Vitamin C industrial residue after evaporation (RAE) acts as both a rapid-release carbon source and a microbial activity promoter. A two-year maize field experiment assessed the effectiveness of RAE in improving soil quality in degraded semi-arid regions. The RAE formulation was applied via drip irrigation during the sixth true leaf unfolded (BBCH 24), fourteenth true leaf unfolded (BBCH 38), and middle of grain filling (BBCH 66) stages, which consisted of three treatments: (1) untreated control (CK), (2) low RAE rate (LR: 150 L/ha), and (3) high RAE rate (HR: 300 L/ha). Soil physicochemical properties, enzyme activities, maize nutrient accumulations, and yields were comprehensively analyzed at the maize maturity stage. RAE application significantly improved the following soil nutrients: dissolved organic carbon (10.40–25.92%), ammonium nitrogen (14.04–70.67%), nitrate nitrogen (14.80–78.63%), and available phosphorus (11.79–42.55%). Soil enzyme activities also increased: sucrase (12.38–30.25%), amidase (1.95–25.69%), peptidase (0.56–48.79%), β-1,4-N-acetylglucosaminidase (3.11–9.48%), protease (17.41–226.29%), and acid phosphatase (8.73–60.04%). These changes enhanced maize nitrogen (17.63–40.73%) and phosphorus (20.09–42.11%) uptake, increasing yield by 7.12–13.46%. Statistical analysis showed strong correlations between yields and nutrient accumulations (r = 0.82, p < 0.01), particularly phosphorus (r = 0.91, p < 0.001). RAE enhances crop productivity in degraded agricultural systems by improving soil nutrient availability and plant assimilation, making it a viable alternative to conventional fertilizers.

Restoring soil microbial functioning in reclaimed coal gangue soils is critical for ecosystem recovery, yet how different organic amendments, particularly industrial by-products, regulate bacterial communities remains unclear. Here, we tested three organic inputs—the residue after evaporation (RAE) from vitamin C production, Trichoderma inoculation, and cattle manure—applied alone and in combination in a photovoltaic agroforestry system on coal gangue spoil. Our results indicate that the treatment based on manure increased bacterial α-diversity and favored taxa associated with organic matter transformation, including Actinobacteria and Acidobacteriota, suggesting expanded niche partitioning in response to heterogeneous substrates and nutrients. RAE alone supported communities closer to non-manure controls but, when co-applied with manure, further enhanced network connectivity and the prevalence of positive associations, indicating strengthened cooperative interactions and functional redundancy. In contrast, RAE combined with Trichoderma in the absence of manure reduced diversity, and simplified the co-occurrence network, suggesting resource monopolization and antagonism. Overall, RAE acted as a key driver of microbial cooperation and potential ecosystem resilience, and RAE-based amendments, particularly when integrated with manure, appear to be effective strategies for improving soil microbial functionality in degraded coal gangue soils.

The decline of Mongolian Scots pine (Pinus sylvestris var. mongolica) plantations in the “Three-North” shelterbelt region is closely linked to soil degradation. This study compared rhizosphere and non-rhizosphere soils across different stand ages, focusing on nutrient availability, microbial biomass, enzyme activities, and soil particle morphology. Results showed that SOC and TN accumulated with age, whereas AP, AK, and pH declined in older stands, indicating progressive acidification. Results demonstrated that SOC and TN increased with stand age, whereas AP, AK, and pH exhibited a marked decline in the older stands (stands aged ≥ 40 years), reflecting progressive acidification and nutrient depletion. Rhizosphere soils consistently displayed higher SOC, TN, microbial biomass, and enzyme activities than non-rhizosphere soils, largely driven by root exudation and enhanced microbial turnover. The increasing C_mic/N_mic ratio with age suggested a fungal-dominated microbial community, which may exacerbate stand decline by fostering pathogenic fungi. Scanning electron microscopy revealed pronounced particle fragmentation and surface roughness with increasing stand age, particularly in rhizosphere soils, indicating root-driven physical and biochemical weathering. These findings highlight the synergistic effects of stand development and rhizosphere processes on soil structure and fertility, providing a theoretical basis for the sustainable management and restoration of declining plantations.

Early-spring chilling disrupts redox balance and limits leafy-vegetable growth. This study aimed to determine whether residue after evaporation (RAE), a vitamin C fermentation by-product, could improve chilling tolerance in pak choi, and whether its effects varied with application route and co-application of KH₂PO₄. Treatments were control (CK), foliar 0.2% KH₂PO₄ (KP), foliar or root-zone RAE (Rf and Rr), and their RAE+KP combinations (Rf-KP and Rr-KP). Plants were assessed 24 h after treatment before chilling (T1), after 48 h at 4 °C (T2), and after 72 h of post-chilling growth (T3). At T1, RAE-containing treatments increased ascorbate (AsA) by 13.91–26.16% and the AsA/dehydroascorbate (DHA) ratio by 17.08–32.90%, before detectable growth or oxidative-injury differences. At T2, RAE-containing treatments increased AsA and AsA/DHA by 25.58–49.38% and 38.52–69.13%, enhanced antioxidant defenses, and reduced chilling injury, leaf damage, and hydrogen peroxide accumulation. Root activity increased by 25.40% (Rr) and 39.37% (Rr-KP). At T3, all treatments increased aboveground fresh weight by 22.71–109.05%, and the damaged-leaf rate decreased by 42.40–71.24%. Rf-KP and Rr-KP had the highest comprehensive chilling-tolerance scores at T2 and T3. The RAE × KH₂PO₄ interaction for this score was significant at T2 but not at T3. Both RAE routes improved chilling tolerance. Early ascorbate redox changes preceded later stress responses, while RAE × KH₂PO₄ interactions varied among traits and stages. These findings support further evaluation of RAE as a potential agricultural input for improving chilling tolerance in leafy vegetables.