Effects of nitrogen limitation on hydrological processes in CLM4-CN

[1] The role of nitrogen limitation on photosynthesis downregulation and stomatal conductance has a significant influence on evapotranspiration and runoff. In the current Community Land Model with coupled Carbon and Nitrogen cycles (CLM4-CN), however, the carbon and water coupling in stomata is not linked to nitrogen limitation. We modify the incomplete linkages between carbon, nitrogen, and water, and examine how nitrogen limitation affects hydrological processes in CLM4-CN. We then evaluate if the modification can improve the simulation of carbon and water fluxes. Applying the effects of nitrogen limitation on stomatal conductance significantly decreases leaf photosynthesis. It leads to a reduction in canopy transpiration, thereby increasing total runoff, mainly due to increasing subsurface runoff. More available soil water for vegetation from the reduced transpiration helps increase gross primary productivity (GPP) in the relatively moisture-limited regions of grassland/steppe and savanna. However, in the tropics and boreal forest regions, changes in soil water by nitrogen limitation are insignificant, and GPP decreases directly by down-regulated leaf photosynthesis. Decreasing canopy transpiration and increasing runoff from nitrogen limitation improve simulating latent heat flux and runoff by reducing high biases for latent heat flux in the tropics and low biases for runoff in the tropics and northern high latitudes. In addition, the CLM4-CN with leaf-level nitrogen limitation reduces model biases in tropical GPP. Nitrogen limitation on the leaf-level significantly affects hydrological processes in CLM4-CN and improves the simulation of carbon and water fluxes. This process should be included with other recent improvements to reduce model biases as much as possible

Impacts of ozone on trees and crops

Author Posting. © The Author(s), 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Comptes Rendus Geosciences 339 (2007): 784-798, doi:10.1016/j.crte.2007.08.008.In this review article, we explore how surface-level ozone affects trees and crops with special emphasis on consequences for productivity and carbon sequestration. Vegetation exposure to ozone reduces photosynthesis, growth, and other plant functions. Ozone formation in the atmosphere is a product of NOx that are also a source of nitrogen deposition. Reduced carbon sequestration of temperate forests resulting from ozone is likely offset by increased carbon sequestration from nitrogen fertilization. However, since fertilized croplands are generally not nitrogen-limited, capping ozone-polluting substances in the U.S., Europe, and China can reduce future crop yield loss substantially.This study was funded by the Biocomplexity Program of the U.S. National Science Foundation (ATM-0120468), the Methods and Models for Integrated Assessment Program of the U.S. National Science Foundation (DEB-9711626) and the Earth Observing System Program of the U.S. National Aeronautics and Space Administration (NAG5-10135)

Correction to “Importance of carbon-nitrogen interactions and ozone on ecosystem hydrology during the 21st century”

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): G03009, doi:10.1029/2009JG001083

Nitrogen effect on carbon-water coupling in forests, grasslands, and shrublands in the arid western United States

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): G03023, doi:10.1029/2010JG001621.As greenhouse gases, including CO2, accumulate in the atmosphere, the western United States is predicted to undergo large-scale climate warming and reduced summer precipitation in the coming decades. In this study we explore the role of these climate changes with elevated CO2 to determine the plant physiological response on primary productivity and associated feedbacks on evapotranspiration (ET) and runoff using a biogeochemistry model, TEM-Hydro, with downscaled climate data for the western United States from the NCAR CCSM3 A2 scenario. Net primary productivity increases by 32% in forests due to feedbacks between warmer temperatures and enhanced nitrogen mineralization but decreases in shrublands by 24% due to excessive drying and reduced nitrogen mineralization. Warming directly increases nitrogen mineralization rates but indirectly decreases them by reducing soil moisture, so the net effect is highly dependent on climatic conditions within each biome. Increased soil moisture resulting from larger water use efficiency from the elevated CO2 leads to more net nitrogen mineralization in forests, which reduces N-limiting conditions. The effect of CO2 on stomatal conductance is therefore enhanced because of its effect on reducing nitrogen limiting conditions. Runoff decreases over the 21st century by 22% in forests, 58% in grasslands, and 67% in shrublands due to the reduced precipitation in each region but is modulated by the plant-induced changes in ET. The role of moisture limitation is therefore a crucial regulator of nitrogen limitation, which determines the future productivity and water availability in the West.This study was funded by the Department of Energy, Basic Research and Modeling to Support Integrated Assessment, DE‐FG02‐08ERG64648

Effects of tropospheric ozone pollution on net primary productivity and carbon storage in terrestrial ecosystems of China

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): D22S09, doi:10.1029/2007JD008521.We investigated the potential effects of elevated ozone (O3) along with climate variability, increasing CO2, and land use change on net primary productivity (NPP) and carbon storage in China's terrestrial ecosystems for the period 1961–2000 with a process-based Dynamic Land Ecosystem Model (DLEM) forced by the gridded data of historical tropospheric O3 and other environmental factors. The simulated results showed that elevated O3 could result in a mean 4.5% reduction in NPP and 0.9% reduction in total carbon storage nationwide from 1961 to 2000. The reduction of carbon storage varied from 0.1 Tg C to 312 Tg C (a decreased rate ranging from 0.2% to 6.9%) among plant functional types. The effects of tropospheric O3 on NPP were strongest in east-central China. Significant reductions in NPP occurred in northeastern and central China where a large proportion of cropland is distributed. The O3 effects on carbon fluxes and storage are dependent upon other environmental factors. Therefore direct and indirect effects of O3, as well as interactive effects with other environmental factors, should be taken into account in order to accurately assess the regional carbon budget in China. The results showed that the adverse influences of increasing O3 concentration across China on NPP could be an important disturbance factor on carbon storage in the near future, and the improvement of air quality in China could enhance the capability of China's terrestrial ecosystems to sequester more atmospheric CO2. Our estimation of O3 impacts on NPP and carbon storage in China, however, must be used with caution because of the limitation of historical tropospheric O3 data and other uncertainties associated with model parameters and field experiments.This research is funded by NASA Interdisciplinary Science Program (NNG04GM39C)

Importance of carbon-nitrogen interactions and ozone on ecosystem hydrology during the 21st century

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): G01020, doi:10.1029/2008JG000826.There is evidence that increasing CO2 concentrations have reduced evapotranspiration and increased runoff through reductions in stomatal conductance during the twentieth century. While this process will continue to counteract increased evapotranspiration associated with future warming, it is highly dependent upon concurrent changes in photosynthesis, especially due to CO2 fertilization, nitrogen limitation, and ozone exposure. A new version of the Terrestrial Ecosystem Model (TEM-Hydro) was developed to examine the effects of carbon and nitrogen on the water cycle. We used two climate models (NCAR CCSM3 and DOE PCM) and two emissions scenarios (SRES B1 and A2) to examine the effects of climate, elevated CO2, nitrogen limitation, and ozone exposure on the hydrological cycle in the eastern United States. While the direction of future runoff changes is largely dependent upon predicted precipitation changes, the effects of elevated CO2 on ecosystem function (stomatal closure and CO2 fertilization) increase runoff by 3–7%, as compared to the effects of climate alone. Consideration of nitrogen limitation and ozone damage on photosynthesis increases runoff by a further 6–11%. Failure to consider the effects of the interactions among nitrogen, ozone, and elevated CO2 may lead to significant regional underestimates of future runoff.This study was funded by the Interdisciplinary Science Program of the U.S. National Aeronautics and Space Administration (NNG04GJ80G, NNG04GM39G), the Dynamic Global Economic Modeling of Greenhouse Gas Emissions and Mitigation from Land-Use Activities of the U.S. Environmental Protection Agency (XA-83240101), and the Nonlinear Response to Global Change in Linked Aquatic and Terrestrial Ecosystems of the U.S. EPA (XA-83326101)

Global economic effects of changes in crops, pasture, and forests due to changing climate, carbon dioxide, and ozone

Author Posting. © The Author(s), 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Energy Policy 35 (2007): 5370-5383, doi:10.1016/j.enpol.2006.01.040.Multiple environmental changes will have consequences for global vegetation. To the extent that crop yields and pasture and forest productivity are affected there can be important economic consequences. We examine the combined effects of changes in climate, increases in carbon dioxide, and changes in tropospheric ozone on crop, pasture, and forest lands and the consequences for the global and regional economies. We examine scenarios where there is limited or little effort to control these substances, and policy scenarios that limit emissions of CO2 and ozone precursors. We find the effects of climate and CO2 to be generally positive, and the effects of ozone to be very detrimental. Unless ozone is strongly controlled damage could offset CO2 and climate benefits. We find that resource allocation among sectors in the economy, and trade among countries, can strongly affect the estimate of economic effect in a country.This research was supported by the US Department of Energy, US Environmental Protection Agency, US National Science Foundation, US National Aeronautics and Space Administration, US National Oceanographic and Atmospheric Administration; and the Industry and Foundation Sponsors of the MIT Joint Program on the Science and Policy of Global Chang

Corrigendum

Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 23 (2010): 2230–2231, doi:10.1175/2009JCLI3566.1.Corrigendum: Sokolov, A., and Coauthors, 2009: Probabilistic forecast for twenty-first-century climate based on uncertainties in emissions (without policy) and climate parameters. J. Climate, 22, 5175–5204

Consequences of considering carbon–nitrogen interactions on the feedbacks between climate and the terrestrial carbon cycle

Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 21 (2008): 3776–3796, doi:10.1175/2008JCLI2038.1.The impact of carbon–nitrogen dynamics in terrestrial ecosystems on the interaction between the carbon cycle and climate is studied using an earth system model of intermediate complexity, the MIT Integrated Global Systems Model (IGSM). Numerical simulations were carried out with two versions of the IGSM’s Terrestrial Ecosystems Model, one with and one without carbon–nitrogen dynamics. Simulations show that consideration of carbon–nitrogen interactions not only limits the effect of CO2 fertilization but also changes the sign of the feedback between the climate and terrestrial carbon cycle. In the absence of carbon–nitrogen interactions, surface warming significantly reduces carbon sequestration in both vegetation and soil by increasing respiration and decomposition (a positive feedback). If plant carbon uptake, however, is assumed to be nitrogen limited, an increase in decomposition leads to an increase in nitrogen availability stimulating plant growth. The resulting increase in carbon uptake by vegetation exceeds carbon loss from the soil, leading to enhanced carbon sequestration (a negative feedback). Under very strong surface warming, however, terrestrial ecosystems become a carbon source whether or not carbon–nitrogen interactions are considered. Overall, for small or moderate increases in surface temperatures, consideration of carbon–nitrogen interactions result in a larger increase in atmospheric CO2 concentration in the simulations with prescribed carbon emissions. This suggests that models that ignore terrestrial carbon–nitrogen dynamics will underestimate reductions in carbon emissions required to achieve atmospheric CO2 stabilization at a given level. At the same time, compensation between climate-related changes in the terrestrial and oceanic carbon uptakes significantly reduces uncertainty in projected CO2 concentration

CO2 and CH4 exchanges between land ecosystems and the atmosphere in northern high latitudes over the 21st century

Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 33 (2006): L17403, doi:10.1029/2006GL026972.Terrestrial ecosystems of the northern high latitudes (above 50oN) exchange large amounts of CO2 and CH4 with the atmosphere each year. Here we use a process-based model to estimate the budget of CO2 and CH4 of the region for current climate conditions and for future scenarios by considering effects of permafrost dynamics, CO2 fertilization of photosynthesis and fire. We find that currently the region is a net source of carbon to the atmosphere at 276 Tg C yr-1. We project that throughout the 21st century, the region will most likely continue as a net source of carbon and the source will increase by up to 473 Tg C yr-1 by the end of the century compared to the current emissions. However our coupled carbon and climate model simulations show that these emissions will exert relatively small radiative forcing on global climate system compared to large amounts of anthropogenic emissions.This study was supported by a NSF Biocomplexity (ATM-0120468) and ARCSS programs; the NASA Land Cover and Land Use Change and EOS Interdisciplinary Science (NNG04GJ80G) programs; and by funding from MIT Joint Program on the Science and Policy of Global Change, which is supported by a consortium of government, industry and foundation sponsors