不同施氮下双季稻田白天CO2交换与叶面积、生物量的相互影响

研究缓/控释氮肥、氮肥配施硝化抑制剂和微生物菌剂对稻田生态系统白天CO_2净交换、群体叶面积和生物量的影响及其相互关系,有助于进一步了解这几类新型氮肥对稻田碳同化的促进作用及增产效果。为此于2012—2013年在湖北荆州进行大田试验,设置了五种氮肥处理:常规尿素(CK)、树脂包膜控释尿素(CRU)、尿素添加硝化抑制剂氯甲基吡啶(NU)、尿素添加硝化抑制剂二甲基吡唑磷酸盐(DMPP)、尿素配施微生物菌剂(EM)。采用静态箱-气相色谱法连续观测双季稻生态系统白天的CO_2净交换通量,并在各生育期测定水稻群体的叶面积和地上生物量,分析不同氮肥处理下这些指标的变化。结果表明:水稻生长季稻田生态系统白天表现为CO_2的净吸收,净交换通量受气温、降水等气象要素影响较大,在拔节-抽穗阶段出现较高值。相比普通尿素,新型氮肥在不同程度上提高了稻田CO_2净交换,在单个水稻生长季NU提高了13.2%~51.6%的平均CO_2净吸收通量,其次为CRU提高了9.8%~34.1%。在各生育期,新型氮肥对水稻群体叶面积指数和地上生物量表现出更高的促进效果,其中以CRU最为显著,其最大峰值相比CK分别提高了12.4%~18.6%和9.1%~18.8%。通过回归分析发现,水稻群体叶面积指数与CO_2净吸收通量为线性正相关关系,地上生物量与CO_2净吸收通量为抛物线型关系,这在一定程度上说明了水稻群体生长状况与稻田生态系统CO_2同化速率间的关系。包膜控释尿素、添加硝化抑制剂、添加微生物菌剂有助于提高水稻群体叶面积和生物量,促进稻田生态系统CO_2同化,其中树脂包膜控释尿素效果最佳。

Interrelations of CO2 exchange in daytime, leaf area, and biomass with different nitrogen fertilizers applied in a double-rice cropping system

Effects of controlled-release urea, nitrification inhibitor, and microbial inoculants on net CO₂ exchange, leaf area development, and biomass production in a double-rice cropping system were investigated, for a further understanding of carbon assimilation in rice paddies with the application of these new nitrogen fertilizers. Five different fertilizer treatments were set in situ to conduct a 2-year(2012-2013) field experiment in Jingzhou, Hubei Province, i.e. CK:conventional urea, CRU:polymer-coated controlled-release urea, NU:urea containing nitrapyrin, DMPP:urea containing 3,4-dimenthylpyrazole phosphate, and EM:urea combined with effective microorganism inocula. Static chamber gas chromatography was employed to monitor CO₂ exchange fluxes in rice paddies in the daytime. Leaf area index and aboveground biomass were also measured during different rice growing stages. The results showed that CO₂ was assimilated from air to plants in the daytime during the rice growing season and net CO₂ exchange fluxes varied with the change of ambient temperature and precipitation, and attained a peak value at the jointing and heading stages. The application of new nitrogen fertilizers resulted in higher CO₂ assimilation rates, of which NU caused an increase of 13.2%~51.6%, followed by CRU at 9.8%~4.1%, each compared to CK(on average) during each rice season. Promotion of leaf area and aboveground biomass were also investigated in different growing stages, and CRU caused the highest increase for the peak values, by 12.4%~18.6% and 9.1%~18.8% respectively. Through regression analysis, a linear positive relationship was found between leaf area and CO₂ assimilation rate, and a parabolic relationship was found between aboveground biomass and CO₂ assimilation rate. Thus, the application of controlled-release urea, nitrification inhibitor, and microorganisms all contribute to the increase of leaf area and biomass and promote CO₂ assimilation in rice paddy ecosystems; controlled-release urea had the best effects.