Influence of Sampling Time on CO₂ and CH₄ Fluxes in a Temperate Peatland Under Nitrogen and Warming Treatments

Understanding the temporal variability of greenhouse gas (GHG) fluxes is critical for accurately assessing peatland carbon dynamics. Some recommended time periods have been used for a long time, but whether temporal variations within the periods affect comparisons between treatments remains unexamined. In this study, we investigated the effects of sampling time on CO₂ and CH₄ fluxes under control, nitrogen addition, and warming treatments in a temperate peatland ecosystem, and compared these results with random sampling. We found that gross primary productivity and CH₄ fluxes exhibited relatively stable patterns across different sampling periods. In contrast, ecosystem respiration and net ecosystem productivity were more sensitive to sampling time, particularly under N addition. With the delay in sampling time, CO₂ emissions increased significantly, causing the peatland to shift from a carbon sink to a source. This was attributed to asynchronous diurnal variations between gross primary productivity and ecosystem respiration driven by changes in vegetation structure and soil microclimate. Our findings highlight the importance of sampling design in GHG flux monitoring and recommend the use of multi-timepoint or randomized sampling strategies to minimize temporal bias and variation between treatments, improving the accuracy of peatland carbon budget assessments.