The effects of afforestation on soil bacterial communities in temperate grassland are modulated by soil chemical properties

Organic matter stability and lability in terrestrial and aquatic ecosystems: A chemical and microbial perspective

Terrestrial and aquatic ecosystems have specific carbon fingerprints and sequestration potential, due to the intrinsic properties of the organic matter (OM), mineral content, environmental conditions, and microbial community composition and functions. A small variation in the OM pool can imbalance the carbon dynamics that ultimately affect the climate and functionality of each ecosystem, at regional and global scales. Here, we review the factors that continuously contribute to carbon stability and lability, with particular attention to the OM formation and nature, as well as the microbial activities that drive OM aggregation, degradation and eventually greenhouse gas emissions. We identified that in both aquatic and terrestrial ecosystems, microbial attributes (i.e., carbon metabolism, carbon use efficiency, necromass, enzymatic activities) play a pivotal role in transforming the carbon stock and yet they are far from being completely characterised and not often included in carbon estimations. Therefore, future research must focus on the integration of microbial components into carbon mapping and models, as well as on translating molecular-scaled studies into practical approaches. These strategies will improve carbon management and restoration across ecosystems and contribute to overcome current climate challenges.

Unravelling the dynamics of soil microbial communities under the environmental selection and range shift process in afforestation ecosystems

The process of forest range shift not only affects the vegetation aboveground but also influences the dynamics of belowground microbial communities. To investigate the changes in soil under forest range shift, we examined the natural forest soil microbiome along with its corresponding physicochemical properties, as well as the afforestation of natural forest by seedlings and sowing. By utilizing natural forests and employing different afforestation methods, we simulated the three stages of forest range shift: the staging stage, regeneration, and colonization. We employed network analysis and phylogenetic assemblages to examine the structure of soil microbial communities during these three stages in a macro-environmental change context. Ordination and regression analyses were also used to explore the correlation between microorganisms, environmental factors, and changes in their niches. The findings revealed that different afforestation (range shift) types led to distinct microbial compositions. Seedling afforestation exhibited similarities to mature forests, suggesting a significant influence on below-ground microorganisms. In contrast, sowing-based afforestation resulted in small changes in soil microbes, indicating a legacy effect on grassland soils. The impact of the rhizosphere on microbial composition remained consistent across the three forest types. Overall, this study underscores the significance of forest range shift in shaping soil microbial communities and emphasizes the need to consider these dynamics in forest management and restoration endeavours.

Effects of different types of vegetation cover on soil microorganisms and humus characteristics of soda-saline land in the Songnen Plain

Introduction

In the soda-saline grasslands of the Songnen Plain, Jilin Province, China, the prohibition of grazing has led to significant changes in plant communities and soil properties. However, the intricate interplay between soil physical and chemical attributes, the soil microbial community, and their combined influence on soil humus composition remains poorly understood.

Methods

Our study aimed to evaluate the impact of natural vegetation restoration on soil properties, microbial community diversity, and composition in the soda-saline soil region of the Songnen Plain. We conducted assessments of soil physical and chemical properties, analyzed community diversity, and composition at a soil depth range of 0-20 cm. The study covered soils with dominant soda-saline vegetation species, including Suaeda glauca Bunge, Puccinellia chinampoensis Ohwi, Chloris virgata Swarta, Phragmites australis (Clay.), Leymus chinensis (Trin.), and Tzvelev. We compared these vegetated soils to bare land devoid of any plants.

Results

We found that soil organic content (SOC) in vegetation restoration areas was higher than in bare land, with SOC content varying between 3.64 and 11.15 g/kg in different vegetated areas. Notably, soil pH emerged as a pivotal factor, explaining 11.4% and 12.2% of the variance in soil bacteria and fungi, respectively. There were correlations between SOC content and the relative abundance of specific microbial groups, with Acidobacteria and Mortierella showing a positive correlation, while Actinobacteria, Gemmatimonadetes, and Ascomycota exhibited significant negative correlations with SOC.

Discussion

The disparities in SOC composition and content among the soda-saline vegetation types were primarily attributed to variations in pH. Consequently, reducing soil pH is identified as a critical step in the process of vegetation restoration in soda-saline land. Prohibiting grazing has the potential to increase soda-saline SOC content and enhance microbial diversity, with Leymus chinensis and Phragmites australis showing particularly promising results in terms of higher SOC carbon content and microbial diversity.

Physicochemical and Biotic Changes and the Phylogenetic Evenness of Microbial Community in Soil Subjected to Phytoreclamation

Phytoreclamation is the intervention of plants to improve degraded soil quality, changing soil biotic and abiotic properties. Many studies have focused on microbial composition and bioactivity, but few explored the changes in phylogenetic assemblages of soil microbiota after phytoreclamation. This study compared microbiomes of bare land to those of planted soils and investigated how the rhizosphere environment affects microbial assemblages from monocot Poa pratensis and eudicot Dianthus plumarius plantings using 16S rRNA metabarcoding. The results showed that the biotic susceptibility of soil to the rhizosphere environment was higher than that of the abiotic. A noticeable change was in some soil physicochemical properties like Na, P, Zn, Cu, C, and sand-to-silt proportion before and after phytoreclamation, but not between the rhizosphere and bulk soil of plantings. Contrastingly, microbial composition and diversity were significantly affected by both turfing and rhizosphere effects and were more susceptible to differences in turfing or not than in planting species. In the turfgrass, the microbiome differences between plants were greater in the rhizosphere than in the surrounding bulk soil, indicating the proximal influence of root exudates. We also found that the main abiotic factors that influenced microbial composition were Na, Zn, NO_x, N, and S; as for the phylogenetic assemblages, were by K levels and the increase of silt. Turfgrass decomposes soil aggregates and changes the physicochemical properties, thereby evens the phylogenetic clustering of the soil microbial community. We demonstrated that the deterministic process affects the microbial assemblage and acts as a selective agent of the soil microbiota in fundamental and realized niches. Phytoreclamation may lead to abiotic soil changes that reallocate resources to microbes. This could affect the phylogeny of the microbial assemblages and increase microbial richness.

Improving Effects of Afforestation with Different Forest Types on Soil Nutrients and Bacterial Community in Barren Hills of North China

Afforestation can improve soil nutrient content and microbial community structure, increase soil carbon sequestration, and reduce greenhouse gas emissions. However, at present, there is a lack of research on the low hills and mountainous areas in North China. In order to scientifically evaluate the effect of afforestation recovery with different forest types on the improvement of the soil ecological system, the Fanggan ecological restoration in North China was taken as the research sample, and the coniferous forests, mixed coniferous and broad-leaved forest quadrats and broad-leaved forests, as well as the contrast of barren hills bushes were set to achieve the research goals. Research results of different forest types on soil nutrient and bacterial community in the Fanggan ecological restoration area have shown that afforestation with broad-leaved forests most obviously improved the nutrition properties and bacterial community of soil. (1) Broad-leaved forest afforestation obviously improved water retention and ammonia nitrogen content but reduced the content of available phosphorus and nitrate nitrogen of surface soil. It also increased available phosphorus, ammonia nitrogen, and nitrate nitrogen content of lower soil. (2) Broad-leaved forest afforestation significantly increased α-diversity of the bacterial community in surface soil, but only enhanced the Chao1 and ACE indices of lower soil. In addition, afforestation has also significantly changed the structure of soil bacterial community and β-diversity index. (3) Proteobacteria, Acidobacteria, Actinobacteria, and Verrucomicrobia accounted for the highest proportion of soil bacterial community. Proteobacteria and Verrucomicrobia occupied higher proportion in broad-leaved forests than in other forest types, while the proportion of Acidobacteria and Actinobacteria was the opposite. (4) Afforestation decreased cooperation and increased competition among bacteria of surface soil as well as increased coexistence and rejection among subsoil bacteria. (5) pH, ammonia nitrogen, organic carbon, and available phosphorus have exhibited a significant impact on the structure of bacterial community in the surface soil, while the bacterial community structure of the lower soil was mainly affected by pH and available phosphorus. Results have fully demonstrated the positive effects of broad-leaved forest on the restoration of soil nutrients and microbial community structure. Meanwhile, the important combinations of soil physical and chemical factors affecting soil bacterial community structure were also explored. The results can provide scientific basis for revealing the mechanism of soil organic matter, nutrient and ecological function restoration by artificial afforestation, and also offer theoretical support and practical reference for the restoration of artificial afforestation in the hilly and mountainous areas of North China.

High throughput sequencing-based analysis of the soil bacterial community structure and functions of Tamarix shrubs in the lower reaches of the Tarim River

Tamarix is a dominant species in the Tarim River Basin, the longest inland river in China. Tamarix plays an important role in the ecological restoration of this region. In this study, to investigate the soil bacterial community diversity in Tamarix shrubs, we collected soil samples from the inside and edge of the canopy and the edge of nebkhas and non-nebkhas Tamarix shrubs located near the Yingsu section in the lower reaches of Tarim River. High throughput sequencing technology was employed to discern the composition and function of soil bacterial communities in nebkhas and non-nebkhas Tamarix shrubs. Besides, the physicochemical properties of soil and the spatial distribution characteristics of soil bacteria and their correlation were analyzed. The outcomes of this analysis demonstrated that different parts of Tamarix shrubs had significantly different effects on soil pH, total K (TK), available K (AK), ammonium N (NH₄⁺), and available P (AP) values (P < 0.05), but not on soil moisture (SWC), total salt (TDS), electrical conductivity (EC), organic matter (OM), total N (TN), total P (TP), and nitrate N (NO₃⁻) values. The soil bacterial communities identified in Tamarix shrubs were categorized into two kingdoms, 71 phyla, 161 classes, 345 orders, 473 families, and 702 genera. Halobacterota, unidentified bacteria, and Proteobacteria were found to be dominant phyla. The correlation between the soil physicochemical factors and soil bacterial community was analyzed, and as per the outcomes OM, AK, AP, EC, and NH₄⁺ were found to primarily affect the structure of the soil bacterial community. SWC, TK and pH were positively correlated with each other, but negatively correlated with other soil factors. At the phyla level, a significantly positive correlation was observed between the Halobacterota and AP, OM as well as Bacteroidota and AK (P < 0.01), but a significantly negative correlation was observed between the Chloroflexi and AK, EC (P < 0.01). The PICRUSt software was employed to predict the functional genes. A total of 6,195 KEGG ortholog genes were obtained. The function of soil bacteria was annotated, and six metabolic pathways in level 1, 41 metabolic pathways in level 2, and 307 metabolic pathways in level 3 were enriched, among which the functional gene related to metabolism, genetic information processing, and environmental information processing was found to have the dominant advantage. The results showed that the nebkhas and canopy of Tamarix shrubs had a certain enrichment effect on soil nutrients content, and bacterial abundance and significant effects on the structure and function of the soil bacterial community.

Comparison of soil bacterial community and functional characteristics following afforestation in the semi-arid areas

Changes in soil bacterial communities, which are crucial for the assessment of ecological restoration in Chinese plantations, have never been studied in the "Three North Shelterbelt" project in the semi-arid areas. We used high-throughput sequencing of the 16S rDNA gene to investigate the soil bacterial community diversity, structure, and functional characteristics in three plantation forests, including Populus × canadensis Moench (PC), Pinus sylvestris var. mongolica (PS), and Pinus tabuliformis (PT). In addition, soil environment factors were measured. There were distinct differences in soil characteristics among different plantation forests. Compared to PS and PT, PC had a higher soil pH, dissolved organic carbon (DOC), and available P, as well as a lower C/N ratio. Furthermore, afforestation with different tree species significantly altered the abundance of Proteobacteria, and Chloroflexi in the soil, and its influence on the bacterial diversity indices. The bacterial community compositions and functional groups related to C and N cycling from PS, and PT were grouped tightly, indicating that the soil bacterial phylogenetic distance of PS and PT were closer than that between PS plus PT and PC. Our results implied that the soil characteristics, as well as the diversity, compositions and functions related to C and N cycling of soil bacterial community obviously differed from the following afforestation, especially between PC and PS plus PT, which in turn enormously established the correlation between the soil microbial community characteristics and the afforestation tree species.