Macrosystems Ecology Lab

Our paper on the US N fertilizer management history is published in Earth System Science Data

We developed time-series gridded maps to depict crop-specific N fertilizer use rates, application timing, and the fractions of ammonium N (NH4+-N) and nitrate N (NO3−-N) used across the contiguous US at a resolution of 5 km  ×  5 km during the period from 1850 to 2015.

Our paper of US land use history is published in Global Ecology and Biogeography.

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We reconstructed the cropland density maps by harmonizing multiple sources of inventory data and high-resolution satellite images. The time-series gridded data depicts the distribution and percentage of cultivated land each year (excluding summer idle/fallow, cropland pasture). The reconstructed annual cropland percentage maps were at 1 km×1 km resolution covering the conterminous U.S. spanning from 1850 to 2016.

Anthropogenic activities such as land-use change and agricultural management have altered terrestrial biogenic greenhouse gas (GHG) fluxes. Global carbon (C) emission associated with land cover and land use change (LUCC) was estimated with a large uncertainty, which is the most uncertain term in the C budget estimation at both global and regional scales. To better manage agroecosystem, it is of critical importance to comprehensively and accurately quantify the magnitude and spatiotemporal patterns of terrestrial C storage and sequestration capacity. In this study, based on state- and national census, field experiments, and model simulation, we comprehensively examined long-term carbon storage change in response to LUCC and agricultural management in the Midwest from 1850 to 2015.

• Model estimation showed LUCC led to a reduction of 1.35 Pg (with a range of 1.3-1.4 Pg) in vegetation C pool of the Midwest, yet agricultural management barely affected vegetation C change.

• In comparison, LUCC reduced SOC by 4.5 Pg (3.1 to 6.2 Pg), while agricultural management practices increased SOC stock by 0.9 Pg.

• Our results imply that proper land management practices can potentially contribute to strengthen carbon sequestration of the terrestrial ecosystems in Midwestern U.S., which may serve as a major contributor to carbon sinks in the U.S. In addition, our study brings forth insightful points for accurate C budget assessment and management in intensively managed landscape.

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This study has been featured by ISU News: Iowa State University researchers model how Midwestern land-use changes affect carbon storage over the last 165 years.

https://www.news.iastate.edu/news/2018/05/01/landusechanges

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Lu’s study published in Nature revealed that Human activity makes terrestrial biosphere contribute to climate change

In a recently published paper in Nature, Dr. Lu played a major role among an international research team of 23 scientists from 16 institutions in four countries. 
Methane and nitrous oxide emissions that result from human activity make the terrestrial biosphere a net contributor of greenhouse gas emissions, according to a new study published in Nature. The findings reverse the commonly held view among climate scientists that the terrestrial biosphere, a term used to refer to all land-based ecosystems on the planet, slows climate change by acting as a carbon dioxide sink, or a reservoir that absorbs carbon dioxide and temporarily takes it out of circulation. Instead, the methane and nitrous oxide released from the terrestrial biosphere is roughly two times larger than the cooling effect of the biospheric carbon dioxide sink, said Chaoqun Lu, an ISU assistant professor of ecology, evolution and organismal biology and co-author of the study.

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More reports on this study could be found in: 
Nature 
Iowa State University 
The Washington Post 
Auburn University 
The conversation 
Carnegie Science

The 16th National Conference and Global Forum on Science, Policy and the Environment, Washington, DC

As one of panelists, Dr. Lu shared her understanding of " food-energy-water (FEW) Nexus" in Asia. 
Her current research focuses on the role of nitrogen cycle in FEW nexus through crop production, N2O emission and nitrogen yield from soil to runoffs, and modification of climate extremes to FEW nexus (e.g., climate impacts on grassland productivity, water yield and its implication to livestock production in the Mongolian Plateau). Dr. Lu contributes to regional assessment and quantification of natural and human controls over food-energy-water nexus.

As one of corresponding authors, Dr. Lu has recently published a paper on Global Biogeochemical Cycles. Researchers from thirteen major international institutions compiled century-long (1901–2010) estimates of soil organic carbon (SOC) storage and heterotrophic respiration—the production of carbon dioxide from decomposing soil organic matters—from ten terrestrial biosphere models in the Multi-scale Synthesis and Terrestrial Model Intercomparison Project and two observation-based data sets.
Researchers provided key recommendations for filling major gaps in knowledge, which will reduce uncertainties in terrestrial biosphere models. This study paves the way for accurate estimates of global soil carbon dynamics. Accurate assessment of the soil carbon reservoir is essential for understanding the impact of environmental changes on soil carbon stocks, predicting soil carbon dynamics and effect on climate change.
Click to read more.