The intercropping of Camellia oleifera with leguminous and gramineous herbage not only helps to improve soil fertility and soil quality but also effectively enhances its production potential and ecological advantages. Therefore, exploring the effects of different herbage intercropping patterns on the soil fungal community of young C. oleifera forest will provide a scientific basis for ecosystem diversity management and increase the comprehensive benefit of C. oleifera production.

We set 5 different intercropping patterns: C. oleifera × Dactylis glomerata, C. oleifera × Trifolium repens, C. oleifera × Medicago sativa, C. oleifera × D. glomerata + T. repens, C. oleifera × D. glomerata + M. sativa in this study, and determined the most efficiency intercropping pattern for improving the soil environment of C. oleifera. The fungal community was analyzed by high-throughput Illumina sequencing of the 16SrRNA gene, and the driving factors were clarified based on soil physicochemical properties.

Compared with single-species cropping, mixed-species intercropping showed higher contents of SOC, TN and TP. The contents of total K and Mg were the highest in soils of single D. glomerata intercropping, followed by the CK soils, and the lowest content was found in soils with the two mixed intercropping. Herbage intercropping generally reduced the contents of available nutrients. The content of NO₃ in CK was the highest, and the content of NH₄ in M. sativa was the highest. For trace elements, the contents of Zn, Fe and Mn were the highest in CK, followed by single species cropping and the lowest contents were found in the mixed species intercropping pattern. The content of As in the soil was generally reduced by planting herbage. The sequencing data showed that there were 586 OTUs of fungus species shared by the five different intercropping patterns, among which 120 OTUs were found in intercropping and mixed species intercropping, and Ascomycota, Basidiomycota and Mortierellomycota were dominant phyla in fungi. Additionally, intercropping increased the soil fungal richness. According to RDA analysis, the most important soil properties that determine the dominant genus (relative abundance >1%) in the fungus community were pH, TN, NH₄ and PO₄.

Multiple herbage intercropping, especially the soybean and grass species intercropping, improves the stability of the soil environment and the diversity of fungi. Therefore, intercropping can increase the survival rate of young C. oleifera forest, improve the rational property of soil, promote the growth of C. oleifera, and improve the economic benefits of forest land.

Camellia oleifera, as a “money spinner” for poverty alleviation in southern China, has an important effect on local economy. In recent years, due to the surging demand for grain and oil reserves in China, it is urgent to reform the low-yield and low-efficiency old forest. However, the influence of the transformation process on soil quality and fungal community is still unclear. On the forest land replanted after clear cutting, the composition of litter and rhizosphere sediment has been changed, showing an impact on soil properties. By comparing the soil before and after the transformation, the key factors regulating the soil nutrients in the stand were clarified, which had important guiding significance for the transformation of the low-yield C. oleifera forest.

This study collected soil samples from the old C. oleifera forest, young C. oleifera, Pinus massoniana forest and Cunninghamia lanceolata forest. We then determined 13 indexes including soil chemical properties, enzyme activity indexes and the community diversity of fungi. The minimum data set was selected and revised by the principal component analysis (PCA) and discriminant (MDA) analysis. The evaluation index system of soil quality in this area was established, and comprehensively evaluated.

There were significant differences in pH, soil organic carbon (SOC), total potassium (K), magnesium (Mg), iron (Fe), manganese (Mn) and nitrate nitrogen (NO₃) in the soil after transformation. The activities of acid phosphatase (AP), N-acetylglucosaminidase (NAG) and β-glucosidase (BG) in the replanted P. massoniana forest were higher than others. Finally, it was demonstrated that the minimum data set of soil fertility evaluation indexes of C. oleifera in this area was significantly affected by nitrate, K, available K, NAG, total nitrogen (N), pH, SOC, total phosphorus (P), and fungal Shannon indexes. Moreover, SOI was improved by stand transformation.

Acidic soil environment is conducive to the growth of C. oleifera. Besides N, P, K and Mg, the trace mineral contents of Fe and Mn should be paid attention to in C. oleifera forests. Besides, as C. oleifera is a mycorrhizal-dependent woody oil plant, the use of fungal fertilizer can be considered when applying bacterial fertilizers. This study provides guidance for future soil management and precise fertilization in this area.

The increasing levels of nitrogen deposition have varying impacts on forest ecosystems. Excessive input of available nitrogen leads to changes in plant root strategies for nutrient acquisition, consequently altering the structure and ecological functions of important soil microorganisms such as ectomycorrhizal (ECM) communities associated with tree roots. Understanding and determining the threshold of changes in root-associated microbial community activity in response to nitrogen deposition are of crucial importance for studying nutrient cycling characteristics and sustainable management practices in forests.

The present experiment employed an indoor pot experiment, selecting four tree species, namely Pinus massoniana, Pinus armandii, Pinus elliottii and Pinus taeda. Five gradients of nitrogen addition (0, 15, 30, 60, 150 kg·hm^-2·a^-1) were applied to study the dynamic changes in the structure and enzymatic activity of ECM communities under different nitrogen deposition levels. The nutrient content of seedlings and ECM root tip enzyme activity were analyzed to investigate the variations in the ECM community structure and enzymatic activity among the different pine species in response to nitrogen deposition levels.

1) The extracellular enzyme activity of most pine seedlings reached a threshold at 30 kg·hm^-2·a^-1. β-D-Glucosidase, mainly involved in cellulose decomposition, continues to increase with increasing N concentration in slash pine, loblolly pine, and China Armand pine. Even when N application reached 10 times the local N deposition level (150 kg·hm^-2·a^-1), the enzyme activity still did not reach the threshold; 2) The analysis of the ECM community revealed that the genus Tomentella was a dominant species in all four tree species, while the abundance of the genera Rhizopogon and Phialocephala varies depending on the host species; 3) There was no significant difference in the enzyme activities of ECM mycorrhizal communities of P. armandii and P. taeda at different N concentrations, indicating the ecological redundancy.

In the scenario of a long-term increase in N input levels, the composition of the ECM community undergoes adjustments in response to changes in both host plants and N deposition levels. Determining the threshold for these changes serves as a criterion for assessing this process. This process holds crucial academic significance in terms of guiding the understanding of carbon, nitrogen, and phosphorus cycles within soil nutrient dynamics and forest management practices.