Studies on the effect of elevated CO2 on C dynamics in cultivated croplands are critical to a better understanding of the C cycling in response to climate change in agroecosystems. To evaluate the effects of elevated CO2 and different N fertilizer application levels on soil respiration, winter wheat （Triticum aestivum L. cv. Yangmai 14） plants were exposed to either ambient CO2 or elevated CO2 （ambient [CO2] ＋ 200 μmol mol-1）, under N fertilizer application levels of 112.5 and 225 kg N ha-1 （as low N and normal N subtreatments, respectively）, for two growing seasons （2006-2007 and 2007-2008） in a rice-winter wheat rotation system typical in China. A split-plot design was adopted. A root exclusion method was used to partition soil respiration （RS） into heterotrophic respiration （RH） and autotrophic respiration （RA）. Atmospheric CO2 enrichment increased seasonal cumulative RS by 11.8% at low N and 5.6% at normal N when averaged over two growing seasons. Elevated CO2 significantly enhanced （P 〈 0.05） RS （12.7%）, mainly due to the increase in RH （caused by decomposition of larger amounts of rice residue under elevated CO2） during a relative dry season in 2007-2008. Higher N supply also enhanced RS under ambient and elevated CO2. In the 2007-2008 season, normal N treatment had a significant positive effect （P 〈 0.01） on seasonal cumulative RS relative to low N treatment when averaged across CO2 levels （16.3%）. A significant increase in RA was mainly responsible for the enhanced RS under higher N supply. The correlation （r2） between RH and soil temperature was stronger （P 〈 0.001） than that between RS and soil temperature when averaged across all treatments in both seasons. Seasonal patterns of RA may be more closely related to the plant phenology than soil temperature. The Q10 （the multiplier to the respiration rate for a 10 ℃ increase in soil temperature） values of RS and RH were not affected by elevated CO2 or higher N supply. These results main
SUN Hui-FengZHU Jian-GuoXIE Zu-BinLIU GangTANG Hao-Ye
Biochar added to soil can improve crop growth through both direct and indirect effects, particularly in acidic, highly weathered soils in subtropical and tropical regions. However, the mechanisms of biochar improving crop growth are not well understood. The objectives of this study were i) to determine the crop responses to biochar addition and ii) to understand the effect of biochar addition on N use efficiency. Seven acidic red soils varying in texture, p H, and soil nutrient were taken from southern China and subjected to four treatments: zero biochar and fertilizer as a control(CK), 10 g kg-1biochar(BC), NPK fertilizers(NPK), and 10 g kg-1biochar plus NPK fertilizers(BC+NPK).15N-labeled fertilizer was used as a tracer to assess N use efficiency. After a 46-d pot experiment,biochar addition increased soil p H and available P, and decreased soil exchangable Al3+, but did not impact soil availabe N and cation exchange capacity(P > 0.05). The N use efficiency and N retained in the soil were not significantly affected by biochar application except for the soil with the lowest available P(3.81 mg kg-1) and highest exchanageable Al3+(4.54 cmol kg-1). Greater maize biomass was observed in all soils amended with biochar compared to soils without biochar(BC vs. CK, BC+NPK vs. NPK). This agronomic effect was negatively related to the concentration of soil exchangeable Al3+(P < 0.1). The results of this study implied that the liming effect of biochar improved plant growth through alleviating Al toxicity and P deficiency, especially in poor acidic red soils.
