History metal (Pb, Zn, and Cu) deposition and Pb isotope variability in multiple peatland sites in the northern Great Hinggan Mountains, Northeast China

Burning alters the decomposition of residual plant litters in Calamagrostis angustifolia wetlands in the Sanjiang Plain (Northeast China)

Wetlands store >30% of the global soil carbon pool, which is important for global carbon cycling. However, with global warming and the increase in regional human activities, an increasing number of wetlands are being threatened by fires, which have serious effects on carbon cycling in wetlands. Although plant litter decomposition is one of the key stages of carbon cycling in wetlands, it is still unclear whether fires affect residual plant litter decomposition in burnt wetlands and whether the fire season also causes different effects. To address these knowledge gaps, a plant litter decomposition experiment was conducted during the growing season in autumn burnt, spring burnt, and unburnt sites in a Calamagrostis angustifolia wetland in the Sanjiang Plain (Northeast China). The results show that autumn burning promotes more mass loss (i.e., 15.9 ± 1.6% in autumn burnt sites and 14.8 ± 1.7% in autumn unburnt sites) and accelerates the decomposition of plant litter, whereas spring burning decreases the decomposition rates of plant litter (i.e., 15.7 ± 1.7% in spring burnt sites and 22.0 ± 2.5% in spring unburnt sites). As the decomposition time increased, the accumulation index indicated that carbon was released from plant litter to the surrounding environment accompanied by mass loss and nutrient elements accumulated in the residual plant litter. The N/P ratio of plant litter decreased from ca. 20 on day 26th to ca. 9 on day 121st, indicating that N acts as the limiting element for plant litter decomposition in C. angustifolia wetlands, and the limitation increased with increasing decomposition time. Our results also suggest that the autumn burning may promote more carbon loss and nutrient elements accumulated in plant litter in C. angustifolia wetlands than the spring burning.

A Novel Strategy to Evaluate the Aromaticity Degree of Natural Organic Matter Based on Oxidization-Induced Chemiluminescence

Due to its complex composition and structure, many of the properties of natural organic matter (NOM) are poorly understood. In this study, the oxidization-induced chemiluminescence (OCL) of NOM was investigated, and a flow-injection OCL method was developed using alkaline persulfate-H₂O₂ as the oxidizing agent. The method is suitable for the direct analysis of NOM in both homogeneous and heterogeneous samples without isolation or concentration. A strong linear relationship (p < 0.001) was found between the normalized organic carbon OCL (OCL_OC) and the percentage of aromatic carbon in standard NOM and soil samples, suggesting that OCL_OC can be used as an empirical indicator to assess the aromaticity degree of NOM in both homogeneous and heterogeneous samples. By using this method, the percentages of aromatic carbon in a forest soil profile with low organic carbon content were estimated, and a decrease in the degree of aromaticity in deeper soil was observed. Considering the high sensitivity (lower than 0.1 mg C L^-1) and throughput (13 s per detection) and low sample consumption (less than 1 mg) of the method, the proposed OCL_OC indicator shows great promise for the high-throughput evaluation of the aromaticity degree of NOM for a wide variety of environmental and geochemical samples.