Reich Peter B, Luo Yunjian, Bradford John B, Poorter Hendrik, Perry Charles H, Oleksyn Jacek
Department of Forest Resources, University of Minnesota, St. Paul, MN 55108; Hawkesbury Institute for the Environment, University of Western Sydney, Penrith, NSW 2751, Australia;
Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China;
Proc Natl Acad Sci U S A. 2014 Sep 23;111(38):13721-6. doi: 10.1073/pnas.1216053111. Epub 2014 Sep 15.
Whether the fraction of total forest biomass distributed in roots, stems, or leaves varies systematically across geographic gradients remains unknown despite its importance for understanding forest ecology and modeling global carbon cycles. It has been hypothesized that plants should maintain proportionally more biomass in the organ that acquires the most limiting resource. Accordingly, we hypothesize greater biomass distribution in roots and less in stems and foliage in increasingly arid climates and in colder environments at high latitudes. Such a strategy would increase uptake of soil water in dry conditions and of soil nutrients in cold soils, where they are at low supply and are less mobile. We use a large global biomass dataset (>6,200 forests from 61 countries, across a 40 °C gradient in mean annual temperature) to address these questions. Climate metrics involving temperature were better predictors of biomass partitioning than those involving moisture availability, because, surprisingly, fractional distribution of biomass to roots or foliage was unrelated to aridity. In contrast, in increasingly cold climates, the proportion of total forest biomass in roots was greater and in foliage was smaller for both angiosperm and gymnosperm forests. These findings support hypotheses about adaptive strategies of forest trees to temperature and provide biogeographically explicit relationships to improve ecosystem and earth system models. They also will allow, for the first time to our knowledge, representations of root carbon pools that consider biogeographic differences, which are useful for quantifying whole-ecosystem carbon stocks and cycles and for assessing the impact of climate change on forest carbon dynamics.
尽管根系、茎干或叶片中分配的森林总生物量比例对于理解森林生态和全球碳循环建模很重要，但其是否会随地理梯度系统变化仍不清楚。有一种假说认为，植物应该在获取最限制资源的器官中保持相对更多的生物量。因此，我们推测在气候日益干旱以及高纬度寒冷环境中，根系中的生物量分布会更大，而茎干和叶片中的生物量分布会更小。这样的策略将增加干旱条件下土壤水分的吸收以及寒冷土壤中土壤养分的吸收，因为在这些地方土壤水分和养分供应不足且流动性较差。我们使用一个大型全球生物量数据集（来自61个国家的>6200片森林，年均温度梯度为40°C）来解决这些问题。涉及温度的气候指标比涉及水分可利用性的指标能更好地预测生物量分配，因为令人惊讶的是，生物量在根系或叶片中的分配比例与干旱无关。相反，在气候日益寒冷的情况下，被子植物和裸子植物森林中，根系中森林总生物量的比例更大，而叶片中的比例更小。这些发现支持了关于森林树木对温度的适应性策略的假说，并提供了生物地理学明确关系，以改进生态系统和地球系统模型。据我们所知，它们还将首次允许考虑生物地理差异的根系碳库表示，这对于量化整个生态系统的碳储量和碳循环以及评估气候变化对森林碳动态的影响很有用。
