Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , 205 North Mathews Avenue, Urbana, Illinois 61801-2352, United States.
Environ Sci Technol. 2014 Oct 21;48(20):12090-8. doi: 10.1021/es5023762. Epub 2014 Oct 1.
Because of increasing demands for bioenergy, a considerable amount of land in the midwestern United States could be devoted to the cultivation of second-generation bioenergy crops, such as switchgrass and miscanthus. The foliar carbon/nitrogen ratio (C/N) in these bioenergy crops at harvest is significantly higher than the ratios in replaced crops, such as corn or soybean. We show that there is a critical soil organic matter C/N ratio, where microbial biomass can be impaired as microorganisms become dependent upon net immobilization. The simulation results show that there is a threshold effect in the amount of aboveground litter input in the soil after harvest that will reach a critical organic matter C/N ratio in the soil, triggering a reduction of the soil microbial population, with significant consequences in other microbe-related processes, such as decomposition and mineralization. These thresholds are approximately 25 and 15% of aboveground biomass for switchgrass and miscanthus, respectively. These results suggest that values above these thresholds could result in a significant reduction of decomposition and mineralization, which, in turn, would enhance the sequestration of atmospheric carbon dioxide in the topsoil and reduce inorganic nitrogen losses when compared to a corn-corn-soybean rotation.
由于对生物能源的需求不断增加，美国中西部地区的相当多土地可能会被用于种植第二代生物能源作物，如柳枝稷和芒草。这些生物能源作物在收获时的叶片碳氮比（C/N）明显高于玉米或大豆等替代作物的比例。我们表明，存在一个临界土壤有机质 C/N 比，在此比下微生物生物量可能会受到损害，因为微生物变得依赖于净固氮。模拟结果表明，在收获后输入土壤的地上凋落物量存在一个阈值效应，当达到土壤中临界有机质 C/N 比时，会触发土壤微生物种群减少，对其他与微生物相关的过程（如分解和矿化）产生重大影响。这些阈值分别约为柳枝稷和芒草地上生物量的 25%和 15%。这些结果表明，超过这些阈值的值可能会导致分解和矿化的显著减少，这反过来又会增加表土中二氧化碳的固存，并减少与玉米-玉米-大豆轮作相比无机氮的损失。
