Field Measurements of Leaf Photosynthetic Capacity (Vcmax) for Carbon Cycle Research

目前全球碳循环模拟的现状是根据植物功能类型(PFT)将叶片的最大光合作用能力(羧化速率，Vcmax)指定为常数，这是由于缺乏Vcmax观测。这在模拟的碳和水循环中造成了很大的不确定性，因为对于相同的PFT，Vcmax在空间和季节上都可能变化2-3倍。在我之前的NSERC和其他赠款的支持下，我们最近使用卫星太阳诱导的叶绿素荧光(SIF)数据制作了第一个全球Vcmax地图系列(每月，36公里分辨率，2007-2017)，并使用中分辨率成像光谱仪(MERIS)卫星数据制作了第一个全球叶片叶绿素含量(LCC)地图系列(弱，300米分辨率，2003-2011年)。这两篇文章都发表在《环境遥感》杂志上。我最近资助的NSERC Discovery Grant(2020-2025年)的主要目标是获取Vcmax、SIF和LCC的大型地面数据集，以验证SIF派生的Vcmax地图，并将LCC地图转换为Vcmax地图。在这项提案中，需要资金购买Li-6800F便携式光合作用系统，用于田间测量叶片Vcmax和荧光参数，而LCC将使用我们现有的湿实验室设备进行测量。与过时的Li-6400相比，Li-6800F可以在更短的时间内提供更准确的Vcmax测量(一个值需要5分钟而不是45分钟)，允许从大容量叶片样本中收集数据。LI-6800F还具有测量叶片荧光参数的内置能力，这对于进一步开发和验证我们基于SIF的Vcmax检索算法至关重要。通过现有的合作，将在安大略省博登和火鸡湖附近的阔叶和针叶树塔通量站点收集Vcmax、SIF和LCC的测量结果，以便证明这些参数在碳循环和水循环建模中的有效性。此外，将在加拿大的草原和农田收集大量类似的数据集，以验证从卫星SIF和LCC获得的Vcmax图。将对这两套Vcmax地图进行相互比较，以评估其时空可靠性，并使用地面数据和高分辨率遥感数据(哨兵，10-20米分辨率)进行验证。这些Vcmax数据集的获得将是在减少全球陆地碳循环估计的不确定性方面向前迈出的一大步。 这一要求的仪器对HQP培训也是必不可少的，并将立即和密集地用于1名博士后研究员、3名博士生和以后几年更多的研究生，用于与全球Vcmax推导和验证相关的各种任务。这些学员有机会使用这一要求的仪器，将极大地增强他们的学习体验，并使他们能够取得前沿的研究成果。这也将使他们的技能和知识更具市场价值，对研究机构和公司更具吸引力。

The current state of the art in global carbon cycle modeling is to assign the leaf maximum photosynthetic capacity (carboxylation rate, Vcmax) as constants by plant functional type (PFT) due to lack of Vcmax observations. This causes large uncertainties in modeled carbon and water cycles because for the same PFT, Vcmax can vary by a factor of 2-3 both spatially and seasonally. Under the support of my previous NSERC and other grants, we have recently produced the first ever global Vcmax map series using satellite solar-induced chlorophyll fluorescence (SIF) data (monthly, 36 km resolution, 2007-2017) and the first ever global leaf chlorophyll content (LCC) map series using the Medium Resolution Imaging Spectrometer (MERIS) satellite data (weakly, 300 m resolution, 2003-2011). Both are published in Remote Sensing of Environment. The main objectives of my recently funded NSERC Discovery Grant (2020-2025) are to acquire a large ground-based dataset of Vcmax, SIF and LCC to validate SIF-derived Vcmax maps and to convert LCC maps into Vcmax maps. In this proposal, funds are requested to purchase a LI-6800F Portable Photosynthesis System for field measurement of leaf Vcmax and fluorescence parameters, while LCC will be measured using our existing wet lab facility. Compared with the obsolete LI-6400, LI-6800F can provide more accurate Vcmax measurements in much shorter time (5 vs 45 minutes for one value), allowing for data collection from large leaf samples. LI-6800F also has a built-in capacity to measure leaf fluorescence parameters, critical for further developing and validating our SIF-based Vcmax retrieval algorithm. Through existing collaborations, measurements of Vcmax, SIF, and LCC will be collected at the broadleaf and conifer tower flux sites near Borden and Turkey Lake, Ontario, so that the usefulness of these parameters for carbon and water cycle modeling can be demonstrated. In addition, a large number of similar datasets will be collected over grassland and cropland in Canada to validate Vcmax maps derived from satellite-based SIF and LCC. These two sets of Vcmax maps will be mutually compared to assess their spatio-temporal reliability and validated using ground-based data and high-resolution remote sensing data (Sentinel, 10-20 m resolution). The derivation of these Vcmax datasets would be a large step forward in reducing the uncertainty in global terrestrial carbon cycle estimation. This requested instrument is also essential for HQP training and will be immediately and intensively used for 1 postdoctoral fellow, 3 PhD students, and additional graduate students in later years for various tasks associated with global Vcmax derivation and validation. The opportunity for these trainees to use this requested instrument will greatly enhance their learning experience and allow them to achieve cutting edge research results. It will also make their skills and knowledge more marketable and attractive to research organizations and companies.