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

由于缺乏Vcmax观测，目前全球碳循环建模的最新技术是将叶片最大光合能力（羧化速率，Vcmax）按植物功能类型（PFT）指定为常数。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在空间和季节上可能变化2-3倍。在我之前的NSERC和其他资助的支持下，我们最近使用卫星太阳诱导叶绿素荧光（SIF）数据（每月，36公里分辨率，2007-2017）制作了有史以来第一个全球Vcmax地图系列，并使用中分辨率成像光谱仪（MERIS）卫星数据（弱，300米分辨率，2003-2011）制作了有史以来第一个全球叶片叶绿素含量（LCC）地图系列。两者都发表在《遥感环境》杂志上。我最近资助的NSERC发现基金（2020-2025）的主要目标是获取Vcmax， SIF和LCC的大型地面数据集，以验证SIF衍生的Vcmax地图，并将LCC地图转换为Vcmax地图。在本提案中，申请资金用于购买LI-6800F便携式光合作用系统，用于现场测量叶片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5 vs 45分钟），允许从大叶片样品中收集数据。LI-6800F还具有内置测量叶片荧光参数的能力，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，Vcmax、SIF和LCC的测量数据将在安大略省博登湖和土耳其湖附近的阔叶和针叶树塔通量站点收集，以便证明这些参数对碳和水循环建模的有用性。此外，将在加拿大的草地和农田收集大量类似的数据集，以验证基于卫星的SIF和LCC导出的Vcmax地图。将对这两组Vcmax地图进行相互比较，以评估其时空可靠性，并使用地基数据和高分辨率遥感数据（Sentinel， 10-20米分辨率）进行验证。这些Vcmax数据集的推导将在减少全球陆地碳循环估算的不确定性方面向前迈出一大步。

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.