Water soluble carbon, nitrogen and phosphorus dynamics of twig litter in subtropical secondary and forest plantations

Twig litter is an important component of forest litter. It is of great significance to reveal the dynamics of water soluble carbon, nitrogen and phosphorus for understanding the forest material cycle. However, the previous researches paid more attention to leaf litter than twig litter. In this regard, we investigated water soluble carbon, nitrogen, phosphorus, and aromatization index as well as stoichiometric ratio dynamics of twig litter in a year round in Pinus massoniana plantation, Cunninghamia lanceolata plantation and Castanopsis carlesii secondary forest. Our results showed that:(1) water soluble carbon, nitrogen and phosphorus as well as aromatization index of twig litter in Castanopsis carlesii secondary forest were significantly higher than those of Pinus massoniana and Cunninghamia lanceolata plantations;(2) water soluble carbon and phosphorus, water soluble carbon-phosphorus ratio and nitrogen-phosphorus ratio, as well as aromatization index of twig litter varied significantly in different seasons;(3) there were significant interactions between forest types and sampling seasons in affecting water soluble carbon and nitrogen, water soluble nitrogen-phosphorus ratio, and aromatization index.(4) the seasonal variation of water soluble substance of twig litter in Pinus massoniana, Cunninghamia lanceolata plantation and Castanopsis carlesii secondary forest were negatively correlated with air temperature and precipitation. These results suggest that subtropical secondary forests may have a more efficient nutrients cycling process based on twig litter than plantations, and the concentrations of nutrients cycling back to soil via twig litter will decrease in subtropical forests under future warming scenarios.