A better understanding of tree‐based intercropping effects on soil physicochemical properties and bacterial community has a potential contribution to improvement of agroforestry productivity and sustainability. In this study, we investigated the effects of mulberry/alfalfa intercropping on soil physicochemical properties and soil bacterial community by MiSeq sequencing of bacterial 16S rRNA gene. The results showed a significant increase in the contents of available nitrogen, available phosphate, available potassium, and total carbon in the rhizosphere soil of the intercropped alfalfa. Sequencing results showed that intercropping improved bacterial richness and diversity of mulberry and alfalfa based on richness estimates and diversity indices. The relative abundances of Proteobacteria, Actinobacteria, and Firmicutes were significantly higher in intercropping mulberry than in monoculture mulberry; and the abundances of Proteobacteria, Bacteroidetes, and Gemmatimonadetes in the intercropping alfalfa were markedly higher than that in monoculture alfalfa. Bacterial taxa with soil nutrients cycling were enriched in the intercropping system. There were higher relative abundances of Bacillus (0.32%), Pseudomonas (0.14%), and Microbacterium (0.07%) in intercropping mulberry soil, and Bradyrhizobium (1.0%), Sphingomonas (0.56%), Pseudomonas (0.18%), Microbacterium (0.15%), Rhizobium (0.09%), Neorhizobium (0.08%), Rhodococcus (0.06%), and Burkholderia (0.04%) in intercropping alfalfa soil. Variance partition analysis showed that planting pattern contributed 26.7% of the total variation of bacterial community, and soil environmental factors explained approximately 56.5% of the total variation. This result indicated that the soil environmental factors were more important than the planting pattern in shaping the bacterial community in the field soil. Overall, mulberry/alfalfa intercropping changed soil bacterial community, which was related to changes in soil total carbon, available phosphate, and available potassium.

A better understanding of soil fungal communities is very useful in revealing the effects of an agroforestry system and would also help us to understand the fungi-mediated effects of agricultural practices on the processes of soil nutrient cycling and crop productivity. Compared to conventional monoculture farming, agroforestry systems have obvious advantages in improving land use efficiency and maintaining soil physicochemical properties, reducing losses of water, soil material, organic matter, and nutrients, as well as ensuring the stability of yields. In this study, we attempted to investigate the impact of a mulberry/alfalfa intercropping system on the soil physicochemical properties and the rhizosphere fungal characteristics (such as the diversity and structure of the fungal community), and to analyze possible correlations among the planting pattern, the soil physicochemical factors, and the fungal community structure. In the intercropping and monoculture systems, we determined the soil physicochemical properties using chemical analysis and the fungal community structure with MiSeq sequencing of the fungal ITS1 region. The results showed that intercropping significantly improved the soil physicochemical properties of alfalfa (total nitrogen, alkaline hydrolysable nitrogen, available potassium, and total carbon contents). Sequencing results showed that the dominant taxonomic groups were Ascomycota, Basidiomycota, and Mucoromycota. Intercropping increased the fungal richness of mulberry and alfalfa rhizosphere soils and improved the fungal diversity of mulberry. The diversity and structure of the fungal community were predominantly influenced by both the planting pattern and soil environmental factors (total nitrogen, total phosphate, and total carbon). Variance partitioning analysis showed that the planting pattern explained 25.9% of the variation of the fungal community structure, and soil environmental factors explained 63.1% of the variation. Planting patterns and soil physicochemical properties conjointly resulted in changes of the soil fungal community structure in proportion.

Under the background of global nitrogen deposition, temperate forest ecosystems are suffering increasing threats, and species diversity is gradually decreasing. In this study, nitrogen addition experiments were conducted on Korean pine (Pinus koraiensis) plantations in Northeast China to explore the effect of long‐term nitrogen addition on herb species diversity to test the following hypothesis: long‐term nitrogen addition further reduced plant species diversity by affecting plant growth, which may be due to soil acidification caused by excessive nitrogen addition. Experimental nitrogen addition was conducted from 2014 to 2021, and the nitrogen treatment levels were as follows: N0 (control treatment, 0/(kg N ha⁻¹ year⁻¹)), N20 (low nitrogen treatment, 20/(kg N ha⁻¹ year⁻¹)), N40 (medium nitrogen treatment, 40/(kg N ha⁻¹ year⁻¹)) and N80 (high nitrogen treatment, 80/(kg N ha⁻¹ year⁻¹)). A herb community survey was conducted in the region from 2015 to 2021. The results showed that long‐term nitrogen addition decreased soil pH, changed the species and composition of herbaceous plants, and decreased the species diversity of understory herbaceous plants. With the increase in nitrogen application years, middle‐ and high‐nitrogen treatments significantly reduced the diversity of early‐spring flowering herbs and early‐spring foliating herbs, and their diversity decreased with the decrease in soil pH, indicating that soil acidification caused by long‐term nitrogen addition may lead to the decrease of plant diversity. However, for early‐spring growing herbs, adequate nitrogen addition may promote their growth. Our results show that plants have evolved different life‐history strategies based on their adaptation mechanisms to the environment, and different life‐history strategies have different responses to long‐term nitrogen addition. However, for most plants, long‐term nitrogen application will have a negative impact on the growth and diversity of herbs in temperate forests.

Introduction: Soil microorganisms play a critical role in maintaining ecological functions; however, their responses to grassland reclamation and tillage remain poorly understood. This study aims to investigate the effects of these practices on soil bacterial communities in the Northeast China Black Soil Region.Methods: We utilized high-throughput sequencing to compare soil bacterial community characteristics between undisturbed grasslands (CK) and reclaimed croplands (F). The analysis focused on assessing structural changes and shifts in ecological strategies of soil bacterial communities under both land-use types.Results: Our findings revealed that croplands exhibited higher soil pH and elevated concentrations of nutrients such as ammonium nitrogen, nitrate nitrogen, and total phosphorus compared to pristine grasslands. The Average Variation Degree (AVD) indicated that bacterial communities in cropland soils had greater compositional stability. Additionally, dominant bacterial genera, particularly Sphingomonas and Pseudarthrobacter, were more prevalent in croplands. Using random forest classification modeling, we identified several rare bacterial genera, including Rhodomicrobium, Amycolatopsis, and Clostridium, which, despite each representing less than 1% of the community, played critical roles in shaping microbial community structure. Co-occurrence network analysis showed that reclamation reduced interspecies interactions and significantly decreased network complexity, connectivity, and cohesion (P < 0.05). Neutral community assembly modeling further indicated that stochastic processes were more dominant in the assembly of bacterial communities in croplands compared to undisturbed grasslands.Discussion: This study provides a comprehensive understanding of how grassland reclamation and tillage influence soil bacterial communities in the Songnen Plain black soil region. The findings enhance our ecological understanding of land use changes and offer valuable insights for the sustainable management of black soil resources and ecosystems.

With the development of agriculture and industry, the increase in nitrogen (N) deposition has caused widespread concern among scientists. Although emission reduction policies have slowed N releases in Europe and North America, the threat to biodiversity cannot be ignored. Arbuscular mycorrhizal (AM) fungi play an important role in the establishment and maintenance of plant communities in forest ecosystems, both their distribution and diversity have vital ecological functions. Therefore, we analyzed the effects of long-term N addition on AM fungi and understory herbaceous plants in Korean pine plantation in northern China, measured the soil properties, AM fungal and herbaceous community structure and diversity with different concentrations of NH4NO3 (0,20,40,80 kg N ha-1 year-1) applied for 7 consecutive years. The results showed that long-term nitrogen fertilization affected soil properties, decreased soil pH, increased soil ammonium content, and caused significant fluctuations in P elements. Nitrogen application improved the stability of soil aggregates by increasing the content of GRSP (glomus-related soil protein); N addition changed the AM fungal community composition, and Glomus genus was more adaptable to the acidic environment treated with the highest nitrogen concentration; with the increase of N treatment, The species of AM fungi and herbaceous plants and the biomass of fine roots decreased. In summary, we concluded that long-term understory application of different concentrations of N altered soil pH, changed the distribution of N, P elements, and the soil aggregate fractions, reduced AM fungal and herb diversity. The importance of AM fungi in maintaining forest ecosystem diversity under the pressure of global change was verified.