Innovative use of tea bags to investigate the interactive effect of nutrient status and climatic factors on litter decomposition

Interactive effects of nutrient status and climatic factors on litter decomposition remain unclear, partly due to the difficulty of extracting these effects from multiple decomposition data obtained from geographically diverse locations. Conducting the tea bag method repeatedly across different seasons, using the same fertilization study site and a short 90-day period, can be a useful tool for examining the interactive effects, as this method allows for a high degree of control over site effects by using an identical study site. In this study, we explored the sensitivity of the tea bag method in detecting the impacts of nutrient addition on tea material decomposition, as well as the interactive effects of nutrient addition and climatic factors on decomposition. At a 38-year continuous nitrogen and phosphorus fertilization experimental Sakhalin fir stand, we demonstrated that the mass loss ratio of rooibos tea and decomposition constant k, both of which are indicators of early-stage decomposition, were elevated by fertilization in summer, but not in winter. This was probably because, in summer when decomposition rates are less constrained by climatic conditions, the impact of nutrient availability on decomposition rates was relatively stronger compared to other seasons. Thus, the tea bag method can serve as a suitable tool for examining the effect of nutrient addition on early-stage litter decomposition and their interaction with climatic effects. Meanwhile, we concluded that the effects of nutrient addition on late-stage litter decomposition are undetectable by the tea bag method, because this method does not take into account lignin degradation.