Affect Soil Enzyme Activities Research Articles

Effect of polyethylene microplastics on antibiotic resistance genes: A comparison based on different soil types and plant types

Microplastics (MPs) and antibiotic resistance genes (ARGs) are two types of contaminants that are widely present in the soil environment. MPs can act as carriers of microbes, facilitating the colonization and spread of ARGs and thus posing potential hazards to ecosystem safety and human health. In the present study, we explored the microbial networks and ARG distribution characteristics in different soil types (heavy metal (HM)-contaminated soil and agricultural soil planted with different plants: Bidens pilosa L., Ipomoea aquatica F., and Brassica chinensis L.) after the application of MPs and evaluated environmental factors, potential microbial hosts, and ARGs. The microbial communities in the three rhizosphere soils were closely related to each other, and the modularity of the microbial networks was greater than 0.4. Moreover, the core taxa in the microbial networks, including Actinobacteriota, Proteobacteria, and Myxococcota, were important for resisting environmental stress. The ARG resistance mechanisms were dominated by antibiotic efflux in all three rhizosphere soils. Based on the annotation results, the MP treatments induced changes in the relative abundance of microbes carrying ARGs, and the G1–5 treatment significantly increased the abundance of MuxB in Verrucomicrobia, Elusimicrobia, Actinobacteria, Planctomycetes, and Acidobacteria. Path analysis showed that changes in MP particle size and dosage may indirectly affect soil enzyme activities by changing pH, which affects microbes and ARGs. We suggest that MPs may provide surfaces for ARG accumulation, leading to ARG enrichment in plants. In conclusion, our results demonstrate that MPs, as potentially persistent pollutants, can affect different types of soil environments and that the presence of ARGs may cause substantial environmental risks.

Pristine and Fe-functionalized biochar for the simultaneous immobilization of arsenic and antimony in a contaminated mining soil

This study examined the effectiveness of pristine biochar (BC) and Fe-functionalized biochar (FBC) in remediating As-Sb co-contaminated soil, and revealed the resulting impact on soil enzymatic activities and bacterial communities. Results from incubation experiments showed that the 1.5% FBC treatment reduced the bioavailable As and Sb concentration by 13.5% and 27.1%, respectively, in compared to the control, and reduced the proportion of specifically adsorbed and amorphous Fe-Mn oxide-bound metal(loid) fractions in the treated soil. Among the BC treatments, only the 1.5% BC treatment resulted in a reduction of bioavailable As by 11.7% and Sb by 21.4%. The 0.5% BC treatment showed no significant difference. The FBC achieved high As/Sb immobilization efficiency through Fe-induced electrostatic attraction, π-π electron donor-acceptor coordination, and complexation (Fe–O(H)–As/Sb) mechanisms. Additionally, the 1.5% FBC treatment led to a 108.2% and 367.4% increase in the activities of N-acetyl-β-glucosaminidase and urease in soils, respectively, compared to the control. Furthermore, it significantly increased the abundance of Proteobacteria (15.2%), Actinobacteriota (37.0%), Chloroflexi (21.4%), and Gemmatimonadota (43.6%) at the phylum level. Co-occurrence network analysis showed that FBC was better than BC in increasing the complexity of bacterial communities. Partial least squares path modeling further indicated that the addition of biochar treatments can affect soil enzyme activities by altering soil bacterial composition. This study suggests that FBC application offers advantages in simultaneous As and Sb immobilization and restructuring the bacterial community composition in metal(loid)-contaminated soil.

Effects of Clay Minerals on Enzyme Activity as a Potential Biosensor of Soil Pollution in Alice Township

Inadequate waste management and illegal trash dumping continue to be the leading causes of severe environmental pollution. Human exposure to harmful heavy metals has emerged as a serious health concern on the continent. Some people in Alice, a small town, grow their food in home gardens. They use animal manure and compost derived from soil obtained from landfills to enhance the fertility of the garden soil. Heavy metal heaps in garbage disposals are constantly present, releasing dangerous amounts of metal into the environment. The harmful effects of heavy metals on plants lead to unsanitary conditions and environmental problems. Animals and people who consume these vegetables may also be at risk for health problems. Assessing the soil’s enzyme activity can potentially lessen the negative effects of the accumulated pollutants and improve the soil’s overall health and quality. Soil enzymes are biologically active components that have a catalytic impact and are released from root exudates, crop residues, and animal remains. The activity of enzymes serves as an excellent bioindicator of soil cleanliness and quality because they are sensitive to heavy metals. X-ray diffraction (XRD) was used to quantify the mineral elements in soil using 40 kV parallel beam optics, 30 mA, and CuKα radiation. Meanwhile, the activity of the enzyme was essayed in different coupled substrates. Thirteen (13) clay minerals were found, including Talc 2M, Kaolinite 2M, and Chlorite Lawsonite Muscovite 2M1. The detected trace elements have high concentration levels that exceed the World Health Organization’s (WHO) allowed levels. The identified elements affected the enzyme activity at different levels. The Mn, Al, Si, V, Ti, and Ca negatively affect soil enzyme activity, specifically invertase (INV). However, the amount of Mg, K, Fe, and Zn showed a slightly positive effect on the same enzyme (INV). According to this view, these elements come from several sources, each with a particular impact on soil contamination and enzyme activity. High levels of heavy metals in this study may be due to improper waste disposal, limited recycling opportunities, lack of public awareness, and inadequate enforcement of waste management regulations. It is essential to employ Fourth Industrial Revolution (4IR) technologies, correct disposal techniques, suitable agricultural methods, preventive regulations, and efficient waste management to mitigate the negative effects of heavy metals on the environment.

Assessment of degradation mechanism of imidacloprid residues in grape rhizosphere soil by UHPLC-Orbitrap™-MS and its residual impact on soil enzyme activity.

Imidacloprid (IM) is a systemic insecticide persistent in the environment and possesses a negative impact on the non-targeted ecosystem. The objective of the present study was to evaluate the dissipation and degradation mechanism of IM residues in grape rhizosphere soil and to investigate its residual effect on soil enzyme activity at different IM spiking levels. The half-life of IM residue in soil was 27, 36, and 43.5days at a spiking level of 1, 10, and 50mgkg-1, respectively following a bi-phasic first + first-order dissipation kinetics. UHPLC-Orbitrap™-MS analysis by targeted metabolomics approach revealed that IM metabolites such as IM-amine analogue, guanidine (reduction), 5-hydroxy IM (hydroxylation), IM-Urea (oxidation), reduced NO analogue of IM (oxidation), and olefin of guanidine IM (dehydrogenation) were identified and proposed the degradation mechanism in grape rhizosphere soil. Toxicity of IM residues on five extracellular enzymes, viz., dehydrogenase, acid phosphatase, alkaline phosphatase, β-glucosidase, and urease revealed that activity of dehydrogenase, acid phosphatase, and alkaline phosphatase remained unaffected at 60th day of sampling. The β-glucosidase and urease were negatively affected throughout the incubation period indicating the influence of IM residues on carbon and nitrogen mineralization in soil. Thus, long-term exposure of IM to grape rhizosphere through soil drenching could affect soil enzyme activity which has a negative effect on the soil nutrient cycle and soil microbiome.

Foliar applications of a zeolite-based biostimulant affect soil enzyme activity and N uptake in maize and wheat under different levels of nitrogen fertilization

There is a growing interest in developing agricultural practices that can improve crop performance while preserving natural resources. Plant biostimulants are thought to play a role in reaching this goal, in particular by increasing the nitrogen use efficiency. However, a notable research gap exists concerning the effects of foliar applications of natural zeolites as plant biostimulants on crop performance. To address this knowledge gap, a greenhouse experiment was set up in order to study the response of maize and wheat traits, specifically the biomass productivity and nitrogen uptake, as well as the response of soil extracellular enzymes to the foliar applications of a natural zeolite in combination with different levels of nitrogen fertilization, that is, 100%, 75%, and 50% of the optimal dose. Foliar application of zeolite in wheat and maize plants led to an increase in root nitrogen concentration of about 10%, particularly at the lowest nitrogen fertilization rate. This response was accompanied by an increase in aboveground to belowground uptake nitrogen ratio. Furthermore, there was a significant reduction of about 20% in root biomass in both crops with zeolite application across the entire nitrogen fertilization gradient. These plant-level responses were associated with a significant increase in the activity of carbon-degrading and nitrogen-degrading enzymes at the soil level in response to zeolite applications. Our findings provide a compelling proof-of-concept for the beneficial effects of foliar-applied zeolite as a biostimulant for crops, emphasizing the critical need for additional field research to validate our greenhouse results.

Effects of experimental warming on soil enzyme activities in an alpine swamp meadow on the Qinghai-Tibetan Plateau

Information about the response of soil enzymes to field warming in permafrost regions is scarce, and the potential mechanisms by which warming combined with biotic and abiotic factors affect soil enzyme activities in alpine grasslands remain unclear. A 3-year in situ experiment with two warming levels (2.7 °C and 5.3 °C) was conducted in an alpine swamp meadow to investigate the effects of experimental warming on 5 soil enzyme activities involved in soil carbon and nitrogen cycling, and the relationships between soil enzyme activities and soil variables related to physicochemical properties and nutrient levels were examined. Results showed that warming had obvious positive effects on soil moisture (SM), soil organic carbon, total nitrogen, and NH4+-N contents, especially in the surface soil layer. Soil NO3--N tended to decrease under moderate warming, while it significantly increased under high warming. Meanwhile, during the entire growing season, warming strongly enhanced invertase and amylase activities by 39.2–49.0% and 109.9–191.0%, respectively. In contrast, urease activities were significantly decreased by 36.8–55.7% in warming plots and there were no significant differences in catalase or cellulase activities among treatments during the whole growing season, while catalase activities in warming plots were significantly decreased by 2.6–4.0% in June. These inconsistent responses of soil enzyme activities to experimental warming could be partially explained by warming-induced changes in soil variables. Redundancy analysis showed that soil NO3--N and SM were the most important factors, which explained 29.8% and 19.7% of the variations in soil enzyme activities, respectively, suggesting that the warming-induced increase in SM could weaken the soil aeration status and enhance enzyme and substrate diffusion, strongly affecting soil nitrification and microbial enzyme production.

Selected Enzyme Activities Under Different Land Use Management in Lower Missouri River Floodplain Soils

ABSTRACT Floodplains are vital and productive ecosystems that provide essential biological, and hydrologic functions. However, human modifications to floodplains, such as urbanization, and agriculture have increased the need to assess the impacts of land use changes on the sustainability of their functions. Riparian forest (RF), agroforestry (AF), and row-crop agriculture (AG) are among common land-use systems in the lower Missouri River Floodplain (MRF) region in New Franklin, MO. This study tested the hypothesis that variations in soil physicochemical and biological parameters in relation to land management could affect soil enzyme activities. Soil samples were collected from three land use systems, and enzyme activities were measured in three seasons fall 2019, summer 2020, and spring 2021. Soil properties such as soil C and N, bulk density, organic matter, and water-holding capacity were measured. The results revealed significantly higher levels of β-glucosidase, β-glucosaminidase, and dehydrogenase activity in agroforestry (AF) and riparian forest (RF) treatments relative to agriculture (AG) management in all three studied seasons. No substantial differences in total PLFA were detected among land use systems. This research demonstrated that tree-based systems can substantially enhance soil bulk density and organic matter concentration, leading to increased activity of the selected enzymes. Efforts to incorporate agroforestry systems help to create a more diverse and complex ecosystem compared to monoculture cropping systems. This, in turn, stimulates connections among diverse plant species, microorganisms, and soil fauna, leading to improved nutrient cycling, organic matter decomposition, and overall soil health.

How does grassland degradation affect soil enzyme activity and microbial nutrient limitation in saline‐alkaline meadow?

AbstractSoil enzyme activity and its stoichiometry are excellent representatives of soil microorganisms' response to changing conditions, and act as a good indicator of microbial energy and nutrient demands. However, how soil enzyme activity and microbial nutrient limitation will be modified by grassland degradation is not well understood, especially in the saline‐alkaline meadow. Here, we presented how soil enzyme activity and microbial nutrient limitation shifted along a well‐characterized gradient of salinized degraded grasslands (non‐degraded, moderately degraded, and severely degraded). Our results showed soil enzyme activity was the highest in moderately degraded grasslands, which was mainly regulated by soil bacterial diversity. Soil microbial community metabolism in alkali‐saline meadow grasslands was limited by both carbon and phosphorus. Microbial carbon limitation showed a hump‐shaped pattern along the grassland degradation gradient, while microbial phosphorus limitation showed a gradually decreasing trend. Soil bacterial diversity is a key regulator of soil microbial carbon limitation, but the structure of the soil bacterial and plant community determines microbial phosphorus limitation. Taken together, our findings, taken together, provide evidence that soil bacteria are direct drivers of soil enzyme activity and microbial nutrient limitation along a grassland degradation gradient with salinization and suggest that these changes are regulated by soil salinity.

Effect of two broad-spectrum fungicides on the microbial communities of a soil subjected to different degrees of water erosion

The impact of both fungicide and water erosion on soil microbial communities has been little studied, and far less in subhumid-dry climates. To help fill this knowledge gap, we evaluated the influence of two broad-spectrum fungicides applied to soil subjected to different degrees of water erosion on microbial population and function. Soil samples were taken from an experimental site under three water erosion levels: an agricultural land subjected to minimum water erosion by terrace farming (MIN), an agricultural land subjected to moderate water erosion without terrace farming (MOD), and a land with no water erosion control treatment (non-eroded, NON). Three dosages of both carbendazim and iprodione were applied to microcosms, and the responses of microbial community and function were examined after 30-day exposure. Phospholipid fatty acid (PLFA) analysis, soil enzyme activities, and microbial abundances estimated by quantitative real-time PCR (qPCR) were used to evaluate the impact of carbendazim and iprodione fungicides applied at three dosages on microbial community structure and enzyme activities. The lowest values of fluorescein diacetate hydrolase (FDA), dehydrogenase, urease, and glucosidase activities were registered in soil under moderate erosion, while the highest ones were observed in non-eroded soils. Both carbendazim and iprodione decreased C- and P-related activities, even when those fungicides were applied at field rate doses. Thus, phosphomonoesterase, glucosidase, and xylosidase in soil treated with fungicides applied at recommended field rate decreased by 46 %, 61 %, and 34 % compared to soil without fungicide application. The lowest values of PLFA biomarkers for Gram-positive bacteria, Gram-negative bacteria, and arbuscular mycorrhizal fungi were registered in soils treated with the highest dose of both carbendazim and iprodione. Thus, Gram-positive bacteria, Gram-negative bacteria, arbuscular mycorrhizal fungi, and fungal PLFA biomarkers in soils without fungicide application were about 36 %, 3 %, 47 %, and 82 % higher than those soils treated with the highest doses of fungicides, respectively. In addition, the highest doses of fungicide application tended to greater decrease total PLFAs in both non-eroded and minimum eroded compared to moderate eroded soils. Similarly, the response of bacterial and fungal populations to fungicide treatment was more pronounced in non-eroded soils than in eroded soils. This study illustrates how the interactions between fungicides and water erosion levels affect soil enzyme activities, microbial abundances, and microbial community structure in agroecosystems.

Effects of arbuscular mycorrhizae and extraradical mycelium of subtropical tree species on soil nitrogen mineralization and enzyme activities.

Through symbiosis with plants, arbuscular mycorrhizal (AM) fungi effectively improve the availability of soil nitrogen (N). However, the mechanism through which AM and associated extraradical mycelium affect soil N mineralization remains unknow. We carried out an in situ soil culture experiment by using in-growth cores in plantations of three subtropical tree species, Cunninghamia lanceolata, Schima superba, and Liquidambar formosana. We measured soil physical and chemical properties, net N mineralization rate, and the activities of four kinds of hydrolase (leucine aminopeptidase (LAP), β-1,4-N-acetylglucosaminidase (NAG), β-1,4-glucosidase (βG), cellobiohydrolase (CB)) and two kinds of oxidases (polyphenol oxidase (POX) and peroxidase (PER)) involved in soil organic matter (SOM) mineralization in treatments of mycorrhiza (with absorbing roots and hyphae), hyphae (hyphae only), and control (mycorrhiza-free). The results showed that mycorrhizal treatments significantly affected soil total carbon and pH but did not affect N mineralization rates and all enzymatic activities. Tree species significantly affected net ammonification rate, net N mineralization rate and activities of NAG, βG, CB, POX and PER. The net N mineralization rate and enzyme activities in the C. lanceolata stand were significantly higher than that in monoculture broad-leaved stands of either S. superba or L. formosana. There was no interactive effect of mycorrhizal treatment and tree species on any of soil properties, nor on enzymatic activities or net N mineralization rates. Soil pH was negatively and significantly correlated with five kinds of enzymatic activities except for LAP, while net N mineralization rate significantly correlated with ammonium nitrogen content, available phosphorus content, and the activity level of βG, CB, POX, and PER. In conclusion, there was no difference in enzymatic activities and N mineralization rates between rhizosphere and hyphosphere soils of three subtropical tree species in the whole growing season. The activity of particular carbon cycle-related enzymes was closely related to soil N mineralization rate. It is suggested that differences in litter quality and root functional traits among different tree species affect soil enzyme activities and N mineralization rates through organic matter inputs and shaping soil condition.

Effect of the Different Fertilization Treatments Application on Paddy Soil Enzyme Activities and Bacterial Community Composition

The application amount of fertilizer is believed to dramatically influence soil bacteria in paddy fields, and soil bacteria critically affect soil enzyme activities and the growth of rice in paddy fields. Thus, providing a suitable amount of fertilization to ensure rice yields is an important issue in field management. In this study, four treatments were carried out in a paddy field, including control (fertilization methods commonly used by farmers in the past), IT + RF 10, IT + RF 20, and IT + RF 30 (integrated technology and 10%, 20%, and 30% reduction in nitrogen fertilizer, respectively). Soil samples were collected in two periods, the rice booting stage and the harvest period. High-throughput sequencing was used for analysis of soil bacterial diversity and community composition across different fertilizer treatments, and clarified the effects of different fertilizer treatments on soil enzyme activities and bacterial community composition. This study showed that a reduction in chemical fertilizer application has a certain impact on the soil pH, total nitrogen (TN), total phosphorus (TP), soil organic matter (SOM) value, and bacterial community of the rice planting system, and that the IT + RF 10 treatment was the best way to reduce fertilizer application, which can reduce nutrient loss in the paddy soil. The application of organic fertilizer partially replaces chemical fertilizer, which not only effectively stimulates soil enzyme activity, but also enriches bacterial groups that may participate in complex organic matter decomposition and soil nutrient mobilization.

Effect of nonbiodegradable microplastics on soil respiration and enzyme activity: A meta-analysis

Nonbiodegradable microplastics (MPs) are emerging contaminants in the environment and potentially threaten soil health. In recent years, the impact of MPs on soil ecology has attracted widespread attention, but the responses of soil respiration and enzyme activity to MPs exposure remain unclear. Here, a meta-analysis including 1980 observations was used to assess the effects of MPs on soil microbial activity. MPs exposure significantly (p < 0.05) increased soil respiration by 18.2 % but did not significantly (p > 0.05) affect soil enzyme activity; moreover, these effects varied with MP type, concentration, size, and exposure period. The amendment of polypropylene (PP) MP increased soil respiration and enzyme activity by 58.8 % and 10.2 %, respectively, whereas exposure to polyethylene terephthalate (PET), polyethylene (PE) and polystyrene (PS) MPs reduced soil enzyme activities by 13.0 %, 6.8 % and 5.0 %, respectively. The soil respiration was unaffected and increased when the MPs concentrations were below and above 5 %, respectively, whereas soil enzyme activity was stimulated and inhibited when the MPs concentrations were less and >10 %, respectively. The size of MPs only significantly (p < 0.05) affected the response of soil respiration to MPs, as small (<500 μm) and large (≥500 μm) sizes of MPs increased and reduced soil respiration by 53.4 % and 5.8 %, respectively. Short-term (≤30 days) exposure to MPs increased soil respiration by 50.2 %, whereas the presence of MPs inhibited soil enzyme activity by 3.3 % when the incubation period ranged from 30 to 100 days. In addition, MPs exposure significantly (p < 0.05) increased soil respiration by 77.9 % in alkaline soil (pH > 7.5) and by 41.6 % in the absence of plants. The amendment of MPs significantly (p < 0.05) increased and reduced soil enzyme activities in acidic and alkaline soils by 4.3 % and 5.5 %, respectively, and significantly (p < 0.05) improved soil enzyme activity by 4.5 % in the presence of plants. Specifically, MPs significantly (p < 0.05) increased the activities of acid phosphatase and fluorescein diacetate hydrolase by 8.3 % and 17.1 %, respectively, but did not significantly (p > 0.05) influence urease, β-glucosidase, and catalase activities. Overall, our results suggested that MPs have nonnegligible impacts on soil microbial activity, and it is urgently necessary to explore the long-term effects of MPs on soil ecology in the natural environment.

Effects of elevated CO2 concentration, warming, and winter wheat planting on soil enzyme activities.

Understanding the responses of soil enzyme activities to elevated CO2 concentration and warming can provide a scientific basis for nutrient management of croplands under global climate change. We conducted a pot expe-riment with climate chamber to examine the effects of elevated CO2 concentration and warming and winter wheat growth on soil enzyme activities. There were four climate scenarios: control (CK, 400 μmol·mol-1 CO2 concentration+normal ambient temperature), and CO2 concentration elevation (ECO2, 800 μmol·mol-1 CO2 concentration+normal ambient temperature), elevated temperature (ET, 400 μmol·mol-1 + temperature increased 4 ℃), and elevated CO2 concentration and temperature (ECO2+T, 800 μmol·mol-1 CO2 concentration + temperature increased 4 ℃). We measured the activities of soil β-glucosidase (βG), β-N-acetyl glucosidase (NAG), alkaline phosphate (ALP) and polyphenol oxidase (PPO) at four growth stages (JS, jointing stage; AS, anthesis stage; FS, filling stage and MS, maturity stage), with and without winter wheat planting. Without winter wheat planting, there was no significant difference in four kinds of soil enzyme activities between ECO2 and CK, while ET and ECO2+T treatments had significant negative effect on soil enzyme activities. With winter wheat planting, compared with CK, ECO2 and ECO2+T treatments did not affect the activities of those four soil enzyme; but the ET treatment had great impact on soil ALP and PPO activities. The activities of four kinds of soil enzyme were significantly diffe-rent between the ET and ECO2+T treatments. Compared with ET treatment, ECO2+T treatment increased soil βG activity at the JS, decreased NAG activity at the JS, increased ALP activity at both AS and FS, decreased PPO activity in the JS and increased in the AS. The interaction of elevated CO2 concentration and warming had significant effect on soil NAG and ALP activities with and without winter wheat planting. The interaction of warming and expe-rimental stage had significant effect on four kinds of soil enzyme activities without winter wheat planting, but the interaction of warming and crop growth stage had significant effect on ALP and PPO activities with winter wheat planting. The interaction of elevated CO2 concentration, warming and experimental period had significant effect on soil βG, ALP and PPO activities without winter wheat growth, while with winter wheat growth, it had significant impact on NAG, ALP and PPO activities. The winter wheat growth had significantly inhibitory effect on βG, NAG and ALP activities in the two early growth periods (JS+AS), significant promoting effect in the later growth periods (FS+MS), and significantly inhibitory effect on PPO activity during whole growth period. Overall, elevated CO2 concentration did not affect soil enzyme activities, while the elevation of CO2 concentration and temperature on soil enzyme activities differed among the soil enzymes at different growth stages. In addition, the responses of four soil enzyme activities to the interaction of elevated CO2 concentration and warming varied with and without winter wheat planting.

Application of dry olive residue-based biochar in combination with arbuscular mycorrhizal fungi enhances the microbial status of metal contaminated soils

Biochar made-up of dry olive residue (DOR), a biomass resulting from the olive oil extraction industry, has been proposed to be used as a reclamation agent for the recovery of metal contaminated soils. The aim of the present study was to investigate whether the soil application of DOR-based biochar alone or in combination with arbuscular mycorrhizal fungi (AMF) leads to an enhancement in the functionality and abundance of microbial communities inhabiting metal contaminated soils. To study that, a greenhouse microcosm experiment was carried out, where the effect of the factors (i) soil application of DOR-based biochar, (ii) biochar pyrolysis temperature (considering the variants 350 and 500 °C), (iii) soil application dose of biochar (2 and 5%), (iv) soil contamination level (slightly, moderately and highly polluted), (v) soil treatment time (30, 60 and 90 days) and (vi) soil inoculation with Funneliformis mosseae (AM fungus) on β-glucosidase and dehydrogenase activities, FA (fatty acid)-based abundance of soil microbial communities, soil glomalin content and AMF root colonization rates of the wheat plants growing in each microcosm were evaluated. Biochar soil amendment did not stimulate enzyme activities but increased microbial abundances. Dehydrogenase activity and microbial abundances were found to be higher in less contaminated soils and at shorter treatment times. Biochar pyrolysis temperature and application dose differently affected enzyme activities, but while the first factor did not have a significant effect on glucosidase and dehydrogenase, a higher biochar dose resulted in boosted microbial abundances. Soil inoculation with F. mosseae favored the proliferation of soil AMF community and increased soil glomalin content as well as rates of AMF root colonization. This factor also interacted with many of the others evaluated to significantly affect soil enzyme activities, microbial abundances and AMF community. Our results indicate that the application of DOR-based biochar along with AMF fungi is an appropriate approach to improve the status of microbial communities in soils with a moderate metal contamination at short-term.

Soil Enzyme Activity Regulates the Response of Soil C Fluxes to N Fertilization in a Temperate Cultivated Grassland

Exogenous nitrogen (N) inputs greatly change the emission and uptake of carbon dioxide (CO2) and methane (CH4) from temperate grassland soils, thereby affecting the carbon (C) budget of regional terrestrial ecosystems. Relevant research focused on natural grassland, but the effects of N fertilization on C exchange fluxes from different forage soils and the driving mechanisms were poorly understood. Here, a three-year N addition experiment was conducted on cultivated grassland planted with alfalfa (Medicago sativa) and bromegrass (Bromus inermis) in Inner Mongolia. The fluxes of soil-atmospheric CO2 and CH4; the content of the total dissolved N (TDN); the dissolved organic N (DON); the dissolved organic C (DOC); NH4+–N and NO3−–N in soil; enzyme activity; and auxiliary variables (soil temperature and moisture) were simultaneously measured. The results showed that N fertilization (&gt;75 kg N ha−1 year−1) caused more serious soil acidification for alfalfa planting than for brome planting. N fertilization stimulated P-acquiring hydrolase (AP) in soil for growing Bromus inermis but did not affect C- and N-acquiring hydrolases (AG, BG, CBH, BX, LAP, and NAG). The oxidase activities (PHO and PER) of soil for planting Bromus inermis were higher than soil for planting Medicago sativa, regardless of N, whether fertilization was applied or not. Forage species and N fertilization did not affect soil CO2 flux, whereas a high rate of N fertilization (150 kg N ha−1 year−1) significantly inhibited CH4 uptake in soil for planting Medicago sativa. A synergistic effect between CO2 emission and CH4 uptake in soil was found over the short term. Our findings highlight that forage species affect soil enzyme activity in response to N fertilization. Soil enzyme activity may be an important regulatory factor for C exchange from temperate artificial grassland soil in response to N fertilization.

Effects of Cotton Stalk Returning on Soil Enzyme Activity and Bacterial Community Structure Diversity in Cotton Field with Long-term Saline Water Irrigation

Long-term saline water irrigation will increase soil salinity, adversely affect soil physical and chemical properties, and change the diversity of soil bacteria. Straw returning can improve the soil microenvironment and subsequently affect soil enzyme activity and bacterial community structure diversity. This experiment used two types of irrigation water salinity:fresh water (FW, 0.35 dS·m-1) and saline water (SW, 8.04 dS·m-1). Under each irrigation water salinity, the amount of cotton straw applied was 0 and 6000 kg·hm-2 (represented by FWST and SWST, respectively). The results showed that:compared with those under fresh water irrigation, saline water irrigation significantly increased the soil salt, bulk density, total carbon, and available phosphorus but significantly decreased available potassium content. Under saline water irrigation, straw returning significantly increased the soil total carbon, total nitrogen, available potassium, and available phosphorus but reduced soil bulk density. Compared with those under fresh water irrigation, soil sucrase, alkaline phosphatase, and catalase activities under saline water irrigation decreased by 57.24%, 35.15%, and 3.91%, respectively, whereas urease activity increased by 26.73%. However, straw returning significantly increased sucrase, alkaline phosphatase, and catalase activities but decreased urease activity. Saline water irrigation decreased the relative abundance of Acidobacteriota, Actinobacteriota, Bacteroidota, Verrucomicrobiota, and Firmicutes and increased the abundance of Gemmatimonadota and Myxococcota. Under saline water irrigation, straw returning significantly increased the relative abundance of Actinobacteriota, Bacteroidetes, Firmicutes, Crenarchaeota, Sphingomonas, Dongia, and Steroidobacter. NMDS results also showed that saline water irrigation and straw returning changed the bacterial community structure. In conclusion, straw returning can improve soil nutrient content, reduce soil bulk density and salinity, and then change soil enzyme activity and bacterial community structure diversity. The change in soil bacterial community composition was mainly affected by soil salinity and bulk density. Therefore, straw returning can improve soil fertility and help maintain the health of soil ecosystem. This study revealed a relationship between soil enzyme activities and bacterial communities, which provides a theoretical basis and mechanism for applying cotton stalk to regulate the soil enzyme and micro-ecological environment.

Terricolous mosses impact soil microbial biomass carbon and enzymatic activity under temperate forest types of the Garhwal Himalayas.

Estimates of enzymatic activity are used as indices for soil quality, microbial nutrient demand, microbial growth, and activity. Mosses trap soil moisture, influence soil temperature, and create a microenvironment promoting an overall higher level of microbial activity, thus making the decomposition of organic matter more favorable. This study determines the role of mosses in influencing soil biochemical properties in three temperate forest types of the Garhwal Himalayas, Uttarakhand, viz., moist temperate deciduous forest, Ban oak forest, and moist deodar forest. Activities of major soil enzymes (dehydrogenase, β-glucosidase, acid phosphatase, aryl sulfatase, phenol oxidase, and urease) and soil microbial biomass carbon (SMBC) were determined under two different substrates, i.e., with and without moss cover in two different seasons, viz., monsoon and winter. The Pearson correlation of enzymes with specific soil nutrients they act upon has also been shown. The SMBC and on average activities of all the enzymes were predominantly higher in soil with moss cover during monsoon season and without moss cover in the winter season. SMBC in the three study sites ranged from 280.55 to 1707.64µg C/g. Statistically significant differences (p < 0.01) were observed for all the properties within the substrates among all the three sites and across the two seasons. Our results suggest that mosses play a significant role in positively influencing soil biochemical properties in both seasons by creating a microscale mosaic that offers a high degree of heterogeneity in soil function. Our study emphasizes that mosses strongly affect soil enzyme activities and microbial biomass, thus improving soil health.

Land conversion from cropland to grassland alleviates climate warming effects on nutrient limitation: Evidence from soil enzymatic activity and stoichiometry

Climate warming and land conversion are key factors affecting ecosystem functions. Investigating the effects of these two factors on soil enzyme activity and stoichiometry will provide insights into soil nutrient limitation in terrestrial ecosystems. However, how climate warming and land conversion affect soil nutrient limitation remains poorly understood. Here, we investigated the effects of climate warming and land conversion on soil enzyme activity and stoichiometry. An 8-year mesocosm experiment was set up with climate warming in soil transplants from a temperate gradient region and land conversion from cropland to grassland. The results showed that land conversion from cropland to grassland increased the activity of C- and N-acquired enzymes but decreased the activity of P-acquired enzyme. Moreover, the enzyme stoichiometry of C:P and N:P increased under grassland over cropland. The changes in soil enzyme activity and stoichiometry suggested that land conversion from cropland to grassland increased C and N limitation but decreased P limitation. In cropland, climate warming did not significantly affect soil enzyme activity and stoichiometry. In grassland, as temperature increased, C-acquired enzyme, enzyme stoichiometry of C:P and N:P, and vector length decreased, but P-acquired enzyme and vector angle increased. This result suggested decreased C limitation and increased P limitation with climate warming. Additionally, redundancy analysis demonstrated that soil pH, soil dissolved nutrients, and soil stoichiometry were important factors for soil enzymes in grassland. Our findings suggested that long-term climate warming could alter C and P limitation of soil microbes following land conversion.

Vegetation rehabilitation increases soil enzyme activities in degraded land via carbon supply and nitrogen retention

The details of how vegetation rehabilitation affects soil enzyme activities via changes of soil nutrients are unclear. To investigate how soil carbon and available nitrogen affect soil enzyme activities during the process of vegetation restoration, a factorial experiment was conducted with vegetation cover and nitrogen addition on degraded lands, and then a carbon addition experiment was performed with soil incubation. Soil enzyme activities were significantly higher under vegetation plots than those under bare plots and were highly related to the soil total carbon and nitrogen concentrations. For soils from bare plots, C addition increased β-1,4-glucosidase (BG) activities, β-N-acetyl glucosaminidase (NAG) activities, leucine aminopeptidase (LAP) activities and acid phosphomonoesterase (AP) activities by 93%, 784%, 268% and 272%, respectively. By comparision, C addition only increased activities of BG, NAG, LAP and AP by 6%, 54%, 45% and 214% for soils from vegetation plots, respectively. Furthermore, the interaction between C and N significantly affected the activities of AP and BG. These findings indicate that the elevation of enzyme activities during vegetation rehabilitation is mainly driven by the relaxation of C–N limitation for microorganisms.

Response of Soil Enzyme Activity and Chemical Properties to Nitrogen Addition in a Korean Pine Plantation

Soil enzymes participate in numerous complex biochemical processes that take place in the soil and play an important role in the material circulation of terrestrial ecosystems. To explore the response of soil enzyme activities and chemical properties to nitrogen deposition in temperate forests, this study analyzed four soil enzyme activities based on the nitrogen addition experiment plot of Korean pine (Pinus koraiensis) plantation, which was located in the Liangshui National Natural Reserve, Heilongjiang Province. The results showed that the activities of N-acetyl-glucosidase (NAG) and alkaline phosphatase (AKP) increased significantly with increasing nitrogen application concentration. The activity of beta-glucosidase (BG) and acid phosphatase (ACP) was not significantly different among different nitrogen application treatments. The contents of total carbon, total nitrogen, total phosphorus, and available nitrogen and four enzyme activity in the upper soil (0-10 cm) under the same nitrogen application level were significantly higher than those in the lower soil (10-20 cm), but the pH values were not significantly different. Total carbon has an extremely significant positive correlation with NAG, BG, AKP, and ACP. Total nitrogen has an obvious or extremely significant positive correlation with BG, NAG, and AKP as well as ACP. The available nitrogen has an obvious and highly significant positive correlation with NAG and AKP. The total phosphorus has an obvious and extremely significant positive correlation with ACP and AKP, respectively. The nitrogen application level and the soil layer had different effects on soil enzyme activity and soil chemical properties. Long-term large input of nitrogen can directly or indirectly change soil chemical properties and affect soil enzyme activity.