Fang Zhang

Mulberry (Morus alba L.) is a woody plant primarily cultivated for silkworm breeding, with significant economic and ecological functions. Its nitrogen use efficiency directly affects leaf yield, quality, and environmental adaptability. The main inorganic nitrogen forms available for plant uptake in soil are ammonium nitrogen and nitrate nitrogen, and plant uptake and assimilation of these two nitrogen sources often exhibit species-specific preferences. This review systematically summarizes the research progress on nitrogen uptake preferences in mulberry, confirming that this species generally shows a preferential uptake of nitrate. Specifically, when supplied with nitrate or a mixed nitrogen source dominated by nitrate, mulberry exhibits better performance in growth and development, photosynthetic efficiency, and accumulation of secondary metabolites. This review further discusses the physiological characteristics and underlying regulatory mechanisms responsible for this preference, and analyzes key factors affecting nitrogen uptake preferences, including soil properties, environmental stresses, and microbial interactions. It should be noted that while controlled experiments have yielded important insights, the applicability of these findings under complex field conditions still requires further validation through field trials. Finally, future research directions are prospected, including in-depth dissection of molecular mechanisms, field validation, plant-microbe interactions, and nutritional strategies for stress resistance, aiming to provide a theoretical basis for efficient cultivation and precise nitrogen management of mulberry.

The fragile Karst landscapes of southwest China face persistent challenges of soil degradation and rocky desertification. While sustainable land use such as mulberry plantation can support ecological restoration, the dynamics of soil organic carbon (SOC) and its driving mechanisms across contrasting soil types remain poorly understood, limiting the development of targeted pedogenically aware carbon management strategies. A comparative field study was conducted in central Guizhou, China, over an eight-month mulberry growing season (April to November). We monitored SOC, physicochemical properties, GRSP, and enzyme activities in plantations established on two contrasting limestone-derived soils (Calcisols and Chromic Luvisols). This study aimed to clarify the relationships between SOC and key soil parameters within each soil type and to identify their dominant driving factors. Soil type significantly influenced SOC concentration, dynamics, and its regulatory mechanisms. SOC was significantly higher and exhibited greater seasonal variability in Calcisols (31.51–39.71 g·kg⁻¹) than in Chromic Luvisols (22.50–28.51 g·kg⁻¹), with Calcisols maintaining 1.28–1.57 times the SOC concentration of Chromic Luvisols. Regression analysis revealed that SOC was significantly positively correlated with TN, AN, AK, and GRSP, but significantly negatively correlated with AP. Random forest modeling further identified distinct key correlated factors in each soil type as follows: TN, T-GRSP, and Urease were primary in Calcisols, whereas TN, T-GRSP, and pH dominated in Chromic Luvisols. Partial least squares path modeling confirmed that soil type does not directly associate with SOC but exerts an indirect effect by modulating core biochemical mediators specifically (Alkaline protease, T-GRSP, and TN); The model also indicated that pH and TN exert direct positive effects on SOC accumulation. In Karst mulberry systems, pedogenically distinct soils (Calcisols vs. Chromic Luvisols) shape SOC storage, stability, and regulatory mechanisms through divergent biogeochemical pathways. SOC management should therefore be soil-type-specific, prioritizing nitrogen synergy in Calcisols and pH-mediated stabilization in Chromic Luvisols, rather than applying uniform strategies. This study thereby establishes a mechanistic framework for understanding and managing SOC in heterogeneous Karst landscapes, providing a critical foundation for developing targeted, soil-specific carbon sequestration practices in ecologically vulnerable regions.

In the initial stages of restoring rocky desertification, the proliferation of nutrients strongly influences plant survival. The carbon–nitrogen doctrine in plants argues that a lower leaf carbon–nitrogen (C:N) ratio enhances the growth of plant nutrients. However, the mechanisms by which inoculation with arbuscular mycorrhizal fungi (AMF) can influence plants during the restoration of rocky desertification are not thoroughly understood. This study used mulberry as a suitable example of a mycorrhizal plant in desertification areas to examine changes in growth, leaf carbon, nitrogen accumulation, and the carbon–nitrogen ratio post inoculation using AMF. The correlation between leaf carbon–nitrogen ratio and root morphology following AMF inoculation was also examined. The results demonstrated that inoculating mulberry with the dominant strains Funneliformis mosseae (Fm) and Rhizophagus intraradices (Ri) not only enhanced above-ground growth and improved carbon and nitrogen nutrient absorption but also had a more pronounced effect on leaf nitrogen accumulation than on carbon accumulation, resulting in a potential decrease in the leaf C:N ratio by 42.13%. It also significantly improved root morphology by exponentially increasing the number of connections and crossings by 120.5% and 109.8%, respectively. Further analysis revealed a negative correlation between leaf C:N ratio and root morphology, as well as between root length and the number of connections. Plants with more developed root systems exhibited greater competitiveness for nitrogen, resulting in a lower leaf C:N ratio. This study suggests that the inoculation of AMF could enhance leaf nitrogen accumulation and reduce the leaf C:N ratio by expanding the spatial absorption range of the root through positive changes in root morphology, thereby promoting plant nutrient growth. This study forms a fundamental scientific basis for the successful management of desertification.