[Impacts of elevated ozone concentration on N2O emission from arid farmland].

To investigate the impact of elevated surface ozone (O3) concentration on nitrous oxide (N2O) emission from arid farmland, field experiments were carried out during winter-wheat and soybean growing seasons under the condition of simulating O3 concentrations, including free air (CK), 100 nL x L(-1) O3 concentration (T1), and 150 nL x L(-1) O3 concentration (T2). N2O emission fluxes were measured by static dark chamber-gas chromatograph method. The results showed that the accumulative amount of N2O (AAN) were decreased by 37.8% (P = 0.000 ) and 8.8% (P = 0.903 ) under T1 and T2 treatments, respectively, in the turning-green stage of winter wheat. In the elongation-booting stage, ANN were decreased by 15.0% (P = 0.217) and 39.1% (P = 0.000) under T1 and T2 treatments, respectively. ANN were decreased by 18.9% (P = 0.138) and 25.6% (P = 0.000) under T1 and T2 treatments, respectively, during the whole winter-wheat growing season. No significant impact of elevated O3 concentration on N2O emission from soil-soybean system was found due to the less rainfall during the soybean growing season, drought had a stronger stress on soybean than O3 concentration. The results of this study suggested that elevated O3 concentration could reduce N2O emission from arid farmland.

[Effects of elevated ozone concentration on CO2 emission from soil-winter wheat system].

To investigate the impact of elevated ozone (O3) on CO2 emission from soil-winter wheat system, outdoor experiments with simulating elevated O3 concentration were conducted, and static dark chamber-gas chromatograph method was used to measure CO2 emission fluxes. Results indicated that the elevated O3 did not change the seasonal pattern of CO2 emissions from soil-winter wheat system, but significantly decreased CO2 emission fluxes during turning-green stage and elongation-pregnant stage. From heading to maturity, CO2 emission fluxes were not found to be significant difference under 100 nL x L(-1) O3 treatment compared with the control, while 150 nL x L(-1) O3 treatment significantly declined CO2 emission fluxes. Significant relationships were found between respiration rate and air temperature under the control, 100 nL x L(-1) and 150 nL x L(-1) O3 treatment, and the fitting equation determined coefficients R2 were 0.139, 0.513 and 0.211, respectively. In addition, the Q10 (temperature sensitivity coefficients) for soil-winter wheat system's respiration were 1.13, 1.58 and 1.21, respectively. The results of this study suggested that elevated O3 could reduce CO2 emissions from agroecosystem.

[Effects of simulated nitrogen deposition on soil respiration in northern subtropical deciduous broad-leaved forest].

To investigate the effects of elevated nitrogen deposition on forest soil respiration, a simulated nitrogen deposition field experiment was conducted in northern subtropical deciduous broad-leave forest from April 2008 to April 2009. Nitrogen treatments included the control (no N addition, CK), low-N [50 kg x (hm2 x a)(-1), T(L)], medium-N [100 kg x (hm2 x a)(-1), T(M)], and high-N [150 kg x (hm2 x a)(-1), T(H)]. The respiration rates were measured by a static chamber-gas chromatograph method. Results showed that nitrogen deposition did not change the seasonal and daily variation patterns of soil respiration. Compared to the control, T(L), T(M) and T(H) treatments reduced soil annual average respiration rates by 8.51%, 9.74% and 11.24%, respectively. Meanwhile, T(L), T(M) and T(H) treatments decreased daily average soil respiration rates by 4.42%, 11.09% and 12.17%, respectively. Significant relationship was found between soil respiration rate and soil temperature. The Q10 (temperature sensitivity coefficients) for soil respiration of CK, T(L), T(M), and T(H) treatments were 2.53, 3.22, 2.64 and 2.92, respectively. Our findings suggested that nitrogen deposition reduced soil respiration, and increased soil respiration temperature sensitivity in northern subtropical deciduous broad-leave forest.

[Influence of enhanced UV-B radiation and straw application on soil respiration in soybean field].

Field experiment was carried out in 2008 in order to investigate the effects of enhanced UV-B radiation and straw application on soil respiration in soybean field. LI-8100 automated soil CO2 flux system was used to measure soil respiration under 20% enhanced UV-B radiation, straw application, 20% enhanced UV-B radiation + straw application and control. Environmental factors such as air temperature, soil temperature and moisture were also measured. Results indicated that supplemental UV-B radiation reduced soil respiration rate by 30.31%, straw application increased soil respiration rate by 14.51%, while enhanced UV-B radiation + straw application combined treatment had no significant effect on soil respiration. Enhanced UV-B radiation enhanced the carbon conversion rate of straw. Significant relationship were found between soil respiration rate and soil temperature under the control, enhanced UV-B, straw application, and enhanced UV-B + straw application, the fitting equation determined coefficients R2 were 0.434, 0.563, 0.451 and 0.513. The Q10 (temperature sensitivity coefficients) for soil respiration were 1.55, 1.91, 1.80 and 1.71, respectively. It was reflected that enhanced UV-B radiation, straw application and enhanced UV-B radiation + straw returning increased the Q10 for soil respiration.

[Influence of enhanced UV-B radiation on chlorophyll fluorescence characteristics of soybean].

To investigate the influence of enhanced UV-B radiation on chlorophyll fluorescence characteristics of soybean, pulse amplitude modulation fluorometer was employed to measure the fluorescence parameters and rapid light curves during different growth stages under the condition of simulating 20% enhancement of UV-B. Results showed that enhanced UV-B radiation reduced the chlorophyll contents by 5.03%, 7.70% and 10.38% in seedling, branching-flowering and pod-setting periods, respectively. In branching-flowering period, the value of Fv/Fm decreased by 6.13%. In seedling and branching-flowering periods, effective quantum yield(Y) diminished significantly during PAR >366 micromol x (m2 x s)(-1), the maximal potential relative electron transport rate (Pm) diminished by 28.92% and 15.49%, respectively. But Y and Pm had no significant difference in 3-leave and pod setting periods. Semi-light saturation points (l(k)) were diminished by 21.18% and 23.17% in 3-leave and seedling periods. Initial slope (a) was decreased by 21.05% in branching-flowering period. Enhanced UV-B radiation also significantly reduced non-photochemical quenching (NPQ) during PAR >366 micromol x (m2 x s)(-1) in seedling period and photochemical quenching (qP) during PAR >366 micromol x (m2 x s)(-1) in branching-flowering period. The results of this study suggested that enhanced UV-B radiation inhibited electron transport activity of PS II, injured light-harvesting systems and dissipative protection mechanisms, damaged photosynthesis system, thus diminished photosynthetic efficiency of soybean.