Bren School of Environmental Science and Management , University of California , Santa Barbara , California 93106 , United States.
Earth Research Institute , University of California , Santa Barbara , California 93106 , United States.
ACS Nano. 2020 Jan 28;14(1):585-594. doi: 10.1021/acsnano.9b06970. Epub 2019 Dec 18.
Engineered nanomaterials (ENMs) can enter agroecosystems because of their widespread use and disposal. Within soil, ENMs may affect legumes and their dinitrogen (N) fixation, which are critical for food supply and N-cycling. Prior research focusing on end point treatment effects has reported that N-fixing symbioses in an important food legume, soybean, can be impaired by ENMs. Yet, it remains unknown how ENMs can influence the actual amounts of N fixed and what plant total N contents are since plants can also acquire N from the soil. We determined the effects of one already widespread and two rapidly expanding carbonaceous nanomaterials (CNMs: carbon black, multiwalled carbon nanotubes, and graphene; each at three concentrations) on the N economy of soil-grown soybeans. Unlike previous studies, this research focused on processes and interactions within a plant-soil-microbial system. We found that total plant N accumulation was unaffected by CNMs. However, as shown by N isotope analyses, CNMs significantly diminished soybean N fixation (by 31-78%). Plants maintained N stoichiometry by assimilating compensatory N from the soil, accompanied by increased net soil N mineralization. Our findings suggest that CNMs could undermine the role of legume N fixation in supplying N to agroecosystems. Maintaining productivity in leguminous agriculture experiencing such effects would require more fossil-fuel-intensive N fertilizer and increase associated economic and environmental costs. This work highlights the value of a process-based analysis of a plant-soil-microbial system for assessing how ENMs in soil can affect legume N fixation and N-cycling.
由于工程纳米材料（ENMs）的广泛使用和处置，它们可能会进入农业生态系统。在土壤中，ENMs 可能会影响豆类及其固氮作用，这对粮食供应和氮循环至关重要。先前的研究集中于终点处理效应，报告称，ENMs 可能会损害重要粮食豆类——大豆中的固氮共生体。然而，由于植物也可以从土壤中获取氮，因此仍不清楚 ENMs 如何影响实际固定的氮量以及植物的总氮含量是多少。我们确定了一种已经广泛存在的和两种快速扩展的碳质纳米材料（CNMs：炭黑、多壁碳纳米管和石墨烯；每种材料设三个浓度）对土壤生长大豆氮素经济的影响。与以前的研究不同，这项研究侧重于植物-土壤-微生物系统内的过程和相互作用。我们发现，CNMs 对总植物氮积累没有影响。然而，正如氮同位素分析所示，CNMs 显著降低了大豆固氮（减少 31-78%）。植物通过从土壤中同化补偿性氮来维持氮化学计量平衡，同时增加净土壤氮矿化。我们的研究结果表明，CNMs 可能会削弱豆科植物固氮在为农业生态系统提供氮的作用。在经历这种影响的豆科农业中保持生产力将需要更多依赖化石燃料的氮肥，并增加相关的经济和环境成本。这项工作突出了基于过程的植物-土壤-微生物系统分析在评估土壤中的 ENMs 如何影响豆科植物固氮和氮循环的价值。
