RELATIONSHIPS BETWEEN NDVI, CANOPY STRUCTURE, AND PHOTOSYNTHESIS IN 3 CALIFORNIAN VEGETATION TYPES
RELATIONSHIPS BETWEEN NDVI, CANOPY STRUCTURE, AND PHOTOSYNTHESIS IN 3 CALIFORNIAN VEGETATION TYPES
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DOI：
10.2307/1942049
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发表时间：
1995-02-01
影响因子：
5
通讯作者：
VALENTINI, R
中科院分区：
文献类型：
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作者：
GAMON, JA;FIELD, CB;VALENTINI, R
在一系列的植物物种从三个加州植被类型，我们研究了广泛使用的“归一化植被指数”（NDVI）和“简单比率”（SR）的冠层结构，光吸收和光合活性的指标。这些指数，这是来自冠层反射率在红色和近红外波段，突出了万年青和落叶冠层之间的物候差异。由于这些植被类型中非绿色生物量的丰度不同，它们是总冠层生物量的不良指标。而在稀疏的冠层中（叶面积指数[LAI]接近0-2），NDVI是冠层结构和化学成分（绿色生物量、绿色叶面积指数、叶绿素含量和叶片氮含量）的敏感指标。在较高的冠层绿色叶面积指数值（> 2;典型的密集灌木和乔木），NDVI是相对不敏感的冠层结构的变化。与SR相比，NDVI与冠层结构和化学含量指标的相关性更好，但相当于SR的对数。与理论预期一致，NDVI和SR在很宽的郁闭度范围内与绿色叶截获的PAR分数呈近线性相关。一年生草地和半落叶灌木的最大日光合速率与NDVI和SR呈显著正相关，其冠层发育与光合活性同步。这些指标也与常绿植物春季冠层光合速率峰值相关。然而，在一年的大部分时间里，这些指数是万年青树种的光合性能差的预测，由于光合辐射利用效率的季节性减少，发生在冠层绿度没有大幅下降。我们的研究结果支持使用这些植被指数作为PAR吸收的远程指标，从而潜在的光合活性，即使在异质景观。为了提供准确的估计植被-大气气体通量，远程NDVI和SR测量需要加上仔细估计冠层光合辐射利用效率。
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.