Calcium (Ca) is an essential plant nutrient and cell signal element, but in the cultivation of container seedlings, the regulatory effect of Ca on seedling nitrogen nutrition and its regulatory mechanism have been neglected. Ectomycorrhizal fungi (ECMF) inoculation is widely used in forest container seedling cultivation. Thus, we added a certain amount of Ca to the culture matrix to determine how the cooperation between Ca and ECMF improves the nitrogen nutrition of Pinus massoniana ectomycorrhizal (ECM) container seedlings. We found that addition Ca significantly increased the relative abundance of Actinomycetota and Bacillota in the rhizosphere of ECM seedlings. These enriched bacteria cooperated with the ECMF and significantly enhanced extracellular enzyme NAG and LAP secretion. Meanwhile, adding Ca promoted the microbial nitrogen cycle in the ECM seedlings rhizosphere, and the relative abundances of nitrogen fixation genes (nifD, nifH, nifK) and the dissimilatory nitrate reduction gene (narH) significantly increased. In addition, Ca promoted the infection of ECMF on seedlings and induced the sprouting of absorptive roots with larger diameter (0.5 mm < RD ≤ 2.0 mm), i.e., ECM seedlings adopted a dual strategy of enhancing mycorrhizal symbiosis and improving root absorption area to obtain soil nitrogen. These effects contributed to an increase in microbial biomass nitrogen (MBN) and seedling nitrogen content by 20.65% and 54.38%, respectively. The results provide an effective method and theoretical reference for improving the quality of container seedlings and increasing the ECM plantations early productivity.

Rosa sterilis S.D.Shi pomace (RSP), a nutrient-rich by-product of fruit processing, holds considerable potential for valorization. Given the increasing interest in recycling agricultural residues for edible fungi cultivation, RSP may represent a viable, sustainable substrate component. This study evaluated the effects of partial substitution of wood chips with RSP on the mycelial growth of Phallus rubrovolvatus and aimed to identify an optimal substrate formulation. The results showed that the addition of 10% and 20% RSP to the substrates significantly promoted mycelial growth and shortened the mycelial colonization time by 4–5 days. The addition of RSP increased total phosphorus and potassium contents by 12.2%–65.9% and by 0.4- to 4.4-fold, respectively. No significant differences in the C:N ratio were observed among treatments with 5%, 10%, and 20% RSP compared to the control. Extracellular enzyme activities varied across treatments, with the 10% RSP group yielding the maximum increments in pectinase (45.9%), laccase (11.9%), xylanase (12.5%), and protease (35.6%). Although substrate pH remained relatively stable, the total organic acid content decreased, whereas the levels of citric, acetic, and succinic acids increased. Overall, 10% RSP substitution significantly enhanced mycelial growth and enzymatic activity. These findings suggest that RSP improves the mycelial ability to degrade and assimilate substrate nutrients, demonstrating its potential as an effective and sustainable substrate amendment for P. rubrovolvatus cultivation. This study provides a practical strategy for agricultural waste valorization and supports the circular utilization of biomass resources.