Extracellular Enzyme Activities Research Articles

Soil microbial community responses to long-term experimental warming in an alpine Dryas octopetala heath in Norway

Over the last century, high-altitude and high-latitude regions have experienced global warming at rates higher than the worldwide average. Climate change influences complex soil-microbe-plant-atmosphere interactions, leading to changes in plant-associated soil microbial diversity and functioning and alterations in nutrient cycling, carbon fluxes, and storage. This study analyzed how two decades of global warming simulated by open-top chambers (OTCs) affected soil bacterial and fungal communities in an alpine dwarf-shrub heath dominated by Dryas octopetala in Norway. We collected soil samples from 10 OTCs and 10 control plots and compared their physicochemical properties, microbial biomass, extracellular enzyme activities, and bacterial and fungal community diversity and composition. Warming did not significantly affect the bacterial community despite the tendency to reduce alpha diversity and increase the degree of specialisation. In contrast, two decades of warming significantly affected fungal community composition, which was dominated by ectomycorrhizal Basidiomycota. While there was no significant effect on the total fungal community diversity, a significant shift in saprotrophic Ascomycota taxa was observed between the warmed and control plots. Their positive correlations with oxidative enzymes and fungal biomass suggest that long-term warming might lead to an increase in fungal biomass and the activity of oxidative enzymes, promoting the decomposition of more recalcitrant biopolymers. This may result in an increase in CO2 flux into the atmosphere and a decrease in ecosystem C storage.

Effects of seasonal precipitation regimes on microbial biomass and extracellular enzyme activity during shrub foliar litter decomposition in a subtropical forest

Elucidating the mechanisms underlying microbial biomass and extracellular enzyme activity responses to the seasonal precipitation regime during foliar litter decomposition is highly important for understanding the material cycle of forest ecosystems in the context of global climate change; however, the specific underlying mechanisms remain unclear. Hence, a precipitation manipulation experiment involving a control (CK) and treatments with decreased precipitation in the dry season and extremely increased precipitation in the wet season (IE) and decreased precipitation in the dry season and proportionally increased precipitation in the wet season (IP) was conducted in a subtropical evergreen broad-leaved forest in China from October 2020 to October 2021. The moisture, microbial biomass, and extracellular enzyme activities of foliar litter from two dominant shrub species, Phyllostachys violascens and Alangium chinense, were measured at six stages during the dry and wet seasons. The results showed that (1) both IE and IP significantly decreased the microbial biomass carbon and microbial biomass nitrogen content and the activities of β-1,4-glucosidase, β-1,4-N-acetylglucosaminidase, acid phosphatase and cellulase in the dry season, while the opposite effects were observed in the wet season. (2) Compared with those of IE, the effects of IP on foliar litter microbial biomass and extracellular enzyme activity were more significant. (3) The results from the partial least squares model indicated that extracellular enzyme activity during foliar litter decomposition was strongly controlled by the foliar litter water content, microbial biomass nitrogen, the ratio of total carbon to total phosphorus, foliar litter total carbon, and foliar litter total nitrogen. These results provide an important theoretical basis for elucidating the microbial mechanisms driving litter decomposition in a subtropical forest under global climate change scenarios.

Green Manuring Enhances Soil Multifunctionality in Tobacco Field in Southwest China

The use of green manure can substantially increase the microbial diversity and multifunctionality of soil. Green manuring practices are becoming popular for tobacco production in China. However, the influence of different green manures in tobacco fields has not yet been clarified. Here, smooth vetch (SV), hairy vetch (HV), broad bean (BB), common vetch (CV), rapeseed (RS), and radish (RD) were selected as green manures to investigate their impact on soil multifunctionality and evaluate their effects on enhancing soil quality for tobacco cultivation in southwest China. The biomass of tobacco was highest in the SV treatment. Soil pH declined, and soil organic matter (SOM), total nitrogen (TN), and dissolved organic carbon (DOC) content in CV and BB and activity of extracellular enzymes in SV and CV treatments were higher than those in other treatments. Fungal diversity declined in SV and CV but did not affect soil multifunctionality, indicating that bacterial communities contributed more to soil multifunctionality than fungal communities. The abundance of Firmicutes, Rhizobiales, and Micrococcales in SV and CV treatments increased and was negatively correlated with soil pH but positively correlated with soil multifunctionality, suggesting that the decrease in soil pH contributed to increases in the abundance of functional bacteria. In the bacteria–fungi co-occurrence network, the relative abundance of key ecological modules negatively correlated with soil multifunctionality and was low in SV, CV, BB, and RS treatments, and this was associated with reductions in soil pH and increases in the content of SOM and nitrate nitrogen (NO3−-N). Overall, we found that SV and CV are more beneficial for soil multifunctionality, and this was driven by the decrease in soil pH and the increase in SOM, TN, NO3−-N, and C- and N-cycling functional bacteria.

Changes in nutrient availability substantially alter bacteria and extracellular enzymatic activities in Antarctic soils.

In polar regions, global warming has accelerated the melting of glacial and buried ice, resulting meltwater run-off and mobilisation of surface nutrients. Yet, the short-term effects of altered nutrient regimes, on the diversity and function of soil microbiota in poly-extreme environments such as Antarctica, remains poorly understood. We studied these effects by simulating such environments via constructing soil microcosms through augmented carbon, nitrogen, and moisture supplements. Addition of nitrogen significantly decreased the diversity of Antarctic soil microbial assemblages, compared with other treatment groups. Other treatments led to shift in relative abundances of these microbial assemblages with random distributional patterns. Only nitrogen treatment appeared to show clear community structural patterns, with increase in abundance of Proteobacteria (Gammaproteobateria) and decrease in Verrucomicrobiota (Chlamydiae, Verrucomicrobiae). Effects of extracellular enzyme activities and soil parameters on changes in microbial taxa also showed significance impacts of nitrogen treatment. Microbial response to nutrient addition was predicted using structural equation modelling which revealed that nutrient source and extracellular enzyme activities were positive predictors of microbial diversity. Our study highlights the effect of nitrogen addition on Antarctic soil microorganisms which showed resilience to nutrient increases. Rather than being resistant to change, these microorganisms rapidly responded to augmented nutrient regimes.

Cellulolytic potentials of aspergillus oryzae and streptomyces griseus isolated from waste dump soil in Nile University Of Nigeria, Abuja

The potential of using microorganisms as biological sources of industrially economic enzymes has stimulated interest in the exploitation of extracellular enzymatic activity in several microorganisms. The aim of this research is to assess the cellulose degrading potentials of two microorganisms, Aspergillus oryzae and Streptomyces griseus using cellulose Congo red agar media. Soil sample collected from waste dump was serially diluted and inoculated in starch casein agar and SDA to isolate S. griseus and A. oryzae respectively. To assess their potentials to utilize cellulose, each of the two microorganisms was inoculated on cellulose Congo-red media and incubated at 30 ºC for 7days. A zone of clearing around the colonies after incubation confirms the secretion of extracellular cellulase, and was used as an indication for cellulose utilization. The zone of clearing was measured with a meter rule. In the results obtained, both microorganisms demonstrated cellulose utilization ability with Aspergillus oryzae showing a zone of clearing of 30.50 ± 0.50 mm while Streptomyces griseus showed a wider zone of clearing of 60.00 ± 1.00 mm. The results indicate that both microorganisms can be potent producers of the enzyme cellulase, with Streptomyces griseus having a higher cellulase-producing ability.

Phosphorus addition enhances heterotrophic respiration but reduces root respiration in a subtropical plantation forest

Soil respiration (Rs) is a major component of the global carbon (C) cycle and is influenced by the availability of nutrients such as phosphorus (P). However, the response of Rs to P addition in P-limited subtropical forest ecosystems and the underlying mechanisms remain poorly understood. To address this, we conducted a P addition experiment (50 kg P ha−1 yr−1) in a subtropical Chinese fir (Cunninghamia lanceolata) plantation forest. We separated Rs into heterotrophic respiration (Rh), root respiration (Rr), and mycorrhizal hyphal respiration (Rm), and quantified soil properties, microbial biomass (phospholipid fatty acid, PLFA), fungal community composition (ITS), and the activity of extracellular enzymes. Phosphorus addition significantly increased Rs and Rh, but decreased Rr and did not influence Rm. Further, P addition increased fungal, bacterial, and total PLFAs, and phenol oxidase activity. Conversely, P application decreased root biomass and did not alter the relative abundance of symbiotrophic fungi. Phosphorus enrichment therefore enhances soil C emissions by promoting organic matter decomposition by heterotrophic activity, rather than via increases in root or mycorrhizal respiration. This advances our mechanistic understanding of the relationship between fertility and soil respiration in subtropical forests, with implications for predicting soil C emissions under global change.

Development and evaluation of the inactivated vaccine against Aeromonas schubertii in hybrid snakehead

Aeromonas schubertii is a global pathogen of fish that causes internal nodular diseases and death in severe cases. In the present study, we isolated nine pathogenic strains from diseased hybrid snakehead (Channa argus♂ × Channa maculata♀) which were formally identified as A. schubertii by molecular identification, including 16S rRNA and gyrB gene sequencing. Subsequently, we determined the extracellular enzyme activity of six isolates and compared pathogenicity to investigate potential relationships with geographic characteristics. Two highly pathogenic strains, AS-14 and AS-16, were finally identified as inactivated vaccine candidates. Subsequently, we evaluated different concentrations of the antigen for each vaccine by performing experiments in hybrid snakehead; fish were inoculated with inactivated vaccine via the intraperitoneal route and a booster injection was administered 14 days later. Relative percent survival (RPS) for fish immunized with high doses of the two vaccines (1 × 108 CFU/fish) were 54.4% and 57.4%, respectively; these values were higher than other groups of fish receiving different doses (1 × 106 and 1 × 107 CFU/fish). The bacterial load of tissues harvested from the fish immunized with high doses of the vaccine groups were significantly lower than those of fish immunized with low doses. Titers of specific antibodies against A. schubertii in fish immunized with a high dose of AS-16 vaccine were maintained at high levels when tested six weeks after the booster injection. Furthermore, immune-related genes in the spleen, including MHC I, MHC II, CD4, CD8α and IgM, all exhibited high levels of expression, thus suggesting that hybrid snakehead underwent an adaptive immune response post-vaccination. Collectively, our findings enrich our understanding of the specific causative agents underlying nodular diseases in hybrid snakehead and provide scientific reference guidelines for the development of vaccines against A. schubertii. The development of such vaccines will be conducive to the sustainable development of hybrid snakehead in commercial aquaculture.

Inhibitory Effect and Potential Antagonistic Mechanism of Isolated Epiphytic Yeasts against Botrytis cinerea and Alternaria alternata in Postharvest Blueberry Fruits.

This study evaluated the biocontrol effect of isolated epiphytic yeasts (Papiliotrema terrestris, Hanseniaspora uvarum, and Rhodosporidium glutinis) against Botrytis cinerea and Alternaria alternata in blueberry fruits and its possible mechanisms. Our findings indicated that the three tested yeasts exerted a good biocontrol effect on postharvest diseases in blueberry, and that H. uvarum was the most effective. In addition, the three tested yeasts could improve the postharvest storage quality of blueberry fruits to some extent. H. uvarum demonstrated the strongest direct inhibitory effect on pathogens by suppressing spore germination, mycelial growth, and antifungal volatile organic compound (VOC) production. P. terrestris showed the highest extracellular lytic enzymes activities. It also had better adaptation to low temperature in fruit wounds at 4 °C. The biofilm formation capacity was suggested to be the main action mechanism of R. glutinis, which rapidly colonized fruit wounds at 20 °C. Several action mechanisms are employed by the superb biocontrol yeasts, while yeast strains possess distinctive characteristics and have substantially different action mechanisms.

Long-term cultivation reduces soil carbon storage by altering microbial network complexity and metabolism activity in macroaggregates

Cultivation alters soil aggregation, microbial compositions and the potential for carbon sequestration in cropland soils. However, the specific effects of long-term cultivation and the underlying mechanisms on soil organic carbon (SOC) storage at different aggregate sizes remain poorly understood. We characterized the dynamics of SOC storage in macroaggregates (>0.25 mm) and microaggregates (<0.25 mm) across four paddy soils successively cultivated for 60, 100, 125, and 150 years. Microbial community compositions, network patterns, enzyme activities and carbon use efficiency (CUE) were examined to elucidate the underlying microbial pathways governing SOC storage. The results showed that prolonged cultivation led to an average reduction of 45 % in SOC storage, particularly in macroaggregates. Partial least squares path modeling revealed that shifts in microorganisms in macroaggregates explained almost 80 % of the variation in SOC storage. Specifically, variations in fungal composition and decreased complexity of microbial interaction networks were strongly correlated with SOC storage. Fungal community and microbial interactions also indirectly affected SOC storage by positively correlating with extracellular enzyme activity. Moreover, bacterial composition indirectly regulated SOC storage by positively correlating with carbon use efficiency. Our findings indicated that the macroaggregate-associated microbial interactions and the metabolism activities had significant implications for SOC sequestration in paddy fields. We suggest that implementation of management practices targeted at improvement of these microbial attributes could enhance agroecosystems sustainability.

Phytoplankton-derived polysaccharides and microbial peptidoglycans are key nutrients for deep-sea microbes in the Mariana Trench

BackgroundThe deep sea represents the largest marine ecosystem, driving global-scale biogeochemical cycles. Microorganisms are the most abundant biological entities and play a vital role in the cycling of organic matter in such ecosystems. The primary food source for abyssal biota is the sedimentation of particulate organic polymers. However, our knowledge of the specific biopolymers available to deep-sea microbes remains largely incomplete. One crucial rate-limiting step in organic matter cycling is the depolymerization of particulate organic polymers facilitated by extracellular enzymes (EEs). Therefore, the investigation of active EEs and the microbes responsible for their production is a top priority to better understand the key nutrient sources for deep-sea microbes.ResultsIn this study, we conducted analyses of extracellular enzymatic activities (EEAs), metagenomics, and metatranscriptomics from seawater samples of 50–9305 m from the Mariana Trench. While a diverse array of microbial groups was identified throughout the water column, only a few exhibited high levels of transcriptional activities. Notably, microbial populations actively transcribing EE genes involved in biopolymer processing in the abyssopelagic (4700 m) and hadopelagic zones (9305 m) were primarily associated with the class Actinobacteria. These microbes actively transcribed genes coding for enzymes such as cutinase, laccase, and xyloglucanase which are capable of degrading phytoplankton polysaccharides as well as GH23 peptidoglycan lyases and M23 peptidases which have the capacity to break down peptidoglycan. Consequently, corresponding enzyme activities including glycosidases, esterase, and peptidases can be detected in the deep ocean. Furthermore, cell-specific EEAs increased at 9305 m compared to 4700 m, indicating extracellular enzymes play a more significant role in nutrient cycling in the deeper regions of the Mariana Trench.ConclusionsTranscriptomic analyses have shed light on the predominant microbial population actively participating in organic matter cycling in the deep-sea environment of the Mariana Trench. The categories of active EEs suggest that the complex phytoplankton polysaccharides (e.g., cutin, lignin, and hemicellulose) and microbial peptidoglycans serve as the primary nutrient sources available to deep-sea microbes. The high cell-specific EEA observed in the hadal zone underscores the robust polymer-degrading capacities of hadal microbes even in the face of the challenging conditions they encounter in this extreme environment. These findings provide valuable new insights into the sources of nutrition, the key microbes, and the EEs crucial for biopolymer degradation in the deep seawater of the Mariana Trench.6w3UcpMmGbcStWK5zJqVACVideo

Weed control, soil health, and yield tradeoffs of between-bed management strategies in organic plasticulture vegetable production

Planting a cover crop living mulch between plastic mulch beds in fresh market vegetable production can reduce soil erosion and runoff, and offers an opportunity to grow an income generating cash crop alongside a soil building cover crop. However, potential negative impacts on yield, variable weed control, unclear impacts on soil health, and limited management recommendations challenge adoption of this practice, despite grower interest. In a two-year study in southwest Michigan, living mulches were evaluated in the production of plasticulture organic summer squash (Cucurbita pepo cv. Lioness) and bell pepper (Capsicum annuum cv. Paladin). Strategies evaluated included three common grower practices (cultivation, dead straw mulch, mowing ambient weeds) and three mowed living mulch treatments (Italian ryegrass [Lolium multiflorum] monoculture, rye [Secale cereale] monoculture, and a Dutch white clover [Trifolium repens]/rye mixture). We determined the impact of these strategies on weed control, organic matter inputs, vegetable crop performance, nitrogen retention, and soil microbial communities. We found that cultivation and dead mulch provided superior in-season weed control, reducing weed biomass by an average of 86% compared to 18% among living mulch treatments, with associated reductions in the weed seedbank compared to living mulches and mowed weeds. In most cases, living mulch establishment was a challenge and weed biomass on average accounted for 99, 74, and 94% of organic matter inputs in rye, ryegrass, and clover/rye treatments, respectively. Squash performance was unaffected by our treatments, but pepper yield reductions ranged from 41 to 54% in all treatments relative to cultivation in one of two years. Living mulches and the weedy treatment showed the ability to reduce end-of-season potentially leachable nitrogen by 61% compared to cultivation and dead mulching. Soil microbial abundance and functional diversity were similar across treatments, but extracellular enzyme activity was higher in dead mulch, living mulch and weedy treatments compared to cultivation. Results from this study help quantify tradeoffs between common grower practices for managing weeds and soil between plastic mulch beds, highlight key challenges with living mulch alternatives, and identify areas for future research.

Microbial interactions with microplastics: Insights into the plastic carbon cycle in the ocean

The fate of microplastics (MPs) in the ocean is mostly driven by (i) photo-oxidation to smaller particles and dissolved constituents, which fuel the dissolved organic carbon pool (plastic-derived DOC, pDOC), and (ii) interactions with organic matter forming sinking aggregates (marine plastic snow). Two separate laboratory experiments were conducted to investigate the two pathways of MPs. In the first experiment, we measured potential rates of microbial pDOC utilization in bottle incubations over 15 days with microbial assemblages from coastal and offshore waters. Microbial utilization of pDOC was more efficient in the coastal (72% bioreactive pDOC) compared with the offshore experiment (32% bioreactive pDOC) 15 days. Changes in bacterial cell abundance and extracellular enzyme activities (glucosidase, peptidase, esterases) indicated that a fraction of pDOC was repackaged into microbial exopolymeric substances (EPS), stimulating growth of known EPS degrading bacteria within the phyla Verrucomicrobiota and Planctomycetota. Microbial EPS likely also played a key role in our second experiment that showed the formation of marine plastic snow in roller tanks with cultured cells of Emiliana huxleyi but not with cells of an Isocrysis sp. culture. Average sinking velocities of marine plastic snow were a factor of 1.2 lower compared with marine snow without MPs. Both aggregate types showed reduced sinking velocities in a density stratified sinking column. Our results from the two experiments on (i) microbial utilization of pDOC and (ii) the formation and sinking of marine plastic snow indicate potential effects of plastic-derived compounds on microbial elemental cycles (i.e., pDOC repackaged into EPS) with consequences for the efficiency of the biological carbon pump (i.e., marine plastic snow reduces carbon export) and the fate of plastic-derived compounds in the ocean.

Mixed Chinese Fir Plantations Alter the C, N, and P Resource Limitations Influencing Microbial Metabolism in Soil Aggregates

Assessing the limitations of microbial metabolic resources is crucial for understanding plantation soil quality and enhancing fertility management. However, the variation of microbial resource limitations at the aggregate level in response to changes in stands remains unclear. This research explores carbon (C), nitrogen (N), and phosphorus (P) limitations affecting microbial metabolism in bulk soils and aggregates in two mixed and one pure Chinese fir stands in subtropical China, analyzing resource limitations concerning soil carbon, nutrients, and microbial indicators. The results revealed that microbes in all aggregates of the pure stands and in the micro aggregates (&lt;0.25 mm) of the three stands were relatively limited by C and P. In contrast, microbial metabolism was more N-limited in macroaggregates (&gt;2 mm) and small aggregates (2–0.25 mm) in the mixed stands. Additionally, in the mixed stands the proportion of soil macroaggregates increased, and that of micro aggregates decreased, resulting in a shift from C and P limitation to N limitation for bulk soil microbial metabolism. Redundancy analysis identified soil aggregate organic carbon and nutrient content as the main factors affecting microbial resource limitation, rather than their stoichiometric ratios. Pathway analysis further confirmed that soil nutrients and their stoichiometric ratios indirectly influenced soil microbe resource limitation by regulating microbial biomass, microbial respiration, and extracellular enzyme activities. Thus, the impact of mixed plantations on soil nutrients and microbial activity at the aggregate level may be crucial for maintaining land fertility and achieving sustainability.

Straw return with fertilizer improves soil CO2 emissions by mitigating microbial nitrogen limitation during the winter wheat season

Straw return is the key measure of green agricultural production. Nitrogen (N) and phosphorus (P) play pivotal roles in crop growth and carbon (C) cycling in agroecosystems. However, the mechanism of soil CO2 emissions and enzyme stoichiometry regulation by straw return with N and P application remain unknown. Therefore, this study is aimed to use enzyme stoichiometry to investigate the effects of straw return with N and P fertilizer application on soil CO2 emissions, enzyme activity, and microbial nutrient limitation through a two-year field experiment. A split-plot experimental design was used (straw as the main plot and fertilizer as the sub plot). The results indicated that the addition of N, P (SNP) increased CO2 emissions by 25.54 %, and N application (SN) reduced CO2 emissions by 27.01 %, compared with straw return (SW). Enzyme stoichiometry indicated that straw return with N and P application exhibited significant C and N limitations. In soil nutrients and nutrient stoichiometry, compared with the S0W treatment, straw return with fertilizer (SNP, SN) significantly increased microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON); SNP treatment increased β-1,4- n −acetylaminoglucosidase (NAG) enzyme activity by 53.72 %, increased l −leucine aminopeptidase (LAP) enzyme activity by 58.11 %, and increased one P-acquiring enzyme alkaline monoalkaline phosphatase (AKP) enzyme activity by 39.49 % (P < 0.05). Structural equation modeling suggested that straw return and fertilization can influence microbial biomass phosphorus (MBP) and vector length (VL) by affecting MBN, which, in turn, affects CO2 emissions. Soil microbes regulate CO2 emissions using stoichiometric flexibility to maintain a stoichiometric balance of nutrients and microbes. Therefore, straw return with N and P fertilizers to winter wheat soils can meet the requirements of microbial stoichiometry, modulate microbial and extracellular enzyme activities, and effectively regulate CO2 emissions and resource limitations.

Effects of Land-Use Type and Salinity on Soil Carbon Mineralization in Coastal Areas of Northern Jiangsu Province

Sea level rise due to glacier melting caused by climate warming is a major global challenge, but the mechanism of the effect of salinity on soil carbon (C) mineralization in different land types is not clear. The pathways by which salinity indirectly affects soil carbon mineralization rates need to be investigated. Whether or not the response mode is consistent among different land-use types, as well as the intrinsic links and interactions between soil microbial resource limitation, environmental stress, microbial extracellular enzyme activity, and soil carbon mineralization, remain to be demonstrated. In this paper, three typical land-use types (wetland, forest, and agroforestry) were selected, and different salinity levels (0‰, 3‰, 6‰, and 32‰) were designed to conduct a 125-day laboratory incubation experiment to determine the soil CO2 release rate, soil physicochemical properties, and soil enzyme activities, and to correlate C mineralization with biotic and abiotic factors. A correlation analysis of soil physical and chemical properties, extracellular enzyme activities, and carbon mineralization rates was conducted to investigate their intrinsic linkages, and a multiple linear regression of C mineralization at different sites was performed to explore the variability of mineralization among different site types. Structural equation models were established in the pre- and post-incubation stages to study the pathways of soil C mineralization at different incubation times, and the mechanism of mineralization was further verified by enzyme stoichiometry. The results showed that, at the end of 125 days of incubation, the 32‰ salinity addition reduced the cumulative mineralization of forest and agroforestry types by 28.41% and 34.35%, respectively, compared to the 0‰ salinity addition. Soil C mineralization in the three different land-use types was highly correlated with the active C fractions of readily oxidizable C (ROC), dissolved organic C, and microbial biomass C (MBC) in the soil, with the standardized coefficients of multivariate linear regression reaching 0.67 for MBC in the wetland and −0.843 for ROC in the forest. Under long-term salinity additions, increased salinity would reduce the microbial respiratory quotient value by inhibiting β-glucosidase activity, thus indirectly affecting the rate of CO2 release. With added salinity, the mineralization of non-saline soil was more susceptible to the inhibitory effect of salinity, whereas the mineralization of salinized soil was more controlled by soil C pools.

Gastrointestinal response to the early administration of antimicrobial agents in growing turkeys infected with Escherichia coli

This study investigated the effects of the early administration of enrofloxacin (E) or doxycycline (D) for the first 5 consecutive days of life, or the continuous administration of the coccidiostat monensin (M) throughout the rearing period on gastrointestinal function in turkeys infected with avian pathogenic Escherichia coli (APEC) in an early or later stage of rearing. Experiment 1 lasted 21 d, and turkeys in groups E, D, and M were infected with APEC on d 15. Experiment 2 lasted 56 d, and it had a factorial arrangement of treatments where birds in groups E, D, and M were infected with APEC on d 15 or d 50. In both experiments, control groups (C) consisted of infected and uninfected birds without antibiotic or coccidiostat administration. On d 21 (Experiment 1) and d 56 (Experiment 2), 8 birds from each subgroup were killed, and the ileal and cecal digesta were sampled to analyze the activity of bacterial enzymes and the concentrations of short-chain fatty acids (SCFA). The experimental treatments did not affect the final body weight or body weight gain of birds. Both experiments demonstrated that APEC contributed to an increase in ammonia levels of the cecal digesta (means from 2 experiments: 0.311 vs. 0.225 mg/g in uninfected birds) and ileal pH (6.79 vs. 6.00) and viscosity (2.43 vs. 1.83 mPa⋅s). Moreover, the E. coli challenge enhanced the extracellular activity of several cecal bacterial enzymes, especially in older turkeys infected with APEC in a later stage of life. The continuous administration of monensin throughout the rearing period resulted in a weaker gastrointestinal response in older birds, compared with the other 2 antibiotics administered for the first 5 d of life. The results of the study are inconclusive as both desirable and undesirable effects of preventive early short-term antibiotic therapy were observed in turkeys, including normalization of ileal viscosity and cecal ammonia concentration (positive effect), and disruption in cecal SCFA production (negative effect).

Long‐term straw mulching alleviates microbial nutrient limitations and increases carbon‐use efficiency within aggregates

AbstractLong‐term straw mulching was known to change soil nutrient content, aggregate distribution and extracellular enzyme activities. However, the impact of long‐term straw mulching on microbial nutrient limitations and carbon‐use efficiency (CUEst) within aggregates remains unclear. To fill the gap, we conducted a 10‐year field experiment in a semi‐arid region and used an ecoenzymatic stoichiometry model to quantify microbial resource limitations in soil aggregates under long‐term mulching. We studied the effects of two mulching measures (plastic film mulching [FM] and straw mulching [SM], with no mulching as the control [CK]) on the nutrient content and limitations within aggregates. The results show that compared with FM, SM increased the proportion of aggregates to larger &gt;2 mm and decreased the proportion of aggregates in the 2–0.25 mm classes. Additionally, FM resulted in carbon (C) and phosphorus (P) limitations in the soil, particularly in the &gt;2 mm class, while SM alleviated these constraints. This effect was primarily attributed to the increase in soil organic carbon (SOC) and microbial biomass carbon content (Cm), especially the enhanced carbon content associated with larger aggregates (&gt;2 mm) and the increased activities of carbon–nitrogen (C–N)‐acquiring enzymes. SM also resulted in high CUEst by influencing microbial P limitation. Random forest analysis indicates that soil abiotic factors, particularly SOC and total nitrogen (TN), were the main drivers of microbial resource limitations within the aggregates. These findings suggest that the mulching material determines the development of soil aggregates and resource allocation within these aggregates. Thus, the study provides valuable insights for formulating effective carbon management strategies in semi‐arid regions.

Heterogeneity of phosphorus sources invokes distinct niche partitioning pathways of ectomycorrhizal fungi in forest soils

Ectomycorrhizal (ECM) fungi are pivotal in acquiring phosphorus (P) in nutrient-deficient soils, especially beyond the rhizosphere. However, the extent to which ECM community structure and function affect the utilization of various P-containing substrates in forest soils is not fully understood. This study explored the influence of different P substrates — calcium orthophosphate, phosphate-saturated goethite, fluorapatite, and wheat bran—on the release of plant-available P using hyphal in-growth mesh bags. Our results show that these substrates released comparable amounts of plant-available P to the Pinaceae hosts. A significant correlation was observed between the relative abundance of Tylospora (Atheliaceae) and Hourangia (Boletaceae), and their extracellular enzyme activities involved in P acquisition and trivalent iron reduction. This correlation was particularly evident in fungal taxa characterized by long/medium-distance hyphal exploration types. These findings underscore the ECM fungi's distinct preferences for different P-containing substrates, emphasizing the importance of recognizing these preferences to enhance forest management in low P environments.

Thinning enhances forest soil C storage by shifting the soil toward an oligotrophic condition

Forests are significant carbon reservoirs, with approximately one-third of this carbon stored in the soil. Forest thinning, a prevalent management technique, is designed to enhance timber production, preserve biodiversity, and maintain ecosystem functions. Through its influence on biotic and abiotic factors, thinning can profoundly alter soil carbon storage. Yet, the full implications of thinning on forest soil carbon reservoirs and the mechanisms underpinning these changes remain elusive. In this study, we undertook a two-year monitoring initiative, tracking changes in soil extracellular enzyme activities (EEAs), microbial communities, and other abiotic parameters across four thinning intensities within a temperate pine forest. Our results show a marked increase in soil carbon stock following thinning. However, thinning also led to decreased dissolved organic carbon (DOC) content and a reduced DOC to soil organic carbon (SOC) ratio, pointing toward a decline in soil carbon lability. Additionally, fourier transform infrared spectroscopy (FTIR) analysis revealed an augmented relative abundance of aromatic compounds after thinning. There was also a pronounced increase in absolute EEAs (per gram of dry soil) post-thinning, implying nutrient limitations for soil microbes. Concurrently, the composition of bacterial and fungal communities shifted toward oligotrophic dominance post thinning. Specific EEAs (per gram of soil organic matter) exhibit a significant reduction following thinning, indicating a deceleration in organic matter decomposition rates. In essence, our findings reveal that thinning transitions soil toward an oligotrophic state, dampening organic matter decomposition, and thus bolstering the soil carbon storage potential of forest. This study provides enhanced insights into the nuanced relationship between thinning practices and forest soil carbon dynamics, serving as a robust foundation for enlightened forest management strategies.

Short-term responses of soil enzyme activities and stoichiometry to litter input in Castanopsis carlesii and Cunninghamia lanceolata plantations.

Litter input triggers the secretion of soil extracellular enzymes and facilitates the release of carbon (C), nitrogen (N), and phosphorus (P) from decomposing litter. However, how soil extracellular enzyme activities were controlled by litter input with various substrates is not fully understood. We examined the activities and stoichiometry of five enzymes including β-1,4-glucosidase, β-D-cellobiosidase, β-1,4-N-acetyl-glucosaminidase, leucine aminopeptidase and acidic phosphatase (AP) with and without litter input in 10-year-old Castanopsis carlesii and Cunninghamia lanceolata plantations monthly during April to August, in October, and in December 2021 by using an in situ microcosm experiment. The results showed that: 1) There was no significant effect of short-term litter input on soil enzyme activity, stoichiometry, and vector properties in C. carlesii plantation. In contrast, short-term litter input significantly increased the AP activity by 1.7% in May and decreased the enzymatic C/N ratio by 3.8% in August, and decreased enzymatic C/P and N/P ratios by 11.7% and 10.3%, respectively, in October in C. lanceolata plantation. Meanwhile, litter input increased the soil enzymatic vector angle to 53.8° in October in C. lanceolata plantations, suggesting a significant P limitation for soil microorganisms. 2) Results from partial least squares regression analyses showed that soil dissolved organic matter and microbial biomass C and N were the primary factors in explaining the responses of soil enzymatic activity to short-term litter input in both plantations. Overall, input of low-quality (high C/N) litter stimulates the secretion of soil extracellular enzymes and accelerates litter decomposition. There is a P limitation for soil microorganisms in the study area.