Our previous investigation has indicated that the natural regeneration of Pinus koraiensis occurs solely in soil covered by Climacium dendroides. This study aimed to determine whether C. dendroides-covered soil enhances seed germination or reduces seed decay. The experiment was divided into two parts: a simulated natural regeneration field experiment, and a greenhouse-based potted trial. For the field experiment, soils were categorized into three treatments based on C. dendroides coverage: high coverage (HCD), low coverage (LCD), and no coverage (NCD). Four forest microsites were considered: a gap in the mixed coniferous forest (GCF), a closed stand in the mixed coniferous forest (SCF), a gap in the mixed broadleaf–coniferous forest (GBC), and a closed stand in the mixed broadleaf–coniferous forest (SBC). The greenhouse experiment consisted of four treatments: HCD and LCD with similar C. dendroides coverage as the field experiment, litter-covered soil (LC), and bare soil (CK). P. koraiensis seeds were sown in each treatment’s soil in both the field and greenhouse experiments and collected after one year to analyze their germination rates, decay rates, and antioxidant capacity based on each treatment. Correlations of the germination rate, decay rate, and antioxidant capacity of P. koraiensis seeds with the soil water content (SWC) and secondary metabolites of C. dendroides in soil were examined. The results revealed that, compared to soil without C. dendroides, HCD exhibited higher germination rates (increased by 15.2% and 32.5% for dormant field seeds and dormancy-broken greenhouse seeds, respectively), ABTS+ free radical scavenging activity (RSAABTS) (22.84% and 5.98% increases, respectively), catalase activity (CAT) (5.49 U·min−1·g−1 and 1.71 U·min−1·g−1 increases, respectively), and superoxide dismutase (SOD) activity (0.33 U·g−1 and 0.68 U·g−1 increases, respectively). In the field experiment, seeds in HCD exhibited higher DPPH free radical scavenging activity (RSADPPH) (26.24% increase) and peroxidase (POD) activity (4.0 U·min−1·g−1 increase) compared to seeds in NCD. Greenhouse seeds in HCD showed a lower rot rate (27.6% decrease) than seeds in CK. In both the field and greenhouse experiments, SWC, soil p-hydroxybenzoic acid content (PHBA), soil p-coumaric acid content (PCMA), and soil vanillic acid content (VA) were significantly positively correlated with the germination rate and antioxidant capacity of P. koraiensis. Soil total phenolic content (TPH) and total flavonoid content (TFL) had minimal impacts on P. koraiensis seed germination. The primary findings suggest that C. dendroides may alleviate drought stress and enhance seed antioxidant and germination capabilities by increasing SWC, PHBA, PCMA, and VA.
Coarse wood debris (CWD) plays a critical role in forest productivity, nutrient cycling, decomposition, and carbon sequestration, and shapes the carbon pool in the forest ecosystem. However, the elemental composition of CWD varies among different forest types and decay classes for the same dominant tree species (Pinus koraiensis, PK). We compared CWD elemental composition across different forest types (Picea koraiensis-Abies nephrolepis-Pinus koraiensis forest (PAPF), Betula costata-Pinus koraiensis forest (BPF), Tilia amurensis-Pinus koraiensis forest (TPF)), considering four classes of wood decay. Results showed that N, P, Mg, Mn, Na, Zn, S, Al, and Fe concentrations almost totally increased with decay level for all three forest types, except for K in all three forest types and B in Picea koraiensis-Abies nephrolepis-Pinus koraiensis forest (PAPF). Similarly, maximum concentrations of N, P, B, Mg, K, C, Zn, and Mn of CWD were observed in Betula costata-Pinus koraiensis forest (BPF) under varying decay classes, but their maximum concentrations of Fe and S were found in Picea koraiensis-Abies nephrolepis-Pinus koraiensis forest (PAPF) and Tilia amurensis-Pinus koraiensis forest(TPF), respectively. Only C content did not significantly differ in decay classes across all three forest types. The C:N ratio decreased significantly with increasing decay levels across all forest types. The decay rates were significantly related to N concentration and C:N ratio in decay classes across all forest types. These results suggest that C and N concentration are the key factors affecting its decomposition. The variation in nutrient concentrations observed here underscores the complexity of nutrients stored in wood debris in forested ecosystems.
Globally, atmospheric nitrogen (N) deposition is rising, adversely impacting soil health, i.e., increasing soil acidity. While phosphorus (P) is the limiting element in the temperate environment and plays a key role in making the ecosystem more vulnerable to N-derived acidification. The impact of elevated N and P inputs on soil acidity and exchangeable base cations have been extensively studied; however, few studies have focused on these parameters, especially within various soil aggregate fractions in the temperate forest. In 2017, a field experiment was conducted under N and P additions with four soil aggregate fractions (>5 mm, 2–5 mm, 0.25–2 mm, and <0.25 mm) in two forests, i.e., the broad leave Korean pine forest (BKPF) and Korean pine plantation (KPP) in the Liangshui National Natural Reserves in Northeast China. Results showed that high NP addition decreases pH, base cations, Mg2+ Ca2+, and BS% and increases in Fe3+, Al3+, and E.A (effective acidity) in all four aggregate fractions, in descending order; overall concentration of the base cations is ranked as BKPF > KPP. Thus, soil acidification is primarily caused by a decrease in base cations, such as Ca2+ and Mg2+, and increase in exchangeable Fe3+ and Al3+ ions in large macro-aggregates and macro-aggregates, which leads to the depletion of soil nutrients. The initial pH value (5.69) in >5 mm soil aggregate was decreased to (5.4) under high fertilizer application, while a minimum value of 5.36 was observed in 0.25–2 mm aggregates under high fertilizer application. The same trend was observed in all aggregates because of decrease in base cations, which, in turn, affects the vitality and health of the forests.
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