Abstract:

Soil organic matter (SOM), the largest organic carbon reservoir in terrestrial ecosystems, plays an important role in global carbon cycles. The addition of exogenous substances alters the turnover of soil organic matter, and thus produces priming effects. If antibiotics that can inhibit bacteria or fungi are added to the soil as exogenous substances, substrate-induced respiration is selectively inhibited. Although extensive research has been conducted on the factors and mechanisms of the priming effect of soil organic matter, there has been no research on the priming effect on the selective induction of respiration inhibition technology for soil organic matter utilization in karst ecosystems at different successional stages. Therefore, this study used the “space instead of time” method to investigate the influence of cycloheximide and streptomycin on soil organic matter in different successional stages of karst ecosystems in southwestern China. In September 2021, soil samples from primary forests, secondary forests, shrubland, grasslands, and cornfields were collected from Gongcheng Yao Autonomous County in the Guangxi Zhuang Autonomous Region, which has a subtropical monsoon climate. The soil was brown and calcareous. The results showed that the addition of single or combined antibiotics that inhibit bacteria or fungi to the soil induced an increase in respiration rate. Owing to the strong adsorption ability of alkaline streptomycin on the soil particles, its inhibitory effect on induced respiration was not significant. The addition of cycloheximide significantly inhibited soil respiration, which was dominated by r-strategy or k-strategy microorganisms. The soil organic matter priming effect index under different successional stages was less than 1, indicating the occurrence of negative priming effects, which are displayed in the form of apparent priming effects and real priming effects. Although streptomycin and cycloheximide can inhibit bacteria and fungi, they cannot inhibit archaeal, viral, or extracellular enzymes. Therefore, when streptomycin and cycloheximide are used alone or in combination, soil organic matter can be utilized by microorganisms, resulting in a change in the relative proportion of functional groups. The fundamental reason for these changes lies in different soil microbial community structures and species under different successional vegetation conditions. Different microbes usually have different preferences and specificities for substrates, resulting in varying degrees of decomposition on soil organic matter. As a result, the relative proportion of soil organic matter functional groups changed owing to in vitro modification and in vivo turnover of microorganisms. Moreover, this result contradicts the traditional hypothesis of substrate priority utilization, that is, soil microorganisms preferentially utilize the input of exogenous organic matter rather than relying on the existing organic matter in the soil. The results showed a decrease in the decomposed organic matter, which triggered a negative priming effect. The results indicated that the soil carbon functional groups were relatively stable. Considering that the obtained results were from simulation experiments, further experiments are needed regarding the effects of cycloheximide and streptomycin on in situ soil organic matter from karst ecosystems at different successional stages. In addition, by applying the selective induction of respiration inhibition technology for soil organic matter utilization with streptomycin and cycloheximide, it not only considers the soil texture but also clarifies the vegetation succession stage of the soil to avoid experimental deviations from the expected results. These results provide a theoretical foundation for elucidating the negative excitation effect of soil organic matter and potential changes in soil organic matter chemistry. In addition, they will contribute to the understanding of the role of soil as a source or sink of atmospheric CO₂ under conditions of antibiotic use.

Key words: karst, soil organic matter mineralization, cycloheximide, streptomycin, ¹³C nuclear magnetic resonance

摘要：

外源有机物添加会改变土壤有机质周转并产生激发效应，而添加抗生素后微生物的基质诱导呼吸则会受到选择性抑制，进而影响土壤有机质矿化过程。利用“空间代替时间”法结合选择性抑制诱导呼吸技术，通过室内实验研究环己酰亚胺和链霉素添加对中国西南岩溶区不同演替阶段生态系统土壤有机质的影响。结果表明：向土壤加入单一或者联合抑制细菌或真菌的抗生素时呈现诱导呼吸量增加的变化规律。尽管链霉素对诱导呼吸抑制作用不显著，但环己酰亚胺能够对以r-策略菌或k-策略菌为主导的土壤产生显著抑制作用。由于不同演替阶段生态系统下的土壤激发效应指数均小于1，表明产生负激发效应，并以表观激发和真实激发的形式显示，进而涉及活性基质的利用以及土壤固有有机质的分解。虽然链霉素和环己酰亚胺对细菌和真菌产生抑制作用，但不能对古菌、病毒和胞外酶产生抑制作用。因此，单独使用链霉素、环己酰亚胺或者同时使用二者时，土壤有机质仍能被微生物利用进而造成官能团相对比例发生变化。该研究结果为揭示土壤有机质负激发效应产生的原因以及明晰土壤有机质化学组分的相对稳定性提供了理论依据。

关键词: 岩溶, 土壤有机质矿化, 环己酰亚胺, 链霉素, ¹³C核磁共振