Non-additive effects of European black pine (Pinus nigra Arnold) and tree of heaven (Ailanthus altissima Mill.) mixed leaf litters on decomposition and nutrient dynamics of leaf litters

In nature, Leaf litter of different plant species is typically mixed and the mixtures decompose together. Leaf litter mixing effects may be caused by chemical interactions between the component leaf litters, by changes in the microenvironment in which the litter is decomposed or by changes in the diversity of associated microorganisms. The purpose of this study was to evaluate the interactions between black pine needles and tree of heaven litters using the litterbag method in Shahed's forest park of Malayer. For this purpose, 120 litterbags placed in the study area and incubated for 180 days at 30, 60, 120 and 180 days. In this study, mass loss was measured and non-additive effects of litter composition was studied regarding the nutrient dynamics and release. The results showed that tree of heaven litter had a higher quality than black pine needles (nitrogen values and C: N ratio of tree of heaven litter were 6.42 mg/g and 0.33 while the values for pine needles were 3.31 mg/g and 0.71, respectively). The non-additive effects of litter mixtures regarding the rate of decomposition and nutrient dynamics of black pine needles such as nitrogen, phosphorus and calcium were positive and neutral for potassium and magnesium. In addition, the non-additive effects of pine needles on the tree of heaven litter was negative in terms of nitrogen dynamics and were neutral regarding phosphorus, potassium, calcium and magnesium. According to the results of the study, no positive non-additive effects was observed on nutrient release. Overall, the results of this study confirmed the positive non-additive effects of tree of heaven litter on black pine needles in terms of the decomposition, dynamics of nitrogen, phosphorus and calcium concentrations of the needles.