Dissolved organic matter dynamics and spectral characteristics of twig litter from different Castanopsis carlesii forests in the middle subtropical region, China

Abstract

To assess the dynamics and spectral characteristics of dissolved organic matter of twig litter in continuous increase stage, peak stage, and continuous decrease stage of twig litter production in different types of Castanopsis carlesii forest in middle subtropical China, a field experiment was conducted in C. carlesii natural forest, secondary forest and plantation. The results showed that litter production stage and forest type significantly affected the content and spectral characteristics of dissolved organic matter of twig litter were . Compared with the secondary forest and plantation, natural forest had higher dissolved organic carbon (DOC) content and lower special ultraviolet-visible absorption values at 254, 260 and 280 nm (SUVA254, SUVA260, SUVA280) at the continuous decrease stage of twig litter production, indicating high twig litter quality of natural forest and high cycling efficiency with dissolved organic matter in the natural forest at this stage. In contrast, the higher contents of total nitrogen (TN), total phosphorus (TP), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and lower DOC:TDP and TDN:TDP ratios of twig litter in the plantation were observed at the peak stage of twig litter production, while no differences were detected in dissolved organic matter contents and spectral values in the secondary forest among the stages. In addition, the DOC, TDN, TDP of twig litter were negatively correlated with temperature and precipitation in the natural forests and secondary forests, but TDN and TDP of twig litter were positively correlated with temperature and precipitation in the plantations. These results suggested that the higher nutrient content at the peak stage of twig litter production in the C. carlesii plantation might lead to more efficient material cycling and that there would be a higher efficiency of material cycling for twig litter dissolved organic matter in C. carlesii natural forest at reduction stage of twig litter production.