Soil microbial diversity and network complexity drive the ecosystem multifunctionality of temperate grasslands under changing precipitation

High-elevation-induced decrease in soil pH weakens ecosystem multifunctionality by influencing soil microbiomes

Plant environmental stress response has become a global research hotspot, yet there is a lack of clear understanding regarding the mechanisms that maintain microbial diversity and their ecosystem services under environmental stress. In our research, we examined the effects of moderate elevation on the rhizosphere soil characteristics, microbial community composition, and ecosystem multifunctionality (EMF) within agricultural systems. Our findings revealed a notable negative correlation between EMF and elevation, indicating a decline in multifunctionality at higher elevations. Additionally, our analysis across bacterial and protistan communities showed a general decrease in microbial richness with increasing elevation. Using random forest models, pH was identified as the key environmental stressor influencing microbial communities. Furthermore, we found that microbial community diversity is negatively correlated with stability by mediating complexity. Interestingly, while pH was found to affect the complexity within bacterial networks, it did not significantly impact the ecosystem stability along the elevation gradients. Using a Binary-State Speciation and Extinction (BiSSE) model to explore the evolutionary dynamics, we found that Generalists had higher speciation rates and lower extinction rates compared to specialists, resulting in a skewed distribution towards higher net diversification for generalists under increasing environmental stress. Moreover, structural equation modeling (SEM) analysis highlighted a negative correlation between environmental stress and community diversity, but showed a positive correlation between environmental stress and degree of cooperation & competition. These interactions under environmental stress indirectly increased community stability and decreased multifunctionality. Our comprehensive study offers valuable insights into the intricate relationship among environmental factors, microbial communities, and ecosystem functions, especially in the context of varying elevation gradients. These findings contribute significantly to our understanding of how environmental stressors affect microbial diversity and ecosystem services, providing a foundation for future ecological research and management strategies in similar contexts.

Topography- and depth-dependent rhizosphere microbial community characteristics drive ecosystem multifunctionality in Juglans mandshurica forest

Rhizosphere microbial community characteristics and ecosystem multifunctionality (EMF), both affected by topographic factors, are closely correlated. However, more targeted exploration is yet required to fully understand the variations of rhizosphere microbial communities along topographic gradients in different soil layers, as well as whether and how they regulate EMF under specific site conditions. Here, we conducted relevant research on Juglans mandshurica forests at six elevation gradients and two slope positions ranging from 310 to 750 m in Tianjin Baxian Mountain. Results demonstrated that rhizosphere soil physicochemical properties and enzyme activities of both layers (0-20 cm and 20-40 cm) varied significantly with elevation, while only at top layer did slope position have significant impacts on most indicators. Bacterial richness and diversity were higher in the top layer at slope bottom and middle-high elevation, the difference in fungi was not as noticeable. Both topographic factors and soil depth significantly impacted microbial community structure, with Candidatus_Udaeobacter of bacteria, Mortierella, Sebacina, and Hygrocybe of fungi mainly contributing to the dissimilarity between communities. EMF rose with increasing elevation, bacteria were more critical drivers of this process than fungi, and topographic factors could affect EMF by altering bacterial diversity and dominant taxa abundance. For evaluating EMF, the aggregate structure of sub layer and the carbon cycle-related indicators of top layer were of higher importance. Our results revealed the depth-dependent characteristics of the rhizosphere microbial community along topographic gradients in studied stands, as well as the pivotal regulatory role of bacteria on EMF, while also highlighting depth as an important variable for analyzing soil properties and EMF. This work helps us better understand the response of individuals and communities of J. mandshurica to changing environmental conditions, further providing a scientific reference for the management and protection of secondary forests locally and in North China.

Soil Fungal Community Differences in Manual Plantation Larch Forest and Natural Larch Forest in Northeast China

Soil fungal communities are pivotal components in ecosystems and play an essential role in global biogeochemical cycles. In this study, we determined the fungal communities of a natural larch forest and a manual plantation larch forest in Heilongjiang Zhongyangzhan Black-billed Capercaillie Nature Reserve and Gala Mountain Forest using high-throughput sequencing. The interactions between soil fungal communities were analysed utilising a co-occurrence network. The relationship between soil nutrients and soil fungal communities was determined with the help of Mantel analysis and a correlation heatmap. The Kruskal-Wallis test indicated that different genera of fungi differed in the two forest types. The results show that there was a significant change in the alpha diversity of soil fungal communities in both forests. In contrast, nonmetric multidimensional scaling (NMDS) analysis showed significant differences in the soil fungal community structures between the manual plantation larch forest and the natural larch forest. The soil fungal co-occurrence network showed that the complexity of the soil fungal communities in the manual plantation larch forest decreased significantly compared to those in the natural larch forest. A Mantel analysis revealed a correlation between the soil fungal co-occurrence network, the composition of soil fungi, and soil nutrients. The RDA analysis also showed that AN, TK, and pH mainly influenced the soil fungal community. The null model test results showed the importance of stochastic processes in soil fungal community assembly in manual plantation larch forests. Overall, this study enhances our understanding of the differences in soil fungal communities in manual plantation larch forests and natural larch forests, providing insights into their sustainable management. It also serves as a reminder that the ecological balance of natural ecosystems is difficult to restore through human intervention, so we need to protect natural ecosystems.

Biodiversity drives ecosystem multifunctionality in sandy grasslands?

Plant communities and soil microbiomes play a crucial role in regulating ecosystem multifunctionality (EMF). However, whether and how aboveground plant diversity, belowground soil microbial diversity and interactions with environmental factors affect EMF in sandy grasslands under climate change conditions is unclear. Here, we selected 15 typical grassland communities from the Horqin sandy grassland along temperature and precipitation gradients, using the mean annual temperature (AMT), mean annual precipitation (AP), soil temperature (ST), soil water content (SW) and pH as abiotic factors, and plant diversity (PD) and soil microbial diversity (SD) as biodiversity indicators. The effects of biodiversity and abiotic factors on individual ecosystem functions and EMF were studied. We found that PD and its components, plant species richness (SR), species diversity (PR) and genetic diversity (GD), had significant effects on aboveground biomass (AGB) and major factors involved in ecosystem nitrogen cycling (plant leaf nitrogen content (PLN) and soil total nitrogen content (STN)) (P < 0.05). Soil fungal diversity (FR) has a greater impact on ecosystem function than soil bacteria (BR) and archaea (ABR) in sandy grasslands and mainly promotes the accumulation of soil microbial carbon and nitrogen (MBC, MBN) (P < 0.05), STC and STN (P < 0.01). PD and two types of SD (FR and ABR) significantly regulated EMF (P < 0.01). Among the abiotic factors, soil pH and SW regulated EMF (P < 0.05), and SW and ST directly drove EMF (P < 0.05). PD drove EMF significantly and indirectly (positively) through soil pH and ST (P < 0.001), while SD drove EMF weakly and indirectly (negatively) through AP and PD (P > 0.05). PD was a stronger driving force on EMF than SD. These results improve our understanding of the drivers of multifunctionality in sandy grassland ecosystems.

Granular bacterial inoculant alters the rhizosphere microbiome and soil aggregate fractionation to affect phosphorus fractions and maize growth

The constraint of phosphorus (P) fixation on crop production in alkaline calcareous soils can be alleviated by applying bioinoculants. However, the impact of bacterial inoculants on this process remains inadequately understood. Here, a field study was conducted to investigate the effect of a high-concentration, cost-effective, and slow-release granular bacterial inoculant (GBI) on maize (Zea mays L.) plant growth. Additionally, we explored the effects of GBI on rhizosphere soil aggregate physicochemical properties, rhizosphere soil P fraction, and microbial communities within aggregates. The outcomes showed a considerable improvement in plant growth and P uptake upon application of the GBI. The application of GBI significantly enhanced the AP, phoD gene abundance, alkaline phosphatase activity, inorganic P fractions, and organic P fractions in large macroaggregates. Furthermore, GBI impacted soil aggregate fractionation, leading to substantial alterations in the composition of fungal and bacterial communities. Notably, key microbial taxa involved in P-cycling, such as Saccharimonadales and Mortierella, exhibited enrichment in the rhizosphere soil of plants treated with GBI. Overall, our study provides valuable insight into the impact of GBI application on microbial distributions and P fractions within aggregates of alkaline calcareous soils, crucial for fostering healthy root development and optimal crop growth potential. Subsequent research endeavors should delve into exploring the effects of diverse GBIs and specific aggregate types on P fraction and community composition across various soil profiles.

Microbial network structure, not plant and microbial community diversity, regulates multifunctionality under increased precipitation in a cold steppe

It is known that the dynamics of multiple ecosystem functions (i. e., multifunctionality) are positively associated with microbial diversity and/or biodiversity. However, how the relationship between microbial species affects ecosystem multifunctionality remains unclear, especially in the case of changes in precipitation patterns. To explore the contribution of biodiversity and microbial co-occurrence networks to multifunctionality, we used rainfall shelters to simulate precipitation enhancement in a cold steppe in Northeast China over two consecutive growing seasons. We showed that an increased 50% precipitation profoundly reduced bacterial diversity and multidiversity, while inter-annual differences in precipitation did not shift microbial diversity, plant diversity, or multidiversity. Our analyses also revealed that increased annual precipitation significantly increased ecosystem, soil, nitrogen, and phosphorous cycle multifunctionality. Neither increased precipitation nor inter-annual differences in precipitation had a significant effect on carbon cycle multifunctionality, probably due to the relatively short period (2 years) of our experiment. The co-occurrence network of bacterial and fungal communities was the most dominant factor affecting multifunctionality, the numbers of negative interactions but not positive interactions were linked to multifunctionality. In particular, our results provided evidence that microbial network topological features are crucial for maintaining ecosystem functions in grassland ecosystems, which should be considered in related studies to accurately predict the responses of ecosystem multifunctionality to predicted changes in precipitation patterns.

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.