Department of Biology, University of Toronto Mississauga, Mississauga, ON, Canada.
Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada.
Glob Chang Biol. 2020 Sep;26(9):5217-5234. doi: 10.1111/gcb.15150. Epub 2020 Jul 3.
In higher-latitude trees, temperature and photoperiod control the beginning and end of the photosynthetically active season. Elevated temperature (ET) has advanced spring warming and delayed autumn cooling while photoperiod remains unchanged. We assessed the effects of warming on the length of the photosynthetically active season of three provenances of Pinus strobus L. seedlings from different latitudes, and evaluated the accuracy of the photochemical reflectance index (PRI) and the chlorophyll/carotenoid index (CCI) for tracking the predicted variation in spring and autumn phenology of photosynthesis among provenances. Seedlings from northern, local and southern P. strobus provenances were planted in a temperature-free-air-controlled enhancement (T-FACE) experiment and exposed to ET (+1.5/3°C; day/night). Over 18 months, we assessed photosynthetic phenology by measuring chlorophyll fluorescence, gas exchange, leaf spectral reflectance and pigment content. During autumn, all seedlings regardless of provenance followed the same sequence of phenological events with the initial downregulation of photosynthesis, followed by the modulation of non-photochemical quenching and associated adjustments of zeaxanthin pool sizes. However, the timing of autumn downregulation differed between provenances, with delayed onset in the southern provenance (SP) and earlier onset in the northern relative to the local provenance, indicating that photoperiod at the provenance origin is a dominant factor controlling autumn phenology. Experimental warming further delayed the downregulation of photosynthesis during autumn in the SP. A provenance effect during spring was also observed but was generally not significant. The vegetation indices PRI and CCI were both effective at tracking the seasonal variations of energy partitioning in needles and the differences of carotenoid pigments indicative of the stress status of needles. These results demonstrate that PRI and CCI can be useful tools for monitoring conifer phenology and for the remote monitoring of the length of the photosynthetically active season of conifers in a changing climate.
在高纬度地区，温度和光照时长控制着树木光合作用季节的开始和结束。气温升高（ET）会使春季变暖提前，秋季降温推迟，而光照时长保持不变。我们评估了升温对三个不同纬度的湿地松（Pinus strobus L.）种源幼苗光合作用活跃季节长度的影响，并评估了光化学反射指数（PRI）和叶绿素/类胡萝卜素指数（CCI）在跟踪种源间光合作用春、秋物候变化的准确性。从北部、当地和南部的湿地松种源采集的幼苗被种植在温度自由空气控制增强（T-FACE）实验中，并暴露于 ET（+1.5/3°C；白天/夜晚）。在 18 个月的时间里，我们通过测量叶绿素荧光、气体交换、叶片光谱反射率和色素含量来评估光合作用物候。在秋季，所有幼苗，无论种源如何，都遵循相同的物候事件序列，最初是光合作用的下调，随后是非光化学猝灭的调制以及叶黄素池大小的相关调整。然而，秋季下调的时间在种源之间有所不同，南部种源（SP）的开始时间较晚，而北部种源的开始时间比当地种源更早，这表明种源起源的光照时长是控制秋季物候的主要因素。实验性升温进一步延迟了 SP 秋季光合作用的下调。在春季也观察到了种源效应，但通常不显著。植被指数 PRI 和 CCI 都能有效地跟踪针叶能量分配的季节性变化以及指示针叶胁迫状态的类胡萝卜素色素的差异。这些结果表明，PRI 和 CCI 可用于监测针叶树物候，以及在气候变化下远程监测针叶树光合作用活跃季节的长度。
