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Nitrous oxide emissions from soils and tree stems of rainforests and cacao agroforests in the Congo basin, Cameroon

喀麦隆刚果盆地雨林和可可农林土壤和树干的一氧化二氮排放量

基本信息

批准号：
278857140
负责人：
Professor Dr. Edzo Veldkamp
金额：
--
依托单位：
Abteilung Ökopedologie der Tropen und Subtropen
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2019-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/278857140?language=en
关键词：
Nitrous oxide emissions soils tree

项目摘要

The humid tropical forest biome plays a dominant role in the global budget of the greenhouse gas nitrous oxide (N2O). However, the estimated source strength of N2O emissions from tropical rainforest soils using a bottom-up approach (extrapolation of measured/modeled soil-atmosphere flux data) has decreased in the past decades. This appears to be in contrast with top-down studies that used global N2O atmospheric observations and inversion methods to estimate N2O emissions, which continue to point at the tropics as an important N2O source. This apparent mismatch of the bottom-up and top-down estimates of N2O emissions may be explained in two ways. 1) Tropical trees on well drained soils may serve as a conduit for N2O produced in the soil, a potential emission pathway that has been largely ignored. Recent studies have shown that not only trees with aerenchyma (serving as channel for soil-atmosphere gas exchange) but also trees without this feature showed evidence of N2O emission. In a preliminary study we were able to show that the ability to emit N2O from tree stems is widespread in tropical trees in Cameroon. 2) Geographic bias of the existing field measurements may have reduced estimates of the N2O source strength of the humid tropical forests biome. Even though the majority of remaining tropical rainforests in the Amazon and Congo basins are located on relatively heavily weathered nitrogen-rich soils, most trace gas studies were conducted on less weathered soils which tend to have lower N availability and consequently emit less N2O. Especially measurements from the Congo basin in Africa are notably absent. In the preliminary study we showed that the forest sites where we plan to conduct our study have a high N availability which strongly hints that these sites will have high gaseous nitrogen losses. Using a combination of chamber methods, gas chromatography, 15N natural abundance signatures of N2O and 15N isotope tracing techniques, I propose to measure N2O fluxes from heavily weathered forest and agroforestry soils and from tree stems in the Congo Basin of Cameroon. The methods for soil N2O flux measurements and 15N tracing to N2O have been tested in tropical forest sites by my group. The method for measuring N2O emissions from tree stems we tested at two sites in Cameroon. This proposed study will provide the first ever robust measurements of soil N2O fluxes in a never-before measured important biome in Africa (rainforest in the Congo Basin), and will also provide the first evidence of whether or not tropical trees on well-drained soils serve as important conduits of N2O from the soil.

潮湿的热带森林生物群落在温室气体一氧化二氮 (N2O) 的全球预算中发挥着主导作用。然而，在过去几十年中，使用自下而上的方法（测量/模拟的土壤-大气通量数据外推）估算的热带雨林土壤氧化亚氮排放源强度有所下降。这似乎与使用全球 N2O 大气观测和反演方法来估计 N2O 排放量的自上而下的研究形成鲜明对比，后者继续指出热带地区是重要的 N2O 来源。 N2O 排放量自下而上和自上而下估算的这种明显不匹配可以用两种方式来解释。 1) 排水良好的土壤上的热带树木可以作为土壤中产生的 N2O 的管道，这是一种在很大程度上被忽视的潜在排放途径。最近的研究表明，不仅具有通气组织（作为土壤与大气气体交换的通道）的树木，而且没有这种特征的树木也显示出N2O排放的证据。在一项初步研究中，我们能够证明喀麦隆的热带树木普遍具有从树干排放氧化亚氮的能力。 2) 现有实地测量的地理偏差可能减少了对潮湿热带森林生物群落 N2O 源强度的估计。尽管亚马逊和刚果盆地大部分剩余的热带雨林位于风化相对严重的富氮土壤上，但大多数痕量气体研究都是在风化程度较低的土壤上进行的，这些土壤往往具有较低的氮利用率，因此排放的氧化亚氮也较少。尤其是非洲刚果盆地的测量数据明显缺失。在初步研究中，我们表明，我们计划进行研究的森林地点具有较高的氮利用率，这强烈暗示这些地点将有较高的气态氮损失。我建议结合使用室法、气相色谱法、N2O 的 15N 自然丰度特征和 15N 同位素示踪技术，测量喀麦隆刚果盆地严重风化的森林和农林土壤以及树干中的 N2O 通量。我的小组已在热带森林地区测试了土壤 N2O 通量测量和 15N 追踪 N2O 的方法。我们在喀麦隆的两个地点测试了测量树干氧化亚氮排放的方法。这项拟议的研究将首次对非洲一个从未测量过的重要生物群落（刚果盆地的雨林）中的土壤 N2O 通量进行可靠的测量，并且还将提供第一个证据，证明排水良好的土壤上的热带树木是否是土壤中 N2O 的重要通道。