Carney Karen M, Hungate Bruce A, Drake Bert G, Megonigal J Patrick
Smithsonian Environmental Research Center, P.O. Box 28, Edgewater, MD 21037, USA.
Proc Natl Acad Sci U S A. 2007 Mar 20;104(12):4990-5. doi: 10.1073/pnas.0610045104. Epub 2007 Mar 13.
Increased carbon storage in ecosystems due to elevated CO(2) may help stabilize atmospheric CO(2) concentrations and slow global warming. Many field studies have found that elevated CO(2) leads to higher carbon assimilation by plants, and others suggest that this can lead to higher carbon storage in soils, the largest and most stable terrestrial carbon pool. Here we show that 6 years of experimental CO(2) doubling reduced soil carbon in a scrub-oak ecosystem despite higher plant growth, offsetting approximately 52% of the additional carbon that had accumulated at elevated CO(2) in aboveground and coarse root biomass. The decline in soil carbon was driven by changes in soil microbial composition and activity. Soils exposed to elevated CO(2) had higher relative abundances of fungi and higher activities of a soil carbon-degrading enzyme, which led to more rapid rates of soil organic matter degradation than soils exposed to ambient CO(2). The isotopic composition of microbial fatty acids confirmed that elevated CO(2) increased microbial utilization of soil organic matter. These results show how elevated CO(2), by altering soil microbial communities, can cause a potential carbon sink to become a carbon source.
由于二氧化碳浓度升高，生态系统中碳储存的增加可能有助于稳定大气中的二氧化碳浓度并减缓全球变暖。许多实地研究发现，二氧化碳浓度升高会导致植物更高的碳同化，还有研究表明，这会导致土壤中更高的碳储存，土壤是最大且最稳定的陆地碳库。在此我们表明，在一个灌丛橡木生态系统中，6年的实验性二氧化碳浓度翻倍尽管植物生长加快，但土壤碳却减少了，抵消了在二氧化碳浓度升高时地上和粗根生物量中积累的额外碳的约52%。土壤碳的下降是由土壤微生物组成和活性的变化驱动的。暴露于高浓度二氧化碳的土壤中真菌的相对丰度更高，且一种土壤碳降解酶的活性更高，这导致土壤有机质的降解速度比暴露于环境二氧化碳的土壤更快。微生物脂肪酸的同位素组成证实，高浓度二氧化碳增加了微生物对土壤有机质的利用。这些结果表明，高浓度二氧化碳如何通过改变土壤微生物群落，使一个潜在的碳汇变成一个碳源。
