Soil carbohydrates and glomalin-related soil proteins (GRSPs), as important components of soil organic matter, are the essential basis for maintaining soil aggregate stability. They interact with each other and influence each other. Exploring the relationships and mechanisms of action between these two components and soil aggregates is of great significance for improving soil quality and promoting the sustainable development of forest stands. This study focused on investigating soil aggregate composition (including >2, 2–1, 1–0.25, and <0.25 mm fractions) and stability (as indicated by the mean weight diameter (MWD) and geometric mean diameter (GMD)) as well as aggregate-associated carbohydrates and GRSP components in Chinese fir plantations with different stand types, including Chinese fir × Michelia macclurei (stand I), Chinese fir × Mytilaria laosensis (stand II), and pure Chinese fir (stand III). The results indicated that in the 0–20 cm and 20–40 cm soil layer, the MWD and GMD of the two mixed Chinese fir stands were significantly (p < 0.05) higher than that of the pure Chinese fir stand. The contents of carbohydrates and GRSP in the soil also showed similar trends. This suggests that mixed Chinese fir stands (especially the Chinese fir × Michelia macclurei) enhance soil aggregate stability as well as the contents of carbohydrates and GRSP in the soil. The results also revealed that although both carbohydrates and GRSP significantly contribute to the formation and stability of large soil aggregates, PLS-PM analysis showed that in the 0–20 cm and 20–40 cm soil layer, the path coefficient of GRSP to aggregate stability was 0.840 and 0.576, while that of carbohydrates was 0.134 and 0.398. Therefore, compared with carbohydrates, GRSP (especially the easily extractable fraction of GRSP) has a more pronounced effect on soil aggregate stability. This finding provides a scientific basis and practical guidance for enhancing the productivity of Chinese fir plantations.

Dalbergia odorifera, a cornerstone tree species for ecological restoration in karst regions, exhibits remarkable adaptability to karst rocky desertification (KRD) environments characterized by high heterogeneity and nutrient poverty. Yet, the mechanisms underlying its root system’s response to spatially variable KRD stress remain poorly elucidated. In this study, a split-root system was employed to simulate heterogeneous substrate conditions, including loam, uniform gravel (global stress), and partitioned loam/gravel (partial stress). We found that under partial stress, the root system underwent functional specialization, and roots in loam enhanced resource acquisition, whereas roots in gravel significantly elevated stress tolerance. This was supported by increased root:shoot ratio, improved nutrient conservation, and localized upregulation of key enzymes and metabolites. Multi-omics profiling further uncovered profound reprogramming of critical pathways such as phenylpropanoid biosynthesis, fatty acid metabolism, and glutathione metabolism, highlighting robust antioxidant defense and membrane stabilization mechanisms. Our findings demonstrate that D. odorifera optimizes resource use in heterogeneous karst habitats through spatial division of labor at the root system level, orchestrated by integrated morphological, physiological, and molecular adaptations. This study provides a novel perspective on plant adaptation to environmental heterogeneity and offers practical insights for cultivating stress-resilient trees and restoring degraded karst ecosystems.