沼液中$\mathrm{HCO}_{3}^{-}$对土壤CO2释放的影响

【目的】揭示沼液施用过程中$\mathrm{HCO}_{3}^{-}$对土壤CO₂释放的影响机制。【方法】分别向土壤添加沼液原液(BS)、原液去除$\mathrm{HCO}_{3}^{-}$ (BS-B)、去离子水加HC(W+B)和去离子水(W)后,对土壤进行30 d的培养,观测土壤CO₂释放特征。【结果】BS处理下,土壤CO₂释放速率从2 h时的36.6 mg/(kg·h)快速降至30 d时的2.7 mg/(kg·h),BS-B处理CO₂释放速率从最高时的9.3 mg/(kg·h)(第1 天)降至1.9 mg/(kg·h)(第30 天),前者显著高于后者。30 d内,BS处理下土壤CO₂累计释放193.0 g/kg,BS-B处理下仅为97.8 g/kg。由此可见,沼液中的$\mathrm{HCO}_{3}^{-}$显著促进了土壤CO₂的释放。相比较而言,W+B处理下土壤CO₂释放速率从最高时的12.0 mg/(kg·h)降至15 d时的0.6 mg/(kg·h),培养期内土壤CO₂累计释放54.5 g/kg;W处理下土壤CO₂释放速率在培养期内的变化为0.2~1.6 mg/(kg·h),CO₂累计释放34.4 g/kg。培养期内,BS处理下土壤CO₂释放量是BS-B与W+B两处理之和的1.6倍。$\mathrm{HCO}_{3}^{-}$对土壤CO₂释放的贡献主要发生在上覆水层,且以$\mathrm{HCO}_{3}^{-}$水解及$\mathrm{NH}_{4}^{+}$氧化贡献的H⁺与$\mathrm{HCO}_{3}^{-}$的相互作用为主要途径。【结论】施用沼液后,大量$\mathrm{HCO}_{3}^{-}$的添加是引起土壤CO₂释放加快且释放量增加的主要原因之一,土壤CO₂释放的增加并非$\mathrm{HCO}_{3}^{-}$本身与除$\mathrm{HCO}_{3}^{-}$之外沼液其他组分贡献的加和,二者存在显著的协同作用。

Effects of $\mathrm{HCO}_{3}^{-}$ in the biogas slurry on CO2 release from soils

【Objective】 The biogas slurry is rich not only in N, but also in $\mathrm{HCO}_{3}^{-}$. This study aimed to reveal the impact of $\mathrm{HCO}_{3}^{-}$ on the release of CO₂. 【Mothed】 when the biogas slurry was applied in farmlands, by arranging and adding four types of culture mediums, namely, the original biogas slurry, original liquid for removing $\mathrm{HCO}_{3}^{-}$, deionized water plus $\mathrm{HCO}_{3}^{-}$ and deionization water, designated as BS, BS-B, W+B and W treatments, respectively, to the paddy soil for a 30-day cultivation experiment. 【Result】 The soil CO₂ release rates were observed. The results indicated that under the BS treatment, the soil CO₂ release rates decreased rapidly from 36.6 mg/(kg·h) at 2 h to 2.7 mg/(kg·h) at 30 d, and those for the BS-B treatment decreased from the highest 9.3 mg/(kg·h) at 1 d to 1.9 mg/(kg·h) at 30 d. The CO₂ release rates in the BS treatment were significantly higher than those in the BS-B. Within 30 d, the cumulative CO₂ emission under the BS was 193.0 g/kg, while that in BS-B was only 97.8 g/kg. It was evident that the presence of $\mathrm{HCO}_{3}^{-}$ in the biogas slurry significantly increased the release of CO₂ from the soil. In comparison, the CO₂ release rate under the W+B treatment decreased from the highest value of 12.0 mg/(kg·h) to 0.6 mg/(kg·h) at 15 d, with a cumulative CO₂ emission of 54.5 g/kg during the culture period. The CO₂ release rate under W treatment varied from 0.2 to 1.6 mg/(kg·h) during the culture period, and the cumulative CO₂ emission was only 34.4 g/kg. It is evident that the CO₂ emission under the BS treatment was 1.6 times higher than that under BS-B and W+B treatments together. Further analysis indicated that the contribution of $\mathrm{HCO}_{3}^{-}$ to the CO₂ release in the paddy soils mainly occurred in the overlying water layer, which was dominated by $\mathrm{HCO}_{3}^{-}$ hydrolysis and the reaction between $\mathrm{HCO}_{3}^{-}$ and H⁺ from $\mathrm{NH}_{4}^{+}$ oxidation. 【Conclusion】 With biogas slurry applying, the addition of a large amount of $\mathrm{HCO}_{3}^{-}$ was one of the main reasons for the acceleration and increase of soil CO₂ release, which was not just a simple sum of contributions from HC and the other components of the biogas slurry, and there was a significant synergistic effect between the two.