Influences of Root Hydraulic Redistribution on N2O Emissions at AmeriFlux Sites

It has long been suspected that root hydraulic redistribution (HR) affects the carbon and nitrogen cycles. Nitrous oxide (N2O) is an important greenhouse gas and is the primary stratospheric ozone-depleting substance. To our knowledge, the influences of HR on N2O emissions have not been investigated. Here we use the HR schemes of Ryel et al. and Amenu and Kumar incorporated into CLM4.5 to examine N2O emissions at five AmeriFlux sites. The results show that HR reduced N2O emissions by 28-92% in the four natural ecosystems experiencing a dry season, whereas it had a very limited effect on the Corn Belt site that has strong emissions but with no distinct dry season. We hypothesize that N2O emissions in ecosystems with a distinct dry season are likely overestimated by CENTURY-based Earth system models. Plain Language Summary The findings of this study suggest that hydraulic redistribution (HR) may play an important role in N2O emissions from agricultural regions that have a clearly defined dry season. For example, the expansive corn-growing regions of China are all located in the monsoon area with a distinct dry season. We hypothesize that the HR mechanism acts to significantly reduce N2O emissions in these regions. HR may also play an important role in limiting N2O emissions in the Amazonian regions with a tropical monsoon climate, where forests have been converted to agricultural use.