● Soil acidification caused severe losses of soil inorganic carbon stock worldwide. ● SIC losses could be mitigated via alkalinity regeneration approaches. ● Rock/mineral powder can supply substantial basic cations to soil to reduce acidification. ● Microorgnisms could be utilized to enhance weathering of rock/mineral powder. ● Biochar and bone biochar could reduce SIC losses via alkalinity regeneration.
Soil inorganic carbon (SIC) accounts for about half of the C reserves worldwide and is considered more stable than soil organic carbon (SOC). However, soil acidification, driven mainly by nitrogen (N) fertilization can accelerate SIC losses, possibly leading to complete loss under continuous and intensive N fertilization. Carbonate-free soils are less fertile, productive, and more prone to erosion. Therefore, minimizing carbonate losses is essential for soil health and climate change mitigation. Rock/mineral residues or powder have been suggested as a cheaper source of amendments to increase soil alkalinity. However, slow mineral dissolution limits its efficient utilization. Soil microorganisms play a vital role in the weathering of rocks and their inoculation with mineral residues can enhance dissolution rates. Biochar is an alternative material for soil amendments, in particular, bone biochar (BBC) contains higher Ca and Mg that can induce even higher alkalinity. This review covers i) the contribution and mechanism of rock residues in alkalinity generation, ii) the role of biochar or BBC to soil alkalinity, and iii) the role of microbial inoculation for accelerating alkalinity generation through enhanced mineral dissolution. We conclude that using rock residues/BBC combined with microbial agents could mitigate soil acidification and SIC losses and also improve agricultural circularity.
● This study reviewed the effect of warming on microbial carbon use efficiency (CUE). ● Different measurement method is one of the key reasons for the variation of CUE. ● The warming effect on CUE is complicated by changes in biotic and abiotic factors. ● Future research on CUE should focus on new methods, multi-factor experiments, etc.
Microbial carbon use efficiency (CUE) is an important factor driving soil carbon (C) dynamics. However, microbial CUE could positively, negatively, or neutrally respond to increased temperature, which limits our prediction of soil C storage under future climate warming. Experimental warming affects plant production and microbial communities, which thus can have a significant impact on biogeochemical cycles of terrestrial ecosystems. Here, we reviewed the present research status of methods measuring microbial CUE and the response of microbial CUE to the changes of biotic and abiotic factors induced by warming. Overall, current measurement methods mainly include metabolic flux analysis, calorespirometry, stoichiometric model, 13C and 18O labeling. Differences in added substrate types can lead to an overestimation or underestimation on microbial CUE, particularly when using the 13C labeling method. In addition, changes in the dominant microbial community under warming may also affect CUE. However, there is still uncertainty in CUE characteristics of different microorganisms. Microbial CUE is generally decreased under warming conditions as microbes are subjected to water stress or soil labile organic matter is much more depleted compared to ambient conditions. In contrast, considering that warming increases soil nutrient availability, warming may enhance microbial CUE by alleviating nutrient limitations for microbes. In conclusion, the response of microbial CUE to warming is more complex than expected. The microbial growth and physiological adaptation to environmental stress under warming is one of the main reasons for the inconsistence in microbial CUE response. Finally, we propose five aspects where further research could improve the understanding of microbial CUE in a warmer world, including using new technologies, establishing multi-factor interactive experiments, building a network of experimental research platform for warming, and strengthening studies on response of CUE to warming at different soil depths and on different temporal scales.
• Metabolic and non-metabolic benefits of AM fungi under intercropping were reviewed. • Changes of AM fungi themselves respond to intercropping practices were summarized. • Mechanistic understanding the synergy between intercropping and AM fungi is needed. • It’s valuable to harness AM fungal benefits for maximizing intercropping production.
Intercropping, which gains productivity and ecological benefits through plant facilitative interactions, is a practice often associated with sustainable agriculture. In such systems, arbuscular mycorrhizal (AM) fungi and the hyphal networks play key roles in plant facilitation by promoting connectivity, mediating interplant transfer of metabolic resources, and managing weeds, pathogens, and contaminants. This review states that the symmetrically or unsymmetrically delivered resources via AM fungi are imperative to maintain facilitative interactions between intercrops. In addition, the responses of AM fungi to intercropping are also discussed, including changes in abundance, diversity, community composition and colonization level. Although general proliferations in AM fungi via intercropping have been shown, the plant hosts and neighbors may exert different influences on AM fungi. Therefore, further research is needed in quantifying the mediating role of AM fungi on outputs of intercropping systems, clarifying the driving forces, and exploring the causation between these processes and the changes in AM fungi themselves. To conclude, the integration with AM fungi extends the understanding of key soil biological processes driving plant facilitation and will guide efforts to optimizing intercropping systems.
• SIC was higher at a low salinity of<6‰, and declined with increased salinity. • SOC and microbial residues exponentially decreased during increasing salinity. • Microbial residues and SOC was tightly related to the variations in SIC. • Microbial residues act as the proxy converting SIC to SOC in saline lands.
Soil inorganic carbon (SIC), including mainly carbonate, is a key component of terrestrial soil C pool. Autotrophic microorganisms can assimilate carbonate as the main or unique C source, how microorganisms convert SIC to soil organic carbon (SOC) remains unclear. A systematic field survey (n = 94) was performed to evaluate the shift in soil C components (i.e., SIC, SOC, and microbial residues) along a natural salinity gradient (ranging from 0.5‰ to 19‰), and further to explore how microbial necromass as an indicator converting SIC into SOC in the Yellow River delta. We observed that SIC levels linearly decreased with increasing salinity, ranging from ~12 g kg−1 (salinity<6‰) to ~10 g kg−1 (salinity >6‰). Additionally, the concentrations of SOC and microbial residues exponentially decreased from salinity<6‰ to salinity >6‰, with the decline of 39% and 70%, respectively. Microbial residues and SOC was tightly related to the variations in SIC. The structural equation model showed the causality on explanation of SOC variations with SIC through microbial residues, which can contribute 89% of the variance in SOC storage combined with SIC. Taken together, these two statistical analyses can support that microbial residues can serve as an indicator of SIC transition to SOC. This study highlights the regulation of microbial residues in SIC cycling, enhancing the role of SIC playing in C biogeochemical cycles and enriching organic C reservoirs in coastal saline soils.
• Both organic and inorganic fertilizations stimulate soil aggregation. • Organic and inorganic fertilizers enhance organic carbon storage at aggregate scale. • Aggregate-associated bacterial communities were more sensitive to organic fertilizers than to chemical ones. • The complexity of bacterial network structures decreased with decreasing of aggregate size. • The competitive interactions among bacterial communities were intensified with decreasing of aggregate size.
Differently sized soil aggregates, with non-uniform distribution of space and nutrients, provide spatially heterogeneous microenvironments for microorganisms and are important for controlling microbial community ecology and biogeochemistry in soils. Here, we investigated the prokaryotic communities within different aggregate-size fractions: macroaggregate (>0.25 mm), microaggregate (0.053–0.25 mm) and silt+ clay (<0.053 mm). These were isolated from fluvo-aquic soils under 39-year fertilization strategies: no fertilizer (CK), chemical fertilizer (NPK), manure fertilizer (M), and combination of manure and chemical fertilizers (MNPK). The results showed that the proportion of macroaggregate, soil aggregate-associated organic carbon (SOC) content and aggregate stability were all significantly increased by both manure and chemical fertilizations. Organic fertilizations (M and MNPK) more effectively boosted formation and stability of macroaggregates and enhanced SOC concentration than NPK. The distribution patterns of microorganisms in aggregates were primarily shaped by fertilization and aggregate size. They explained 76.9% of the variance in bacterial community compositions. Fertilizations, especially with organic fertilizers primarily transitioned bacterial communities from slow-growing oligotrophic groups (e.g., Chloroflexi) dominance to fast-growing copiotrophic groups (e.g., Proteobacteria and Bacteroidetes) dominance across all aggregate sizes. Macroaggregates possessed a more stable bacterial community and efficiency of resource transfer, while smaller aggregates increased antagonism and weakened mutualism among bacterial communities. Overall, combination of manure and chemical fertilizers was crucial for increasing SOC content and aggregation, leading to a clear shift in bacterial community structures at aggregate scale.
• Fungal communities were more sensitive to N fertilizers than P, K fertilizers. • More harmonious and stable fungal network induced by P, K fertilizers. • N fertilizers induced lower fungal community resistance with detriments on crop yields.
Nitrogen (N), phosphate (P), and potassium (K) are the three most important nutrients applied into agricultural soils, but the impacts of their single or combined application on soil fungal community structure and stability are still open questions. Using qPCR and Illumina Miseq sequencing, the variation of soil fungal communities in response to long-term addition of N, P, or K fertilization alone and their combinations in a Mollisol field was investigated in this study. In addition, the fungal community resistance indices and network structure were studied. Results showed that N fertilizations (N, NK, NP and NPK treatments) rather than P, K fertilizations (P, K and PK treatments) significantly increased fungal abundance, but decreased fungal diversity and shifted fungal community structures when compared to non-fertilization (NoF). Additionally, N fertilization treatments presented lower resistance of fungal communities to environment disturbances than those of P, K fertilization treatments. More numbers and higher abundances of changed fungal taxa at the genus and OTU levels were induced by N fertilizations rather than by addition of P, K fertilizers. In addition, N fertilizations induced a more changeable fungal network and complex pathogenic subnetwork with many positive interactions among responding plant pathogens (RP, the changeable plant pathogens induced by fertilizers addition compared to NoF) when compared to P, K fertilizations. These RP directly and negatively influenced fungal community resistance examined by structural equation modeling (SEM), which were indirectly detrimental to soybean yields. Our findings revealed that addition of N fertilizers significantly disturbed fungal communities and promoted pathogenic interactions, and provided insights into the optimization of fertilization strategies toward agricultural sustainability.
• Both plants and microbes were strictly homeostatic. • Companion species were more susceptible to P limitation than dominant species. • Added N aggravated stoichiometric niche overlap among species. • Compositae had a greater effect on soil microbes than Gramineae in the rhizosphere. • Effects of N addition on species were different across functional groups.
Nitrogen (N) deposition, the source of N input into terrestrial ecosystems, is exhibiting an increasingly serious impact on the biogeochemical cycle and functional stability of ecosystems. Grasslands are an important component of terrestrial ecosystems and play a key role in maintaining terrestrial ecosystem balance. Therefore, it is critical to understand the effects of nitrogen addition on grassland ecosystems. We conducted gradient N addition experiments (0, 3, 6, and 9 g N m−2 y−1) for three years in grassland communities with similar site conditions. We utilized four typical herbaceous plants, including the dominant species Bothriochloa ischemum (B. ischemum) and companion species Stipa bungeana (S. bungeana), Artemisia gmelinii (A. gmelinii), and Cleistogenes squarrosa (C. squarrosa), to explore how different plant–soil–microbe systems respond to N addition. Stoichiometric homeostasis analysis demonstrated that both plants and microbes were strictly homeostatic. However, the companion species were found to be more susceptible to P dominant species. Furthermore, aggravated overlap in stoichiometric niches between plant species were observed at the N6 and N9 levels. Vector analysis indicated that the vector angle was >45° regardless of plant species and N levels, suggesting that there was a strong P limitation in the rhizosphere microbial community. Variation partitioning analysis revealed that the Composite roots exhibited a greater effect (explaining 34.7% of the variation) on the rhizosphere microbes than on the Gramineae, indicating that there may be more intense nutrient competition in its rhizosphere. In general, the effects of N addition on species were different across functional groups, with a significant positive effect on the Gramineae (B. ischemum, S. bungeana, and C. squarrosa) and a significant negative effect on the Compositae (A. gmelinii), which should be fully considered in the future ecological management and restoration.
• Snow absence increased soil N availabilities within soil aggregates. • Snow absence did not change net N mineralization rate within soil aggregates. • Soil enzyme activities affected by snow were different within soil aggregates.
Winter climate change has great potential to affect the functioning of terrestrial ecosystems. In particular, increased soil frost associated with reduced insulating snow cover may impact the soil nitrogen (N) dynamics in cold ecosystems, but little is known about the variability of these effects among the soil aggregates. A snow manipulation experiment was conducted to investigate the effects of snow absence on N cycling within soil aggregates in a spruce forest on the eastern Tibetan Plateau of China. The extractable soil available N (ammonium and nitrate), net N mineralization rate, and N cycling-related enzyme activities (urease, nitrate reductase, and nitrite reductase) were measured in large macroaggregate (>2 mm), small macroaggregate (0.25–2 mm), and microaggregate (<0.25 mm) during the early thawing period in the years of 2016 and 2017. Snow absence increased soil N availabilities and nitrite reductase activity in microaggregate, but did not affect net N mineralization rate, urease or nitrate reductase activities in any of the aggregate fractions. Regardless of snow manipulations, both soil inorganic N and nitrate reductase were higher in small macroaggregate than in the other two fractions. The effect of aggregate size and sampling year was significant on soil mineral N, net N mineralization rate, and nitrite reductase activity. Our results indicated that snow cover change exerts the largest impact on soil N cycling within microaggregate, and its effect is dependent on winter conditions (e.g., snow cover and temperature). Such findings have important implications for soil N cycling in snow-covered subalpine forests experiencing pronounced winter climate change.
•No notable effect from long-term warming on activity of nutrient-acquiring enzymes. •Long-term warming does not notably affect enzymatic stoichiometry. •Significant, positive correlation between ecoenzyme activity and soil nutrients, microbial biomass. •Phosphorus limitation found for all soil microbes at different depths.
Microbes play an important role in the carbon cycle and nutrient flow of the soil ecosystem. However, the response of microbial activities to long-term warming over decades is poorly understood. To determine how warming changes ecoenzyme activity and microbial nutrient limitation, we conducted a long-term, 21 years, experiment, on the Qinghai–Tibet Plateau. We selected typical grass- and shrub-covered plots, used fiberglass open-top chambers (OTCs) to raise the temperature, conducted soil sampling at different depths, studied the response of nutrient-acquiring enzyme activity and stoichiometry, and conducted vector analysis of stoichiometry. Our results showed that long-term warming did not have a notable effect on the activity of nutrient-acquiring enzymes or enzymatic stoichiometry. However, Spearman correlation analysis indicated a significant and positive correlation between ecoenzyme activity and the available nutrients and microbial biomass in soil. Vector analysis of stoichiometry showed phosphorus limitation for all soil microbes at different depths, regardless of whether the soil experienced warming. These changes in enzymatic stoichiometry and vector analysis suggested that microbial nutrient limitation was not alleviated substantially by long-term warming, and warming did not considerably affect the stratification of microbial nutrient limitation. Our research has also shown that long-term warming does not significantly change soil ecoenzyme activity and original microbial nutrient limitation at different soil depths within the OTUsʼ impact range. These results could help improve understanding of microbial thermal acclimation and response to future long-term global warming.
• A calibration models for the rapid determination of TOC and TN contents using FTIRS. • A rapid analytical method for quantitatively calculating TOC and TN. • A general model for TOC and TN quantitative analysis in reservoir sediments in the southwest China.
This study aims to quantitatively assess the total organic carbon (TOC) and total nitrogen (TN) content of reservoir sediments in southwest China using Fourier transform infrared spectroscopy (FTIRS). FTIRS measurements were performed on 187 sediment samples from four reservoirs to develop calibration models that relate FTIR spectral information with conventional property concentrations using partial least squares regression (PLSR). Robust calibration models were established for TOC and TN content. The external validation of these models yielded a significant correlation between FTIR-inferred and conventionally measured concentrations of R2 = 0.88 for TOC, R2 = 0.90 for TN. This method can be performed with a small sample size and is non-destructive throughout the simple measurement process. The TOC and TN content in the sediment can be determined with high effectiveness without being overly expensive, making it an advantageous method when measuring a large number of samples.
• Tire abrasion particles reduced aboveground and belowground biomass. • Soil respiration and soil pH increased with increasing amount of added tire particles. • Litter decomposition is affected by addition of tire particles. • Effects are apparent already at the lowest added concentration.
Tire particles (TPs) are a major source of microplastic on land, and considering their chemical composition, they represent a potential hazard for the terrestrial environment. We studied the effects of TPs at environmentally relevant concentrations along a wide concentration gradient (0–160 mg g−1) and tested the effects on plant growth, soil pH and the key ecosystem process of litter decomposition and soil respiration. The addition of TPs negatively affected shoot and root growth already at low concentrations. Tea litter decomposition slightly increased with lower additions of TPs but decreased later on. Soil pH increased until a TP concentration of 80 mg g−1 and leveled off afterwards. Soil respiration clearly increased with increasing concentration of added TPs. Plant growth was likely reduced with starting contamination and stopped when contamination reached a certain level in the soil. The presence of TPs altered a number of biogeochemical soil parameters that can have further effects on plant performance. Considering the quantities of yearly produced TPs, their persistence, and toxic potential, we assume that these particles will eventually have a significant impact on terrestrial ecosystems.
• Soil macrofaunal biomass varied in a nonlinear pattern during degradation. • Detritivores responded more sensitively than other trophic groups to degradation. • The dominant trophic group shifted from herbivores to detritivores during degradation. • Macrofauna have stage-specific trophic structures during degradation. • Soil properties outweigh vegetation on determining soil macrofaunal trophic structure.
The alpine wetlands in the Qinghai-Tibetan Plateau have degraded in recent decades. However, the response of the soil food web to the degradation is still unclear. Four habitats including a wet meadow (WM), a grassland meadow (GM), a moderately degraded meadow (MDM) and a severely degraded meadow (SDM) (sandy meadows) were selected along the degrees of degradation. The soil macrofaunal biomass and the environmental factors of vegetation and soil were investigated. The soil macrofaunal community biomass increased significantly from WM to MDM and decreased to a very small amount in SDM, with most taxa disappearing. The biomass of the trophic groups of detritivores, herbivores and predators exhibited similar responses to soil macrofaunal communities. The relative biomass of detritivores increased from WM to MDM, but herbivores responded in an opposite manner, resulting in the dominant trophic group and trophic structure varying progressively from WM to GM to MDM. Soil properties but not vegetation determined the changes in trophic groups and trophic structure. The results implied that the higher trophic levels (carnivores or omnivores) responded more sensitively than the lower trophic levels (herbivores) to alpine wetland degradation. Our results also suggested that soil macrofauna have a habitat-specific characteristic trophic structure and can be used as indicators of soil health conditions.
• Soil nematode samples can be quite turbid, which are not satisfactory for microscopy. • Three methods were designed for cleaning turbid nematode suspensions. • Nematode abundance did not significantly differ among control and the three methods. • Repeated centrifugation had slightly higher recovery rate of nematodes than the other methods.
Soil nematodes are useful ecological indicators and can be extracted from soil by a variety of techniques. Because the extracted nematode samples (suspensions) can be quite turbid (i.e., they contain soil particles and organic particles in addition to nematodes), quantitative and taxonomic analyses of the nematodes by microscopy can be difficult. In this study, the following three methods for cleaning turbid suspensions obtained from Baermann funnels were assessed: repeated centrifugation at 692.5´g for 1 min, repeated settling at low-temperature (4°C) for 24 h, and a combination of low-temperature settling and centrifugation. Nematodes were extracted with Baermann funnels from soil samples collected from four land-use types (since land-use type can affect the turbidity of nematode suspensions), and the resulting suspensions were cleaned by the three methods before nematode abundance was assessed. As a control, samples (i.e., suspensions) were simply diluted with water, and nematodes were counted in the entire volume. The results showed that, within each land-use type, nematode abundance did not significantly differ between the control and the three cleaning methods. Averaged across all land-use types, however, the nematode recovery rate was slightly higher with repeated centrifugation than with the other two cleaning methods. Therefore, the proposed methods are sound for cleaning turbid nematode suspensions, and repeated centrifugation is the most efficient method.
• AgNPs transferred and accumulated though soil animal food chain. • AgNPs trophic transfer disturbed nutrient element N transfer. • Ag accumulated in body tissue, but no biomagnification effects. • Ag2S was harmful to F. candida on survival and reproduction.
The development of nanotechnology has accelerated the use of silver nanoparticles (AgNPs) in household chemicals and the accumulation of Ag in sewage treatment systems. The application of sewage sludge products to soils raises concerns over the safety of Ag in the function and biogeochemical cycles of the soil belowground ecosystem. Here, we assess the potential risk of the accumulation and transfer of Ag under AgNPs exposure and its effects on the trophic transfer of nitrogen (N) through a soil animal food chain (Folsomia candida–Hypoaspis aculeifer). The formation of stable silver sulfide (Ag2S) was also studied via a single species test using F. candida. Concentrations of Ag in F. candida increased with increasing AgNPs concentration, as did those in the predator H. aculeifer, but the Ag bioaccumulation factors of both animals were<1. Folsomia candida body tissue 15N abundance declined markedly compared with that of H. aculeifer. Silver sulfide did have adverse effects on the survival and reproduction of F. candida. The Ag concentrations of F. candida increased with increasing Ag2S concentration in sludge-treated soils. Silver sulfide showed ecotoxicity to the collembolan, therefore ecotoxicity resulting from the transformation and fate of AgNPs in soils needs to be considered before biosolid products are applied to agricultural soils.
•Intercropping effects on yield advantages are crop species specific. •We measured kinetic parameters of three important enzymes in the rhizospheres of individual crop species in both mono and mixed cultures. •In moderately nitrogen enriched soils, phosphorus becomes important nutrient element, involved in nutrient facilitation. •Positive relative interaction index for faba bean when intercropped with either lupine or maize showed net facilitative interactions.
Less attention has been given to soil enzymes that contribute to beneficial rhizosphere interactions in intercropping systems. Therefore, we performed a field experiment by growing faba bean, lupine, and maize in mono and mixed cultures in a moderately fertile soil. We measured shoot biomass and the kinetic parameters (maximal velocity (Vmax) and Michaelis-constant (Km)) of three key enzymes in the rhizosphere: Leucine-aminopeptidase (LAP), β-1,4-N-acetylglucosaminidase (NAG), and phosphomonoesterase (PHO). Faba bean benefitted in mixed cultures by greater shoot biomass production with both maize and lupine compared to its expected biomass in monoculture. Next, LAP and NAG kinetic parameters were less responsive to mono and mixed cultures across the crop species. In contrast, both the Vmax and Km values of PHO increased in the faba bean rhizosphere when grown in mixed cultures with maize and lupine. A positive relative interaction index for shoot P and N uptake for faba bean showed its net facilitative interactions in the mixed cultures. Overall, these results suggest that over-productivity in intercropping is crop-specific and the positive intercropping effects could be modulated by P availability. We argue that the enzyme activities involved in nutrient cycling should be incorporated in further research.
• Soil fungal community composition varied significantly between study sites. • Plant species richness (PSR) contributed most to the variation in soil fungi community. • Both α and β diversity of soil fungi coupled well with that of plant. • Plant diversity can predict soil fungal diversity in the temperate steppe of northeastern China.
Soil fungi and aboveground plant play vital functions in terrestrial ecosystems, while the relationship between aboveground plant diversity and the unseen soil fungal diversity remains unclear. We established 6 sites from the west to the east of the temperate steppe that vary in plant diversity (plant species richness: 7-32) to explore the relationship between soil fungal diversity and aboveground plant diversity. Soil fungal community was characterized by applying 18S rRNA gene sequencing using MiSeq PE300 and aligned with Silva 132 database. As a result, soil fungal community was predominately composed of species within the Ascomycota (84.36%), Basidiomycota (7.22%) and Mucoromycota (6.44%). Plant species richness occupied the largest explanatory power in structuring soil fungal community (19.05%–19.78%). The alpha (α) diversity of the whole soil fungi and Ascomycota showed a hump-backed pattern with increasing plant species richness, and the beta (β) diversity of the whole soil fungi and Ascomycota increased with increasing plant β diversity. Those results indicated that soil fungi and external resources were well balanced at the 20-species level of plant and the sites were more distinct in the composition of their plant communities also harbored more distinct soil fungal communities. Thus, plant diversity could predict both soil fungal α and β diversity in the temperate steppe of northeastern China.
