Soil properties, such as carbon stock, nitrogen stock, cation exchange capacity (CEC), bulk density (BD), and pH, may have a different status when the forest type changes. We were interested in how tree species identity and diversity affect soil properties. Forest soil profiles were sampled at a fixed depth (0–10, 10–20, 20–40, and 40–60 cm). The abovementioned soil properties were compared by species to demonstrate the influence of tree species identity. We calculated the true Shannon diversity index and evaluated tree species diversity effects on soil properties. We found that the soil BD, CEC, and pH were all influenced by tree species identity. Tree species diversity only showed a negative effect on soil carbon stock; in contrast, a positive effect on soil nitrogen stock in the 0‐ to 10‐cm soil layer was found. High diversity could lead to a change in the soil nutrient conditions in the form of C/N ratio decreases. In contrast, tree species diversity had a marginal effect on the soil BD, pH, and CEC. We concluded that tree species identity was a strong driver of soil properties in the study area, especially in the 0‐ to 10‐cm layer, and that tree species diversity only altered the soil nutrient condition to some extent.

Agroforestry (tree-based intercropping) is regarded as a promising practice in sustainable agricultural management. However, the impacts of converting cropland to an agroforestry system on microbial communities remain poorly understood. In this study, we assessed the soil bacterial communities in conventional wheat monoculture systems and a chronosequence (5–14 years) walnut-wheat agroforestry system through the high-throughput sequencing of 16S rRNA genes to investigate the effect of agroforestry age on soil bacterial communities and the correlation between soil properties and bacterial communities in the agroecosystem. Our results demonstrate that establishing and developing walnut tree-based agroforestry increased soil bacterial diversity and changed bacterial community structure. Firmicutes, Proteobacteria, Actinobacteria and Acidobacteria were the dominant soil bacterial phyla and Bacillus was the dominant genus. Crop monoculture systems were characterized by the Bacillus (Firmicutes)-dominated microbial community. The relative abundance of Bacillus decreased with agroforestry age; however, subgroups of Proteobacteria and Actinobacteria increased. Of the selected soil physicochemical properties, soil pH and bulk density were significantly correlated with bacterial alpha diversity, and soil pH and organic carbon were the principal drivers in shaping the soil microbial structure as revealed by redundancy analysis (RDA).

Soil degradation has been reported worldwide. To better understand this degradation, we selected Pinus armandii and Quercus aliena var. acuteserrata forests, and a mixed forest of Q. aliena var. acuteserrata and P. armandii in the Qinling Mountains in China for our permanent plots and conducted three investigations over a 20-year period. We determined the amounts of available nitrogen (N) and phosphorus (P) in the soil to track the trajectory of soil quality and compared these with stand characteristics, topographic and climatic attributes to analyze the strength of each factor in influencing the available N and P in the soil. We found that the soil experienced a severe drop in quality, and that degradation is continuing. Temperature is the most critical factor controlling the soil available N, and species composition is the main factor regulating the soil available P. Given the huge gap in content and the increasing rate of nutrients loss, this reduction in soil quality will likely negatively affect ecosystem sustainability.

Historically, intense forest hazards have resulted in an increase in the quantity of fallen wood in the Qinling Mountains. Fallen wood has a decisive influence on the nutrient cycling, carbon budget and ecosystem biodiversity of forests, and fungi are essential for the decomposition of fallen wood. Moreover, decaying dead wood alters fungal communities. The development of high-throughput sequencing methods has facilitated the ongoing investigation of relevant molecular forest ecosystems with a focus on fungal communities. In this study, fallen wood and its associated fungal communities were compared at different stages of decomposition to evaluate relative species abundance and species diversity. The physical and chemical factors that alter fungal communities were also compared by performing correspondence analysis according to host tree species across all stages of decomposition. Tree species were the major source of differences in fungal community diversity at all decomposition stages, and fungal communities achieved the highest levels of diversity at the intermediate and late decomposition stages. Interactions between various physical and chemical factors and fungal communities shared the same regulatory mechanisms, and there was no tree species-specific influence. Improving our knowledge of wood-inhabiting fungal communities is crucial for forest ecosystem conservation.

Afforestation of croplands has been widely adopted on the semi-arid Loess Plateau in recent decades. However, knowledge of soil carbon and nitrogen changes after afforestation is still limited because of the complexity of afforestation approaches. Therefore, an experiment was conducted on two dominant arable soils (tableland soil and terrace soil) on the southern Loess Plateau to evaluate the impact of two afforestation approaches (walnut monocultures and walnut-based agroforestry) on the soil organic carbon (SOC) and soil total nitrogen (STN) content within 2 m soil profiles. In the tableland soil, compared with the continuous crop monoculture (135.90 t C ha⁻¹), SOC stocks in the agroforestry and walnut monoculture system increased by 7.91% and 1.91%, respectively. While in the terrace soil, compared with crop monoculture (102.95 t C ha⁻¹), SOC stocks in the agroforestry and walnut monoculture system decreased by 3.86% and 0.20%, respectively. The STN stock was lower in the tree monocultures and SOC content was significantly correlated with STN. Afforestation increased the SOC and STN stocks in the 0–10 cm soils, but decreased them in the 10–60 cm soils. In the deep soil layers (60–200 cm), SOC content increase was only found in agroforestry in the tableland soil, and no significant differences were found in the terrace soil. Converting cropland to agroforestry has advantages in terms of soil carbon sequestration.

Similar to pathogenic bacteria, rhizobia can inject effector proteins into host cells directly to promote infection via the type III secretion system (T3SS). Nodulation outer protein P (NopP), a specific T3SS effector of rhizobia, plays different roles in the establishment of multiple rhizobia-legume symbiotic systems. Mesorhizobium amorphae CCNWGS0123 (GS0123), which infects Robinia pseudoacacia specifically, secretes several T3SS effectors, including NopP. Here, we demonstrate that NopP is secreted through T3SS-I of GS0123 during the early stages of infection, and its deficiency decreases nodule nitrogenase activity of R. pseudoacacia nodules. A trafficking protein particle complex subunit 13–like protein (TRAPPC13) has been identified as a NopP target protein in R. pseudoacacia roots by screening a yeast two-hybrid library. The physical interaction between NopP and TRAPPC13 is verified by bimolecular fluorescence complementation and coimmunoprecipitation assays. In addition, subcellular localization analysis reveals that both NopP and its target, TRAPPC13, are colocalized on the plasma membrane. Compared with GS0123-inoculated R. pseudoacacia roots, some genes associated with cell wall remodeling and plant innate immunity down-regulated in ΔnopP-inoculated roots at 36 h postinoculation. The results suggest that NopP in M. amorphae CCNWGS0123 acts in multiple processes in R. pseudoacacia during the early stages of infection, and TRAPPC13 could participate in the process as a NopP target. [ ] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .