Department of Ecology, Evolution, and Environmental Biology, Columbia University, New York, New York, 10027, USA.
Department of Plant Sciences, University of California, Davis, California, 95616, USA.
Ecology. 2021 Aug;102(8):e03414. doi: 10.1002/ecy.3414. Epub 2021 Jul 9.
Forests are a significant CO sink. However, CO sequestration in forests is radiatively offset by emissions of nitrous oxide (N O), a potent greenhouse gas, from forest soils. Reforestation, an important strategy for mitigating climate change, has focused on maximizing CO sequestration in plant biomass without integrating N O emissions from soils. Although nitrogen (N)-fixing trees are often recommended for reforestation because of their rapid growth on N-poor soil, they can stimulate significant N O emissions from soils. Here, we first used a field experiment to show that a N-fixing tree (Robinia pseudoacacia) initially mitigated climate change more than a non-fixing tree (Betula nigra). We then used our field data to parameterize a theoretical model to investigate these effects over time. Under lower N supply, N-fixers continued to mitigate climate change more than non-fixers by overcoming N limitation of plant growth. However, under higher N supply, N-fixers ultimately mitigated climate change less than non-fixers by enriching soil N and stimulating N O emissions from soils. These results have implications for reforestation, suggesting that N-fixing trees are more effective at mitigating climate change at lower N supply, whereas non-fixing trees are more effective at mitigating climate change at higher N supply.
森林是一个重要的二氧化碳汇。然而，森林对二氧化碳的固存作用被土壤中一氧化二氮（N O）的排放所抵消，而一氧化二氮是一种强大的温室气体。作为缓解气候变化的重要策略，重新造林侧重于最大限度地增加植物生物量中的二氧化碳固存，而不考虑土壤中一氧化二氮的排放。尽管固氮树种因其在贫瘠土壤上的快速生长而经常被推荐用于重新造林，但它们会刺激土壤中产生大量的一氧化二氮。在这里，我们首先使用野外实验表明，固氮树种（刺槐）最初比非固氮树种（黑桦）更能缓解气候变化。然后，我们利用现场数据对一个理论模型进行参数化，以研究随着时间的推移这些效应。在较低的氮供应下，固氮树种通过克服植物生长的氮限制，继续比非固氮树种更能缓解气候变化。然而，在较高的氮供应下，固氮树种最终通过富集土壤氮和刺激土壤一氧化二氮排放，对气候变化的缓解作用不如非固氮树种。这些结果对重新造林具有启示意义，表明在氮供应较低的情况下，固氮树种在缓解气候变化方面更有效，而在氮供应较高的情况下，非固氮树种在缓解气候变化方面更有效。
