[Show abstract][Hide abstract] ABSTRACT: Rice is the staple food in China, and the country’s enlarging population puts increasing pressure on its rice production as well as on that of the world. In this study, we estimate the impact of climate change, CO2 fertilization, crop adaptation and the interactions of these three factors on the rice yields of China using model simulation with four hypothetical scenarios. According to the results of the model simulation, the rice yields without CO2 fertilization are predicted to decrease by 3.3 % in the 2040s. Considering a constant ricegrowing
season (GS), the rice yields are predicted to increase by 3.2 %. When the effect of CO2 fertilization is integrated into the Agro-C model, the expected rice yields increase by 20.9 %. When constant GS and CO2 fertilization are both integrated into the model, the predicted rice yield increases by 28.6 %. In summary, the rice yields in China are predicted to decrease in the 2040s by 0.22 t/ha due to climate change, to increase by 0.44 t/ha due to a constant GS and to increase by 1.65 t/ha due to CO2 fertilization. The benefits of crop adaptation would completely offset the negative impact of climate change. In the future, the most of the positive effects of climate change are expected to occur in northeastern and northwestern China, and the expansion of rice cultivation in northeastern China should further enhance the stability of rice production in China.
[Show abstract][Hide abstract] ABSTRACT: Cropland soils have been shown to emit nitrous oxide (N2O) and methane (CH4) into the atmosphere and to sequester carbon when field management is improved, yet the spatiotemporal changes in the N2O and CH4 emissions and the soil organic carbon (SOC) in China's croplands are unclear with regard to an integrated global warming potential (GWP). This limits our overall evaluation of anthropogenic GHG emissions and impairs effective decision making. Based primarily on model simulations from 1980 to 2009, we estimated a 69% increase in the gross GWP of CH4 and N2O emissions, from 244 Tg CO2-eq. yr-1 in the early 1980s to 413 Tg CO2-eq. yr-1 in the late 2000s. The SOC was estimated to have increased from 54 Tg CO2-eq. yr-1 to 117 Tg CO2-eq. yr-1 during the same period. A reduction in the carbon input during the rice season, along with an improvement of synthetic nitrogen use efficiency in crops to 40%, would mitigate GHG emissions by 111 Tg CO2-eq. yr-1 and keep SOC sequestration at 82 Tg CO2 yr-1. Together, this would amount to a reduction of 193 Tg CO2-eq. yr-1, representing ~47% of the gross GWP in the late 2000s. The mitigation of GHG emissions in Henan, Shandong, Hunan, Jiangsu, Hubei, Sichuan, Anhui, Jiangxi, Guangdong and Hebei Provinces could lead to a ~66% national improvement and should be given priority.
[Show abstract][Hide abstract] ABSTRACT: It is widely recognized that global warming promotes soil organic carbon (SOC) decomposition, and soils thus emit more CO2 into the atmosphere because of the warming; however, the response of SOC decomposition to this warming in different soil textures is unclear. This lack of knowledge limits our projection of SOC turnover and CO2 emission from soils after future warming. To investigate the CO2 emission from soils with different textures, we conducted a 107-day incubation experiment. The soils were sampled from temperate forest and grassland in northern China. The incubation was conducted over three short-term cycles of changing temperature from 5°C to 30°C, with an interval of 5°C. Our results indicated that CO2 emissions from sand (>50 µm), silt (2-50 µm), and clay (<2 µm) particles increased exponentially with increasing temperature. The sand fractions emitted more CO2 (CO2-C per unit fraction-C) than the silt and clay fractions in both forest and grassland soils. The temperature sensitivity of the CO2 emission from soil particles, which is expressed as Q10, decreased in the order clay>silt>sand. Our study also found that nitrogen availability in the soil facilitated the temperature dependence of SOC decomposition. A further analysis of the incubation data indicated a power-law decrease of Q10 with increasing temperature. Our results suggested that the decomposition of organic carbon in fine-textured soils that are rich in clay or silt could be more sensitive to warming than those in coarse sandy soils and that SOC might be more vulnerable in boreal and temperate regions than in subtropical and tropical regions under future warming.
PLoS ONE 01/2014; 9(4):e95348. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rice paddies are a major anthropogenic source of the atmospheric methane. However, because of the high
spatial heterogeneity, making accurate estimations of the methane emission from rice paddies is still a big challenge, even with complicated models. Data scarcity is one of the substantial causes of the uncertainties in estimating the methane emissions on regional scales. In the present study, we discussed how data scarcity affected the uncertainties in model estimations of rice paddy methane emissions, from county/provincial scale up to national scale. The uncertainties in methane emissions from the rice paddies of China was calculated with a local-scale model and the Monte Carlo simulation. The data scarcities in five of the most sensitive
model variables, field irrigation, organic matter application, soil properties, rice variety and production were included in the analysis. The result showed that in each individual county, the within-cell standard deviation of methane flux, as calculated via Monte Carlo methods, was 13.5–89.3% of the statistical mean. After spatial aggregation, the national total methane emissions were estimated at 6.44–7.32 Tg, depending on the base scale of the modeling and the reliability of the input data. And with the given data availability, the overall aggregated standard deviation was 16.3% of the total emissions, ranging from 18.3–28.0% for early, late and middle rice ecosystems. The 95% confidence interval of the estimation was 4.5–8.7 Tg by assuming a gamma distribution. Improving the data availability of the model input variables is expected to reduce the uncertainties significantly, especially of those factors with high model sensitivities.
Geoscientific Model Development 01/2014; 7:1211-1224. · 5.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Projected changes in soil organic carbon stocks of China's croplands under different agricultural managements, 2011–2050 a b s t r a c t The timing, magnitude, and regional distribution of soil organic carbon (SOC) changes are uncertain when factoring in climate change and agricultural management practices. The goal of this study is to analyze the implications of changes in climate and agricultural management for Chinese soil carbon sequestration over the next 40 years. We used the Agro-C model to simulate climate and agricultural management scenarios to investigate the combined impacts of climate change and management on future SOC stocks in China's croplands. The model was run for croplands on mineral soils in China, which make up a total of 130 M ha of cropland. The model used climate data (years 2011–2050) from the FGOALS and PRECIS climate models based on four Intergovernmental Panel on Climate Change (IPCC) emissions scenarios. Three equidistant agricultural management scenarios were used. S0 was a current scenario, and S2 was an optimal scenario. Under the S2 scenario, crop yields increased annually by 1%, the proportion of crop residue retained in the field reached 90% by 2050, and the area of no-tillage increased to 50% of the cultivated area by 2050. The S1 scenario applied half of the increased rates in crop yields, residue retention and no-tillage area values that were used in the S2 scenario. Across all croplands in China, the results suggest that SOC will increase under all combinations of climate and management and that the effect of climate change is much smaller than the effect of changes in agricultural management. Most croplands in China show a significant increase in SOC stocks, while very few zones (mainly in northeastern China) show a decrease. Rice paddy soils under the intensive farming management scenario show higher rates of carbon sequestration than dry-land soils. The maximum carbon sequestration potential of the croplands of China is estimated to be 2.39 Pg C under S2. Annual increases in SOC stocks could offset a maximum of 2.9% of the CO 2 emissions from fossil-fuel combustion in 2009. These results suggest that China's croplands, especially rice paddies, may play an important role in C sequestration and future climate change mitigation.
[Show abstract][Hide abstract] ABSTRACT:  Soil organic carbon (SOC) in cropland is of great importance to the global carbon (C) balance and to agricultural productivity, but it is highly sensitive to human activities such as irrigation and crop rotation. It has been observed that under certain improved management practices, cropland soils can sequestrate additional C beyond their existing SOC level before reaching the C saturation state. Here we use data from worldwide, long-term agricultural experiments to develop two statistical models to determine the saturated SOC level (SOCS) in upland and paddy agroecosystems, respectively. We then use the models to estimate SOC sequestration potential (SOCP) in Chinese croplands. SOCP is the difference between SOCS and existing SOC level (SOCE). We find that the models for both the upland and paddy agroecosystems can reproduce the observed SOCS data from long-term experiments. The SOCE and SOCS stock in Chinese upland and paddy croplands (0–30 cm soil) are estimated to be 5.2 and 7.9 Pg C with national average densities of 37.4 and 56.8 Mg C ha−1, respectively. As a result, the total SOC sequestration potential is estimated to be 2.7 Pg C or 19.4 Mg C ha−1 in Chinese cropland. Paddy has a relatively higher SOCE (45.4 Mg C ha−1) than upland (34.7 Mg C ha−1) and also a greater SOCP at 26.1 Mg C ha−1 compared with 17.2 Mg C ha−1 in the upland. The SOC varies dramatically among different regions. Northeast China has the highest SOCE and SOCS density, while the Loess Plateau has the greatest SOCP density. The time required to reach SOC saturation in Chinese cropland is highly dependent on management practices applied. Chinese cropland has relatively low SOC density in comparison to the global average but could have great potentials for C sequestration under improved agricultural management strategies.
Global Biogeochemical Cycles 09/2013; 27(3):711-722. · 4.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An extensive dataset on rice phenology in China, including 202 series broadly covering the past three decades (1980s-2000s), was compiled. From these data, we estimated the responses of growth duration length to temperature using a regression model based on the data with and without detrending. Regression coefficients derived from the detrended data reflect only the temperature effect, whereas those derived from data without detrending represent a combined effect of temperature and confounding cultivar shifts. Results indicate that the regression coefficients calculated from the data with and without detrending show an average shortening of the growth duration of 4.1-4.4 days for each additional increase in temperature over the full growth cycle. Using the detrended data, 95.0% of the data series exhibited a negative correlation between the growth duration length and temperature; this correlation was significant in 61.9% of all of the data series. We then compared the difference between the two regression coefficients calculated from data with and without detrending and found a significantly greater temperature sensitivity using the data without detrending (-2.9 days °C(-1) ) than that derived from the detrended data (-2.0 days °C(-1) ) in the period of emergence to heading for the late rice, producing a negative difference in temperature sensitivity (-0.9 days °C(-1) ). This implies that short-duration cultivars were planted with increase in temperature and exacerbated the undesired phenological change. In contrast, positive differences were detected for the single (0.6 days °C(-1) ) and early rice (0.5 days °C(-1) ) over the full growth cycle, which might indicate that long-duration cultivars were favoured with climate warming, but these differences were insignificant. In summary, our results suggest that a major, temperature induced change in the rice growth duration is underway in China and that using a short-duration cultivar has been accelerating the process for late rice.
Global Change Biology 02/2013; 19(2):563-70. · 8.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Soil organic carbon (SOC) dynamics in Australian wheat-growing areas were simulated from 1960 to 2010 using Agro-C, a calibrated and validated biogeophysical model. Previously published data from field measurements were used to parameterize the Agro-C model. Model simulations show a decreasing trend in SOC over the last 50 years, mainly attributable to relatively low organic carbon (C) inputs. The rate of decrease in SOC tended to slow in the last two decades due primarily to an increase in wheat yields, which resulted in an increase in C input. Overall, we estimate that Australian wheat-growing areas, covering an area of 15.09 million hectares (Mha), lost 156 (86-222, 95% confidence interval) Tg C in the topsoil (to 30 cm depth) from 1960 to 2010. Approximately 80% of the SOC loss occurred in the period between the 1960s and the 1980s. Spatially, the SOC loss in areas with relatively high temperature and low precipitation, such as Queensland, the northern part of New South Wales and Western Australia, was more significant than that in other areas. We suggest that the loss of SOC could be halted, or even reversed, with an additional input of organic C into the soil at a minimum rate of 0.4 Mg ha(-1) yr(-1).
PLoS ONE 01/2013; 8(5):e63324. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mean residence time (MRT) of topsoil organic carbon is one critical parameter for predicting future land carbon sink dynamics. Large uncertainties remain about controls on the variability in global MRT of soil organic carbon. We estimated global MRT of topsoil (0-20 cm) organic carbon in terrestrial ecosystems and found that mean annual air temperature, annual precipitation, and topsoil nitrogen storage were responsible for the variability in MRT. An empirical climate and soil nitrogen - based (Clim&SN) model could be used to explain the temporal and spatial variability in MRT across various ecosystems. Estimated MRT was lowest in the low-latitude zones, and increased toward high-latitude zones. Global MRT of topsoil organic carbon showed a significant declining tendency between 1960 and 2008, particularly in the high-latitude zone of the northern hemisphere. The largest absolute and relative changes (0.2% per yr) in MRT of topsoil organic carbon from 1960 to 2008 occurred in high-latitude regions, consistent with large carbon stocks in, and greater degree of climate change being experienced by, these areas. Overall, global MRT anomalies (differences between MRT in each year and averaged value of MRT from 1960 to 2008) of terrestrial topsoil organic carbon were decreasing from 1960 to 2008. Global MRT anomalies decreased significantly (P<0.001) with the increase of global temperature anomalies, indicating that global warming resulted in faster turnover rates of topsoil organic carbon.
Global and Planetary Change 01/2013; 100(1):99-108. · 3.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Soil respiration is an important process in terrestrial carbon cycle. Concerning terrestrial ecosystems in China, quantifying the spatiotemporal pattern of soil respiration at the regional scale is critical in providing a theoretical basis for evaluating carbon budget. In this study, we used an empirically based, semi-mechanistic model including climate and soil properties to estimate annual soil respiration from terrestrial ecosystems in China from 1970 to 2009. We further analyzed the relationship between interannual variability in soil respiration and climatic factors (air temperature and precipitation). Results indicated that the distribution of annual soil respiration showed clear spatial patterns. The highest and lowest annual soil respiration rates appeared in southeastern China and northwestern China, respectively, which was in accordance with the spatial patterns of mean annual air temperature and annual precipitation. Although the mean annual air temperature in northwestern China was higher than that in some regions of northeastern china, a greater topsoil organic carbon storage in northeastern China might result in the higher annual soil respiration in this region. By contrast, lower temperature, less precipitation and smaller topsoil organic carbon pool incurred the lowest annual soil respiration in northwestern China. Annual soil respiration from terrestrial ecosystems in China varied from 4.58 to 5.19 Pg C•yr-1 between 1970 and 2009. During this time period, on average, annual soil respiration was estimated to be 4.83 Pg C•yr-1. Annual soil respiration in China accounted for 4.93%-6.01% of the global annual soil CO2 emission. The interannual variability in soil respiration depended on the interannual variability in precipitation and mean air temperature. In order to reduce the uncertainty in estimating annual soil respiration at regional scale, more in situ measurements of soil respiration and relevant factors (e.g. climate, soil and vegetation) should be made simultaneously and historical soil property data sets should also be established.
Science China Earth Science 12/2012; · 1.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, we investigated how climate, crop management and variety renewal have interactively affected the rice yields in China for the past three decades. Using the Agro-C model and census yields, the parameters of the photosynthetic ability during the past three decades in the various Agro-ecological Zones were estimated. The Agro-C model, which uses grid-based datasets of climate, crop management and variety renewal, was used to simulate the change in rice yield under various explorative scenarios. Based on these results, we deduced the relative contribution of various factors to the rice yield. The annual increase in rice yields due to genetic improvement in the various AEZs was 0.31–1.63% for single rice, 0.29–1.34% for early rice and 0.07–1.70% for late rice. The rice yield over the past three decades, including all cultivated types, achieved a 79 kg ha−1 or a 1.8% increase per year. The increase in rice yield over the past three decades is comprised of increases that can be attributed to climate (4.4%), management (9.3%) and variety (38.9%). Genetic improvement is the decisive factor and contributed to 74.0% of the total increase in yield.
Field Crops Research 09/2012; 136:65-75. · 2.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
Terrestrial ecosystems may act as a source or a sink for the atmospheric greenhouse gases (GHG) of CO2, CH4 and N2O, depending on land use and management. Over the last decade, scientists have made great efforts to estimate China's terrestrial GHG emissions and uptake. Field measurement-based data, inventory–satellite-based data and process-based models were used in these estimates. This presentation provides an overview of existing estimates from various studies.
Over the period from 1980 to the late 1990s/early 2000s, a net terrestrial carbon sink was estimated to be 190±63Tg C/yr in China, of which ~56% comes from biomass carbon. The estimated higher carbon sink occurred in south and southeast China. Forest ecosystems dominated the carbon sinks, accounting for ~45% of the national total. Large–scale reforestation/afforestation contributes ~40% to the total forest carbon sink. Methane emissions from natural wetlands and irrigated rice cultivation were estimated to be 1.8±0.1Tg/yr and 7.7±1.9Tg/yr, respectively. Higher CH4 emissions occurred in southern China, where double-rice cropping systems dominated, accounting for ~55% of the total rice paddy emissions in China. Methane uptake by aerobic soils was reported to be 2.56Tg/yr. Nitrous oxide emissions were estimated to be 1.32±0.27Tg/yr, of which ~45% comes from cropland. The synthetic fertilizer N-induced direct N2O emission accounts for ~63% of the total cropland emissions, and increased from 1980 to 2000 with an average rate of 14.4Gg/yr. A substantial N2O emission occurred in eastern and south central China, accounting for ~65% of the total cropland emissions. In light of global warming potential at a 100- year time horizon, the terrestrial carbon sink amounted to ~0.76Pg CO2-eq/yr in China. Approximately 83% of the sink was offset by terrestrial CH4 and N2O emissions. The anthropogenic sources of CH4 and N2O offset approximately 40% of the sink.
Although scientists have made great efforts to estimate China’s terrestrial GHG emissions and uptake, large uncertainties existed in these estimates, especially for the soil carbon sequestration and emission. Special attention should be given to reduce the uncertainties. Moreover, the large–scale reforestation/afforestation has greatly contributed to terrestrial carbon sink in China, and the implementation of reforestation/afforestation will be continued. Understanding the future changes in the reforestation/afforestation-induced carbon sink is required.
[Show abstract][Hide abstract] ABSTRACT: China has implemented a soil testing and fertilizer recommendation (STFR) program to reduce the over-usage of synthetic nitrogen (N) fertilizer on cereal crops since the late 1990 s. Using province scale datasets, we estimated an annual reduction rate of 2.5-5.1 kg N ha(-1) from 1998 to 2008 and improving grain yields, which were attributed to the balanced application of phosphate and potassium fertilization. Relative to the means for 1998-2000, the synthetic N fertilizer input and the corresponding N-induced N(2)O production in cereal crops were reduced by 22 ± 0.7 Tg N and 241 ± 4 Gg N(2)O-N in 2001-2008. Further investigation suggested that the N(2)O emission related to wheat and maize cultivation could be reduced by 32-43 Gg N(2)O-N per year in China (26%-41% of the emissions in 2008) if the STFR practice is implemented universally in the future.
[Show abstract][Hide abstract] ABSTRACT: Recent spatiotemporal soil organic carbon (SOC) changes in croplands of China were estimated by using a modified and validated Agro-C model. Estimates revealed that SOC in approximately 81% of China's croplands increased from 1980 to 2009. SOC increases in east, central, south, and southwest China were more significant than those in other regions of the country, while a decrease in SOC was pronounced in Heilongjiang Province in northeast China. Overall, we estimated that China's croplands covering an area of 130 million hectare sequestered 730 (329 to 1095) Tg C in the topsoil to 30 cm depth, during this period. Approximately 73% of the SOC sequestration occurred in east, central and south China. The carbon sequestration was attributed to the improvement of crop production and the decrease in the removal of crop residues. Soils rich in organic carbon that received relatively low carbon inputs during the same period, however, suffered net carbon losses in Heilongjiang Province.
Global and Planetary Change 01/2012; 82–83:115-128. · 3.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Negative climate impacts on crop yield increase pressures on food security in China. In this study, climatic impacts on cereal yields (rice, wheat and maize) were investigated by analyzing climate-yield relationships from 1980 to 2008.
Results indicated that warming was significant, but trends in precipitation and solar radiation were not statistically significant in most of China. In general, maize is particularly sensitive to warming. However, increase in temperature was correlated with both lower and higher yield of rice and wheat, which is inconsistent with the current view that warming results in decline in yields. Of the three cereal crops, further analysis suggested that reduction in yields with higher temperature is accompanied by lower precipitation, which mainly occurred in northern parts of China, suggesting droughts reduced yield due to lack of water resources. Similarly, a positive correlation between temperature and yield can be alternatively explained by the effect of solar radiation, mainly in the southern part of China where water resources are abundant.
Overall, our study suggests that it is inter-annual variations in precipitation and solar radiation that have driven change in cereal yields in China over the last three decades.
Journal of the Science of Food and Agriculture 12/2011; 92(8):1643-52. · 1.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Daily air temperature is a measurement that is required by many biogeochemical models. This study compared daily maximum (T max), minimum (T min) and mean (T mean) air temperature observations collected at 678 standard meteorological stations of China in 2003 with estimates derived from daytime and night-time land surface temperature (LST) observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) on board TERRA and AQUA satellites. Correlation analysis showed that the determination coefficients (R 2 > 0.81) between models using night-time LSTs and the observed air temperatures were higher than those using daytime LSTs (R 2 > 0.57), but with significant seasonal variation. Though estimates derived from coupled daytime and night-time LSTs were more accurate than using night-time or daytime LSTs alone, the available pixels were substantially reduced. Four empirical models were established for T max, T min and T mean with MODIS night-time LSTs alone, or with coupled daytime and night-time LSTs, respectively. Solar declination was incorporated into the models to simulate seasonal variation of the correlations. Model validation showed that percentage of residuals within –3°C to 3°C ranged approximately from 60.2% to 74.3%, 64.4% to 69.9% and 76.8% to 85.7% for T max, T min and T mean, respectively. It was concluded that night-time LST was the optimum predictor for estimating daily T min, T mean and even T max when considering both the performance of the models and the availability of the LST data. Moreover, there was no significant difference between LSTs of TERRA and AQUA for estimating daily air temperatures.
International Journal of Remote Sensing 12/2011; 32(24):9415-9440. · 1.36 Impact Factor