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首页> 外文期刊>Ecological Applications >RELATIONSHIPS BETWEEN NDVI, CANOPY STRUCTURE, AND PHOTOSYNTHESIS IN THREE CALIFORNIAN VEGETATION TYPES
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RELATIONSHIPS BETWEEN NDVI, CANOPY STRUCTURE, AND PHOTOSYNTHESIS IN THREE CALIFORNIAN VEGETATION TYPES

机译：三种加州植被类型的NDVI，冠层结构和光合作用之间的关系

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In a range of plant species from three Californian vegetation types, we examined the widely used ''normalized difference vegetation index'' (NDVI) and ''simple ratio'' (SR) as indicators of canopy structure, light absorption, and photosynthetic activity. These indices, which are derived from canopy reflectance in the red and near-infrared wavebands, highlighted phenological differences between evergreen and deciduous canopies. They were poor indicators of total canopy biomass due to the varying abundance of non-green standing biomass in these vegetation types. However, in sparse canopies (leaf area index [LAI] approximate to 0-2), NDVI was a sensitive indicator of canopy structure and chemical content (green biomass, green leaf area index, chlorophyll content, and foliar nitrogen content). At higher canopy green LAI values (> 2; typical of dense shrubs and trees), NDVI was relatively insensitive to changes in canopy structure. Compared to SR, NDVI was better correlated with indicators of canopy structure and chemical content, but was equivalent to the logarithm of SR. In agreement with theoretical expectations, both NDVI and SR exhibited near-linear correlations with fractional PAR intercepted by green leaves over a wide range of canopy densities. Maximum daily photosynthetic rates were positively correlated with NDVI and SR in annual grassland and semideciduous shrubs where canopy development and photosynthetic activity were in synchrony. The indices were also correlated with peak springtime canopy photosynthetic rates in evergreens. However, over most of the year, these indices were poor predictors of photosynthetic performance in evergreen species due to seasonal reductions in photosynthetic radiation-use efficiency that occurred without substantial declines in canopy greenness. Our results support the use of these vegetation indices as remote indicators of PAR absorption, and thus potential photosynthetic activity, even in heterogeneous landscapes. To provide accurate estimates of vegetation-atmosphere gas fluxes, remote NDVI and SR measurements need to be coupled with careful estimates of canopy photosynthetic radiation-use efficiency. [References: 64]
机译：在来自三种加利福尼亚植被类型的一系列植物物种中，我们研究了广泛使用的“归一化植被指数”（NDVI）和“简单比率”（SR）作为冠层结构，光吸收和光合作用指标的指标。这些指数来自红色和近红外波段的树冠反射率，突出了常绿和落叶树冠之间的物候差异。由于这些植被类型中非绿色常备生物量的丰富程度不同，因此它们不是冠层总生物量的较差指标。但是，在稀疏的树冠中（叶面积指数[LAI]大约为0-2），NDVI是树冠结构和化学含量（绿色生物量，绿色叶面积指数，叶绿素含量和叶面氮含量）的敏感指标。在较高的冠层绿色LAI值（> 2;典型的茂密灌木和树木）下，NDVI对冠层结构的变化相对不敏感。与SR相比，NDVI与冠层结构和化学含量指标的相关性更好，但与SR的对数相等。与理论预期相符，NDVI和SR均表现出与线性PAR的近似线性相关，在宽的冠层密度范围内，PAR均被绿叶截获。在冠层发育和光合活动同步的一年生草地和半落叶灌木中，最大日光合速率与NDVI和SR呈正相关。该指数还与常绿植物的春季冠层光合速率峰值相关。然而，在一年中的大部分时间里，由于常绿树种的光合作用性能预测不佳，这是由于光合辐射利用效率的季节性下降而没有发生冠层绿色度的显着下降。我们的结果支持使用这些植被指数作为PAR吸收的远程指标，因此甚至在异质景观中也具有潜在的光合作用活性。为了提供对植被-大气气体通量的准确估计，需要将远程NDVI和SR测量与对冠层光合辐射利用效率的仔细估计结合起来。 [参考：64]

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