Different Responses of Soil Environmental Factors, Soil Bacterial Community, and Root Performance to Reductive Soil Disinfestation and Soil Fumigant Chloropicrin

Reductive soil disinfestation (RSD) and soil fumigant chloropicrin (SFC) are two common agricultural strategies for the elimination of soil-borne pathogens. However, the differences in soil environmental factors, soil bacterial microbiome, and root performance between SFC and RSD are poorly understood. In this study, three soil treatments, untreated control (CK), SFC with 0.5 t⋅ha–1 chloropicrin, and RSD with 15 t⋅ha–1 animal feces, were compared. We evaluated their effects on soil environmental factors, bacterial community structure, and root activity using chemical analysis and high-throughput sequencing. RSD treatment improved soil composition structure, bacterial diversity, and root performance to a greater extent. Carbon source utilization preference and bacterial community structure were strikingly altered by SFC and RSD practices. Bacterial richness, diversity, and evenness were notably lowered in the SFC- and RSD-treated soil compared with the CK-treated soil. However, RSD-treated soil harbored distinct unique and core microbiomes that were composed of more abundant and diverse potentially disease-suppressive and organic-decomposable agents. Also, soil bacterial diversity and composition were closely related to soil physicochemical properties and enzyme activity, of which pH, available Na (ANa), available Mg (AMg), available Mn (AMn), total Na (TNa), total Ca (TCa), total Cu (TCu), total Sr (TSr), urease (S-UE), acid phosphatase (S-ACP), and sucrase (S-SC) were the main drivers. Moreover, RSD treatment also significantly increased ginseng root activity. Collectively, these results suggest that RSD practices could considerably restore soil nutrient structure and bacterial diversity and improve root performance, which can be applied as a potential agricultural practice for the development of disease-suppressive soil.

After Habitat Changed, Evaluation For Genetic Diversity And Secondary Metabolic Changes of Cultivated And Wild Populations of Medicinal Plants

Background: With the increasing use of traditional herbal medicine, the issue of the genetic diversity of medicinal plants has received considerable critical attention. A high degree of genetic diversity is the basis for maintaining the stability and long-term survival of the population, so the changes in genetic diversity and genetic structure of cultivated medicinal plants caused by habitat changes can not be ignored; Meanwhile, the difference of secondary metabolism of medicinal plants caused by habitat change is also deserving of attention simultaneously. And It is also worth pondering whether the changes between them are consistent. Results: In this study, the wild and cultivated populations of Polygonatum odoratum, Dioscorea nipponica and Acanthopanax sessiliflorus were selected as the research objects. and the genetic structure and HPLC fingerprint between wild and cultivated populations were compared and analyzed by using Simple Sequence Repeats (SSR) marker and HPLC . The results demonstrated that the wild and cultivated populations of the three medicinal plants maintained higher genetic diversity, however, the genetic structure of wild populations of P.odoratum and D.nipponica is more similar. In addition, there was a great genetic differentiation between P.odoratum and D.nipponica populations. There were significant differences in HPLC fingerprints among different populations, in which the secondary metabolites of wild populations were more complex, nevertheless, there was less difference in HPLC fingerprints between wild and cultivated populations of P.odoratum and D.nipponica. Spearman correlation analysis implied that environmental factors (including soil environmental factors, rainfall, temperature) had significant effects on the secondary metabolites of the three medicinal plants, whereas, soil environmental factors had less effect on the genetic structure of the three medicinal plants. Conclusion: In conclusion, during the cultivation years, environmental factors only have a significant effect on the secondary metabolism of the three medicinal plants, their populations still maintain higher genetic diversity and stable genetic structure, what’s more, the secondary metabolites of the same medicinal plants with stable and similar genetic structure may still be different from each other when the habitat is changed. It indicated that there is no obvious consistency between them during the cultivation years.

Two Distinct Soil Disinfestations Differently Modify the Bacterial Communities in a Tomato Field

Reductive soil disinfestation (RSD) and soil solarization (SS) were evaluated based on environmental factors, microbiome, and suppression of Fusarium oxysporum in a tomato field soil. Soil environmental factors (moisture content, electric conductivity, pH, and redox potential (RP)) were measured during soil disinfestations. All factors were more strongly influenced by RSD than SS. 16S rRNA amplicon sequencing of RSD- and SS-treated soils was performed. The bacterial communities were taxonomically and functionally distinct depending on treatment methods and periods and significantly correlated with pH and RP. Fifty-four pathways predicted by PICRUSt2 (third level in MetaCyc hierarchy) were significantly different between RSD and SS. Quantitative polymerase chain reaction demonstrated that both treatments equally suppressed F. oxysporum. The growth and yield of tomato cultivated after treatments were similar between RSD and SS. RSD and SS shaped different soil bacterial communities, although the effects on pathogen suppression and tomato plant growth were comparable between treatments. The existence of pathogen-suppressive microbes, other than Clostridia previously reported to have an effect, was suggested. Comparison between RSD and SS provides new aspects of unknown disinfestation patterns and the usefulness of SS as an alternative to RSD.

Comparative Analysis of Fungal Diversity and Community Structure of Different Volcanic Soils in Wudalianchi, China

The relationship between the fungal community characteristics and soil environmental factors of volcanic ecosystem in Wudalianchi, China were investigated. The soil fungal community structure and diversity of new, old, and non-erupting volcanos were explored through highthroughput sequencing technology. The result showed that the physical and chemical properties of three plots were significantly different. Through sequencing 578 species, 366 genera, 202 families, 89 orders, 32 classes, and 11 phyla were detected. Among them Ascomycota and Basidiomycota were the dominant fungi phyla. The relative abundance of various flora determined by phylum classification showed significant differences. The Shannon, Simpson, Ace, and Chao1 indices for the soil fungi in the three plots were also significantly different. Redundancy and correlation analyses showed that the α diversity of fungi was significantly correlated with pH, organic matter and total nitrogen in the soil. These results indicate that soil environmental factors influence the fungal diversity in the different volcanic ecosystems in Wudalianchi, China. Bangladesh J. Bot. 50(2): 327-334, 2021 (June)

Role of seed bank in aboveground vegetation regeneration signal ecosystem transition from arid grassland to shrubland with decreasing soil moisture

Purpose This study aimed to evaluate the role of seed bank during ecosystem transitions from arid grassland to shrubland. Methods We explored the aboveground vegetation, seed bank and soil environmental factors at 29 sites along a moisture gradient that served as a space-for-time substitution in the Qaidam Basin on the Tibetan Plateau to test whether changes seed bank composition or changes in the ability of the seed bank to restore aboveground vegetation could lead to ecosystem transition. Results We found that the composition of the aboveground vegetation presented nonlinear changes with decreased soil moisture and showed an inflection point in the threshold zone on the spatial scale of ecosystem transition from arid grassland to shrubland; however, an inflection point was not observed for the seed bank. Surprisingly, an inflection point of the similarity between the aboveground vegetation and seed bank also emerged at this threshold zone (ecosystem transition from arid grassland and shrubland). Conclusions Our results suggest that the transition from arid grassland to shrub ecosystem is not caused by changes of the seed bank composition but by the inhibition of the seed bank's restorability to aboveground vegetation. Future work on changes in vegetation composition and species diversity with ecosystem transitions should consider the belowground seed bank.

Influence of soil environmental factors on N2O fluxes just after application of three types of organic fertilizers - 4 years study in a grassland on Andosol in southern Hokkaido, Japan

<p>Appropriate application of organic fertilizer is required to reduce environmental impact from grassland and to achieve sustainable livestock production. However, N<sub>2</sub>O fluxes from soil increase mainly due to changes in soil environmental factors such as temperature, moisture, soil pH and soil mineral nitrogen content, immediately just after fertilization, and it may be different among the types of fertilizer. In this study, we investigated that how N<sub>2</sub>O fluxes are influenced by the application of three types of organic fertilizer (manure, slurry, and digestive fluid) for 4 years in a grassland on Andosol in southern Hokkaido, Japan. Five treatment plots: no fertilizer, chemical fertilizer, manure, slurry, and digestive fluid were established in a managed grassland in Shizunai Livestock farm, Hokkaido University. Fertilizers were applied in late April every year from 2017 to 2020. Organic fertilizers were applied such that the NPK not exceed the regional recommendation rate, and the shortage was compensated by chemical fertilizer. N<sub>2</sub>O flux was measured by using a closed chamber method. At the same time of the flux measurements, soil temperature at 5 cm soil, and soil moisture (WFPS), soil pH, NO<sub>3</sub>-N contents in 0-5 cm soil were measured to see the relationship with N<sub>2</sub>O fluxes.</p><p>In 2017, a large peak of N<sub>2</sub>O flux was observed in slurry plot (195.8μg m<sup>-2</sup>h<sup>-1</sup>) and digestive fluid plot (347.8 μg m<sup>-2</sup>h<sup>-1</sup>), whereas in 2018 and 2019, there were no large peak after the fertilization at all plots, however, in 2020, a large peak of N<sub>2</sub>O flux was observed in manure plot (472.7 and 475.7μg m<sup>-2</sup>h<sup>-1</sup>) and slurry plot (194.9μg m<sup>-2</sup>h<sup>-1</sup>). These peaks of N<sub>2</sub>O flux were significantly larger than those in no fertilizer and chemical fertilizer plots. All N<sub>2</sub>O flux peaks were observed when the soil temperature ranged 10-14 ℃. In 2017 and 2020, a large peak of N<sub>2</sub>O flux was observed although WFPS was always above 80% which is the soil moisture level leading to the complete denitrification. There was a negative relationship between N<sub>2</sub>O flux and soil pH. Low soil pH might reduce the N<sub>2</sub>O reductase activity, leading to the large peak of N<sub>2</sub>O flux at high WFPS above 80%. In addition, there was a positive relationship between N<sub>2</sub>O flux and soil NO<sub>3</sub><sup>-</sup>-N contentin 2017 and 2020. However, in 2018 and 2019, when WFPS was below 80% in most days, there was no positive relationship between N<sub>2</sub>O flux and soil NO<sub>3</sub><sup>-</sup>-N content. In conclusion, the peak of N<sub>2</sub>O flux was different depending on the year and fertilizer, In order to reduce N<sub>2</sub>O flux just after fertilization, it is especially important not to lower the soil pH and not to increase the WFPS.</p><div> </div>

Relationship between Soil Fungi and Seedling Density in the Vicinity of Adult Conspecifics in an Arid Desert Forest

Research Highlights: 1. Soil fungi have a higher influence on seedling density compared to soil environmental factors; 2. Host-specific pathogens and beneficial fungi affect seeding density via different influencing mechanisms. Background and Objectives: The growth and development of seedlings are the key processes that affect forest regeneration and maintain community dynamics. However, the influencing factors of seedling growth around their adult conspecifics are not clear in arid desert forests. Probing the intrinsic relations among soil fungi, soil environmental factors (pH, water content, salinity, and nutrition), and seedling density will improve our understanding of forest development and provide a theoretical basis for forest management and protection. Materials and Methods: Four experimental plot types, depending on the distance to adult conspecifics, were set in an arid desert forest. Soil environmental factors, the diversity and composition of the soil fungal community, and the seedlings’ density and height were measured in the four experimental plot types, and their mutual relations were analyzed. Results: Seedling density as well as the diversity and composition of the soil fungal community varied significantly among the four plot types (p < 0.05). Soil environmental factors, especially soil salinity, pH, and soil water content, had significant influences on the seedling density and diversity and composition of the soil fungal community. The contribution of soil fungi (72.61%) to the variation in seedling density was much higher than the soil environmental factors (27.39%). The contribution of detrimental fungi to the variation in seedling density was higher than the beneficial fungi. Conclusions: Soil fungi mostly affected the distribution of seedling density in the vicinity of adult conspecifics in an arid desert forest. The distribution of seedling density in the vicinity of adults was mainly influenced by the detrimental fungi, while the adults in the periphery area was mainly influenced by the beneficial fungi.