Soil Ecological Processes Research Articles

Understory vegetation had important impact on soil microbial characteristics than canopy tree under N addition in a Pinus tabuliformis plantation

Forest ecosystem is a complex community, and its soil microbes play a vital role in global matter cycling. However, the patterns of rhizosphere soil microbial characteristics among tree-shrub-grass and their responses to nitrogen (N) deposition are still unclear. This study evaluated the microbial biomasses, processes (gas fluxes), and enzyme activities in the rhizosphere soils of tree (Pinus tabuliformis), shrub (Rosa xanthina), and grass (Carex lanceolata) and their responses to N addition (0, 3, 6, 9 g N m−2 y−1 corresponding to N0, N3, N6, N9) in a P. tabuliformis plantation. (1) Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP) contents, as well as CO2, CH4 flux rates in the rhizosphere soil of C. lanceolata were significantly higher than those in the rhizosphere soils of P. tabuliformis and R. xanthina (P < 0.05). The activities of alkaline phosphatase (ALT), leucine aminopeptidase (LAP), β-glucosidase (BG), D-cellulosidase (CBH), N-acetyl-glucosaminidase (NAG), and xylosidase (XYL) in the rhizosphere soils of C. lanceolata and R. xanthina were significantly higher than those in the rhizosphere soil of P. tabuliformis. (2) Soil MBC content, N2O, and CH4 flux rates increased after N addition, while the CO2 flux rate decreased. MBP content initially increased and then reduced with N additions, and the maximum values observed in N3 or N9 treatments. (3) In the rhizosphere soil of P. tabuliformis, N addition enhanced the NAG, BG, CBH, and XYL activities. While low N increased and high N decreased these enzyme activities in the rhizosphere soils of C. lanceolata and R. xanthina, with the maximum values obtained in N3 treatment. (4) N addition directly reduced the CO2 flux rate and indirectly enhanced the gas flux rate by increasing soil MBC and MBP contents. Species change indirectly affected the microbial biomass and enzyme activity by altering soil chemical properties, which eventually affected gas flux rates. Our study emphasizes the effects of tree-shrub-grass on soil microbial characteristics, which can improve the evaluation of soil ecological processes and responses to N deposition in forest ecosystems.

Spatiotemporal distribution patterns of soil nematodes along an altitudinal gradient in the cold temperate zone of China

As important components of the cosmopolitan soil biota, soil nematodes are found at multiple trophic levels of the belowground food web and play an important role in soil function. Exploring the actual patterns of soil nematodes along the altitudinal gradients helps understand the spatial soil ecology. In this study, we used molecular analysis approaches to reveal the soil nematode spatiotemporal changes on Oakley Mountain in the northern Greater Khingan Mountain Ranges Northeast China. Our results showed that although the alpha diversity of nematode communities generally decreased with the increased altitude, it did not exhibit a monotonic decrease pattern. Bacterial feeding nematodes occupied the largest proportion among all nematode feeding types. Altitude had a more significant effect than soil depth on the structure of nematode community in all seasons. Soil bulk density, moisture, dissolved organic carbon, temperature, pH, nitrate nitrogen, and total phosphorus were the significant soil variables driving the composition of nematode community. The co-occurrence networks of soil nematode communities showed a distinct seasonal pattern. The nematode community networks in May and September had more modes and links, higher average degrees, and higher average clustering coefficients than the network in July. We demonstrated that the variance of nematode community structure in different altitudes and soil depths could be well explained by edaphic factors. This study extends our knowledge of the nematode spatial ecology in cold temperate regions and contributes to further investigation of soil ecological processes in global challenges.

Upper Bounds of Maximum Land Surface Temperatures in a Warming Climate and Limits to Plant Growth

AbstractExtremely high land surface temperatures affect soil ecological processes, alter land‐atmosphere interactions, and may limit some forms of life. Extreme surface temperature hotspots are presently identified using satellite observations or deduced from complex Earth system models. We introduce a simple, yet physically based analytical approach that incorporates salient land characteristics and atmospheric conditions to globally identify locations of extreme surface temperatures and their upper bounds. We then provide a predictive tool for delineating the spatial extent of land hotspots at the limits to biological adaptability. The model is in good agreement with satellite observations showing that temperature hotspots are associated with high radiation and low wind speed and occur primarily in Middle East and North Africa, with maximum temperatures exceeding 85°C during the study period from 2005 to 2020. We observed an increasing trend in maximum surface temperatures at a rate of 0.17°C/decade. The model allows quantifying how upper bounds of extreme temperatures can increase in a warming climate in the future for which we do not have satellite observations and offers new insights on potential impacts of future warming on limits to plant growth and biological adaptability.

Effects of nitrogen and phosphorus additions on soil microbial community structure and ecological processes in the farmland of Chinese Loess Plateau

Effects of nitrogen and phosphorus additions on soil microbial community structure and ecological processes in the farmland of Chinese Loess Plateau

The competition between Bidens pilosa and Setaria viridis alters soil microbial composition and soil ecological function

Bidens pilosa is recognized as one of the major invasive plants in China. Its invasion has been associated with significant losses in agriculture, forestry, husbandry, and biodiversity. Soil ecosystems play an important role in alien plant invasion. Microorganisms within the soil act as intermediaries between plants and soil ecological functions, playing a role in regulating soil enzyme activities and nutrient dynamics. Understanding the interactions between invasive plants, soil microorganisms, and soil ecological processes is vital for managing and mitigating the impacts of invasive species on the environment. In this study, we conducted a systematic analysis focusing on B. pilosa and Setaria viridis, a common native companion plant in the invaded area. To simulate the invasion process of B. pilosa, we constructed homogeneous plots consisting of B. pilosa and S. viridis grown separately as monocultures, as well as in mixtures. The rhizosphere and bulk soils were collected from the alien plant B. pilosa and the native plant S. viridis. In order to focus on the soil ecological functional mechanisms that contribute to the successful invasion of B. pilosa, we analyzed the effects of B. pilosa on the composition of soil microbial communities and soil ecological functions. The results showed that the biomass of B. pilosa increased by 27.51% and that of S. viridis was significantly reduced by 66.56%. The organic matter contents in the bulk and rhizosphere soils of B. pilosa were approximately 1.30 times those in the native plant soils. The TN and NO3– contents in the rhizosphere soil of B. pilosa were 1.30 to 2.71 times those in the native plant soils. The activities of acid phosphatase, alkaline phosphatase, and urease in the rhizosphere soil of B. pilosa were 1.98–2.25 times higher than in the native plant soils. Using high-throughput sequencing of the 16S rRNA gene, we found that B. pilosa altered the composition of the soil microbial community. Specifically, many genera in Actinobacteria and Proteobacteria were enriched in B. pilosa soils. Further correlation analyses verified that these genera had significantly positive relationships with soil nutrients and enzyme activities. Plant biomass, soil pH, and the contents of organic matter, TN, NO3–, TP, AP, TK, and AK were the main factors affecting soil microbial communities. This study showed that the invasion of B. pilosa led to significant alterations in the composition of the soil microbial communities. These changes were closely linked to modifications in plant traits as well as soil physical and chemical properties. Some microbial species related to C, N and P cycling were enriched in the soil invaded by B. pilosa. These findings provide additional support for the hypothesis of soil-microbe feedback in the successful invasion of alien plants. They also offer insights into the ecological mechanism by which soil microbes contribute to the successful invasion of B. pilosa. Overall, our research contributes to a better understanding of the complex interactions between invasive plants, soil microbial communities, and ecosystem dynamics.

Changes of soil bacterial community, network structure, and carbon, nitrogen and sulfur functional genes under different land use types

Soil microorganisms participate in almost all soil ecological processes and are essential in maintaining ecosystem functions and terrestrial carbon, nitrogen, and sulfur cycles. Soil bacterial communities, networks, biogeochemical cycles, and land use types influence it. However, there are few studies on the changes in these indicators and their influencing factors under different land use types. Taking Dongting Lake watershed as an example, high-throughput sequencing technology combined with FAPROTAX were used to analyze the characteristics and influencing factors of soil bacterial community, network structure, and C, N, and S cycle function genes under different land use conditions. Land use types include paddy fields (PF), garden plots (GP), woodland (WL), and sloped arable land (SAL). PLS-PM model and redundancy analysis method were used to study the mechanism of soil bacterial community, network structure, functional genes, and environmental variables. The results showed that the relative abundance of dominant phylum and dominant fungi changed significantly in different land use types. The first three dominant gates in WL had the most considerable abundance and the most extensive diversity index of PF. The symbiotic network of PF has the most effective connectivity and average degree, the minor network diameter, the most complex network structure, and fierce competition among species within the same ecological niche. The results of functional genes showed that different land use types significantly changed the abundance of soil C, N, and S cycle functional genes, and soil bacteria predicted the highest abundance of functional genes in GP. C, N, and S circulating function genes were significantly correlated with pH, soil nutrients, and soil texture (P < 0.05). PLS-PM model and redundancy analysis showed that soil pH was the main factor affecting the bacterial community, network structure, and functional genes, followed by soil nutrients.

Soil bacteria, archaea, and enzymatic activity of natural and rewetted peatlands display varying patterns in response to water levels

Peatland restoration is an efficient approach to enhance soil carbon sequestration and mitigate climate change. However, successful restoration outcomes require an in-depth comprehension of the underlying soil ecological processes following restoration. To gain a processed perspective on the distinctions between natural and rewetted peatlands, this study compared the soil properties, enzymatic activities, and bacterial and archaeal community structures under uniform water level gradients. The results confirmed our hypothesis that the ecological processes between rewetted and natural peatlands vary significantly. Although the rewetted peatland exhibited different soil properties compared to the natural peatland, increasing water levels resulted in a shift in soil physicochemical properties and hydrolase activities toward those of the natural peatland. This highlights the importance of maintaining a high water level for successful peatland restoration. However, enzymatic activities in the rewetted and natural peatlands exhibited opposite trends with increased water levels, with the natural peatland exhibiting lower polyphenol oxidase activity (-56.7%), higher archaeal diversity (7.3%) and lower bacterial diversity (-2.1%). As the water level increased, ecological processes in the natural peatland shifted from bacteria-dominated faster processes to archaea-dominated slower processes, while no such trends were observed in the rewetted peatland. The study suggest that the lower pH and more restrictive nutrient conditions in the natural peatland, which were altered by rice cultivation with fertilization and vegetation deterioration in the rewetted peatland, may contribute to the biological differences between the two peatland types. These differences may hinder the restoration process after rewetting. Therefore, to enhance the effectiveness of peatland restoration, particularly in the context of rich fens, it is necessary to consider measures that can promote the development of a nutrient-limited and acidic environment aside from rewetting.

Variations in the soil micro-food web structure and its relationship with soil C and N mineralization during secondary succession of subalpine forests

The soil micro-food web is an important network of belowground trophic relationships and it participates directly and indirectly in soil ecological processes. In recent decades, the roles of the soil micro-food web in regulating ecosystem functions in grasslands and agroecosystems have received much attention. However, the variations in the soil micro-food web structure and its relationship with ecosystem functions during forest secondary succession remain unclear. In this study, we investigated how forest secondary succession affected the soil micro-food web (including soil microbes and nematodes) and soil carbon and nitrogen mineralization across a successional sequence of “grasslands – shrublands – broadleaf forests – coniferous forests” in a subalpine region of southwestern China. With forest successional development, the total soil microbial biomass and the biomass of each microbial group generally increased. The significant influences of forest succession on soil nematodes were mainly reflected in several trophic groups with high colonizer-persister values (particularly bacterivore3, herbivore5 and omnivore-predator5) that are sensitive to environmental disturbance. The increases in the connectance and nematode genus richness, diversity, and maturity index indicated an increasingly stable and complex soil micro-food web with forest succession, which was closely related to soil nutrients, particularly the soil carbon contents. Additionally, we found that the soil carbon and nitrogen mineralization rates also exhibited generally increasing trends during forest succession, which had significant positive correlations with the soil micro-food web composition and structure. The path analysis results indicated that the variances in ecosystem functions induced by forest succession were significantly determined by soil nutrients and soil microbial and nematode communities. Overall, these results suggested that forest succession enriched and stabilized the soil micro-food web and promoted ecosystem functions via the increase in soil nutrients, and the soil micro-food web played an important role in regulating ecosystem functions during forest succession.

Invasive plants alter soil properties and nutrient dynamics: A case study of Anthemis cotula invasion in Kashmir Himalaya

Plant invasion is considerably affecting terrestrial ecosystems by modulating soil nutrient cycling and ecological processes. Below-ground processes are of paramount interest to understand the long-term influences as well as the management of the invaded soil ecosystems. We studied the impact of a global plant invader, Anthemis cotula L. (stinking chamomile; Asteraceae), on key soil physicochemical properties across eight sites in the Kashmir Himalaya, India. At each site, two types (invaded and un-invaded) of adjacent plots (20 × 20 m2) with or without A. cotula were chosen for soil sampling. Soil properties from both invaded and un-invaded plots were analysed. We found significant (P < 0.05) variations in the studied soil parameters in the invaded and un-invaded plots across the study sites. The contents of organic C, total K, total N, total P, available N, and available K were 10–60% higher in the invaded plots compared with the un-invaded plots, whereas the available P content was 21% higher in the un-invaded plots. The findings revealed that A. cotula invasion significantly alters soil nutrient levels by modulating different physicochemical properties in invaded plots, such as soil pH, electrical conductivity, water saturation percentage, and porosity. The influence of plant invasion on soil properties was clearly highlighted by Principal Component Analysis, with the majority of them ordinated towards invaded areas except for the available P and bulk density. Overall, A. cotula alters essential soil properties, thereby potentially influencing the soil nutrient pools and processes, which may further facilitate its establishment and invasion potential in the mountain ecosystems. This study underlines the importance of implementing measures for controlling the invasion of A. cotula, implementing soil reclamation strategies, and conserving native landscape characteristics in the invaded area.

Fungal Hyphosphere Microbiomes Are Distinct from Surrounding Substrates and Show Consistent Association Patterns.

Mat-forming fungi are common in forest and grassland soils across the world, where their activity contributes to important soil ecological processes. These fungi maintain dominance through aggressive and abundant hyphae that modify their internal physical and chemical environments and through these modifications select for what appears to be a suite of mycophilic bacteria. Here, the bacteria associated with the fungal mats of Leucopaxillus gentianeus and Leucopaxillus albissimus from western North America are compared to adjacent nonmat substrates. Within the mats, the bacterial richness and diversity were significantly reduced, and the community composition was significantly different. The bacterial community structure between the two fungal hosts was marginally significant and indicated a shared set of bacterial associates. The genera Burkholderia, Streptomyces, Bacillus, Paenibacillus, and Mycobacterium were significantly abundant within the fungal mats and represent core members of these hypha-rich environments. Comparison with the literature from fungal mat studies worldwide showed that these genera are common and often significantly found within fungal mats, further reinforcing the concept of a mycophilic bacterial guild. These genera are incorporated into a synthesis discussion in the context of our current understanding of the nature of fungal-bacterial interactions and the potential outcomes of these interactions in soil nutrient cycling, plant productivity, and human health. IMPORTANCE Fungi and bacteria are the most abundant and diverse organisms in soils (perhaps more so than any other habitat on earth), and together these microorganisms contribute to broad soil ecosystem processes. There is a suite of bacteria that appears consistently within the physical space called the hyphosphere, the area of influence surrounding fungal hyphae. How these bacteria are selected for, how they are maintained, and what broader ecological functions they perform are subjects of interest in this relatively new field-the cross-kingdom interactions between fungi and bacteria. Understanding their cooccurrence and their interactions can open new realms of understanding in soil ecological processes with global consequences.

Strong variations and shifting mechanisms of altitudal diversity and abundance patterns in soil oribatid mites (Acari: Oribatida) on the Changbai Mountain, China

Biological composition and structure vary strongly with elevation, however, the vertical distribution of soil fauna and its drivers have been rarely investigated. Oribatid mites play an essential role in soil faunal composition, where they can occur at high densities and mediate soil ecological processes and functions. Here, we comprehensively investigated the composition and diversity of soil oribatid mites, at nine altitudes (from 600 to 2200 m asl) and four vegetation types from forest to alpine tundra on the Changbai Mountain in July 2021. In total, 67 species were identified among 37,224 oribatid mite individuals. Oribatid mite species varied strongly with altitude and vegetation type, and only a few species overlapped between elevations. Species abundance and diversity declined significantly as altitude increased, while abundance exhibited a hump-shaped distribution along an elevational gradient, peaking at 1200 m. Beta diversity decomposition analyses revealed that species replacement processes dominated community compositional differences across all study sites (both between vegetation types and elevations). Meanwhile, soil oribatid mite community composition is greatly affected by elevation and vegetation type. Specifically, oribatid mite community varies with elevation across vegetation types. Twelve and twenty indicator species were found at different elevations and vegetation types, respectively. Our study shows that soil moisture content, total phosphorus, available phosphorus, ammonium nitrogen, and nitrate nitrogen are the most dominant drivers of oribatid mite composition patterns. These findings indicate oribatid mite assemblages have a distinct vertical distribution pattern and are coupled with different aboveground vegetation types, implying that changes in aboveground vegetation will cause shifts in soil fauna under future climate change.

Bibliometric Analysis of Black Soil Protection from the Perspective of Land-Use Monitoring

Land use affects ecosystem stability and agricultural ecological security in black soil regions. Additional attention is required regarding the impact of different land-use patterns on black soil. However, the construction of sustainable agricultural ecological security in black soil environments is a dynamic process that depends on the reviews of experts and statistical analyses of literature data. This study quantitatively reviewed the past 20 years of the literature regarding black soil. Using the superposition of the expert knowledge map and machine clustering, knowledge regarding land use in black soil fields was classified structurally. Further, studies directly related to the spatiotemporal pattern of land use were identified, and frequently cited works of the literature were screened to build a dynamic knowledge network of black soil research. The results show that (1) the cooperative relationship among China, the United States, and Canada is the strongest, but the density of cooperation networks between other countries is low; (2) land-use research regarding black soil is divided into four research areas: soil microbial community and activity, soil erosion and ecological processes, ecological management of land use, soil organic matter, and element cycling; (3) the monitoring and management mode of land use in black soil areas should be established to include information management that incorporates knowledge of the cultivated land factor potential, grain production capacity assessment, soil erosion evaluation and prediction, and farmland landscape planning.

Assessment of Variability among Humus Forms and Soil Properties in Relation to Tree Species and Forest Operations in the Kheyrud Forest, Nowshahr

Tree species and litter play a key role in the functioning of forest ecosystems as influential factors affecting soil ecological processes and the distribution of humus forms. This study investigates the morphology of humus under the litter of different trees on compacted skid trails at different time intervals after skidding operations (6, 10, and 20 years) in the Kheyrud forest, Nowshahr. Each skid trail was identified with three replications in pure beech, beech-hornbeam and mixed beech stands and a total of 81 profiles with dimensions of 30 × 30 cm, drilled and classified using the European Humus Group Proposal (EHGP). According to the results, the mull of the most dominant humus was under the mixed beech litter, while in the pure beech litter the amphi humus was the most abundant form of humus. Three types of humus mull, moder, and amphi were observed in the skid trail under the beech-hornbeam litter. Oligomull was the most abundant form of humus mull in the skid trail under mixed beech litter, while in the trails under pure beech Eumacroamphi, Eumesoamphi, and Hemimoder were the most common forms of humus amphi and moder. Also, the thickness of the organic layer (Organic litter, Organic fragmentation, and Organic humus) was higher in all skid trails under the pure beech litter as compared to other treatments, while from younger trails (6 years) to older trails (20 years), the thickness of the organic-mineral horizon (Ah) increased under the beech mixed litter. We can conclude that different litter types were the main factor to control the presence of different forms of humus after forest operations.

Stochastic processes contribute to arbuscular mycorrhizal fungal community assembly in paddy soils along middle and lower Yangtze River

Arbuscular mycorrhizal fungi (AMF) are extensively distributed in environment, and have key effects on regulating soil structure, nutrient cycles, crop productivity, and ecological processes in agricultural ecosystems. However, the biogeographic patterns and underlying ecological processes shaping AMF community assembly remain unclear. The present study examined AMF community composition and diversity in paddy soils along middle and lower reaches of the Yangtze River, and the driving factors and processes of AMF community assembly were assessed based on MiSeq sequencing. The results showed that soil pH, total N and Olsen-P, and soil organic matter (SOM) levels affected AMF community diversity. In addition, there were 4 orders, 8 families along with 8 genera within our study area, where Glomus was the most dominant genus. Moreover, AMF community composition was under the influence of geographic distance and soil characteristics such as pH, SOM, N and P contents, and enzyme activities. However, the contribution of deterministic processes was less than stochastic processes by the null model analysis, suggesting that stochastic processes was the dominant ecological processes shifting AMF community assembly in paddy soils along middle and lower reaches of the Yangtze River. The results sheds more lights on patterns as well as mechanisms driving the assembly of AMF communities within the agricultural ecosystems.

Soil biota community structure and litter traits of grape vine plantation and natural ecosystem from Southern Brazil

Vitis vinifera is a common plant species cultivated in Southern Brazil for vine production. Although this plant species is commonly found near the Mixed Ombrophilous Forest, the V. vinifera plantation is cultivated in areas for a long-term thus changing the soil ecosystem and functional diversity. We aimed to compare the soil chemical properties, soil biota assemblage, litter traits, decay rate and priming effect in the two adjacent environments (e.g., grape vine plantation vs. natural ecosystem). Soil chemical properties, soil biota community composition, and litter traits of V. vinifera plantation were compared with an adjacent natural ecosystem (e.g., Mixed Ombrophilous Forest) from September 2019 to June 2021. Litter decay rate and priming effect was estimated by using native tree residues on litter bags in both studied environments. We also assessed the influence of soil biota on decay rate through a litterbag assay. Our results showed that both studied environments differed in soil chemical properties and soil biota community composition. However, in the V. vinifera plantation litter decay rate, and priming effect were higher, due to the presence and activities of soil organisms from Collembola - Paronellidae. Thermal amplitude, litter quality, and soil organisms’ activity were the main factors contributing to the data variance. Both native tree residues, A. angustifolia and D. sellowiana, showed the highest decay rate and priming effect in the V. vinifera plantation. Our work increases the understanding of the soil food web and ecological processes (litter deposition and nutrient cycling) into subtropical ecosystems. The V. vinifera plantation following a monocropping system does not provide resources to create a well-developed soil food web, which overtime creates negative plant-soil feedback when compared to the natural ecosystem. However, our study opens a new perspective for a future agroforestry system using two endangered species from the Brazilian Mixed Ombrophilous Forest seeking for vine production, soil sustainability, and biodiversity conservation.

Vegetation Restoration with Mixed N2-Fixer Tree Species Alleviates Microbial C and N Limitation in Surface Soil Aggregates in South Subtropical Karst Area, China

Soil extracellular enzyme stoichiometry (EES) is the essential predictor in nutrient status and resource limitation of soil microorganisms, whose metabolism has a vital role in biogeochemical cycling and ecosystem function. However, little is known about how N2-fixer tree species with different planting patterns affect soil nutrient resources in terms of extracellular enzyme activity (EEA) or EES within aggregates in degraded karst ecosystems. In this study, we evaluated soil EEA and EES related to carbon (C), nitrogen (N), and phosphorus (P) cycles across two eight-year-old pure plantations of legume species [Dalbergia odorifera T. Chen (PD) and Acrocarpus fraxinifolius Wight ex Arn. (PA)] and a mixed plantation of the two tree species listed above (MP). Meanwhile, a nearby undisturbed shrubland was used as a control (CK). We concluded that the activities of C-, N-, and P-acquiring enzyme increased to different degrees in the N2-fixer tree species stands (particularly in MP) compared to CK in all aggregates. Compared to CK, MP significantly increased by 39.0%, 54.0%, 39.3%, and 24.8% in total C-acquiring EEA, 41.1%, 60.5%, 47.8%, and 12.5% in total N-acquiring EEA, and 100.4%, 79.7%, 69.2%, and 56.4% in total P-acquiring EEA within &gt;2 mm, 1–2 mm, 0.25–1 mm, and &lt;0.25 mm aggregates, respectively. Furthermore, the logarithmic transformed ratio of C-, N-, and P-acquiring enzyme activities was 1.20:1.08:1, which deviated from the global ratio (1:1:1). Vector analysis of EEA showed that the vector length (VL) within aggregates was significantly lower than that of CK in all stands of N2-fixer species except PD; while in all treatments, vector angle (VA) was &lt;45° for all aggregate sizes, except in MP, where VA reached 45° for &lt;0.25 mm aggregate. These indicated soil microbes were limited by C and N together. However, MP significantly alleviated microbial C and N limitation than CK (p &lt; 0.05). There were obvious positive relationships between enzyme C:N, C:P, and N:P ratios. VL was markedly negatively linked to VA. EES was markedly related to most soil nutrients and microbial biomass stoichiometry ratios. Changes in soil EEA and EES were primarily driven by available phosphorus (AP), microbial biomass carbon (MBC), soil C:N and MBN:MBP ratios. Together, our results demonstrate the influences after introducing N2-fixer tree species (particularly MP) for vegetation recovery on soil microbial nutrient limitation and ecological processes in aggregate level and will contribute to the development of ecological restoration practices and fertility management in degraded karst ecosystems of southwest China.

Deep-injected straw incorporation improves subsoil fertility and crop productivity in a wheat-maize rotation system in the North China Plain

Deep-injected straw incorporation (DI-SI) is a novel soil tillage and straw management, which allowed for the formation of maize straw layer structure in the subsoil (20–38 cm) in wheat-maize rotation systems. However, little is known about how DI-SI affects soil physicochemical and enzymatic processes, as well as crop productivity. Therefore, we conducted a field experiment during 2018–2020 in the North China Plain to determine whether DI-SI would improve soil structure, nutrients, enzyme activities, and crop yield. Three treatments were included: straw removal (SR), conventional straw incorporation (SI), and DI-SI. The results showed that DI-SI improved soil structure and water retention through decreasing the bulk density and penetration resistance in 20–40 cm soil layer. DI-SI significantly increased soil organic C (67.5%), total N (61.3%), and available nutrients (i.e. NO 3 - , NH 4 + , dissolved organic C) compared with SI in the subsoil (20–40 cm), while no differences were detected among straw managements in the topsoil (0–20 cm). This was mainly attributed to the accumulation of microbial biomass C and C-, N-acquisition enzymes in the straw layers, which promoted the straw decomposition and nutrient release. Finally, with the combined effects of soil ecological processes, DI-SI significantly increased the grain yields of wheat and maize by 12.0% and 11.8% compared with SI in the second year, respectively. Our study suggested that deep placement of straw would better promote the utilization of crop residue for farming, and deep-injected straw incorporation represents a viable strategy to improve subsoil physical, chemical, and biological processes, and subsequently crop productivity in wheat-maize rotation systems. • DI-SI improves soil structure and water retention through decreasing the bulk density. • DI-SI considerably increases the SOC, TN, and available nutrients in the subsoil. • DI-SI stimulates microbial and C-, N-acquisition enzymes activities in the straw layers. • Wheat and maize yields were increased under DI-SI, especially in the second year.

Contrasting Effect of Thinning and Understory Removal on Soil Microbial Communities in a Subtropical Moso Bamboo Plantation

Thinning and understory clearance are among the two most popular forest management practices carried out to improve stand productivity in subtropical plantations. Unfortunately, studies have not fully explored the single and combination effect of thinning and understory clearance on soil microbial properties. By conducting a field manipulation experiment in a subtropical moso bamboo (Phyllostachys edulis) plantation in Southern China, we assessed the effects of thinning, understory clearance, and their combination on soil microbial phospholipid fatty acids (PLFAs) three years after treatments were first applied. We also examined the changes in soil properties after thinning and/or understory clearance. Thinning decreased soil fungal and bacterial PLFAs, and consequently soil total microbial PLFAs due to the increased soil NH4+-N, and NO3−N concentrations. Understory clearance decreased soil pH and soil water content resulting in increased soil fungal PLFAs and the ratio of soil fungal to bacterial (F:B). In addition, thinning and understory clearance caused apparent interactive effects on soil total microbial PLFAs and bacterial PLFAs, and the negative influence of thinning on soil total microbial and bacterial PLFAs were partly compensated by understory clearance. These results suggest the contrasting and interactive effect of thinning and understory clearance should be considered to assess the changes of soil microbial community and ecological processes in subtropical moso bamboo (Phyllostachys edulis) plantations in southern China.

Changes in microbial community composition drive the response of ecosystem multifunctionality to elevated ozone

Increasing tropospheric ozone poses a potential threat to both above- and belowground components of the terrestrial biosphere. Microorganisms are the main drivers of soil ecological processes, however, the link between soil microbial communities and ecological functions under elevated ozone remains poorly understood. In this study, we assessed the responses of three crop seedlings (i.e., soybean, maize, and wheat) growth and soil microbial communities to elevated ozone (40 ppb O3 above ambient air) in a pot experiment in the solardomes. Results showed that elevated ozone adversely affected ecosystem multifunctionality by reducing crop biomass, inhibiting soil extracellular enzyme activities, and altering nutrient availability. Elevated ozone increased bacterial and fungal co-occurrence network complexity, negatively correlated with ecosystem multifunctionality. Changes in the relative abundance of some specific bacteria and fungi were associated with multiple ecosystem functioning. In addition, elevated ozone significantly affected fungal community composition but not bacterial community composition and microbial alpha-diversity. Crop type played a key role in determining bacterial alpha-diversity and microbial community composition. In conclusion, our findings suggest that short-term elevated ozone could lead to a decrease in ecosystem multifunctionality associated with changes in the complexity of microbial networks in soils.

Soil aggregate modulates microbial ecological adaptations and community assemblies in agricultural soils

Soil aggregates provide spatially heterogeneous microenvironments for soil microbiome and ecological processes. Revealing the nuances of assembly processes in aggregates is critical for understanding the fine-scale organization of the soil microbiome and associated biogeochemistry. However, the effect of aggregate sizes on microbial assemblies remains poorly explored. In this study, we investigated the mechanism underlying the assembly processes of microbial communities within three different aggregates sizes across five long-term fertilization experimental stations throughout eastern China. Our results showed that although geographic sites explained most of the variations in microbial composition in aggregates, aggregates of the same size selected phylogenetically closely related microbial species with similar ecological preferences for specific nutrient variables. Null model analysis showed that environmental selection and dispersal limitation primarily governed the assembly of aggregate bacterial and fungal communities, respectively. The relative importance of deterministic processes on microbial communities increased with the increasing aggregate size across all sites. Multiple stepwise regression analysis indicated that nutrient variables associated with community assembly are distinct in different aggregate-size fractions. Bacterial assembly is mainly affected by total carbon and soil organic carbon in macro- and micro-aggregates, whereas it is influenced by the C/P ratio in the silt + clay fraction. For fungal community assembly, the C/N ratio was the major factor in macroaggregate and silt + clay fractions, while N/P ratio had stronger effects in the microaggregates. Furthermore, fertilization effects on the microbial community assembly processes varied across aggregate sizes. Organic fertilization led to a decrease for bacteria while an increase for fungi in the sorting/dispersal effect ratio. The magnitude of such an impact was higher for macro- and micro-aggregates. GeoChip and enzymatic results further demonstrated the regulation of ecological clusters and functions by nutrient variables across aggregates. Our findings highlight that microbial assembly and functional traits in large aggregate-size fractions are susceptible to nutrient changes, and thus can act as potential biological indicators for sustainable management of agricultural soils.