Grazing lowers soil multifunctionality but boosts soil microbial network complexity and stability in a subtropical grassland of China

Effects of exogenous calcium on seed germination and physiological traits of alfalfa (Medicago sativa) seedlings

To enhance the cultivation and utility of alfalfa (Medicago sativa) in calcium-rich environments, we assessed the germination, growth, and physiological responses of seven alfalfa varieties-Crown, Dieter, PANGO, Gladiator, Victoria, WL525, and Magnum 801-under varying calcium chloride (CaCl2) concentrations (0, 5, 25, and 50 mmol·L-1). Germination indices, root and shoot growth, enzyme activities, and osmotic regulation parameters were analyzed to evaluate adaptive responses to calcium stress. Our results showed that alfalfa adapts to calcium stress by increasing root length, enhancing enzyme activities, regulating osmotic substance content, and reducing malondialdehyde levels, thereby striving to maintain stable dry matter content. However, the extent of these adaptive responses varied among the different varieties. Based on a comprehensive evaluation, the calcium adaptability of the varieties ranked in the following order: Gladiator > Victoria > Dieter > Magnum 801 > WL525 > Crown > PANGO. Notably, calcium concentrations of 5-25 mmol·L-1 were found to be optimal for germination, physiological regulation, and growth, whereas higher concentrations (50 mmol·L-1) induced oxidative stress and impaired growth. This study highlights the role of exogenous calcium in enhancing physiological resilience and provides a robust framework for selecting calcium-tolerant alfalfa varieties suitable for cultivation in karst landscapes. These findings offer theoretical and practical insights for optimizing forage production in calcium-rich soils.

Long-term grazing reduces soil fungal network complexity but enhances plant-soil microbe network connectivity in a semi-arid grassland

Grazing plays a significant role in shaping both aboveground vegetation and belowground microbial communities in arid and semi-arid grasslands, which in turn affects ecosystem functions and sustainability. Therefore, it was essential to implement effective grazing management practices to preserve ecological balance and support sustainable development in these delicate environments. To optimize the traditional continuous grazing policy, we conducted a 10-year seasonal grazing experiment with five treatments in a typical grassland in northern China: no grazing (NG), continuous summer grazing (CG), and three seasonal grazing treatments (G57 in May and July, G68 in June and August, and G79 in July and September). Our study found that although grazing reduced plant community biomass, G68 treatment maintained high plant height and community diversity (P < 0.05). Grazing did not affect soil bacterial and archaeal alpha diversity, but CG treatment reduced soil fungal diversity (P < 0.05). CG reduced the archaeal network's vertices (which represent microbial taxa, OTUs) and connections (ecological interactions between taxa), but seasonal grazing increased its complexity. Furthermore, grazing did not change bacterial networks but enhanced cross-domain interactions (relationships between different biological groups) of plant-soil fungi and plant-soil archaea. Overall, we used the Mantel test to find that soil microbial diversity was positively correlated with soil physicochemical properties rather than plant community characteristics after grazing. These findings are beneficial for the optimization of sustainable grassland management policies and the protection of plant and soil biodiversity.

Adaptation strategies of soil microorganisms in resource changes and stoichiometric imbalances induced by secondary succession on the loess plateau

Sequestering farmland for secondary succession is an effective method of restoring ecosystem services to degraded farmland, but long-term secondary succession often alters ecosystem environments, resources, and substrate stoichiometry. Currently, it is not known how resource changes and stoichiometric imbalances due to secondary succession affect soil microbial community structure and function, hindering our understanding of the natural resilience for degraded ecosystems. Here, we assessed nutrient limitation elements, community structure, metabolic functions, co-occurrence network complexity, and community stability of soil microorganisms during secondary succession of abandoned farmlands on the Loess Plateau. Results showed that secondary succession significantly altered plant characteristics and soil properties, as well as causing stoichiometry imbalances in nutrient resources. Along the secondary succession chronosequence, microbial nutrient metabolism shifted from phosphorus (P) limitation to carbon (C) and nitrogen (N) co-limitation. Microbial diversity, eutrophic flora, plant growth-promoting bacteria, and metabolism functional groups increased significantly during the 20 years after the abandonment of the farmlands, but decreased significantly with long-term succession. However, oligotrophic flora and P-solubilizing bacteria became dominant after 30 years of secondary succession on abandoned farmlands. The topological features of microbial co-occurring networks, including nodes, degree, closeness, betweenness, and eigenvector complexity, natural connectivity, and community stability first increased and then decreased with secondary succession. Correlation and random forest analyses indicated that secondary succession-induced stoichiometry imbalances in C:N and N:P, as well as changes in soil organic C and lignin phenols, were the key factors influencing microbial community structure and function. Overall, these results enhance our understanding of the adaptation strategies of soil microbial communities in ecologically managed regions to changes in ecosystem resources and stoichiometric imbalances.

Structure and Diversity of Endophytic Bacteria in Maize Seeds and Germinating Roots

Seed endophytes in maize, which facilitate the transmission of microorganisms from one plant generation to the next, may play a crucial role in plant protection and growth promotion. This study aimed to investigate the effects of various maize varieties on the communities of endophytic bacteria in seeds and germinating roots. This study utilized Illumina high-throughput sequencing technology to examine the structural and diversity differences of endophytic bacterial communities within seed maize (BY1507), silage maize (QQ446), and wild maize (Teosinte) in both seeds and germinating roots. The results showed that 416 bacterial genera were detected, with Pantoea, Lachnospiraceae, Pararhizobium, Enterobacteriaceae, Stenotrophomonas, and Pseudonocardia being the most prevalent (relative abundance > 10%) at the genus level. No significant difference was observed in diversity indices (Chao1, ACE, Shannon, and Simpson) of seed endophytes among BY1507, QQ446, and Teosinte. The Shannon and Simpson indices for the germinating root endophyte from the wild variety (Teosinte) were significantly higher than the domesticated varieties (BY1507 and QQ446). PCoA revealed a notable overlap in the endophytic bacterial communities from the seeds of BY1507, QQ446, and Teosinte. Yet, clustering patterns were found. Co-occurrence network analysis showed that BY1507, QQ446, and Teosinte share a notable proportion of shared endophytic bacteria (>30%) between the seeds and germinating roots. This investigation elucidates the characteristics of endophytic microbial communities of seeds and germinating roots with seed maize, silage maize, and wild maize, offering data for future research on the physiological ecological adaptation of these endophytic microbial communities.

Shrub expansion raises both aboveground and underground multifunctionality on a subtropical plateau grassland: coupling multitrophic community assembly to multifunctionality and functional trade-off

Introduction

Shrubs have expanded into grasslands globally. However, the relative importance of aboveground and underground diversity and the relative importance of underground community assembly and diversity in shaping multifunctionality and functional trade-offs over shrub expansion remains unknown.

Methods

In this study, aboveground and underground multitrophic communities (abundant and rare archaea, bacteria, fungi, nematodes, and protists) and 208 aboveground and underground ecosystem properties or indicators were measured at three stages (Grass, Mosaic, Shrub) of shrub expansion on the Guizhou subtropical plateau grassland to study multifunctionality and functional trade-offs.

Results

The results showed that shrub expansion significantly enhanced aboveground, underground, and entire ecosystem multifunctionality. The functional trade-off intensities of the aboveground, underground, and entire ecosystems showed significant V-shaped changes with shrub expansion. Shrub expansion improved plant species richness and changed the assembly process and species richness of soil abundant and rare subcommunities. Plant species diversity had a greater impact on multifunctionality than soil microbial diversity by more than 16%. The effect of plant species diversity on functional trade-offs was only one-fifth of the effect of soil microbial diversity. The soil microbial species richness did not affect multifunctionality, however, the assembly process of soil microbial communities did. Rather than the assembly process of soil microbial communities, the soil microbial species richness affected functional trade-offs.

Discussion

Our study is the first to couple multitrophic community assemblies to multifunctionality and functional trade-offs. Our results would boost the understanding of the role of aboveground and underground diversity in multifunctionality and functional trade-offs.

Grazing practices affect phyllosphere and rhizosphere bacterial communities of Kobresia humilis by altering their network stability

The primary utilization strategy for meadow grasslands on the Qinghai-Tibet Plateau (QTP) is livestock grazing. This practice is considered as one of the major drivers of plant-associated bacterial community construction and changes in soil properties. The species of Kobresia humilis is considered as the most dominant one in grasslands. However, how different grazing practices affect the phyllosphere and rhizosphere bacterial communities of K. humilis is unknown. To address this issue, the effects of the grazing enclosure (GE), single-species grazing (YG and SG, representing yak only and sheep only, respectively), and different ratios of grazing (ratio of yak to sheep is 1:2, 1:4, and 1:6, represented by MG1:2, MG1:4, and MG1:6, respectively) on the dominant plant of K. humilis, it's phyllosphere and rhizosphere bacteria, and soil properties were investigated using artificially controlled grazing and grazing enclosure. Our data showed that grazing enclosure enhanced vegetation coverage, and rhizosphere bacterial richness and diversity, while reduced plant number and bacterial network stability of K. humilis. The NO3--N, K+, and Cl- concentrations were lower under grazing compared to GE. SG reduced the concentration of NH4+-N, TN, K+, and Na+ compared to YG. Moderate grazing intensity had a lower relative abundance of the r-strategists (Bacteroidota and Gammaproteobacteria) with higher bacterial network stability. Yak and sheep grazing showed reversed impacts on the bacterial network stability between the phyllosphere and rhizosphere of K. humilis. Proteobacteria and Actinobacteriota were identified in the molecular ecological network analysis as keystone taxa in the phyllosphere and rhizosphere networks, respectively, under all treatments. This study explained why sheep grazing has more adverse effects on grazing-tolerant grass species, K. humilis, than yak grazing, and will contribute to a better understanding of the impacts of different grazing practices and grazing enclosure on alpine grassland ecosystems on the QTP.

Grazing practices affect soil microbial networks but not diversity and composition in alpine meadows of northeastern Qinghai-Tibetan plateau

Livestock grazing is the primary practice in alpine meadows and can alter soil microbiomes, which is critical for ecosystem functions and services. Seasonal grazing (SG) and continuous grazing (CG) are two kinds of different grazing practices that dominate alpine meadows on the Qinghai-Tibetan Plateau (QTP), and how they affect soil microbial communities remains in-depth exploration. The present study was conducted to investigate the effects of different grazing practices (i.e., SG and CG) on the diversity, composition, and co-occurrence networks of soil bacteria and fungi in QTP alpine meadows. Soil microbial α- and β-diversity showed no obvious difference between SG and CG grasslands. Grazing practices had little impact on soil microbial composition, except that the relative abundance of Proteobacteria and Ascomycota showed significant difference between SG and CG grasslands. Soil microbial networks were more complex and less stable in SG grasslands than that in CG grasslands, and the bacterial networks were more complex than fungal networks. Soil fungal diversity was more strongly correlated with environmental factors than bacteria, whereas both fungal and bacterial structures were mainly influenced by soil pH, total nitrogen, and ammonium nitrogen. These findings indicate that microbial associations are more sensitive to grazing practices than microbial diversity and composition, and that SG may be a better grazing practice for ecological benefits in alpine meadows.

Effect of Trichoderma viride on rhizosphere microbial communities and biocontrol of soybean root rot

Biological seed dressing is a cost-effective means to protect plant roots from pathogens. Trichoderma is generally considered as one of the most common biological seed dressings. However, there is still a dearth of information on the effects of Trichoderma on microbial community of rhizosphere soil. High-throughput sequencing was used to analyze the effects of Trichoderma viride and a chemical fungicide on microbial community of soybean rhizosphere soil. The results showed that both T. viride and chemical fungicide could significantly reduce the disease index of soybean (15.11% for Trichoderma and 17.33% for Chemical), while no significant difference was observed between them. Both T. viride and chemical fungicide could affect the structure of rhizosphere microbial community, they increased the β-diversity of microbial community and significantly reduce the relative abundance of Saprotroph-Symbiotroph. Chemical fungicide could reduce the complexity and stability of co-occurrence network. However, T. viride is beneficial for maintaining network stability and increasing network complexity. There were 31 bacterial genera and 21 fungal genera significantly correlated with the disease index. Furthermore, several potential plant pathogenic microorganisms were also positively correlated with disease index, such as Fusarium, Aspergillus, Conocybe, Naganishia, and Monocillium. From this work, T. viride may be used as a substitute for chemical fungicide to control soybean root rot and be more friendly to soil microecology.