Soil aggregates play a crucial role in substance and energy cycles in soil systems. The fixation of soil organic carbon (SOC) is closely tied to the safeguarding mechanisms of soil aggregates. Carbon fixation involves the conversion of atmospheric carbon dioxide into organic molecules by autotrophic organisms. Soil aggregates play a significant role in carbon stabilization, allowing for the physical occlusion of SOC. This study focuses on five forest types, Betula platyphylla, Betula dahurica, Quercus mongolica, Larix gmelinii, and mixed forests comprised of Larix gmelinii and Quercus mongolica, in the Heilongjiang Central Station Black-billed Capercaillie National Nature Reserve, northeast of China. This study investigated the soil aggregate stability (SAS) (water sieving) and aggregate-associated organic carbon (AAOC) at different soil depths in five forest types. Our findings demonstrated that fine macro-aggregates (0.25–2 mm) were the main types of soil aggregates among all the forest types. The SAS gradually decreased with increasing soil depth. Notably, broad-leaved forests exhibited relatively high soil stability. The fine macro-aggregates (0.25–2 mm) had the highest AAOC content, and the AAOC level was highest in the topsoil layer. The SAS and AOCC levels of the Betula platyphylla forest and Betula dahurica forest were higher than those of other forest types and were significantly affected by the forest type, soil depth, and soil physicochemical properties. Collectively, our findings reveal the key factors influencing aggregate stability and the variations in soil organic carbon content in different forest types. These observations provide a basis for studying the mechanisms of soil aggregate carbon sequestration, as well as for the sustainable development of forest soil carbon sequestration and emission reduction.

Rhododendron aureum is identified as a vulnerable species in China. The establishment of an in vitro regeneration system assists significantly in species protection. Here, an in vitro regeneration system was developed using both direct and indirect organogenesis pathways. The role of thidiazuron (TDZ) in different developmental stages was also investigated. The leaves of wild-harvested R. aureum plants were used for callus induction after hydroponic cultivation. The optimal formula was found to be woody plant basal medium (WPM) supplemented with 0.5 mg·L⁻¹ TDZ and 0.5 mg·L⁻¹ 3-indolebutyric acid (IBA), while the optimal formula for the subculture and induction of adventitious buds was WPM containing 0.1 mg·L⁻¹ TDZ and 0.5 mg·L⁻¹ IBA. The leaves from tissue-cultured seedlings were then used for the induction of bud clusters. An association was observed between the differentiation of bud clusters and the ratio of auxin and cytokinin. The optimal formula for the induction of bud clusters was WPM containing 0.5 mg·L⁻¹ TDZ and 0.1 mg·L⁻¹ IBA, yielding a 50% induction rate and the maximum number of buds. Higher concentrations of TDZ were found to be beneficial for bud proliferation, while a lower concentration was conducive to stem elongation. The optimal formula for subculture was WPM containing 0.1 mg·L⁻¹ TDZ and 0.5 mg·L⁻¹ IBA, while that for stem elongation was WPM supplemented with 0.002 mg·L⁻¹ TDZ and 0.5 mg·L⁻¹ IBA. Only IBA was found to be necessary for rooting, with increased IBA concentrations leading to an increased number of roots and earlier root formation, with larger callus areas; thus, an IBA concentration of 1.0 mg·L⁻¹ was found to be optimal for the rooting of R. aureum. After hardening the seedlings for two days, a substrate composed of vermiculite and peat soil in a 10:1 ratio was identified as a transplantation formula. This system provides directions both for the protection of endangered species and the promotion of industrial development.

Northern artificial forests play a vital role in enhancing carbon sequestration and ecosystem services, yet quantitative evidence on how different management measures affect understory biodiversity and productivity remains limited. This study focused on Larix gmelinii var. principis-rupprechtii (Mayr) Pilg. plantations in Weichang, Hebei Province, and compared three forest management regimes: target-tree management, homogeneous management, and un-managed stands. We systematically examined understory plant diversity indices (Shannon, Simpson, Margalef, Gleason, and Pielou), shrub–herb layer biomass, soil organic carbon (SOC), and total nitrogen (TN), and employed correlation analysis and random forest modeling to identify the main driving factors. Results showed that target-tree management significantly enhanced both understory biodiversity and shrub–herb biomass, followed by homogeneous management, while unmanaged stands had the lowest values. Differences in SOC and TN among treatments were not significant. Stand structural factors were the dominant drivers: stand density and basal area were negatively correlated with diversity and biomass, while community evenness (Pielou) was positively correlated with biomass. Random forest analysis further indicated that basal area and stand density had the highest relative importance, followed by evenness, whereas soil factors contributed less. Mechanistically, target-tree management improved light availability and spatial distribution by reducing stand density, thereby increasing evenness and promoting biomass accumulation. Overall, optimizing stand structure, rather than merely increasing species richness, proved more effective in simultaneously enhancing biodiversity and productivity in light-limited Larix plantations. From a management perspective, target-tree management combined with density regulation and structural optimization is recommended to achieve near-natural management goals and enhance multiple ecological functions.