Responses of leaf litter decomposability to nitrogen and phosphorus additions are associated with cell wall carbohydrate composition in a subtropical plantation

Aims The litter decomposition rate is strongly related to litter chemical quality, which is altered by increased nitrogen (N) and phosphorus (P) availability induced by global changes and human activity in plantation forest ecosystems. However, the effects of litter cell wall carbohydrate composition on litter decomposability after long-term N and P additions remain unclear. Methods A field nutrient manipulation experiment was conducted in a subtropical Cunninghamia lanceolata plantation. Leaf litter and green leaves were collected and divided into 1- and 2-year-old tissues after N and P additions for 5 years. Litter organic carbon (OC), N and P concentrations and their stoichiometries, and cell wall carbohydrate fractions were determined. The leaf litter decomposability was determined by 150 days of decomposition in the laboratory. Results Nitrogen addition decreased leaf litter C/N, whereas P addition decreased C/N and C/P. P addition decreased cell wall pectin, hemicellulose, total extractable carbohydrate (TEC) concentrations and their percentage relative to OC. Litter OC, N and P and their stoichiometries were unaffected by litter age, whereas TEC and TEC/OC increased with increasing litter age. Leaf litter decomposition rate increased by 7.3% with P addition, decreased by 16.8% with increasing litter age, and was unaffected by N addition given the negative correlation between TEC/OC and litter decomposition rate. Conclusions Cell wall carbohydrates constitute an effective indicator of litter quality to predict litter decomposability. Phosphorus but not N addition increases litter decomposability through alterations in carbohydrate composition. Tissue age should be considered when investigating N and P additions effects on litter decomposition in forest ecosystems.