Soil Nutrient Cycling Research Articles

Linkages of Enzymatic Activity and Stoichiometry with Soil Physical-Chemical Properties under Long-Term Manure Application to Saline-Sodic Soil on the Songnen Plain

Excess Na+ and high pH result in poor structures in Saline-Sodic soils, which reduces extracellular enzyme activity (EEA) and causes nutrient limitations. The application of manure improved the Physical-Chemical properties of soil and balanced the soil nutrient supply, which was reflected in the soil EEAs and stoichiometry. Five experimental treatments were designed according to the manure application duration as follows: manure application for 11 years (11a), 16 years (16a), 22 years (22a), and 27 years (27a) and a control treatment with no manure application (CK). The results of the redundancy analysis (RDA) showed that physical properties (mean weight diameter (MWD)) and EEA (β–glucosidase (BG)) significantly increased and bulk density (ρb) significantly decreased when the nutrient content increased. Additionally, soil pH, electrical conductivity (EC), exchangeable sodium percentage (ESP) and sodium adsorption ratio (SAR) significantly decreased after manure application. Based on stepwise multiple linear regression models (SMLR), total nitrogen (TN) was the dominant variable that significantly increased EEA, and the Mantel test showed that soil C:N significantly influenced enzyme stoichiometry. Furthermore, RDA showed that pH, soil C:N and TN were the main factors influencing EEAs and enzyme stoichiometry. Soil EEAs significantly increased with TN and decreased with pH and soil C:N, which affected enzyme stoichiometry. The enzyme stoichiometry increased from 1:2.1:1.2 and 1:2.7:1.5 to 1:1.7:1.2, and the vector angle (vector A) increased, which showed that the N limitation was relieved after the application of manure. The vector length (vector L) showed no significant difference in the C limitation at depths of 0–20 cm and significantly increased at depths of 20–40 cm. In conclusion, soil EEAs and stoichiometry improved with changes in TN and soil C:N, and pH decreased with changes in the soil structure after the application of manure, which accelerated the soil nutrient cycle and balanced the soil nutrient supply.

Increasing complexity of agroforestry systems benefits nutrient cycling and mineral-associated organic carbon storage, in south-eastern Brazil

Agroforestry systems are often promoted as solutions to address land degradation and climate change. However, agroforestry is an umbrella term for a large variety of systems and it is not clear how their degree of complexity influences their provision of soil-based ecosystem services, such as soil organic carbon (SOC) storage and nutrient cycling. Furthermore, a knowledge gap remains whether agroforestry systems perform equally well on all soil types. The objectives of this study were 1) to assess the links between agroforestry complexity, nutrient cycling and SOC fractions, and 2) to assess how soil texture influences these relationships in Brazilian agroforestry systems. We sampled 59 agroforestry plots across 30 sites in Sao Paulo state, Brazil, and 8 monocrop sites (6 pastures and 2 crop monocultures). The 38 sites represented a soil textural gradient, ranging from very sandy to very clayey (clay content range 25 – 620 g kg−1). An Agroforestry Complexity Index (ACI) was defined based on tree species richness, stem density and pruning management. Nutrient (N, P, K, Ca, Mg) and C contents were determined in litter and soil (0–30 cm depth) samples, and mineral-associated organic C (MAOC) and particulate organic C (POC) in soil samples were assessed as well. ACI was positively associated with C, N, P, Ca and Mg stocks in litter, and these litter nutrients were in turn positively associated with the corresponding soil nutrient stocks. Associations between soil nutrients and MAOC were stronger on sandy soils than on clayey soils, particularly for P, Ca and Cation Exchange Capacity (CEC). For POC, robust relationships with nutrients were only found on sandy soils. Structural Equation Models indicated causal relationships between agroforestry complexity, P and Ca cycling, and MAOC and POC stocks in topsoils. Our results indicate that nutrients effectively cycle from in situ mulch into plant-available soil pools and highlight the synergies between nutrient cycling and stable C stocks that can be achieved in complex agroforestry systems. These synergies seem to be particularly strong on sandy soils (<15 % clay).

Shifts in bacterial traits under chronic nitrogen deposition align with soil processes in arbuscular, but not ectomycorrhizal-associated trees.

Nitrogen (N) deposition increases soil carbon (C) storage by reducing microbial activity. These effects vary in soil beneath trees that associate with arbuscular (AM) and ectomycorrhizal (ECM) fungi. Variation in carbon C and N uptake traits among microbes may explain differences in soil nutrient cycling between mycorrhizal associations in response to high N loads, a mechanism not previously examined due to methodological limitations. Here, we used quantitative Stable Isotope Probing (qSIP) to measure bacterial C and N assimilation rates from an added organic compound, which we conceptualize as functional traits. As such, we applied a trait-based approach to explore whether variation in assimilation rates of bacterial taxa can inform shifts in soil function under chronic N deposition. We show taxon-specific and community-wide declines of bacterial C and N uptake under chronic N deposition in both AM and ECM soils. N deposition-induced reductions in microbial activity were mirrored by declines in soil organic matter mineralization rates in AM but not ECM soils. Our findings suggest C and N uptake traits of bacterial communities can predict C cycling feedbacks to N deposition in AM soils, but additional data, for instance on the traits of fungi, may be needed to connect microbial traits with soil C and N cycling in ECM systems. Our study also highlights the potential of employing qSIP in conjunction with trait-based analytical approaches to inform how ecological processes of microbial communities influence soil functioning.

Effects of polyethylene microplastics and heavy metals on soil-plant microbial dynamics

Polyethylene (PE) microplastics are emerging pollutants that pose a significant threat to the environment and human health. However, little is known about the effects of PEs on soil‒plant interactions, especially in heavy metal (HM)-contaminated soil. In this study, the effects of PE on rhizosphere soil enzyme activities, microbial interactions and nutrient cycling processes were analyzed from ecological network and functional gene perspectives for the first time. The results indicated that PE-MP addition significantly reduced the biomass of Bidens pilosa L. In addition, the partial increase in carbon, nitrogen, and phosphorus enzyme activities suggested that the effects of PE as a carbon source on microbial functions in HM-contaminated soil should not be ignored. The average path length of bacterial network nodes was found to be higher than that of fungal network nodes, demonstrating that the bacterial ecological network in PE-MP and HM cocontaminated environments has good buffering capacity against changes in external environmental conditions. Furthermore, structural equation modeling demonstrated that particle size and dosage affect soil nutrient cycling processes and that cycling processes are acutely aware of changes in any factor, such as soil moisture, soil pH and soil nitrogen nutrients. Hence, PE-MP addition in HM-contaminated soil has the potential to alter soil ecological functions and nutrient cycles.

A feasible method of induced biological soil crust propagation through the inoculation of moss and addition of soil amendments in a Pb-Zn tailing pond

The stacking of tailings results in serious environmental pollution and plant growth difficulty. However, moss and microorganisms can successfully colonize in tailings to form biological soil crusts (BSCs) and provide a feasible means to ecologically restore tailing reservoirs. Nonetheless, information on this approach is scarce. In this study, a 90 day field experiment was conducted to form BSCs in a Pb-Zn tailing pond in Jianshui County, China by inoculating in-situ moss crust fragments and adding three soil amendments. Results showed that induced BSCs successfully propagated, and the biomass increased to 15.51–20.33 times the initial value. Moss inoculation considerably increased the soil moisture, water-holding capacity, and phosphatase by 9.2 %, 8.8 %, and 64.0 %, respectively, and decreased exchangeable fraction Pb by 30.7 %. The co-inoculation of moss and biochar remarkably increased soil moisture, water-holding capacity, cation exchange capacity, sucrase, urease, and phosphatase activity by 22.3 %, 23.4 %, 116 %, 80.5 %, 28.6 %, and 240 %, respectively, and decreased the bulk density by 13.3 %. The addition of red soil reduced the total contents of Pb and Zn, whereas that of the stabilizer increased the pH and decreased the bioavailability of Pb and Zn. Co-inoculation greatly increased the biotic community species richness and changed their structure and function. The dominant photosynthetic eukaryotes shifted from Synechococcales to Oscillatoriales. Bacterial nutritional types shifted from chemoautotrophy to photoautotrophy and chemoautotrophy, and fungal nutritional types changed from oligotrophy to copiotrophy. These changes drove alterations in bacterial and fungal community structures. These results indicated that the propagation of induced BSCs can rapidly improve the soil structure and nutrient cycle, restore the biotic abundance and function, and facilitate the soil formation of tailings. Thus, this method holds promise for the ecological restoration of tailings.

Higher colonization but lower diversity of root-associated arbuscular mycorrhizal fungi in the topsoil than in deep soil

Arbuscular mycorrhizal fungi (AMF) colonizing plant roots play a pivotal role in maintaining soil nutrient cycling and ecosystem stability, and this role may vary in different habitat environments. However, the influence of soil depth on root AMF colonization, diversity, and the complex interactions among AMF taxa is still not well understood. In this study, we investigated the frequency, intensity, and abundance of root AMF colonization, as well as root AMF diversity, composition, and co-occurrence patterns across three soil depths: 0–20 cm, 20–40 cm, and the soil-rock mixing layer. Soil nutrients (e.g., organic matter, nitrogen, and phosphorus) and root biomass were higher in the 0–20 cm layer than in the soil-rock mixing layer, while soil pH showed an opposite relationship. The higher root biomass in the upper soil layer may enhance root secretions and exudates, thereby promoting root AMF colonization. In contrast, the lower soil nutrient content and higher soil pH observed in the 20–40 cm and soil-rock mixing layers may contribute to greater AMF diversity in the deeper soil layers compared to the topsoil. Although no significant differences were observed in the composition of the root AMF community, specific amplicon sequence variants affiliated with Glomus, Racocetra, and unclassified taxa were more enriched in the 20–40 cm and soil-rock mixing layers compared to the 0–20 cm layer. Network analysis revealed that deep soil, compared to topsoil, enhances interactions among root AMF by intensifying competitive relationships. This suggests that the complex interactions among root AMF taxa within deep soil contribute to the resilience of root AMF in resource-scarce conditions, particularly in the 20–40 cm layer and the soil-rock mixing layer. At the genus level, Glomus, Racocetra, and unclassified taxa emerged as keystone taxa due to their prominent linkage with other root AMF groups. Collectively, the results suggest that higher soil nutrient levels and root biomass can promote root mycorrhizal colonization but suppress AMF diversity and weaken interactions among root AMF taxa in the upper soil layer compared to deeper soil layers. Furthermore, the distinct functions of AMF colonization and diversity at different soil depths should be considered when evaluating vegetation reconstruction in karst ecosystems with varied soil depth distribution.

Cover crop functional types alter soil nematode community composition and structure in dryland crop-fallow rotations

Increasing dryland cropping intensity by integrating cover crops into crop-fallow rotations can add diversity and alter soil ecosystem functions, including improvements in soil nutrient and water retention and cycling, and suppression of soil-borne pests. However, the use of cover crops can also carry the risk of increasing the abundance of plant-parasitic nematodes that could undermine system productivity. Here, we examined how the integration of diverse cover crops of different functional groups: Poaceae [forage oat (Avena sativa L.)]; Brassicaceae [forage rape (Brassica napus L.)]; and Fabaceae [common vetch (Vicia sativa subsp. sativa L. and fababean (Vicia faba L.) in monocultures and mixtures into a dryland crop-fallow rotation altered soil nematode community composition and structure relative to conventional fallows. We found that cover crop mixtures had greater diversity and complexity of free-living nematodes, indicating enhanced cycling of energy and nutrients (enrichment index >50 %) compared to monocultures. Furthermore, using a structural equation modelling approach, we showed the abundance of free-living nematodes is driven primarily by cover crop residue quality (C:N ratio, and cellulose content) and marginally by cover crop quantity (biomass). The grass-legume mixture had the highest abundance of plant-parasitic nematodes (Pratylenchus neglectus and Merlinius brevidens) but also fostered robust soil food webs with complex soil nematode trophic interactions, indicating promotion of soil ecosystem functions related to N and C cycling and overall improvement in soil health. The results indicate bottom-up effects of cover crops on soil nematode communities are modulated by cover crop functional type and mixture composition. Consequently, cover crops with appropriate traits must be selected if soil health is to be improved via suppression of plant-parasitic nematodes, promotion of free-living nematodes, and enhancement of soil food web complexity.

Responses of Soil Microbial Survival Strategies and Functional Changes to Wet-Dry Cycle Events.

Soil microbial taxa have different functional ecological characteristics that influence the direction and intensity of plant-soil feedback responses to changes in the soil environment. However, the responses of soil microbial survival strategies to wet and dry events are poorly understood. In this study, soil physicochemical properties, enzyme activity, and high-throughput sequencing results were comprehensively anal0079zed in the irrigated cropland ecological zone of the northern plains of the Yellow River floodplain of China, where Oryza sativa was grown for a long period of time, converted to Zea mays after a year, and then Glycine max was planted. The results showed that different plant cultivations in a paddy-dryland rotation system affected soil physicochemical properties and enzyme activity, and G. max field cultivation resulted in higher total carbon, total nitrogen, soil total organic carbon, and available nitrogen content while significantly increasing α-glucosidase, β-glucosidase, and alkaline phosphatase activities in the soil. In addition, crop rotation altered the r/K-strategist bacteria, and the soil environment was the main factor affecting the community structure of r/K-strategist bacteria. The co-occurrence network revealed the inter-relationship between r/K-strategist bacteria and fungi, and with the succession of land rotation, the G. max sample plot exhibited more stable network relationships. Random forest analysis further indicated the importance of soil electrical conductivity, total carbon, total nitrogen, soil total organic carbon, available nitrogen, and α-glucosidase in the composition of soil microbial communities under wet-dry events and revealed significant correlations with r/K-strategist bacteria. Based on the functional predictions of microorganisms, wet-dry conversion altered the functions of bacteria and fungi and led to a more significant correlation between soil nutrient cycling taxa and environmental changes. This study contributes to a deeper understanding of microbial functional groups while helping to further our understanding of the potential functions of soil microbial functional groups in soil ecosystems.

Impact of planting green on soil properties under irrigated no‐till soybean

AbstractPlanting green refers to the practice of planting a row crop into an actively growing cover crop (CC) and terminating it at or after row crop planting. Planting green could have more beneficial impacts on soil properties, erosion control, nutrient cycling, weed suppression, and other soil ecosystem services because it allows greater CC biomass accumulation than early‐terminated CC. The objectives of this 2‐year study were to evaluate the impact of planting green on soil properties (bulk density, wet aggregate stability, sorptivity, particulate organic matter, organic matter, nutrients, and others) and soybean (Glycine max L.) yield in an irrigated no‐till soybean system in south‐central Nebraska. Treatments were cereal rye (Secale cereale L.) CC terminated 2 weeks before planting (2WBP), CC terminated 2 weeks after planting (2WAP) soybean, and no CC. On average, CC produced 2.35 Mg ha−1 of biomass for 2WBP and 12.03 Mg ha−1 for 2WAP. Both 2WBP and 2WAP reduced N concentration by 48% (31.10 vs. 59.70 mg kg−1) but had no effect on other soil properties compared with no CC. Despite the abundant CC biomass production, terminating 2WAP had little to no effect on most soil properties in the short term (2 years). Wet aggregate stability increased as CC biomass production increased, while soil sorptivity (initial water infiltration) increased as wet aggregate stability increased. CC termination timing had inconsistent effects on soybean yield. In general, after 2 years, planting green had no effect on most soil properties or soybean yield, warranting long‐term studies on this topic.

Deciphering microbiomes dozens of meters under our feet and their edaphoclimatic and spatial drivers.

Microbes inhabiting deep soil layers are known to be different from their counterpart in topsoil yet remain under investigation in terms of their structure, function, and how their diversity is shaped. The microbiome of deep soils (>1 m) is expected to be relatively stable and highly independent from climatic conditions. Much less is known, however, on how these microbial communities vary along climate gradients. Here, we used amplicon sequencing to investigate bacteria, archaea, and fungi along fifteen 18-m depth profiles at 20-50-cm intervals across contrasting aridity conditions in semi-arid forest ecosystems of China's Loess Plateau. Our results showed that bacterial and fungal α diversity and bacterial and archaeal community similarity declined dramatically in topsoil and remained relatively stable in deep soil. Nevertheless, deep soil microbiome still showed the functional potential of N cycling, plant-derived organic matter degradation, resource exchange, and water coordination. The deep soil microbiome had closer taxa-taxa and bacteria-fungi associations and more influence of dispersal limitation than topsoil microbiome. Geographic distance was more influential in deep soil bacteria and archaea than in topsoil. We further showed that aridity was negatively correlated with deep-soil archaeal and fungal richness, archaeal community similarity, relative abundance of plant saprotroph, and bacteria-fungi associations, but increased the relative abundance of aerobic ammonia oxidation, manganese oxidation, and arbuscular mycorrhizal in the deep soils. Root depth, complexity, soil volumetric moisture, and clay play bridging roles in the indirect effects of aridity on microbes in deep soils. Our work indicates that, even microbial communities and nutrient cycling in deep soil are susceptible to changes in water availability, with consequences for understanding the sustainability of dryland ecosystems and the whole-soil in response to aridification. Moreover, we propose that neglecting soil depth may underestimate the role of soil moisture in dryland ecosystems under future climate scenarios.

Influence of slurry acidification with H2SO4 on soil pH, N, P, S, and C dynamics: Incubation experiment

Acidifying slurry with sulfuric acid (H2SO4) is practiced in some countries for reducing ammonia (NH3) emissions during slurry storage and spreading to land. However, knowledge on how the application of acidified slurry affects soil health and nutrient cycling is lacking. This is particularly important since acidification with H2SO4 can substitute a sulfur (S) mineral fertilizer to increasingly S-deficient agricultural soils. We hypothesized that (ⅰ) slurry acidification would decrease the soil pH over a prolonged period, and as a result (ⅱ) would increase the extractable N, P, C and S concentrations, (ⅲ) and decrease greenhouse gas emissions. By using laboratory mesocosms, the nutrient (C, N, P and S) dynamics were monitored in an arable sandy clay loam soil receiving acidified and non-acidified cattle slurry in a 2-month incubation. Estimations of greenhouse gas emissions (CO2, CH4, N2O), soil-pore- water components (NO3−, NH4+, PO43−, SO42−, DOC, DON, pH) were performed on static mesocosms. In addition, a parallel set of mesocosms were used for soil extractions using distilled water and 0.5 M K2SO4. There were six treatments: (1) soil (control), (2) soil + slurry, (3) soil + acidified slurry (with H2SO4, pH =5.5), (4) soil + HCl, (5) soil + K2SO4, and (6) soil + K2SO4 + H2SO4. Our results showed that over the incubation, slurry acidification reduced soil pH by at least 0.4 units. Water soluble PO43−-P concentration was also reduced, whilst extractable DOC and NO3—N concentrations were increased; the latter as a result of stimulated N mineralization in the acidification treatments (3, 4 and 6). Differences in water soluble SO42- -S concentrations per treatment were not significant over time.Slurry acidification did not significantly affect N2O emissions but decreased net CO2 and CH4 emissions leading to an overall reduction in the soil's total greenhouse gas footprint (expressed as CO2e). We conclude that application of acidified slurry to soil can reduce soil pH by at least 0.4 pH units for up to 2-months before it is buffered back to the pH level of the soil that received the non-acidified slurry. In addition to increasing organic N mineralization with limited impacts on P and S dynamics of the soil and the slurry.

Seed biopriming as a promising approach for stress tolerance and enhancement of crop productivity: a review.

Chemicals are used extensively in agriculture to increase crop production to meet the nutritional needs of an expanding world population. However, their injudicious application adversely affects the soil's physical, chemical and biological properties, subsequently posing a substantial threat to human health and global food security. Beneficial microorganisms improve plant health and productivity with minimal impact on the environment; however, their efficacy greatly relies on the application technique. Biopriming is an advantageous technique that involves the treatment of seeds with beneficial biological agents. It exhibits immense potential in improving the physiological functioning of seeds, thereby playing a pivotal role in their uniform germination and vigor. Biopriming-mediated molecular and metabolic reprogramming imparts stress tolerance to plants, improves plant health, and enhances crop productivity. Furthermore, it is also associated with rehabilitating degraded land, andimproving soil fertility, health and nutrient cycling. Although biopriming has vast applications in the agricultural system, its commercialization and utilization by farmers is still in its infancy. This review aims to critically analyze the recent studies based on biopriming-mediated stress mitigation by alteration in physiological, metabolic and molecular processes in plants. Additionally, considering the necessity of popularizing this technique, the major challenges and prospects linked to the commercialization and utilization of this technique in agricultural systems have also been discussed. © 2023 Society of Chemical Industry.

Effects of land use and soil properties on taxon richness and abundance of soil assemblages

AbstractLand‐use change and habitat degradation are among the biggest drivers of aboveground biodiversity worldwide but their effects on soil biodiversity are less well known, despite the importance of soil organisms in developing soil structure, nutrient cycling and water drainage. Combining a global compilation of biodiversity data from soil assemblages collated as part of the PREDICTS project with global data on soil characteristics, we modelled how taxon richness and total abundance of soil organisms have responded to land use. We also estimated the global Biodiversity Intactness Index (BII)—the average abundance and compositional similarity of taxa that remain in an area, compared to a minimally impacted baseline, for soil biodiversity. This is the first time the BII has been calculated for soil biodiversity. Relative to undisturbed vegetation, soil organism total abundance and taxon richness were reduced in all land uses except pasture. Soil properties mediated the response of soil biota, but not in a consistent way across land uses. The global soil BII in cropland is, on average, a third of that originally present. However, in grazed sites the decline is less severe. The BII of secondary vegetation depends on age, with sites with younger growth showing a lower BII than mature vegetation. We conclude that land‐use change has reduced local soil biodiversity worldwide, and this further supports the proposition that soil biota should be considered explicitly when using global models to estimate the state of biodiversity.

Linking the rhizosphere effects of 12 woody species on soil microbial activities with soil and root nitrogen status

The rhizosphere effect depicts the changes in soil physical, chemical, and biological properties due to altered microbial activity in response to root activity, which has important implications for soil carbon and nutrient cycling. However, how the plant-induced changes in rhizosphere soil microbial activity correlate with root and soil nutrient status remains uncertain. Here we targeted 12 woody species of distinct growth forms, i.e., tree vs. shrub, in an urban park on a university campus in Beijing, China. We measured root carbon and nitrogen concentrations and soil properties of paired rhizosphere and bulk soils for each plant. We investigated how the rhizosphere effects on microbial properties, as indicated by microbial biomass and potential activity of soil extracellular hydrolases, varied among the 12 woody species and between trees and shrubs, as well as how they were regulated by bulk soil and root nitrogen status. In general, across the 12 species, root nitrogen content, which is a potential indicator of plant life span and nutrient acquisition strategy, was positively correlated with the rhizosphere effect on potential enzyme activity, while the inverse was true for root carbon: nitrogen ratio, which further verified the role of root functional traits in controlling soil nutrient cycling through the rhizosphere effect. Moreover, soil organic carbon, total nitrogen, and available nitrogen concentrations were all found to be negatively correlated with the rhizosphere effect on microbial properties, which highlighted the stimulation of rhizosphere microbial activity for nitrogen acquisition (the nitrogen-mining hypothesis). Trees and shrubs exhibited no significant differences in their rhizosphere effects, and there was a potential difference in the role of rhizosphere effect in regulating soil nitrogen cycling between legumes and non-legumes. Overall, our study highlights the role of plant nutrient acquisition strategy and soil nutrient status in regulating the rhizosphere effect of woody species on microbial-driven soil processes, which is essential for a better understanding of mechanisms by which plants sustain their nutrient supply.

Phytoremediation with application of anaerobic fermentation residues regulate the assembly of ecological clusters within co-occurrence network in ionic rare earth tailings soil: A pot experiment

The cultivation of energy plants (Pennisetum hybrid) with anaerobic fermentation residues has become an important phytoremediation approach in ionic rare earth elements (REEs) tailings because of its advantages in low cost and sustainability recently. In this study, a comparative pot experiment was carried out to determine the interaction pattern and key ecological clusters in microbial community respond to phytoremediation. Results showed that the application of biogas residues or slurry could effectively mitigate soil acidification, increase soil nutrients, alter REEs bioavailability and promote plant growth. Without fertilization, plant growth was restricted and soil acidification and nutrient-deficiency would be further aggravated. This difference in phytoremediation effect was associated with the assembly of seven key ecological clusters in co-occurrence network of rhizosphere soil. And such assembly pattern of cluster, determined by the environmental preference (e.g. pH, REEs), nutrient demand and interaction among clusters, could alter the microbial communities in response to the changes in soil context rapidly and exert corresponding ecological function during phytoremediation, such as participating in soil nutrient cycling, affecting plant biomass and altering REEs bioavailability. These findings provided new insights for anaerobic fermentation residues application, and can be beneficial to support for studying microbe-plant combined remediation in the future.

Relating Threshold Changes in Soil Function to Structural Changes in Woody Vegetation Along Herbivore Utilization Gradients with Different Management Histories in an Arid Thicket Mosaic, South Africa

The hypothesis that transformation of rangelands by domestic herbivores follows state-and-transition models predicts that vegetation communities will cross ecological thresholds when shifting from one state to another. We test this hypothesis by identifying threshold responses of soil function in Gamka Thicket, a variation of Arid Thicket in South Africa. We relate indices of soil water infiltration, nutrient cycling, and soil retention (reflecting ecosystem function) to distance from artificial watering points in four piosphere treatments differing in rangeland management history. Furthermore, we compare the pattern, extent, and variation in transformation at the end regions of our piosphere treatments to each other and to a transformed and untransformed reference site. The changes to all the indices of ecosystem function support the hypothesis that functional thresholds have been crossed. We propose a conceptual model that suggests that Arid Thicket transformation due to herbivory transcends three vegetation states. We contend that during the process of transformation the crossing of structural thresholds lead to the crossing of functional thresholds that ultimately drive the formation of new vegetation states.

Microbial Diversity, Biomass, and Community Structure Differences among Restored and Natural Saltwater Marshes, Louisiana

Tidally influenced, saltwater marsh construction projects are being completed in Louisiana to combat coastal erosion and land loss, as well as to restore critical fisheries and counteract ecosystem injuries caused by oil spills and other anthropogenic activities. Historically, metrics of success for restored marshes have been based on the amount of aboveground biomass, survival of planted vegetation, and recruitment of local endemic versus invasive species. The microbial communities responsible for cycling nutrients within restored soils are not typically evaluated. Therefore, we investigated microbial community structure, biomass, and diversity in marsh soils that had been created from nearby dredge material over the past 10 years in the Lake Hermitage, West Point a La Hache area, and compared the results to those from natural marsh soils from Bay Batiste, as determined using phospholipid fatty acid (PLFA) and gas chromatography/mass spectrometry (GC/MS) techniques and from 16S rRNA gene profiles. Soils were collected from two depths (0-2 cm and 8-10 cm) from four sampling locations along a 100-m transect that extended inland from the coastline. Soil organic carbon content and soil pH were consistently lower at restored sites compared to natural marshes. Natural marsh soil microbial diversity strongly correlated with the biomass of typical marsh plants (e.g., Spartina alterniflora, Juncus roemerianus), whereas restored soil diversity correlated to higher Paspalum spp. (crowngrass) and Schoenoplectus pungens (common bulrush) biomass. Created soils had higher overall microbial diversity, but natural marsh soils had at least twice as much PLFA biomass than the created marshes at the shallow depth and 10X more biomass at the deeper depth. Biomass estimates ranged from below detectable levels to 6 x104 pmol PLFA gdw−1, with shallower soils from all sites exhibiting higher biomass (average 104 pmol PLFA gdw-1) compared to deeper soils (average 103 pmol PLFA gdw-1). Diverse PLFA profiles were observed. Shallow soils were dominated by terminally-branched and midchain-branched saturates that are indicative of Gram-positive microorganisms and actinomycetes. The shallow soils contained polyunsaturates indicative of phototrophs. Deeper soil profiles were dominated by monounsaturates associated with Gram-negative bacteria and sulfate- and metal-reducing bacteria. These monounsaturates contained on average 7% of the total PLFA profile as cyclopropyl fatty acids, which likely indicated anaerobic processes and the presence of nutritional stress. The shallow natural marsh soils exhibited more mid-branched saturates, branched monounsaturates, and polyunsaturates, whereas the shallow created marsh soils had more terminally-branched saturates. In the deeper soils, the natural marshes exhibited more terminally-branched saturates and monounsaturates, but the created marshes contained more saturates. GC/MS analyses of dimethyl disulfide derivatizations revealed shifts in microorganisms, as indicated by the types and bonding positions of monounsaturates, and the changes in the presence/absence of methanotrophic populations within the soils, which was also reflected in the 16S rRNA gene profiles. From these results, the microbial communities from the created marsh soils were different than the natural soil communities, and may reflect not being the best desired outcome for marsh restoration. With time, the expectation would be that created marsh above and belowground microbial diversity and biomass would begin to mimic natural marshes, but continued monitoring through time will be necessary to understand how these linkages develop and affect basic soil processes, nutrient cycling, and recruitment and sustenance of higher organisms like fish or crustaceans.

Evaluation of agricultural soil health after applying atrazine in maize-planted fields based on the response of soil microbes

Soil health is closely linked to the sustainable development of agriculture, and soil microorganisms are the fundamental and pivotal components in maintaining soil health. Atrazine (ATZ) is a triazine herbicide widely used worldwide, and its ecotoxicity to soil microorganisms has been widely studied. However, previous studies have focused on investigating the ecotoxicity of ATZ active ingredients under laboratory conditions. The damage caused by ATZ formulations to soil health in the actual field environment cannot be ignored. Herein, the toxicity of ATZ formulations (1140 and 1710 g hm−2) in maize fields after 1, 28, and 72 d of exposure was investigated in terms of soil microbial abundance, community structure, soil enzyme activities, functional gene abundance, and ATZ residues. The results showed that ATZ disturbed the microbial functions that maintain soil health by disturbing soil nutrient and carbon cycling as well as enhancing pollution degradation. The promotion of both urease activity and AOB-amoA gene abundance indicated that ATZ accelerated the loss of nitrogen from soil, which was detrimental to soil nitrogen cycling. The abundances of the Pontibacter genus and the cbbLG gene were inhibited, indicating that the ability of soil carbon dioxide fixation was hindered. The abundance of Lysobacter, which helps to degrade pollutants, increased. The integrated biomarker response indicated that the comprehensive toxicity of ATZ to soil microorganisms increased with dose. Additionally, the DT50 of ATZ in agricultural soil was 5.4–5.7 d, and the residual level of ATZ in crop grains was in line with the maximum residue limit recommended by the European Union and China. The findings of the present study reflect the effects of ATZ formulation on soil microbes in the actual agricultural environment and provide insights into the mechanisms of soil health regulation mediated by microorganisms.

Vermicompost derived from mushroom residues improves soil C/P cycling, bacterial community, and fungal abundance

AbstractThe utilization of agricultural waste organic materials through composting technology has gained significant traction in agricultural production as an effective means of crop nutrient management. However, the differences in the impact of organic amendments prepared by traditional composting and vermicomposting on soil properties still deserve further research. Based on field experiments conducted in greenhouse, compared to chemical fertilizer treatments as control, we utilized traditional compost (OF) and vermicompost (VcF) derived from agricultural organic waste edible mushroom bran and cow manure (2:8). Variations in soil physiochemical properties, activities of soil enzymes related C and P cycling, abundances and diversities of bacterial 16S rRNA and fungal ITS gene at total DNA level were analyzed. Both compost treatments enhanced soil organic carbon, soil total phosphorus, and soil available P content significantly and also increased the activities of soil α‐glucosidase, β‐glucosidase, acid phosphomonoesterase, and alkaline phosphomonoesterase significantly. The above results suggested that soil C and P transformations were stimulated effectively by both organic amendments. OF and VcF increased the fungal ITS absolute abundances significantly while diversity indices of soil bacterial community increased significantly under both treatments. Correlation analysis indicated that bacterial community composition was strongly correlated with several soil property indexes while fungal community composition was only significantly correlated with soil total phosphorous content. In conclusion, similar to traditional compost, vermicompost significantly improved soil nutrient cycling (especially C and P aspects). In terms of soil microbes, bacteria and fungi showed different responding mechanism to vermicompost: bacteria adjust microbial structure, while fungi tend to proliferated. In consideration of the advantages of vermicompost in technology and economic cost, it could be applied in the subsequent agricultural production more frequently.

Fungal community characteristics and driving factors in Bothriochloa ischaemum litter in a copper mining area

Among influencing biotic and abiotic factors, microorganisms predominate litter decomposition, playing an important role in maintaining the ecosystem material cycle. Bothriochloa ischaemum was the dominant plant species in China's Eighteen River tailings dam, and it was selected as the research object. We explored the dynamic of fungal community characteristics in B. ischaemum litter during different decomposition stages and investigated relevant driving factors affecting associative dynamic changes. Results showed that Ascomycetes and Basidiomycetes were the dominant phyla during litter decomposition. At a class level, the relative abundance of Dothideomycetes gradually decreased as litter decomposition progressed while Sordariomycetes gradually increased, ultimately becoming the dominant class. The community structure of the fungal community was mainly affected by litter pH, total carbon (TC), and copper (Cu) content. The fungal community's network structure was the most complex compared to other decomposition stages after 200 days of litter decomposition. Additionally, the fungal community's modularity gradually increased, while the degree of functional differentiation also increased, strengthening fungal community stability during litter decomposition. This study clarifies fungal community structure during litter decomposition in this copper tailings area, and provides a scientific basis for further improving soil fertility and nutrient cycling in mining areas.