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

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