Xiaonan Duan

Bio: Xiaonan Duan is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Phragmites & Greenhouse gas. The author has an hindex of 14, co-authored 18 publications receiving 860 citations.

Soil carbon sequestrations by nitrogen fertilizer application, straw return and no-tillage in China's cropland

Abstract: Soil as the largest global carbon pool has played a great role in sequestering the atmospheric carbon dioxide (CO(2)). Although global carbon sequestration potentials have been assessed since the 1980s, few investigations have been made on soil carbon sequestration (SCS) in China's cropland. China is a developing country and has a long history of agricultural activities. Estimation of SCS potentials in China's cropland is very important for assessing the potential measures to prevent the atmospheric carbon rise and predicting the atmospheric CO(2) concentration in future. After review of the available results of the field experiments in China, relationships between SCS and nitrogen fertilizer application, straw return and no-tillage (NT) practices were established for each of the four agricultural regions. According to the current agricultural practices and their future development, estimations were made on SCS by nitrogen fertilizer application, straw return and NT in China's cropland. In the current situation, nitrogen fertilizer application, straw return and zero tillage can sequester 5.96, 9.76 and 0.800 Tg C each year. Carbon sequestration potential will increase to 12.1 Tg C yr(-1) if nitrogen is fertilized on experts' recommendations. The carbon sequestration potentials of straw return and NT can reach 34.4 and 4.60 Tg C yr(-1) when these two techniques are further popularized. In these measures, straw return is the most promising one. Full popularization of straw return can reduce 5.3% of the CO(2) emission from fossil fuel combustion in China in 1990, which meets the global mean CO(2) reduction requested by the Kyoto Protocol (5.2%). In general, if more incentive policies can be elaborated and implemented, the SCS in China's cropland will be increased by about two times. So, popularization of the above-mentioned agricultural measures for carbon sequestration can be considered as an effective tool to prevent the rapid rise of the atmospheric CO(2) in China.

Impact of Elevated O3 on Soil Microbial Community Function Under Wheat Crop

Abstract: This study was initiated to explore the effects of ozone (O-3) exposure on potted wheat roots and soil microbial community function Three treatments were performed: (1) Air with daily averaged O-3 concentration of 4-10 ppb (control situation, CK), (2) Air plus 8 h averaged O-3 concentration of 761 ppb (O-3-1), and (3) Air plus 8 h averaged O-3 concentration of 1188 ppb (O-3-2) In treatments with elevated O-3 concentration (O-3-1 and O-3-2), the root and shoot biomass were reduced by 25% and 18%, respectively, compared to the control treatment (CK) On the other hand, root activity was significantly reduced by 58% and 908% in the O-3-1 and O-3-2 treatments, respectively, compared to CK The soil microbial biomass was significantly reduced only in the highest O-3 concentration (O-3-2 treatment) in the rhizosphere soil Soil microbial community composition was assessed under O-3 stress based on the changes in the sole carbon source utilization profiles of soil microbial communities using the Biolog (TM) system Principal component analysis showed that there was significant discrimination in the sole-carbon source utilization pattern of soil microbial communities among the O-3 treatments in rhizosphere soil; however, there was none in the bulk soil In rhizosphere soil, the functional richness of the soil microbial community was reduced by 27% and 38% in O-3-1 and O-3-2 treatments, respectively, compared to CK O-3-2 treatment remarkably decreased the Shannon diversity index of soil microbial community function in rhizosphere soil, but the O-3-1 treatment did not In the dominant microorganisms using carbon sources of carbohydrates and amino acids groups were significantly reduced by an elevated O-3 concentration in the rhizosphere soil Our study shows that the elevated ozone levels may alter microbial community function in rhizosphere soil but not in the bulk soil Hence, this suggests that O-3 effects on soil microbes are caused by O-3 detriments on the plant, but not by the O-3 direct effects on the soil microbes

Net mitigation potential of straw return to Chinese cropland: estimation with a full greenhouse gas budget model

Abstract: Based on the carbon-nitrogen cycles and greenhouse gas (GHG) mitigation and emission processes related to straw return and burning, a compound greenhouse gas budget model, the "Straw Return and Burning Model" (SRBM), was constructed to estimate the net mitigation potential of straw return to the soil in China. As a full GHG budget model, the SRBM addressed the following five processes: (1) soil carbon sequestration, (2) mitigation of synthetic N fertilizer substitution, (3) methane emission from rice paddies, (4) additional fossil fuel use for straw return, and (5) CH4 and N2O emissions from straw burning in the fields. Two comparable scenarios were created to reflect different degrees of implementation for straw return and straw burning. With GHG emissions and mitigation effects of the five processes converted into global warming potential (GWP), the net GHG mitigation was estimated. We concluded that (1) when the full greenhouse gas budget is considered, the net mitigation potential of straw return differs from that when soil carbon sequestration is considered alone; (2) implementation of straw return across a larger area of cropland in 10 provinces (i.e., Shanghai, Jiangsu, Zhejiang, Fujian, Jiangxi, Hubei, Hunan, Guangdong, Guangxi, and Hainan) will increase net GHG emission; (3) if straw return is promoted as a feasible mitigation measure in the remaining provinces, the total net mitigation potential before soil organic carbon (SOC) saturation will be 71.89 Tg CO2 equivalent (eqv)/yr, which is equivalent to 1.733% of the annual carbon emission from fossil fuel use in China in 2003; (4) after SOC saturation, only 13 of 21 provinces retain a relatively small but permanent net mitigation potential, while in the others the net GHG mitigation potential will gradually diminish; and (5) the major obstacle to the feasibility or permanence of straw return as a mitigation measure is the increased CH4 emission from rice paddies. The paper also suggests that comparable scenarios in which all the related carbon-nitrogen cycles are taken into account be created to estimate the mitigation potentials of organic wastes in different utilizations and treatments.

Climate Change 2007: The Physical Science Basis.

Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

Effects of straw carbon input on carbon dynamics in agricultural soils: a meta-analysis.

Abstract: Straw return has been widely recommended as an environmentally friendly practice to manage carbon (C) sequestration in agricultural ecosystems. However, the overall trend and magnitude of changes in soil C in response to straw return remain uncertain. In this meta-analysis, we calculated the response ratios of soil organic C (SOC) concentrations, greenhouse gases (GHGs) emission, nutrient contents and other important soil properties to straw addition in 176 published field studies. Our results indicated that straw return significantly increased SOC concentration by 12.8 ± 0.4% on average, with a 27.4 ± 1.4% to 56.6 ± 1.8% increase in soil active C fraction. CO2 emission increased in both upland (27.8 ± 2.0%) and paddy systems (51.0 ± 2.0%), while CH4 emission increased by 110.7 ± 1.2% only in rice paddies. N2O emission has declined by 15.2 ± 1.1% in paddy soils but increased by 8.3 ± 2.5% in upland soils. Responses of macro-aggregates and crop yield to straw return showed positively linear with increasing SOC concentration. Straw-C input rate and clay content significantly affected the response of SOC. A significant positive relationship was found between annual SOC sequestered and duration, suggesting that soil C saturation would occur after 12 years under straw return. Overall, straw return was an effective means to improve SOC accumulation, soil quality, and crop yield. Straw return-induced improvement of soil nutrient availability may favor crop growth, which can in turn increase ecosystem C input. Meanwhile, the analysis on net global warming potential (GWP) balance suggested that straw return increased C sink in upland soils but increased C source in paddy soils due to enhanced CH4 emission. Our meta-analysis suggested that future agro-ecosystem models and cropland management should differentiate the effects of straw return on ecosystem C budget in upland and paddy soils.

Greenhouse Gas Emissions from Reservoir Water Surfaces: A New Global Synthesis

Abstract: Collectively, reservoirs created by dams are thought to be an important source of greenhouse gases (GHGs) to the atmosphere. So far, efforts to quantify, model, and manage these emissions have been limited by data availability and inconsistencies in methodological approach. Here, we synthesize reservoir CH4, CO2, and N2O emission data with three main objectives: (1) to generate a global estimate of GHG emissions from reservoirs, (2) to identify the best predictors of these emissions, and (3) to consider the effect of methodology on emission estimates. We estimate that GHG emissions from reservoir water surfaces account for 0.8 (0.5-1.2) Pg CO2 equivalents per year, with the majority of this forcing due to CH4. We then discuss the potential for several alternative pathways such as dam degassing and downstream emissions to contribute significantly to overall emissions. Although prior studies have linked reservoir GHG emissions to reservoir age and latitude, we find that factors related to reservoir productivity are better predictors of emission.