Agroecosystem modeling of reactive nitrogen emissions from U.S.agricultural soils with carbon amendments

Fertilizer-intensive agriculture is a leading source of reactive nitrogen(Nr)emissions that damage climate,air quality,and human health.Biochar has long been studied as a soil amendment,but its influence on Nr emissions remains insufficiently characterized.More recently,the pyrolysis of light hydrocarbons has been suggested as a source of hydrogen fuel,resulting in a solid zero-valent carbon(ZVC)byproduct whose impact on soil emissions has yet to be tested.We incorporate carbon amendment algorithms into an agroecosystem model to simulate emission changes in the year following the application of biochar or ZVC to the US.fertilized soils.Our simulations predicted that the impacts of biochar amendments on Nr emissions would vary widely(−17%to+27%under 5 ton ha^(−1) applications,−38%to+18%under 20 ton ha^(−1) applications)and depend mostly on how nitrification is affected.Low-dose biochar application(5 ton ha^(−1))stimulated emissions of all three nitrogen species in 75%of simulated agricultural areas,while high-dose applications(20 ton ha^(−1))mitigated emissions in 76%of simulated areas.Applying zero-valent carbon at 20 ton ha^(−1) exhibited similar effects on nitrogen emissions as biochar applications at 5 ton ha^(−1).Biochar amendments are most likely to mitigate emissions if applied at high rates in acidic soils(pH<5.84)with low organic carbon(<55.9 kg C ha^(−1))and inorganic nitrogen(<101.5 kg N ha^(−1))content.Our simulations could inform where the application of carbon amendments would most likely mitigate Nr emissions and their associated adverse impacts.

Molecular signature of soil organic matter under different land uses in the Lake Chaohu Basin

The concentration and molecular composition of soil organic matter(SOM)are important factors in mitigation against climate change as well as providing other ecosystem services.Our quantitative understanding of how land use influences SOM molecular composition and associated turnover dynamics is limited,which underscores the need for high-throughput analytical approaches and molecular marker signatures to clarify this etiology.Combining a high-throughput untargeted mass spectrometry screening and molecular markers,we show that forest,farmland and urban land uses result in distinct molecular signatures of SOM in the Lake Chaohu Basin.Molecular markers indicate that forest SOM has abundant carbon contents from vegetation and condensed organic carbon,leading to high soil organic carbon(SOC)concentration.Farmland SOM has moderate carbon contents from vegetation,and limited content of condensed organic carbon,with SOC significantly lower than that of forest soils.Urban SOM has high abundance of condensed organic carbon markers due to anthropogenic activities but relatively low in markers from vegetation.Consistently,urban soils have the highest black carbon/SOC ratio among these land uses.Overall,our results suggested that the molecular signature of SOM varies significantly with land use in the Lake Chaohu Basin,influencing carbon dynamics.Our strategy of molecular fingerprinting and marker discovery is expected to enlighten further research on SOM molecular signatures and cycling dynamics.