[Impacts of enhanced UV-B radiation on respiration rate, CH4 and N2O emission fluxes from rice paddy].

To investigate the impacts of enhanced UV-B radiation on respiration rate, CH4 and N2O emission fluxes from soil-rice system, outdoor pot experiment was carried out during the rice growing season in 2004. The enhanced UV-B radiation treatments were simulated by a 20% increase in its intensity. The gas emission fluxes were measured by static chamber-gas chromatograph method. Results showed that enhanced UV-B radiation (T) did not change the seasonal patterns of respiration rate, CH4 and N2O emission. Compared to the control, mean respiration rate of T was decreased by 3.11%, from (1 306.83 +/- 100.21) mg x (m2 x h)(-1) to (1 266.23 +/- 147.60) mg x (m2 x h)(-1); Mean CH4 fluxes was decreased by 15.84%, from (2.40 +/- 0.48) mg x (m2 x h)(-1) to (2.02 +/- 0.52) mg x (m2 x h)(-1); Mean N2O emission fluxes of T was increased by 5.41%, from (217.45 +/- 1.72) microg x (m2 x h)(-1) to (229.22 +/- 26.02) microg x (m2 x h)(-1), while there no significant differences (P > 0.05). Our findings suggested that enhanced UV-B radiation had no significant effects on respiration rate, CH4 and N2O emission fluxes of soil-rice system.

[Effects of elevated ultraviolet-B radiation on the chemical composition of wheat straw and the N2O emission from soil amended with the straw].

An outdoor experiment was carried out to investigate the effects of elevated ultraviolet-B radiation on the chemical composition of wheat straw, and an indoor incubation test was conducted to study the effects of the amendment of the straw on soil N2O emission. Outdoor experiment showed that the enhanced UV-B decreased the aboveground biomass of wheat, increased the lignin and total N contents of wheat straw by 94.2% and 12.3%, respectively, and decreased the C/N ratio of the straw. Incubation test showed that comparing with the amendment of conventional wheat straw, the amendment of wheat straw received enhanced UV-B radiation during plant growth increased soil N2O emission under the dry-land and flooded conditions significantly. When nitrate was applied, the soil N2O emission in the treatment with straw received enhanced UV-B radiation during plant growth was 3.2 times higher than that with the conventional straw under dry-land condition, but did not differ significantly under flooded condition. The amendment of wheat straw which received UV-B radiation during plant growth had no significant effects on soil respiration.

[Effects of management regime on soil respiration from agroecosystems].

In order to examine the effects of management regime, such as nitrogen application and plowing method, on soil respiration from farmland, the static opaque chamber-gas chromatograph method was used to measure soil CO2 fluxes in situ. The field measurement was carried out for 5 growing seasons, which were the 2002-2003 wheat, 2003 maize and soybean, 2003-2004 wheat, 2004 maize and 2004-2005 wheat seasons. Our results showed that soil respiration increased in fertilizer-applied treatments compared with no fertilizer treatment after 3 times of fertilizer application on 9 November 2002, 14 February and 26 March 2003. And the most obvious increase appeared following the third fertilizer application. No significant difference in soil respiration was found among several fertilizer application treatments. The effect of plowing depth on soil respiration was contingent on preceding cropping practice. Over the 2003-2004 wheat-growing seasons (its preceding cropping practice was rice paddy), mean soil respiration rates were not significant different (p > 0.05) between no plowing treatment and shallow plowing treatment. The shallow plowing treatment CT2 led to higher soil CO2 losses compared with no plowing treatment of NT2 in the 2004 maize-growing season, however, the significant higher (p < 0.05) soil respiration rates occurred with no plowing treatment of NT3 in the following 2004-2005 wheat-growing season. Intensive plowing (25 cm depth), compared with no plowing practice (NT4), increased soil respiration significantly during the 2004-2005 wheat-growing season. Regression analysis showed that the exponential function could be employed to fit the relationship between soil respiration and temperature. The exponential relationship yielded the Q10 values which were varied from 1.26 to 3.60, with a mean value of 2.08. To evaluate the effect of temperature on soil respiration, the CO2 emission fluxes were normalized for each treatment and each crop growing season. Plotting the normalized soil respiration against the temperature, the exponential relationship between these two parameters becomes obvious. The temperature coefficient Q10 was then evaluated as 1.66 according to the exponential relationship. Further investigation indicated that soil respiration could be well simulated by an empirical model in which the effects of both soil temperature and moisture on soil respiration were considered. This model described 54% variances of the measured 463 soil respiration rates, with a R2 of 0.54 and a p value less than 0.0001.

[Influence of enhanced UV-B radiation on respiration rate and N2O emission from soil-winter wheat system].

To investigate the impact of enhanced UV-B radiation on respiration rate and N2O emission from soil-winter wheat system, outdoor pot experiments with simulating 20% supplemental of UV-B were conducted, and static dark chamber-gas chromatograph method were used. Results indicated that the enhanced UV-B radiation did not change the seasonal pattern of respiration rate and N2O emission. Enhanced UV-B radiation declined the rate of soil-winter wheat system's respiration but had no significant impact on N2O emission in turning-green stage. While enhanced UV-B radiation declined both respiration rate and the N2O emission in elongation-pregnant stage. From heading to maturity, the respiration rate and N2O emission from soil-winter wheat system were not found to be significantly difference under UV-B radiation compared with ambient conditions. A further analysis suggested that enhanced UV-B radiation declined significantly cumulative amount of N2O from soil-winter wheat system from wheat turning green to full heading stage, while no significant impact occurred from full heading to maturity.

[Study on mechanism of enhanced UV-B radiation influencing on N2O emission from soil-winter wheat system].

To study the influencing mechanisms of enhanced UV-B radiation on the emission of N20 from soil-wheat system, outdoor pot experiments with simulating 20% supplemental level of UV-B were conducted. Results indicate that the enhanced UV-B had no significant impact on the emission of N20 from soil-wheat system in turning- green stage, but declined the N2O flux and the rate of the system's respiration in elongation stage. The impact mechanisms of enhanced UV-B radiation on the N2O flux were to directly change the nitrogen metabolism process of wheat plant, such as significantly increasing soluble protein, total nitrogen and total phosphorus in wheat leaves. But the effects of UV-B radiation on soil N2O emission may be indirect, namely, UV-B treatment by working on wheat plant significantly increased the soil available nitrogen, soil microbial biomass C and N, and also changed the ratio of soil microbial C: N(from 5.0 to 6.8) in winter-wheat rhizosphere.