中恢复过来。尚不清楚更频繁的高品位大火是否会进一步减少生态系统N并​​影响森林恢复。自1988年黄石大火以来的长期研究的基础上，这项研究旨在识别和量化年轻的后火灾后洛德氏菌松树（Pinus contotavar。latifolia）森林的n恢复来源，并确定生态系统n对更频繁的火灾的反应。研究人员将吸引新闻业的学生将他们的发现传达给广泛的受众，并开发新的方法，以向学生传授森林生态系统中有关n的信息。生物N固定（BNF）是维持后火的发展所需的最有可能的来源，研究人员假设新的N输入反映了多个不起眼的N来源的合并活动。使用大黄石（美国怀俄明州）中的现场观测和多年的N施肥实验，本研究将解决三个问题：（1）n个n投入的来源和速率是什么是lodgepole pine Forests（40岁的后火）（40年后），以及自来水的结构和时间的来源和速率与自来的结构和时间之间有何影响？ （2）n的可用性如何调节n固定和n个限制，使年轻（40年）lodgepole pine林随火以来的时间增加？ （3）短间隔（30年）独立替换火力如何影响N固定，N可用性和N股票？这项研究将测试预期的预期，随着洛德柱生物量和n个股票，随着树木的需求随着时间的推移和空间的增加而增加，生物N固定源的总固定率将增加，生物N固定源将从共生，自由生活的N固定器转移。这些良好的研究将直接解决关键的未知数，这些知识限制了随着火灾活动加速的预测能力。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子和更广泛影响的评估来审查标准的评估值得支持的。