Mycorrhizal Regulation of Ecosystem Response to Chronic Nitrogen Deposition

生态系统对慢性氮沉积响应的菌根调节

• 批准号: 0134748
• 负责人: Hormoz BassiriRad
• 金额: $ 49.9万
• 依托单位: University of Illinois at Chicago
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-02-01 至 2008-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0134748&HistoricalAwards=false
• 关键词: Mycorrhizal; Regulation; Ecosystem; Response; Chronic

Readily usable forms of nitrogen are being deposited from the atmosphere in much greater quantities than plants can use. This is mainly nitrate nitrogen produced by the combustion of fossil fuels in urban areas, but some agricultural areas are subject to high deposition of ammonium nitrogen. Effects of atmospheric nitrogen deposition were first noticed in Scandinavia, the Netherlands, and, in the U.S., in the industrial Northeast where it is associated with the death of trees, particularly conifers. These trees showed characteristic responses which included high nitrogen in their needles and loss of fine roots. Currently high levels of atmospheric nitrogen deposition are spreading to other parts of the U.S. including the Los Angeles Basin and the Colorado Front Range. After many years of nitrogen additions many forests show evidence of reaching a point where no further nitrogen can be taken up, tree mortality increases, and nitrate nitrogen leaches into the water table. Initially, plants were thought to take up and store most depositional nitrogen in forests. But studies using nitrogen isotopes as tracers suggested that the nitrogen was stored in the forest floor. This focused attention on two groups of beneficial fungi that occupy forest floors: ecto- and endomycorrhizal fungi. Both groups function as supplementary root systems for plants, and ectomycorrhizal fungi may store depositional nitrogen in sheaths of fungal tissue covering root tips of conifers and oaks. This project asks three kinds of questions in order to learn the role of ectomycorrhizal fungi in nitrogen storage and tree mortality. First, are species numbers and relative abundance of ecto- and endomycorrhizal fungi affected by chronic atmospheric nitrogen deposition? Second, is the metabolic activity of ecto- and endomycorrhizal fungi affected by atmospheric N deposition? Is the ability of ectomycorrhizal fungi to store N decreased when numbers of fine roots decline? Third, does atmospheric nitrogen deposition have the same effect on growth and mortality of ectomycorrhizal as endomycorrhizal trees? To answer these questions the investigators will quantify mycorrhizal and plant responses across the nitrogen deposition gradient in the Chicago metropolitan area in a five-year study. The Chicago metropolitan area is suitable for asking these questions because chronic nitrogen deposition increases 24% along a west to east gradient on similar soils and vegetation. At each site the investigators will use red oak (Quercus rubra, ectomycorrhizal) and sugar maple (Acer saccharum, endomycorrhizal) to test whether nitrogen alters (a) the species and abundance of ecto- and endomycorrhizal fungi, (b) the metabolic activity and nitrogen storage ability of ecto- and endomycorrhizal fungi, (c) the specific rates of ammonium and nitrate uptake by ecto- and endomycorrhizal roots, (d) survivorship, growth, and N leaching from soil under red oak and sugar maple seedlings at ambient and twice-ambient nitrogen deposition rates ranging from 17 to 42 kg ha-1 year-1.

容易利用的氮从大气中沉积下来，其数量远远超过植物所能利用的。 这主要是城市地区化石燃料燃烧产生的硝酸盐氮，但一些农业地区的铵氮沉积量很高。 大气氮沉降的影响首先在斯堪的纳维亚半岛、荷兰和美国被注意到，在东北工业区，它与树木的死亡有关，特别是针叶树。 这些树木表现出特征性的反应，包括针叶中的高氮和细根的损失。 目前，高水平的大气氮沉降正在蔓延到美国的其他地区，包括洛杉矶盆地和科罗拉多前线山脉。 经过多年的氮添加，许多森林显示出达到一个点的证据，没有进一步的氮可以采取，树木死亡率增加，硝酸盐氮渗入地下水位。 最初，人们认为植物吸收并储存了森林中大部分沉积氮。 但使用氮同位素作为示踪剂的研究表明，氮储存在森林的地面上。 这将注意力集中在占据森林地面的两组有益真菌上：外生和内生菌根真菌。 这两个群体的功能作为植物的补充根系，外生菌根真菌可以存储沉积氮的真菌组织覆盖针叶树和橡树的根尖鞘。本计画提出三种问题，以了解外生菌根真菌在氮储存与树木死亡上的角色。 第一，物种数量和相对丰富的外生和内生菌根真菌的影响，慢性大气氮沉降？ 第二，外生和内生菌根真菌的代谢活动是否受到大气氮沉降的影响？ 当细根数量减少时，外生菌根真菌储存氮的能力是否降低？ 第三，大气氮沉降是否对外生菌根和内生菌根的生长和死亡有同样的影响？ 为了回答这些问题，研究人员将在一项为期五年的研究中量化芝加哥大都市区氮沉降梯度上的菌根和植物反应。 芝加哥大都市区是适合问这些问题，因为慢性氮沉降增加沿着西向东梯度相似的土壤和植被24%。在每一个地点，调查人员将使用红橡木（Quercus rubra，ectomycorrhizal）和糖枫（Acer saccharum，endomycorrhizal）来测试氮是否改变（a）外生和内生菌根真菌的种类和丰度，（B）外生和内生菌根真菌的代谢活性和氮储存能力，（c）外生和内生菌根根吸收铵和硝酸盐的比速率，（d）存活率，生长，氮从土壤中浸出红橡树和糖枫树幼苗在环境和两次环境氮沉降率范围从17至42公斤公顷-1年-1。