Jointly soil properties affect N and P uptakes and utilizations in Pinus tabuliformis Carr. and Quercus liaotungensis Koidz. subjected to growing media with decomposed litter

Monocultured pine plantation is suffering ecological degradation that is highly associated with low regeneration. Decomposed litter is an important soil amendment for enhancing regeneration through promoting nitrogen (N) and phosphorus (P) uptakes and utilizations. It is necessary to detect key soil attributes that contributed to this positive effect for regenerations in pine plantations. In this study, in-situ soils and litter were collected from local Chinese pine (Pinus tabuliformis Carr.) plantations (objective) and secondary forests dominated by Liaodong oak (Quercus liaotungensis Koidz.) (control). Soils were used for culturing one-year-old Chinese pine and Liaodong oak seedlings with a prolonged photoperiod in a greenhouse. Litter was composted with effective microorganisms and mixed to soils at ratios of 0% (control), 25%, and 50% (v/v). Compared to the control, the 25% ratio decreased shoot height and root-collar diameter, and the 50% ratio decreased the comprehensive seedling quality. Decomposed litter addition reduced shoot biomass and P content in pine seedlings and utilizations for N and P in both species. Multivariate linear regression indicated that high pH in growing media impaired root P content and biomass increments in shoot and root parts, and high organic matter content inhibited N content and concentration in shoots. Overall, the addition of decomposed litter resulted in overdoses of nutrient supply for both species. Our results contradict the argument that N and P released from decomposed litter are both beneficial for regenerations in plantations, neither did in secondary forests.