Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia.
School of Archaeology, Geography and Environmental Sciences (SAGES), Reading University, Reading, UK.
Sci Rep. 2017 Feb 24;7:43087. doi: 10.1038/srep43087.
Isotopic measurements on junipers growing in southern California during the last glacial, when the ambient atmospheric [CO] (c) was ~180 ppm, show the leaf-internal [CO] (c) was approaching the modern CO compensation point for C plants. Despite this, stem growth rates were similar to today. Using a coupled light-use efficiency and tree growth model, we show that it is possible to maintain a stable c/c ratio because both vapour pressure deficit and temperature were decreased under glacial conditions at La Brea, and these have compensating effects on the c/c ratio. Reduced photorespiration at lower temperatures would partly mitigate the effect of low c on gross primary production, but maintenance of present-day radial growth also requires a ~27% reduction in the ratio of fine root mass to leaf area. Such a shift was possible due to reduced drought stress under glacial conditions at La Brea. The necessity for changes in allocation in response to changes in [CO] is consistent with increased below-ground allocation, and the apparent homoeostasis of radial growth, as c increases today.
在末次冰期（当时大气中的[CO]（c）约为 180ppm），生长在南加州的杜松的同位素测量显示，其叶片内的[CO]（c）接近 C 植物的现代 CO 补偿点。尽管如此，茎的生长速度与今天相似。利用耦合的光利用效率和树木生长模型，我们表明，由于在拉布雷亚，冰期的蒸气压亏缺和温度降低，稳定的 c/c 比值是可能的，这对 c/c 比值有补偿作用。较低温度下的光呼吸减少会部分减轻低 c 对总初级生产力的影响，但维持当今的径向生长还需要将细根质量与叶面积的比例降低约 27%。由于拉布雷亚冰期的干旱胁迫减轻，这种转变成为可能。对[CO]变化的分配变化的必要性与地下分配的增加以及今天 c 增加时径向生长的明显同形一致。
