Abstract

The photosynthetic capacity or the CO₂-saturated photosynthetic rate (V_max), chlorophyll, and nitrogen are closely linked leaf traits that determine C₄ crop photosynthesis and yield. Accurate, timely, rapid, and non-destructive approaches to predict leaf photosynthetic traits from hyperspectral reflectance are urgently needed for high-throughput crop monitoring to ensure food and bioenergy security. Therefore, this study thoroughly evaluated the state-of-the-art physically based radiative transfer models (RTMs), data-driven partial least squares regression (PLSR), and generalized PLSR (gPLSR) models to estimate leaf traits from leaf-clip hyperspectral reflectance, which was collected from maize (Zea mays L.) bioenergy plots with diverse genotypes, growth stages, treatments with nitrogen fertilizers, and ozone stresses in three growing seasons. The results show that leaf RTMs considering bidirectional effects can give accurate estimates of chlorophyll content (Pearson correlation r=0.95), while gPLSR enabled retrieval of leaf nitrogen concentration (r=0.85). Using PLSR with field measurements for training, the cross-validation indicates that V_max can be well predicted from spectra (r=0.81). The integration of chlorophyll content (strongly related to visible spectra) and nitrogen concentration (linked to shortwave infrared signals) can provide better predictions of V_max (r=0.71) than only using either chlorophyll or nitrogen individually. This study highlights that leaf chlorophyll content and nitrogen concentration have key and unique contributions to V_max prediction.

中文翻译：

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叶绿素和氮对通过叶光谱法预测农作物光合能力的独特贡献

摘要

光合能力或CO ₂饱和光合速率（V _max），叶绿素和氮是决定C ₄作物光合作用和产量的紧密联系的叶片性状。为了高通量作物监测，以确保食品和生物能源安全，迫切需要一种准确，及时，快速且无损的方法来根据高光谱反射来预测叶片的光合特性。因此，本研究彻底评估了基于物理的最新辐射传递模型（RTM），数据驱动的偏最小二乘回归（PLSR）和广义PLSR（gPLSR）模型，以从叶夹高光谱估计叶性状反射率是从玉米（玉米）中收集的L.）在三个生长季节中具有不同基因型，生长阶段，氮肥处理和臭氧胁迫的生物能源图。结果表明，考虑双向效应的叶片RTM可以准确估算叶绿素含量（皮尔森相关系数r = 0.95），而gPLSR可以检索叶片氮浓度（r = 0.85）。使用带有现场测量结果的PLSR进行训练，交叉验证表明可以从光谱中很好地预测V _max（r = 0.81）。叶绿素含量（与可见光谱密切相关）和氮浓度（与短波红外信号相关）的积分可以提供对V _max（r = 0.71），而不是单独使用叶绿素或氮。这项研究强调，叶绿素含量和氮浓度对V _max预测具有关键和独特的贡献。