Three causes of variation in the photochemical reflectance index (PRI) in evergreen conifers.
Three causes of variation in the photochemical reflectance index (PRI) in evergreen conifers.
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DOI：
10.1111/nph.13159
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发表时间：
2015-04
期刊：
影响因子：
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通讯作者：
Christopher Y. S. Wong;J. Gamon
中科院分区：
文献类型：
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作者：
Christopher Y. S. Wong;J. Gamon
光化学反射指数(PRI)反映了叶黄素循环的日活动，也受季节变化的类胡萝卜素：叶绿素色素比例的影响。变化的色素池和叶黄素循环活性都有助于北方冬季暴露的常绿针叶树的光保护，但它们在不同的时间尺度上起作用，它们对PRI信号的相对贡献往往还不清楚。为了弄清这些响应及其对PRI信号的贡献，在北方气候条件下，对两种常绿针叶树(旋叶松和黄皮松)的叶片PRI、色素成分、温度和光照进行了长达2年的监测。PRI受到三个不同过程的影响，这些过程在不同的时间尺度上运行，并显示出不同的光谱响应。在两年的研究期间，PRI的最大变化是由于类胡萝卜素：Chl色素比率的季节性变化，其次是之前没有报道的在深度寒冷时期叶片反照率的变化。值得注意的是，最小的变化归因于叶黄素循环。为了正确区分这三种影响，对PRI的解释必须考虑时间背景、对不断演变的环境条件的生理反应和光谱反应。考虑不同时间尺度上影响PRI的不同机制，可以极大地改进利用光学遥感监测光合作用活动变化的努力。
The photochemical reflectance index (PRI) reflects diurnal xanthophyll cycle activity and is also influenced by seasonally changing carotenoid : Chl pigment ratios. Both changing pigment pools and xanthophyll cycle activity contribute to photoprotection in evergreen conifers exposed to boreal winters, but they operate over different timescales, and their relative contribution to the PRI signal has often been unclear. To clarify these responses and their contribution to the PRI signal, leaf PRI, pigment composition, temperature and irradiance were monitored over 2 yr for two evergreen conifers (Pinus contorta and Pinus ponderosa) in a boreal climate. PRI was affected by three distinct processes operating over different timescales and exhibiting contrasting spectral responses. Over the 2 yr study period, the greatest change in PRI resulted from seasonally changing carotenoid : Chl pigment ratios, followed by a previously unreported shifting leaf albedo during periods of deep cold. Remarkably, the smallest change was attributable to the xanthophyll cycle. To properly distinguish these three effects, interpretation of PRI must consider temporal context, physiological responses to evolving environmental conditions, and spectral response. Consideration of the separate mechanisms affecting PRI over different timescales could greatly improve efforts to monitor changing photosynthetic activity using optical remote sensing.