Intercropping, a green and sustainable planting pattern, has demonstrated positive effects on plant growth and the soil environment. However, there is currently little research on the influence of intercropping leguminous plants and using them as green manure on the soil environment and tea quality. During the profuse flowering period of Chinese milkvetch, the contents of tea amino acids and soluble sugar in intercropping tea plants with soybean increased by 6.89 and 54.58%. Moreover, there was 27.42% increase in soil ammonium nitrogen and 21.63% increase in available nitrogen. When Chinese milkvetch was returned to soil for 1 month during its profuse flowering period, the soybean and Chinese milkvetch as green manure enhanced tea amino acids and soluble sugar by 9.11 and 33.96%, and soil ammonium nitrogen, nitrate nitrogen and available nitrogen increased by 25.04, 77.84, and 48.90%. Intercropping systems also have positive effects on tea quality components, soil fertility, and soil microbial communities during the profuse flowering period of soybeans and when soybeans with this period were returned to the field for 1 month. Furthermore, the soil fertility index was significantly increased, especially in the intercropping system of tea–soybean–Chinese milkvetch. The soil bacterial community complexity and fungal community interactions were significantly increased. Soil pH, nitrate nitrogen, and available phosphorus were found to be crucial influencing factors on soil microbial communities, specifically bacterial communities. These results highlight the significance of optimizing intercropping systems to improve the soil environment and tea quality components. They also provide a theoretical foundation for promoting the sustainable development of tea plantations.

Microorganisms play essential roles in soil-ecosystem multifunctionality. However, the contribution of their community assembly processes, composition, diversity, and keystone species to ecosystem multifunctionality is unclear, especially in tea-plantation ecosystems. In order to assess the effects of various intercropping patterns (tea-plant monoculture and tea plants, respectively, intercropped with soybean, soybean—milk vetch, soybean—red clover, and soybean—smooth vetch) on soil rare and abundant taxa, a field experiment was carried out. We found that tea plantation intercropping with legumes improved the soil-ecosystem multifunctionality by altering the soil environment, and ultimately benefited nutrient absorption and quality improvement of tea leaves. Whether it was in bacteria or fungi, rare taxa had a higher proportion of deterministic processes in community assembly than abundant taxa. Additionally, intercropping practices changed the soil environment, and rare bacterial taxa were assembled and shifted from variable selection to homogeneous dispersal. Intercropping practices significantly changed the bacterial and fungal communities’ composition, and rare taxa had higher α-diversity than abundant taxa. Increasing legume species in intercropping practice enhanced community dissimilarity to the tea monoculture by affecting soil pH, ammonium nitrogen, and nitrate nitrogen. Rare bacterial and fungal β-diversity exhibited stronger positive relationships with ecosystem multifunctionality (both average and multi-threshold approaches) compared to the corresponding abundant taxa. Furthermore, ecosystem multifunctionality under different intercropping practices was closely related to the keystone rare operational taxonomic units, especially rare bacterial species of Chloroflexi. Our results emphasize the disparate feedbacks of rare and abundant taxa to diverse intercropping practices, as well as the important connection between rare bacterial taxa and ecosystem multifunctionality.

Rational fertilization boosts crop yields and enhances nutritional value, but over-fertilization is counterproductive. Furthermore, water eutrophication caused by excessive use of nitrogen fertilizers has become a major agricultural non-point source pollution problem in the Erhai Lake Basin of China. This study took high-fertility soil as the research object and set up six treatments: no fertilization (CK), local recommended fertilization (T1), optimized chemical fertilizer (T2), organic fertilizer replacing 20% (T3), 40% (T4), 60% (T5) of chemical fertilizer with equal nitrogen. The results show that replacement of chemical nitrogen fertilizers with organic nitrogen fertilizers at an appropriate ratio can optimize soil nitrogen supply, enhance the activity of soil nitrogen cycle enzymes, thereby promoting the activity of nitrogen metabolism enzymes and nitrogen assimilation capacity in potato plants, and ultimately achieve a synergistic effect of increased yield, improved quality and higher fertilizer use efficiency. Among the treatments, the nitrate reductase (S-NR) activity in potato leaves was 36.74% and 41.66% higher under T3 than T1 and T4, respectively. For potato quality, Vitamin C (VC) content was 17.41% higher under T3 than T2; soluble protein content was 11.44%, 10.63%, and 9.44% higher under T3 than T1, T2, and T4, respectively. The replacement of chemical fertilizers with organic fertilizers mainly enhances the protein content in potato tubers by increasing soil urease (S-URE) activity and leaf relative chlorophyll content (SPAD) value. Based on the comprehensive differential combination evaluation model, considering potato metabolic absorption, yield, quality, and soil nitrogen content, the T3 treatment is the optimal fertilization method in the Erhai Lake Basin of China.

Nitrogen application significantly affects microorganisms in agricultural ecosystems. However, it is still unclear how nitrogen application affects soil chemical properties and microbial communities in purple mudstone weathering products. In this study, a field soil column experiment was conducted in a typical purple soil area with four nitrogen fertilizer application gradients of 0 [CK], 280 [N1], 560 [N2], and 840 [N3] N kg ha⁻¹. Nitrogen addition decreased the bacterial chao1 value and increased the bacterial evenness index. For both α- and β-diversity, the effect of nitrogen addition on bacteria was much greater than that on fungi. Nitrogen addition significantly increased the relative abundance of Proteobacteria, Gemmatimonadetes, Bacteroidetes, and Ascomycota and decreased the relative abundance of Actinobacteria, Cyanobacteria, and Basidiomycota. Both pH and TC are the most important soil chemical properties influencing the bacterial and fungal communities. With the increases in the nitrogen application rate, the co-occurrence network complexity increased and then decreased. In summary, nitrogen fertilizer application could significantly change the soil chemical properties, microbial community diversity, composition, and co-occurrence network of purple mudstone weathering products. Among them, the N2 treatment (560 N kg∙ha⁻¹) can more effectively stimulate the soil nutrients, enhance microbial network complexity, and promote further weathering of purple mudstone.