Canopy Structure and CO2 Exchange of Arctic Vegetation: Key Constraints on Change and Predictability of the Arctic System

这项研究将通过研究北极植被冠层结构、N分配和全系统CO2通量与生态系统呼吸及其主要组成部分--植物和土壤呼吸之间的关系，加深对北极植被功能广泛格局的理解。这项研究是探索植被功能、资源分配和异速生长的一般特征的一部分，这些特征可用于对植被和生态系统特性以及北极生态系统在北极系统中的作用进行大规模、长期的预测。计划进行研究的地点包括阿拉斯加的图利克湖和巴罗、西伯利亚的切尔斯基、格陵兰的图勒，以及加拿大北部的地点。每个地点的实地研究将包括测量不同植被(净生态系统交换，NEE；初级生产总值，GPP；生态系统呼吸，RE；自养呼吸，RA，异养呼吸，RH)中二氧化碳通量的光响应。要评估的植被和土壤变量--冠层光合作用面积及其N含量、NDVI、土壤C和N含量，以及冠层空气和土壤温度等小气候变量--都是调节陆地景观与北极系统能量、水和元素循环之间反馈和相互作用的关键组成部分。要检验的核心假设是：1.在整个北极地区，冠层N含量将比叶面积更好地预测NEE和GPP，因为叶N浓度将在更高、更冷的纬度增加，导致单位叶面积的GPP随纬度的增加而增加，但单位叶N的GPP相似。从长期来看，RE、RA和RH都必须与GPP及其控制相关，因为GPP决定了生态系统的总碳输入。在短期内，RA和RH对环境变化的反应将有所不同：RA将与相对快速的气温变化密切相关，而RH将变化得更慢，并与土壤温度和湿度等变化较慢的变量相关。除了对结果进行经验分析外，NPP、GPP和RE的建模将测试我们从北极内一个站点外推到另一个站点的能力，并将有助于确定是否可以为整个北极开发一个单一的模型参数化。一个关键产品将是一个数据库，用于对北极地区的植被特性和二氧化碳通量进行建模和外推。

This research will improve understanding of the broad patterns of vegetation function across the Arctic through research on the relationships among arctic vegetation canopy structure, N allocation, and whole-system CO2 fluxes, and ecosystem respiration and its main components, plant and soil respiration. The research is part of a search for the general characteristics of vegetation function, resource allocation, and allometry that can be used to develop large-scale, long-term predictions of vegetation and ecosystem properties and of the role of arctic ecosystems in the arctic system.Sites planned for research include Toolik Lake and Barrow, Alaska; Cherskii, Siberia; Thule, Greenland; and perhaps sites in northern Canada. Field research at each site will include measurements of the light response of CO2 flux in diverse vegetation (Net Ecosystem Exchange, NEE; Gross Primary Production, GPP; Ecosystem Respiration, RE; Autotrophic Respiration, RA, Heterotrophic Respiration, RH). The vegetation and soil variables to be evaluated--canopy photosynthetic area and its N content, NDVI, soil C and N content, and microclimatic variables like canopy air and soil temperatures--are all key components of regulation of the feedbacks and interactions between the terrestrial landscape and the cycles of energy, water, and elements in the arctic system. The core hypotheses to be tested are:1. Over the entire arctic region, canopy N content will be a better overall predictor of NEE and GPP than leaf area because leaf N concentrations will increase in higher, colder latitudes, leading to higher GPP per unit leaf area with latitude but similar GPP per unit leaf N.2. In the long term RE, RA, and RH must all be related to GPP and its controls because GPP determines the total C inputs to the ecosystem. In the short term, RA, and RH will respond differently to environmental variation: RA will be most closely correlated with relatively rapid changes in air temperature while RH will change more slowly and in correlation with more slowly-changing variables like soil temperature and moistureIn addition to empirical analysis of results, modeling of NPP, GPP, and RE will test our ability to extrapolate from one site to another within the Arctic and will help to determine whether a single model parameterization can be developed for the entire Arctic. A key product will be a data base for modeling and extrapolation of vegetation properties and CO2 fluxes across the arctic region.