Shutao Chen

Relationship between nitrous oxide emission and winter wheat production

A 3-year field study in southeast China was performed to examine the relationship between N2O emission and winter wheat production. Over the 2002–03, 2003–04 and 2004–05 wheat-cropping seasons, N2O emissions depended on nitrogen addition, plowing practice, and preceding crop type treatments, and showed a pronounced inter-annual variation. N2O–N emission factor, the proportion of fertilizer N released as N2O–N from the wheat field, varied from 1.33% to 2.97%. The relationship between N2O emission (y) and crop yield (x) was well explained by the function y = 3.773Ln(x) + 1.46. Similarly, the function y = 4.445Ln(x) − 3.52 can be employed to address the relationship between N2O emission (y) and above ground biomass (x). About 84% and 87% of variation in seasonal N2O emission were explained by the two functions, while only 66% of the variation was represented by the N input with a linear relationship. The results of this study suggest that seasonal N2O emission of soil under winter wheat could be better predicted by crop yield and biomass than by N input.

Determination of respiration, gross nitrification and denitrification in soil profile using BaPS system

A facility of BaPS (Barometric Process Separation) was used to determine soil respiration, gross nitrification and denitrification in a winter wheat field with depths of 0-7, 7-14 and 14-21 cm. N2O production was determined by a gas chromatograph. Crop root mass and relevant soil parameters were measured. Results showed that soil respiration and gross nitrification decreased with the increase of soil depth, while denitrification did not change significantly. In comparison with no-plowing plot, soil respiration increased significantly in plowing plot, especially in the surface soil of 0-7 cm, while gross nitrification and denitrification rates were not affected by plowing. Cropping practice in previous season was found to affect soil gross nitrification in the following wheat-growing season. Higher gross nitrification rate occurred in the filed plot with preceding crop of rice compared with that of maize for all the three depths of 0-7, 7-14 and 14-21 cm. A further investigation indicated that the nitrification for all the cases accounted for about 76% of the total nitrogen transformation processes of nitrification and denitrification and the N2O production correlated with nitrification significantly, suggesting that nitrification is a key process of soil N2O production in the wheat field. In addition, the variations of soil respiration and gross nitrification were exponentially dependent on root mass (P<0.001).

Chlorophyll content and photosystem II efficiency in soybean exposed to supplemental ultraviolet-B radiation

Chlorophyll (Chl) a fluorescence parameters and rapid light curves of soybean [Glycine max (L.) Merrill] were measured by pulse amplitude modulation fluorometry. Measurements were taken during different stages of soybean growth under field conditions with 20% enhancement in ultraviolet-B (UV-B) radiation. Results showed that supplemental UV-B radiation decreased Chl contents by 5.5% (P=0.048), 8.7% (P=0.046), and 10.5% (P=0.005) in seedling, in branching-flowering, and in pod-setting stages, respectively. In the branching-flowering and pod-setting stages, maximum quantum yield of photosystem (PS) II photochemistry (Fv/Fm) decreased by 6.1% (P=0.001) and 3.0% (P=0.009), respectively. Supplemental UV-B radiation significantly decreased the effective quantum yield (Y). The photosynthetic capacity at light saturation (Pm) also decreased in both the seedling and branching-flowering stages by 28.9% (P=0.007) and 15.5% (P=0.041), respectively. However, Y and Pm showed no significant difference in the trefoil and pod-setting stages with and without the UV treatment. The light saturation parameter (Ek) decreased by 21.1% (P=0.000) and 23.2% (P=0.029) in the trefoil and seedling stages, respectively. Moreover, the initial slope (α) decreased by 21.1% (P=0.001) in the branching-flowering stage. Nonphotochemical quenching (NPQ) in the seedling stage and photochemical quenching coefficient (qp) in the branching-flowering stage decreased significantly under UV-B treatments. The results of the present study suggest that supplemental UV-B radiation adversely affected Chl content and electron transport activity in PSII and consequently decreased the photosynthetic efficiency of soybean plants.

Interannual variability in soil respiration from terrestrial ecosystems in China and its response to climate change

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 a−1 between 1970 and 2009. During this time period, on average, annual soil respiration was estimated to be 4.83 Pg C a−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.

Soil Respiration, Nitrification, and Denitrification in a Wheat Farmland Soil under Different Managements

A field experiment was conducted during the 2010 to 2011 winter wheat–growing season to understand the soil respiration (Rs ), nitrification, and denitrification rates in winter wheat farmland soil under no-tillage (NT) treatment with rice straw incorporation. The experimental treatments include NT, NT with rice straw covers on the surface (NTS), conventional tillage (CT), and CT with straw incorporation (CTS). No-tillage and straw incorporation treatments did not change the seasonal patterns of Rs , gross nitrification (Gn), and denitrification (D) rates compared with CT. Compared with the CT treatment, the NT, NTS, and CTS treatments significantly reduced Rs (P < 0.01), and the NT and NTS treatments significantly increased Gn and D (P < 0.01). CTS also significantly increased Gn (P < 0.01) but had no significant effect on D (P > 0.05). Further analysis showed that the temperature sensitivity of soil respiration (Q 10) of CT, NT, NTS, and CTS were 4.26, 1.86, 3.25, and 2.36, respectively. Our findings suggest that, compared with CT, the NT and straw incorporation treatments reduced Rs and Q 10 and increased Gn and D.

Soil Respiration and N2O Flux Response to UV-B Radiation and Straw Incorporation in a Soybean-Winter Wheat Rotation System

Field experiments were conducted in the 2008–2009 soybean and winter wheat-growing seasons to assess soil respiration (SR) and nitrous oxide (N2O) emission as affected by enhanced UV-B radiation and straw incorporation. The SR rate was measured using a soil CO2 flux system; the N2O flux was measured using a static chamber–gas chromatograph technique. The results showed that in the soybean and winter wheat-growing seasons, enhanced UV-B radiation significantly decreased the SR rates and that straw incorporation increased the SR rates compared to the control treatment. The combined treatment of UV-B and straw incorporation had no obvious influence on the SR rates. Enhanced UV-B radiation, straw incorporation, and the combination treatment increased the temperature sensitivity of SR in the soybean-growing season. The study also showed that N2O emissions were reduced by enhanced UV-B radiation and that straw incorporation had no significant effects on the mean N2O emission fluxes in the soybean and winter wheat-growing seasons. Our findings suggest that enhanced UV-B radiation may lead to a decrease in SR and in N2O emissions, straw incorporation may increase SR, and the combined treatment may have no significant influence on SR and N2O emissions from soybean–winter wheat rotation systems.

Effects of elevated O3 on soil respiration in a winter wheat–soybean rotation cropland

The increasing tropospheric ozone (O3) concentration has been reported to have negative effects on ecosystems. However, few investigations have focussed on the impacts of elevated O3 on soil respiration in cropland. This study aimed to examine the responses of soil respiration to elevated O3 with open-top chambers (OTCs) in a winter wheat (Triticum aestivum L.)–soybean (Glycine max (L.) Merr) rotation. The experiment was performed in the cropland near Nanjing city, south-east China. Seasonal changes in soil respiration rates, soil CO2 production rates, and nitrification and denitrification rates in ambient air (control) and elevated O3 (100 ppb) treatments were investigated in the 2009–10 winter wheat and 2010 soybean growing seasons. Seasonal mean soil respiration rates for the control and 100 ppb treatments were 3.16 and 2.66 μmol/m2.s, respectively, in the winter wheat growing season, and they were 3.59 and 2.51 μmol/m2.s, respectively, in the soybean growing season. Mean soil respiration rate in the control was ~29% higher than that in the 100 ppb treatment across the whole winter wheat–soybean rotation season. Elevated O3 significantly decreased soil respiration in both crops, with a larger effect observed in soybean. Mean soil CO2 production rates were reduced by ~42% in the 100 ppb O3 treatment compared with the control. No O3 effects were observed on soil nitrification and denitrification during the period monitored. A further analysis of covariance showed that soil respiration was significantly correlated with both soil temperature and moisture, and no interaction effects of O3 treatment and covariate (temperature or moisture) were observed.

Experimental Warming Effects on Soil Respiration, Nitrification, and Denitrification in a Winter Wheat-Soybean Rotation Cropland

ABSTRACT A field experiment was conducted to examine responses of soil respiration, nitrification, and denitrification to warming in a winter wheat (Triticum aestivum L.)–soybean (Glycine max (L.) Merr) rotation cropland. The results showed that seasonal variations in soil respiration were positively related to seasonal fluctuations in soil temperature. Seasonal mean soil respiration rates for the experimental warming (EW) and control (CK) plots were 3.98 ± 0.43 and 2.54 ± 0.45 μmol m−2 s−1, respectively, in the winter wheat growing season, and they were 4.59 ± 0.16 and 4.36 ± 0.08 μmol m−2 s−1, respectively, in the soybean growing season. There was a marginally significant level (p = 0.097) for mean nitrification rates between EW and CK plots. Soil temperature and moisture accounted for 58.2% and 58.1% of the seasonal variations observed in the winter wheat and soybean plots, respectively.

Characteristics of soil CO 2 fluxes and N 2 O emission in a winter wheat ecosystem under enhanced UV-B radiation

1 Jiangsu Key Laboratory of Agricultural Meteorology and Yale-NUIST Center on Atmospheric Environment, School of Environmental Science and Engineering, Nanjing University of Information Science and Technology NUIST, 219 Ningliu Road, Nanjing 210044, China. 2 Key Open Laboratory of Arid Climate Change and Disaster Reduction, Institute of Arid Meteorology, China Meteorological Administration, 2070 Donggang Eastern Road, Lanzhou 730020, China.

Ultraviolet-A Radiation Accelerated N2O Emission in Winter-Wheat Ecosystem

Extensive research has been done to find the effect of enhanced UV-B (280-320nm) radiation on ecosystem, however, the available information related to the effect of UV-A (320-400nm) on ecosystem is limited. It merits further studies due to the facts that UV-A constitutes a major portion of the solar radiation and passes through the stratospheric ozone layer almost unattenuated. To investigate the impact of UV-A radiation on trace gases N2O emission from winter-wheat ecosystem, outdoor pot experiments with simulating 0%(CK) and 20% (T) supplemental of UV-A were conducted, and static dark chamber-gas chromatograph method were used to measure N2O fluxes. Results indicated that enhanced UV-A radiation increased N2O fluxes in bare soil, which N2O fluxes of T were 2.86 times larger than that of CK (p=0.059), also accelerated significantly N2O emission from winter-wheat ecosystem, which N2O fluxes of T were 1.33 times larger than that of CK (p=0.012).