Stylinski C, Gamon J, Oechel W
San Diego State University, San Diego, CA, 92182, USA.
California State University, Los Angeles, CA, 90032, USA.
Oecologia. 2002 May;131(3):366-374. doi: 10.1007/s00442-002-0905-9. Epub 2002 May 1.
This study examined the ability of the Photochemical Reflectance Index (PRI) to track seasonal variations in carotenoid pigments and photosynthetic activity of mature evergreen chaparral shrubs. Our results confirm that PRI scales with photosystem two (PSII) photochemical efficiency across species and seasons, as demonstrated by PRI's strong correlation with de-epoxidized (photoprotective) xanthophyll cycle pigment levels (normalized to chlorophyll) and with the chlorophyll fluorescence index, ΔF/Fm'. PRI and carotenoid pigment levels (de-epoxidized xanthophyll cycle pigments normalized to chlorophyll or total carotenoid pigments normalized to chlorophyll) were correlated with seasonal fluctuations in midday net CO uptake of top-canopy leaves. By contrast, chlorophyll levels (as measured by the Chlorophyll Index) were not as strongly linked to photosynthetic activity, particularly when all species were considered together. Likewise, the Normalized Difference Vegetation Index (NDVI, an index of canopy greenness) did not correlate with net CO uptake. Canopy NDVI also did not correlate with canopy PRI, demonstrating that these indices were largely independent over the temporal and spatial scales of this study. Together, these patterns provide evidence for coordinated regulation of carotenoid pigments, PSII electron transport, and carboxylation across seasons and indicate that physiological adjustments are more important than structural ones in modifying CO-fixation capacity during periods of photosynthetic down-regulation for these evergreen species. The strong correlation between PRI of whole canopies and PRI of top-canopy leaves suggests that the canopy can be treated as a "big leaf" in terms of this reflectance index and that PRI can be used in "scalable" models. This along with the links between carotenoid pigments, PSII photochemical efficiency and carboxylation across species and seasons supports the use of optical assays of pigment levels and PSII activity in CO flux models to derive photosynthetic rates.
本研究考察了光化学反射指数（PRI）追踪成熟常绿矮林灌丛中类胡萝卜素色素季节性变化及光合活性的能力。我们的结果证实，PRI在物种和季节间均与光系统II（PSII）光化学效率呈比例关系，PRI与脱环氧化（光保护）叶黄素循环色素水平（以叶绿素标准化）以及叶绿素荧光指数ΔF/Fm'的强相关性证明了这一点。PRI和类胡萝卜素色素水平（脱环氧化叶黄素循环色素以叶绿素标准化或总类胡萝卜素色素以叶绿素标准化）与树冠层顶部叶片中午净CO₂吸收量的季节性波动相关。相比之下，叶绿素水平（通过叶绿素指数测量）与光合活性的联系并不那么紧密，尤其是当所有物种一起考虑时。同样，归一化植被指数（NDVI，一种冠层绿度指数）与净CO₂吸收量不相关。冠层NDVI也与冠层PRI不相关，表明在本研究的时间和空间尺度上，这些指数在很大程度上相互独立。总之，这些模式为类胡萝卜素色素、PSII电子传递和羧化作用在季节间的协同调节提供了证据，并表明在这些常绿物种光合下调期间，生理调节在改变CO₂固定能力方面比结构调节更为重要。整个冠层的PRI与树冠层顶部叶片的PRI之间的强相关性表明，就该反射指数而言，冠层可被视为一片“大叶”，并且PRI可用于“可扩展”模型。这一点以及类胡萝卜素色素、PSII光化学效率和羧化作用在物种和季节间的联系，支持在CO₂通量模型中使用色素水平和PSII活性的光学测定方法来推导光合速率。
