Department of Biological Sciences, University of Manitoba, Winnipeg, Canada.
Sci Rep. 2021 Feb 4;11(1):3038. doi: 10.1038/s41598-021-82701-7.
Small inreases in CO stimulate nitrogen fixation and plant growth. Increasing soil N can inhibit nitrogen fixation. However, no studies to date have tested how nitrogen fixing plants perform under ancient CO levels (100 MYA), when nitrogen fixing plants evolved, with different levels of N additions. The aim of this study was to assess if ancient CO, compared to present, favors nitrogen fixers over a range of soil nitrogen concentrations. Nitrogen fixers (Alnus incana ssp. rugosa, Alnus viridis ssp. crispa, and Alnus rubra) and their close non-nitrogen fixing relatives (Betula pumila, Betula papyrifera, Betula glandulosa) were grown at ancient (1600 ppm) or present (400 ppm) CO over a range of soil N levels, equivalent to 0, 10, 50, and 200 kg N ha year. The growth of non-N fixing plants increased more than N fixing plants in response to the increasing N levels. When grown at an ancient CO level, the N level at which non-nitrogen fixing plant biomass exceeded nitrogen fixing plant biomass was twice as high (61 kg N ha year) as the N level when plants were grown at the ambient CO level. Specific nodule activity was also reduced with an increasing level of soil N. Our results show there was a greater advantage in being a nitrogen fixer under ancient levels of CO compared with the present CO level.
CO 浓度的微小升高会刺激固氮作用和植物生长。增加土壤中的 N 会抑制固氮作用。然而，迄今为止，还没有研究测试在远古 CO 水平（1 亿年前）下，固氮植物在不同 N 添加水平下的表现如何，当时固氮植物进化而来。本研究的目的是评估与现在相比，在一系列土壤氮浓度下，远古 CO 是否更有利于固氮生物。在一系列土壤氮水平下（相当于 0、10、50 和 200 kg N ha year），将固氮植物（Alnus incana ssp. rugosa、Alnus viridis ssp. crispa 和 Alnus rubra）及其近亲非固氮植物（Betula pumila、Betula papyrifera 和 Betula glandulosa）分别在远古（1600 ppm）或现在（400 ppm）CO 下进行培养。非固氮植物的生长比固氮植物对氮水平的增加更为敏感。当在远古 CO 水平下生长时，非固氮植物生物量超过固氮植物生物量的氮水平是在环境 CO 水平下生长时的两倍（61 kg N ha year）。土壤氮水平增加也会降低特定的根瘤活性。我们的结果表明，与现在的 CO 水平相比，在远古 CO 水平下，作为固氮生物具有更大的优势。
