Department of Forest Resources, University of Minnesota, St. Paul, MN 55108, USA.
Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW 2753, Australia.
Science. 2018 Apr 20;360(6386):317-320. doi: 10.1126/science.aas9313.
Theory predicts and evidence shows that plant species that use the C photosynthetic pathway (C species) are less responsive to elevated carbon dioxide (CO) than species that use only the C pathway (C species). We document a reversal from this expected C-C contrast. Over the first 12 years of a 20-year free-air CO enrichment experiment with 88 C or C grassland plots, we found that biomass was markedly enhanced at CO relative to ambient CO in C but not C plots, as expected. During the subsequent 8 years, the pattern reversed: Biomass was markedly enhanced at CO relative to ambient CO in C but not C plots. Soil net nitrogen mineralization rates, an index of soil nitrogen supply, exhibited a similar shift: CO first enhanced but later depressed rates in C plots, with the opposite true in C plots, partially explaining the reversal of the CO biomass response. These findings challenge the current C-CCO paradigm and show that even the best-supported short-term drivers of plant response to global change might not predict long-term results.
理论预测和证据表明，使用 C 光合作用途径的植物物种（C 物种）对二氧化碳（CO）升高的反应不如仅使用 C 途径的物种（C 物种）敏感。我们记录了与预期的 C-C 对比相反的情况。在一项为期 20 年的大气 CO 浓度升高的自由空气实验中，我们对 88 个 C 或 C 草地样地进行了研究，发现与环境 CO 相比，CO 显著增强了 C 但不是 C 样地的生物量，这是预期的结果。在随后的 8 年中，模式发生了逆转：与环境 CO 相比，CO 显著增强了 C 但不是 C 样地的生物量。土壤净氮矿化速率，即土壤氮供应的指标，也表现出类似的变化：CO 首先增强，但后来在 C 样地中降低了速率，而在 C 样地中则相反，这部分解释了 CO 对生物量响应的逆转。这些发现挑战了当前的 C-C-CO 范式，并表明，即使是对植物对全球变化反应的短期驱动因素最有支持的理论，也可能无法预测长期结果。
