Xianyu Yao

Ex situ conservation of the endangered tree Parashorea chinensis, a national first-class protected species in China, hinges on the development of functional belowground ecosystems, a process that remains mechanistically unclear in restoration ecology. This study evaluated the development of conservation plantations by analyzing rhizosphere soil stoichiometry, enzyme activities, and microbial communities across four growth stages in natural forests and ex situ plantations. Results showed that ex situ plantations exhibited obvious soil acidification and persistently low N:P ratios, with phosphorus acting as the primary limiting nutrient. Fungal α-diversity was strongly correlated with stoichiometric imbalance in ex situ plantations. Artificial management drove microbial community shifts toward fungal-enriched assemblages, forming a distinctive functional microbial portfolio to tolerate combined stresses from acidification and nutrient stoichiometric imbalance. Crucially, these managed ecosystems maintain core nutrient cycling functions, and key microbial indicators show distinct developmental trends toward the conditions observed in natural forests as stands mature. In summary, ex situ conservation alters belowground biogeochemical processes rather than merely supporting plant survival. We propose targeted microbial management, particularly inoculation with native functional taxa from natural forests, to accelerate soil stoichiometry rebalancing and enhance nutrient cycling efficiency. These findings provide both evidence for the ecological feasibility of ex situ conservation and practical strategies for optimizing its long-term success through science-based belowground management.

Introducing nitrogen (N)-fixing trees into plantations is a promising strategy to increase soil organic carbon (SOC) storage. However, whether this practice enhances SOC stability, a key determinant of long-term carbon sequestration, and through which specific microbial pathways, remains poorly understood. Here, we compared pure Eucalyptus plantations with mixed plantations containing the N-fixing tree Erythrophleum fordii (E. fordii) in subtropical China by measuring SOC fractions, microbial communities, extracellular enzymes, and microbial-derived carbon (MNC) content. After five years of plantation establishment, mixed plantations significantly increased total SOC by 22.41% compared to pure eucalypt stands. More importantly, this increase was accompanied by a pronounced shift in the carbon pool toward more stable mineral-associated organic carbon (MAOC), which increased by 28.39% in the surface layer. This increase was associated with microbial community restructuring characterized by a greater fungal contribution. The fungal-derived carbon (FNC) rose by 51.20%, and structural equation modeling showed that MNC contributed directly to MAOC formation, a stronger effect than the indirect enzyme-mediated pathway. Our findings provide field-based evidence that mixing Eucalyptus with N-fixing trees enhances SOC stability, primarily through the association between FNC accumulation and MAOC formation. This microbial mechanism provides a process-based perspective for evaluating mixed-species N-fixing tree plantations as a carbon-friendly management strategy in subtropical forestry.

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.

Increasing nitrogen (N) deposition and intensive fertilisation practices have a complex impact on soil phosphorus (P) dynamics and P bioavailability, with significant consequences for ecosystem productivity. However, it remains unclear how N inputs affect soil P pools and to what extent these effects depend on ecosystem type and initial soil pH. To address these knowledge gaps, we conducted a meta‐analysis based on 70 N addition studies (published from 1990 to 2023) and 1989 observations across cropland, grassland and forest ecosystems; the meta‐analysis incorporated 30 variables related to soil P pools. Our results reveal that initial soil pH serves as the dominant regulator of soil P responses to N enrichment. In circumneutral/alkaline soils (pH > 5.5), N addition significantly reduced labile inorganic P (Pi) by 12.4%, likely due to the dissolution of Ca ²⁺ ‐bound P. This, together with observed. Increases in resin‐P, may support enhanced plant higher P demands under N addition. Conversely, in acidic soils, N addition significantly reduced resin‐P by 12.7%, labile organic P (P _o ) by 12.8% and moderately labile P _o by 6.7%. Additionally, N addition increased labile P _i by 12.0%, moderately labile P _i by 8.3% and residual P by 4.7%, respectively. These soil P pool dynamics in acidic soils were associated with enhanced phosphatase activity and greater P _o mineralization, as well as increased adsorption/coprecipitation with Fe/Al‐(hydr)oxides, as suggested by the negative relationship between resin‐P and exchangeable Fe ³⁺ /Al ³⁺ under N addition. In conclusion, the initial soil pH may be a critical determinant of the direction and magnitude of N addition effects on P bioavailability. Understanding this pH‐dependent framework is essential for optimising P management in agroecosystems and sustaining ecosystem productivity in the context of global N enrichment.

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 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.

The study aimed to investigate the effect of soil textural or soil mineral fraction substrates (loam and gravel) from karst desertification areas on the rhizospheric and root-associated bacterial community structure of Dalbergia odorifera (an N-fixing tree), using high-throughput sequencing techniques, based on treatment methods of whole-root and two-chambered split-root systems. Further, this study determined the relative importance of the plant and substrate properties on the rhizospheric, non-rhizospheric and endospheric bacteria composition. The type of substrate exerts a significant influence on both rhizospheric and non-rhizospheric bacterial communities, whereas endophytic communities within the root system are predominantly determined by plant species rather than substrate type. The analysis revealed that endospheric bacterial diversity was considerably lower than that of rhizospheric and non-rhizospheric communities. Cluster analysis indicated that endospheric bacterial samples formed a distinct cluster, while rhizospheric and non-rhizospheric bacteria in the soil substrate grouped into one branch, and those in the gravel substrate formed another branch. In comparison to the gravel treatments, a reduced bacterial abundance was observed in the rhizosphere and non-rhizosphere of nitrogen-fixing plants in soil, potentially due to the interplay of lower nutrient availability and increased porosity in gravel treatments. Proteobacteria, which are involved in the nitrogen cycle, exhibited the highest abundance. In contrast, Acidobacteria, Firmicutes and other bacterial phyla involved in nutrient cycling demonstrated higher abundance, with their presence being more pronounced in extreme environments, such as gravel treatments, compared to soil substrates. These results suggest that nitrogen-fixing plants can respond to extreme environments by increasing bacterial abundance. The findings of this study provide a theoretical basis for the use of D. odorifera for ecosystem recovery and vegetation restoration.

Summary: Introducing N₂‐fixing tree species into Eucalyptus plantations could replace nitrogen (N) fertilization to maintain high levels of N consumption and productivity. However, N enrichment may exacerbate phosphorus (P) limitation as Eucalyptus robusta Smith is extensively planted in P‐poor tropical and subtropical soils. We conducted a field experiment in a pure plantation of Eucalyptus urophylla × grandis to investigate the impacts of N fertilization and introduced an N₂‐fixing tree of Dalbergia odorifera T. Chen on soil P transformation. Nitrogen fertilization significantly enhanced soil occluded P pool and reduced the other P pools due to acidification‐induced pH‐sensitive geochemical processes, lowering Eucalyptus leaf P concentration with higher N : P ratio. By contrast, introduced N₂‐fixing tree species did not change soil pH, labile inorganic P pool, and Eucalyptus leaf N : P ratio, even enhanced organic P pools and reduced occluded P pool probably due to altering microbial community composition particularly stimulating arbuscular mycorrhiza fungal abundance. Our results revealed differential responses and mechanistic controls of soil P transformation in Eucalyptus plantations with N fertilization and introduced N₂‐fixing tree species. The dissolution of occluded P pool along with organic P accumulation observed in the mixed plantations may represent a promising future to better manage soil P availability.