Fermi Surface Nesting Driving the RKKY Interaction in the Centrosymmetric Skyrmion Magnet Gd_{2}PdSi_{3}.

The magnetic skyrmions generated in a centrosymmetric crystal were recently first discovered in Gd_{2}PdSi_{3}. In light of this, we observe the electronic structure by angle-resolved photoemission spectroscopy and unveil its direct relationship with the magnetism in this compound. The Fermi surface and band dispersions are demonstrated to have a good agreement with the density functional theory calculations carried out with careful consideration of the crystal superstructure. Most importantly, we find that the three-dimensional Fermi surface has extended nesting which matches well the q vector of the magnetic order detected by recent scattering measurements. The consistency we find among angle-resolved photoemission spectroscopy, density functional theory, and the scattering measurements suggests the Ruderman-Kittel-Kasuya-Yosida interaction involving itinerant electrons to be the formation mechanism of skyrmions in Gd_{2}PdSi_{3}.

Fe(0)-Dissimilatory Nitrate Reduction to Ammonium for Autotrophic Recovery of Reactive Nitrogen.

Bioreduction of nitrate to value-added ammonium is a potentially sustainable strategy to recycle nutrients from wastewater. Here, we have proven the feasibility of the reduction of autotrophic nitrate to ammonium with electrons extracted from Fe(0). Using a Geobacter-dominated anodic biofilm as an inoculum, we achieved nitrate-to-ammonium efficiency up to 90 ± 3% with a nitrate reduction rate of 35 ± 1.3 mg N/d/L. An electron acceptor instead of an inoculum greatly influenced the Fe(0)-dissimilatory nitrate reduction to ammonium (DNRA), where nitrite as the electron acceptor provided an effective selective pressure to enrich Geobacter from initial 5 to 56%. The DNRA repressing denitrification was demonstrated by the reverse tendencies of upregulated nrfA and downregulated nirS gene transcription. This finding provides a new route for autotrophic nitrate removal and recycling from water, which has a broader implication on biogeochemical nitrogen and iron cycling.

Long-Term Succession Shows Interspecies Competition of Geobacter in Exoelectrogenic Biofilms.

Geobacter spp. are well-known exoelectrogenic microorganisms that often predominate acetate-fed biofilms in microbial fuel cells (MFCs) and other bioelectrochemical systems (BESs). By using an amplicon sequence variance analysis (at one nucleotide resolution), we observed a succession between two closely related species (98% similarity in 16S RNA), Geobacter sulfurreducens and Geobacter anodireducens, in the long-term studies (20 months) of MFC biofilms. Geobacter spp. predominated in the near-electrode portion of the biofilm, while the outer layer contained an abundance of aerobes, which may have helped to consume oxygen but reduced the relative abundance of Geobacter. Removal of the outer aerobes by norspermidine washing of biofilms revealed a transition from G. sulfurreducens to G. anodireducens. This succession was also found to occur rapidly in co-cultures in BES tests even in the absence of oxygen, suggesting that oxygen was not a critical factor. G. sulfurreducens likely dominated in early biofilms by its relatively larger cell size and production of extracellular polymeric substances (individual advantages), while G. anodireducens later predominated due to greater cell numbers (quantitative advantage). Our findings revealed the interspecies competition in the long-term evolution of Geobacter genus, providing microscopic insights into Geobacter's niche and competitiveness in complex electroactive microbial consortia.

Electron Flow Shifts from Anode Respiration to Nitrate Reduction During Electroactive Biofilm Thickening.

As electrons generated through substrate oxidation compete with electrodes, dissimilatory nitrate reduction to ammonium (DNRA), denitrification in bioelectrochemical systems in the presence of nitrate, and nitrate reduction through an electroactive biofilm (EAB) are unpredictable. We find that pathways of nitrate reduction are related to EAB thickness and that 76 ± 2 µm is the critical thickness of a biofilm at which both the inner and outer layers simultaneously include DNRA, leading to a maximum level of DNRA efficiency of 42%. Fractions of electrons flowing during nitrate reduction are relatively stable, but their distributions between DNRA and denitrification vary with biofilm thickness. Electrons prefer denitrification in an EAB that is 66 ± 2 µm, while DNRA reversely surpasses denitrification when the thickness increases in the range of 76 ± 2 to 210 ± 2 µm. Biofilm thickening enhances the DNRA of all biofilms close to solution, where nirK remains constant and nrfA is significantly upregulated. However, nrfA is downregulated in layers close to the electrode when the biofilm is thicker than 76 ± 2 µm. These findings reveal the spatially heterogeneous reduction of nitrate in thick EABs, highlighting the importance of biofilm thickness to the regulation of end products of nitrate reduction.

Bioelectrochemical Ammoniation Coupled with Microbial Electrolysis for Nitrogen Recovery from Nitrate in Wastewater.

Nitrate-N in wastewaters is hard to be recovered because it is difficult to volatilize with an opposite charge to ammonium. Here, we have proved the feasibility of dissimilatory nitrate reduction to ammonia (DNRA) by the easy-acclimated mixed electroactive bacteria, achieving the highest DNRA efficiency of 44%. It was then coupled with microbial electrolysis to concentrate ammonium by a factor of 4 in the catholyte for recovery. The abundance of electroactive bacteria in the biofilm before nitrate addition, especially Geobacter spp., was found to determine the DNRA efficiency. As the main competitors of DNRA bacteria, the growth of denitrifiers was more sensitive to C/N ratios. The DNRA microbial community contrarily showed a stable and recoverable ammoniation performance over C/N ratios ranging from 0.5 to 8.0. A strong competition of the electrode and nitrate on electron donors was observed at the early stage (15 d) of electroactive biofilm formation, which can be weakened when the biofilm was mature on 40 d. Quantitative PCR showed a significant increase in nirS and nrfA transcripts in the ammoniation process. nirS was inhibited significantly after nitrate depletion while nrfA was still upregulated. These findings provided a novel way to recover nitrate-N using organic wastes as both electron donor and power, which has broader implications on the sustainable wastewater treatment and the ecology of nitrogen cycling.

Unignorable toxicity of formaldehyde on electroactive bacteria in bioelectrochemical systems.

Formaldehyde poses significant threats to the ecosystem and is widely used as a toxicity indicator to obtain electrical signal feedback in electroactive biofilm (EAB)-based sensors. Although many optimizations have been adopted to improve the performance of EAB to formaldehyde, nearly no studies have discussed the toxicity of formaldehyde to EAB. Here, EABs were acclimated with a stable current density (8.9 ± 0.2 A/m2) and then injected with formaldehyde. The current density decreased by 27% and 98% after the injection of 1 and 10 ppm formaldehyde, respectively, compared with that in the control. The ecotoxicity of formaldehyde caused the irreversible loss of current with 3% (1 ppm) and 81% (10 ppm). Confocal laser scanning microscopy and scanning electron microscopy results showed that the redox activity was inhibited by formaldehyde, and the number of dead/broken cells increased from 2% to 40% (1 ppm) and 91% (10 ppm). The contents of the total protein and extracellular polymer substances decreased by more than 28% (1 ppm) and 75% (10 ppm) because of the cleavage reaction caused by formaldehyde. Bacterial community analysis showed that the proportion of Geobacter decreased from 81% to 53% (1 ppm) and 24% (10 ppm). As a result, the current production was significantly impaired, and the irreversible loss increased. Toxicological analysis demonstrated that formaldehyde disturbed the physiological indices of cells, thereby inducing apoptosis. These findings fill the gap of ecotoxicology of toxicants to EAB in a bioelectrochemical system.

Phosphorus Competition in Bioinduced Vivianite Recovery from Wastewater.

Phosphorus undergoes a one-way flow from minerals to soil to water, which creates a phosphorus crisis as well as aquatic eutrophication. Dissimilatory metal reduction bacterial (DMRB)-induced vivianite recovery from wastewater is a promising route to solve these problems synthetically. In this study, phosphorus competition between biomass growth and bioinduced vivianite mineralization was investigated at the batch scale. Biomass growth leads to phosphorus utilization over vivianite mineralization. Geobacter was selected as the main functional microorganism and presented higher vivianite recovery rates (20-48%) than sewage biomass (7-33%). An optimal Fe/P stoichiometric ratio of 1:1 was observed for both sewage biomass and Geobacter-inoculated batches. The highest vivianite yield of 4.3 mM was obtained in Geobacter-inoculated batches at a Fe:P of 1:1, with values 59% higher than those at a Fe:P of 1:0.67 (equal to the Fe/P molar ratio in vivianite). Sufficient PO43- stimulated cell growth and yielded a higher Fe3+ reduction rate and vivianite yield. Nevertheless, excessive PO43- facilitated the precipitation of KFe3 (PO4)2(OH)·8H2O and Fe7 (PO4)6, which inhibited vivianite synthesis. In the optimal Geobacter batch, the µ -S curve indicated a mixed order reaction (0 < x < 1) for both vivianite formation and biomass growth. The vivianite growth series proceeded as follows: tiny blue particles, plain pieces, dark blue nodules, and large spherical crystals.

Bioelectro-barriers prevent nitrate leaching into groundwater via nitrogen retention.

Groundwater, the main freshwater resource for humans, has been widely contaminated with nitrate from fertilizers. Here, we report a new and chemical-free strategy to prevent nitrate leaching from soil based on the enrichment of electroactive bacteria, mainly of the genus Geobacter, with bioelectro-barriers, which leads to a nearly 100 % interception of nitrate and partly conserves reactive nitrogen in the form of weakly mobile ammonium by dissimilatory nitrate reduction to ammonium (DNRA). G. sulfurreducens was recognized to efficiently secrete nitrite reductase (NrfA) for rapid DNRA because it lacks nitrate reductase, which inhibits DNRA by competing with nitrite and producing toxic intracellular nitric oxide. With an increase in G. sulfurreducens abundance, near-zero nitrate leaching and 3-fold greater N retention was achieved. Periodic application of weak electricity to the bioelectro-barrier ensured the dominance of G. sulfurreducens in the microbial community and therefore its ability to consistently prevent nitrate leaching. The ability of G. sulfurreducens to intercept nitrate was further demonstrated in more diverse agricultural soils, providing a novel way to prevent nitrate leaching and conserve bioavailable nitrogen in the soil, which has broader implications for both sustainable agriculture and groundwater protection.

Glucose facilitates the acclimation of organohalide-respiring bacteria.

Organohalide respiring bacteria (OHRB) are the mainstay for bioremediation of organohalide contaminated sites. Enrichment screening of OHRB is prerequisite for the development of high performance dehalogenating bacterial agents. Herein, different domestication strategies were formulated for the main factors (nutrients and inocula) affecting the enrichment of OHRB, and the dehalogenation effect was verified with 2-chlorophenol and per/polyfluoroalkyl substances. The nutrients had a greater impact on the dehalogenation of the systems relative to the inocula, where the combination of glucose and anaerobic sludge (Glu-AS) had a faster degradation rate (26 ± 2.5 µmol L-1 d-1) and more complete dechlorination effectiveness. Meanwhile, the dehalogenation results for perfluorooctanoic acid and trifluoroacetic acid showed the biological defluorination was closely related to the position of fluoride. Further, the microbial community structure profiled the resource competition, metabolic cross-feeding and nutrient dynamic exchange among fermenting bacteria, OHRB and methanogenic bacteria under different domestication strategies as endogenous factors affecting the dehalogenation performance, and speculated a hypothetical model for the interaction of different functional bacteria. Our research contributed guidelines and references for the development of efficient dehalogenating bacterial agents, and provided scientific theoretical and technical support for promoting the maximum efficiency of bioremediation of organohalogenated sites.

Layered Design of a Highly Repeatable Electroactive Biofilm for a Standardized Biochemical Oxygen Demand Sensor.

Microbial electrochemical sensors are promising to monitor bioavailable organics in real environments, but their application is restricted by the unpredictable performance of the electroactive biofilm (EAB), which is randomly acclimated from environmental microflora. With a long-term stable EAB as a template, we successfully designed EAB (DEAB) by the sequential growth of Geobacter anodireducens and automatched microbes, achieving a reproducible high current than those naturally acclimated from wastewater (NEAB). Pre-inoculation of planktonic aerobes as oxygen bioscavengers was necessary to ensure the colonization of Geobacter in the inner layer, and the abundant Geobacter (50%) in DEAB guaranteed 4 times higher current density with a 15-fold smaller variation among 20 replicates than those of NEAB. The sensor constructed with DEAB exhibited a shorter measuring time and a precise biochemical oxygen demand (BOD) measurement with acetate, real domestic wastewater, and supernatant of anaerobic digestion. Here, we for the first time proposed an applicable strategy to standardize EABs for BOD sensors, which is also crucial to ensure a stable performance of all bioelectrochemical technologies.

Biosorption behavior and mechanism of heavy metals by the fruiting body of jelly fungus (Auricularia polytricha) from aqueous solutions.

The aim of this study was to investigate the biosorption characteristics of Cd(2+), Cu(2+), and Pb(2+) by the fruiting body of jelly fungus Auricularia polytricha. Batch experiments were conducted to characterize the kinetics, equilibrium, and mechanisms of the biosorption process. Optimum values of pH 5, biomass dosage 4 g L(-1), and contact time 60 min provided maximum biosorption capacities of A. polytricha for Cd(2+), Cu(2+), and Pb(2+) of 63.3, 73.7, and 221 mg g(-1), respectively. The maximum desorption was achieved using 0.05 mol L(-1) HNO(3) as an elute. The fruiting body was reusable at least for six cycles of operations. The pseudo-second-order model was the best to describe the biosorption processes among the three kinetic models tested. Freundlich and Dubinin-Radushkevich models fitted the equilibrium data well, indicating a heterogeneous biosorbent surface and the favorable chemisorption nature of the biosorption process. A Fourier transform infrared spectroscopy analysis indicated that carboxyl, amine/hydroxyl, amino, phosphoryl, and C-N-C were the main functional groups to affect the biosorption process. Synergistic ion exchange and surface complexation were the dominant mechanisms in the biosorption process. The present work revealed the potential of jelly fungus (fruiting body of A. polytricha) to remove toxic heavy metals from contaminated water.

Autotrophic nitrate reduction to ammonium via reverse electron transfer in Geobacter dominated biofilm.

Geobacter dominated electroactive biofilms (EABs) have been demonstrated to perform bidirectional extracellular electron transfer (EET) in bioelectrochemical systems, but it is largely unknown when nitrate is the electron acceptor at the cathode. If reverse EET occurs on biocathode, this EAB has to perform dissimilatory nitrate reduction to ammonia (DNRA) rather than denitrification according to genomes. Here, we have proven the feasibility of reverse bioelectron transfer in EAB, achieving a DNRA efficiency up to 93 ± 3% and high Faraday efficiency of 74 ± 1%. Constant current was found to be more effective than constant potential to maintain Geobacter on the cathode, which highly determines this electrotrophic respiration. The prevalent DNRA at constant current surpassed denitrification, demonstrated by the reverse tendencies of DNRA (nrfA) and denitrification (nirS and nirK) gene transcription. Metatranscriptomics further revealed the possible electron uptake mechanisms by which the outer membrane (OmcZ and OmcB) and periplasmic cytochromes (PpcB and PpcD) may be involved. These findings extend our understanding of the bidirectional electron transfer and advance the applications of EABs.

Genetic Dissection of Epistatic Interactions Contributing Yield-Related Agronomic Traits in Rice Using the Compressed Mixed Model.

Rice (Oryza sativa) is one of the most important cereal crops in the world, and yield-related agronomic traits, including plant height (PH), panicle length (PL), and protein content (PC), are prerequisites for attaining the desired yield and quality in breeding programs. Meanwhile, the main effects and epistatic effects of quantitative trait nucleotides (QTNs) are all important genetic components for yield-related quantitative traits. In this study, we conducted genome-wide association studies (GWAS) for 413 rice germplasm resources, with 36,901 single nucleotide polymorphisms (SNPs), to identify QTNs, QTN-by-QTN interaction (QQI), and their candidate genes, using a multi-locus compressed variance component mixed model, 3VmrMLM. As a result, two significant QTNs and 56 paired QQIs were detected, amongst 5219 genes of these QTNs, and 26 genes were identified as the yield-related confirmed genes, such as LCRN1, OsSPL3, and OsVOZ1 for PH, and LOG and QsBZR1 for PL. To reveal the substantial contributions related to the variation of yield-related agronomic traits in rice, we further implemented an enrichment analysis and expression analysis. As the results showed, 114 genes, nearly all significant QQIs, were involved in 37 GO terms; for example, the macromolecule metabolic process (GO:0043170), intracellular part (GO:0044424), and binding (GO:0005488). It was revealed that most of the QQIs and the candidate genes were significantly involved in the biological process, molecular function, and cellular component of the target traits. The demonstrated genetic interactions play a critical role in yield-related agronomic traits of rice, and such epistatic interactions contributed to large portions of the missing heritability in GWAS. These results help us to understand the genetic basis underlying the inheritance of the three yield-related agronomic traits and provide implications for rice improvement.

An Improved Bayesian Shrinkage Regression Algorithm for Genomic Selection.

Currently a hot topic, genomic selection (GS) has consistently provided powerful support for breeding studies and achieved more comprehensive and reliable selection in animal and plant breeding. GS estimates the effects of all single nucleotide polymorphisms (SNPs) and thereby predicts the genomic estimation of breeding value (GEBV), accelerating breeding progress and overcoming the limitations of conventional breeding. The successful application of GS primarily depends on the accuracy of the GEBV. Adopting appropriate advanced algorithms to improve the accuracy of the GEBV is time-saving and efficient for breeders, and the available algorithms can be further improved in the big data era. In this study, we develop a new algorithm under the Bayesian Shrinkage Regression (BSR, which is called BayesA) framework, an improved expectation-maximization algorithm for BayesA (emBAI). The emBAI algorithm first corrects the polygenic and environmental noise and then calculates the GEBV by emBayesA. We conduct two simulation experiments and a real dataset analysis for flowering time-related Arabidopsis phenotypes to validate the new algorithm. Compared to established methods, emBAI is more powerful in terms of prediction accuracy, mean square error (MSE), mean absolute error (MAE), the area under the receiver operating characteristic curve (AUC) and correlation of prediction in simulation studies. In addition, emBAI performs well under the increasing genetic background. The analysis of the Arabidopsis real dataset further illustrates the benefits of emBAI for genomic prediction according to prediction accuracy, MSE, MAE and correlation of prediction. Furthermore, the new method shows the advantages of significant loci detection and effect coefficient estimation, which are confirmed by The Arabidopsis Information Resource (TAIR) gene bank. In conclusion, the emBAI algorithm provides powerful support for GS in high-dimensional genomic datasets.

Two key Geobacter species of wastewater-enriched electroactive biofilm respond differently to electric field.

Electroactive biofilms have attracted increasing attention due to their unique ability to exchange electrons with electrodes. Geobacter spp. are widely found to be dominant in biofilms in acetate-rich environments when an appropriate voltage is applied, but it is still largely unknown how these bacteria are selectively enriched. Herein, two key Geobacter spp. that have been demonstrated predominant in wastewater-enriched electroactive biofilm after long-term operation, G. sulfurreducens and G. anodireducens, responded to electric field (EF) differently, leading to a higher abundance of EF-sensitive G. anodireducens in the strong EF region after cocultivation with G. sulfurreducens. Transcriptome analysis indicated that two-component systems containing sensor histidine kinases and response regulators were the key for EF sensing in G. anodireducens rather than in G. sulfurreducens, which are closely connected to chemotaxis, c-di-GMP, fatty acid metabolism, pilus, oxidative phosphorylation and transcription, resulting in an increase in extracellular polymeric substance secretion and rapid cell proliferation. Our data reveal the mechanism by which EF select specific Geobacter spp. over time, providing new insights into Geobacter biofilm formation regulated by electricity.

Efficient decolorization of azo dye wastewater with polyaniline/graphene modified anode in microbial electrochemical systems.

Azo dye pollution has become a worldwide issue, and the current treatment methods can hardly meet the expected emission standards. Microbial electrochemical systems (MESs) show promising applications for decolorization, but their performance critically depends on the microorganisms. Electrode modification is an interesting method of improving decolorization performance. However, the mechanisms of how the modification can affect microbial communities and the decolorization process remain unclear. Here, a modified anode with polyaniline (PANI) and graphene was fabricated via electro-deposition. Consequently, the highest decolorization efficiency was obtained. The Congo red (CR) decolorization rate of the MESs with the PANI/graphene-modified electrode (PG) reached 90% at 54 h. By contrast, the CR decolorization rates of the MESs with the PANI-modified electrode (P) and those of the MESs with the unmodified electrode (C) only reached 68% and 79%, respectively. Results of the microbial community analysis showed abundant Methanobrevibacter arboriphilus in PG (11%), which was 5.5 times that in C (2%) at 18 h. This phenomenon may be related to the rapid decolorization. The upregulated metabolism pathways, including arginine and proline metabolism, purine metabolism, arginine biosynthesis, and riboflavin metabolism, provided more electron shuttles and redox mediators that facilitated the extracellular electron transfer. Therefore, the PG-modified electrode facilitated the decolorization by altering certain metabolic pathways. This study can help to improve the guideline on the potential application of MESs for wastewater treatment.

Estimating Potential Distribution of Sweetgum Pest Acanthotomicus suncei and Potential Economic Losses in Nursery Stock and Urban Areas in China.

American sweetgum Liquidambar styraciflua (Altingiaceae) was first introduced to China over 60 years ago. It is an important tree species for increasing landscape value and promoting afforestation in urbanized areas of eastern China in the past 20 years. Sweetgum inscriber Acanthotomicus suncei (Coleoptera: Curculionidae) is a local bark beetle pest and lethal to the introduced American sweetgum. To provide preliminary estimates of the potential economic losses caused by the sweetgum inscriber, a field investigation was conducted to survey the beetles' natural distribution in China. Based on field collections, potential distribution was predicted using Maxent. All nurseries stocking American sweetgum were in the high and very high suitability area of sweetgum inscriber. Additionally, we employed a model of direct loss incorporating tree and removal cost. A questionnaire was sent to maintenance companies, growers, and gardener associations for tree removal prices. We estimated the removal cost of each tree. In addition, the market price and inventory were also gained from telephone interview. Our economic analysis indicates that if sweetgum inscriber were to become established in the main American sweetgum business, the potential losses of nursery stock and urban area could range from USD 12.81 to 14.41 million.

Nutrient conversion and recovery from wastewater using electroactive bacteria.

Wastewater is widely recognized as a sink of active nitrogen and phosphorus, and the recovery of both nutrients as fertilizers is widely studied in recent years. Electroactive bacteria increasingly attract attentions in this area because they are able to produce an electric field in microbial electrochemical systems to concentrate ammonium and phosphate for recovery. Importantly, these unique bacteria are able to convert nitrate and nitrite directly to ammonium, maximizing the active nitrogen species capable of recovery. Ferric ions produced by electroactive bacteria can be precipitated with phosphate to recover as vivianite in neutral wastewaters. All these processes employed electroactive bacteria as both nitrate and iron reducer and bioelectric field generator. The mechanism as well as technologies are summarized, and the challenges to further improve their performance are discussed.

Syntrophic Growth of Geobacter sulfurreducens Accelerates Anaerobic Denitrification.

Nitrate is considered as a contamination since it's over discharging to water incurs environmental problems. However, nitrate is an ideal electron sink for anaerobic pollutant degraders desiring electron acceptors due to the high redox potential. Unfortunately, not all degraders can directly reduce nitrate, and the anaerobic direct interspecies electron transfer (DIET) between degraders and denitrifiers has not been confirmed yet. Here we demonstrated that syntrophic growth of Geobacter sulfurreducens PCA with denitrifying microbial community at anaerobic condition eliminated the lag phase of 15 h and improved the denitrification rate by 13∼51% over a broad C/N ratio of 0.5 to 9. Quantitative PCR revealed that G. sulfurreducens selectively enhanced the expression of nirS coding for a cytochrome cd1-nitrite reductase, resulting in a fast and more complete denitrification. Geobacter also selectively enriched its potential denitrifying partners - Diaphorobacter, Delftia, and Shinella - to form spherical aggregates. More studies of the binary culture system need to be carried out to confirm the syntrophic mechanism of Geobacter and denitrifiers in the future. These findings extend our knowledge on understanding the anaerobic bacterial interspecies electron transfer in the denitrification process, which has broader implications in fast selection and stabilization of denitrifiers in wastewater treatment plant, and general understanding of ecology for nitrogen and metal cycling.

[Dynamics of microbes and enzyme activities during litter decomposition of Pinus massoniana forest in mid-subtropical area].

The dynamics of microbial quantity and enzyme activities during decomposition process of masson pine (Pinus massoniana) leaf litter, oak (Quercus aliena) leaf litter and their mixture (at natural mass ratio, 8: 2) were studied with litterbag method in the pinus forest typical vegetations of mid-subtropical Jinyun Mountain nature reserve. The results showed that the decomposition constant K of leaf litter ranked as follows: mixture (0.94) > oak (0.86) > masson pine (0.67). Microbial groups and enzyme activity exhibited some similar responses to the litter decomposition process. After 135 days, fungal and microbial quantities reached the maximum while bacterial and actinomycetic number reached the minimum, presumably due to the high-temperature environment. The correlative analysis showed that the cellulase and acid phosphatase activity had significant positive relationship with the dry weight remaining rate (P < 0.05), which played a key role for microbes in utilizing the substrates at early stages. Meanwhile, the polyphenol oxidase activity showed highly significant negative correlation with the dry weight remaining rate (P < 0.01) in pine litter and the mixed litter, which worked on further decay of recalcitrant compound at late stages. Through the whole process, the microbial quantity and polyphenol oxidase activity were generally in the order of oak litter > mixed litter > pine litter, while in most cases the oak litter showed the lowest acid phosphatase activity, the ranking of which had some differences with the order of the decomposition constant K, indicating that litter decomposition was the result of integrated action by microbe and many kinds of enzymes. The results suggested that differences in litter composition and seasonal climate strongly influenced the microbial communities and the ecosystem processes they mediate. When mixed with oak leaves in given stand, the pine litter had an accelerating decomposition rate, which might depend on the higher microbial quantity and polyphenol oxidase activity in the mixed litter.