Nutrient dynamics in sugar maple forests and assessment of long-term sensitivity to nitrogen deposition

糖枫林的养分动态和氮沉降的长期敏感性评估

• 批准号: 311790-2011
• 负责人: Watmough, Shaun
• 金额: $ 2.99万
• 依托单位: Trent University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2013
• 资助国家: 加拿大
• 起止时间: 2013-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=526257
• 关键词: Nutrient; dynamics; sugar; maple; forests

Globally, humans have altered the nitrogen (N) cycle to a greater degree than the much more publicized carbon (C) cycle. In Canada, the highest N deposition occurs in southern Ontario, where forest cover is dominated by sugar maple; a species known to be sensitive to enhanced N deposition. Potential impacts of high N deposition on other ecosystem components (lichens, herbs) in southern Ontario are unknown, but current N deposition levels are within the range that has been shown to affect plant and lichen species in the UK and western USA. The effect of N enrichment on forests, however, is not straight forward, and possible outcomes including enhanced nitrate leaching (acidification), declines in soil respiration and a reduction in fine root density may cause deficiencies in other mineral nutrients. In order to estimate the threshold deposition input above which adverse impacts begin to occur, the critical load (CL) for nutrient-N can be determined. There are two approaches for estimating the critical load of N; an empirical approach that links measured deposition with an observed impact, or a process-based approach, which takes into account soil and plant processes, enabling an assessment of long-term chronic N accumulation in soils. These models are appealing to policy makers as they provide an estimate of the 'time to effect', and are thus more readily linked to emission targets. The objective of this work is to undertake an integrated assessment of the impacts of current and predicted N deposition on hardwood forests, with a view to establishing appropriate critical N loads to protect these ecosystems. This will be achieved through six complimentary research projects that investigate N impacts on 1) lichens; 2) herbaceous species; 3) sugar maple chemistry; 4) sugar maple growth and N cycling; 5) biogeochemical cycling and soil respiration and 6) an integrated assessment of the current and predicted impacts of N deposition through biogeochemical modeling. This study will result in the training of six graduate students and at least 4 undergraduate students and will provide the sound scientific basis that is necessary to aid policy decisions with respect to future N emissions in Canada.

在全球范围内，人类对氮（N）循环的改变程度比广为人知的碳（C）循环更大。在加拿大，最高的氮沉降发生在安大略省南部，那里的森林覆盖以糖枫为主；已知对增强的氮沉积敏感的物种。高氮沉降对安大略省南部其他生态系统组成部分（地衣、草本植物）的潜在影响尚不清楚，但目前的氮沉降水平处于已证明会影响英国和美国西部植物和地衣物种的范围内。然而，氮富集对森林的影响并不是直接的，可能的结果包括硝酸盐浸出（酸化）增加、土壤呼吸下降和细根密度降低，可能导致其他矿质营养素的缺乏。为了估计沉积输入阈值（超过该阈值就会开始发生不利影响），可以确定营养物 N 的临界负荷 (CL)。有两种方法可以估计 N 的临界载荷；将测量的沉积与观察到的影响联系起来的经验方法，或基于过程的方法，考虑土壤和植物过程，从而能够评估土壤中长期慢性氮积累。这些模型对政策制定者很有吸引力，因为它们提供了“生效时间”的估计，因此更容易与排放目标联系起来。这项工作的目的是对当前和预测的氮沉降对阔叶林的影响进行综合评估，以期建立适当的临界氮负荷来保护这些生态系统。这将通过六个免费研究项目来实现，这些项目调查氮对 1) 地衣的影响； 2）草本物种； 3）糖枫化学； 4）糖枫生长和氮循环； 5）生物地球化学循环和土壤呼吸；6）通过生物地球化学模型对氮沉降的当前和预测影响进行综合评估。这项研究将培训六名研究生和至少四名本科生，并将提供必要的坚实科学基础，以帮助加拿大未来氮排放的政策决策。