Fundamental aspects of waste sewage sludge treatment: Microbial solids biodegradation in an aerobic thermophilic semi-continuous system

The solubilization and biodegradation of whole microbial cells by an aerobic thermophilic microbial population was investigated over a 72 h period. Various parameters were followed including total suspended solids reduction, changes in the dissolved organic carbon, protein and carbohydrate concentrations, and carboxylic acid production and utilisation. From the rates of removal of the various fractions a simple model for the biodegradation processes is proposed and verified with respect to acetic acid production and utilization, and total suspended solids removal. The process is initiated by enzymic degradation of the substrate microbe cell walls followed by growth on the released soluble substrates at low dissolved oxygen concentration with concommitant carboxylic acid production. Subsequent utilization of the unbranched, lower molecular weight carboxylic acids allows additional energy supply following exhaustion of the easily utilisable soluble substrate from microbial cell hydrolysis.List of Symbols Y _Xp/Xs kg/kg yield process microbes on substrate yeast cells - Y _Xp/Ac kg/kg yield process microbes on acetate - Y _Ac/Ss kg/kg yield acetate produced by process microbes growing on substrate yeast cells - Y _Ss/Xs kg/kg yield soluble substrate from lysis of yeast cells - Y _Ss/Xp kg/kg yield soluble substrate from lysis of process microbes - Y _P/Xs kg/kg yield particulates from lysis of yeast cells - Y _P/Xp kg/kg yield particulates from lysis of process microbes - _{max (Ss)} h^–1 maximum specific growth rate constant for growth of process microbes on soluble substrate - _{max (Ac)} h^–1 maximum specific growth rate constant for growth of process microbes on acetate - Ks _Ss kg/m³ saturation coefficient for growth of process microbes on soluble substrate - Ks _Ac kg/m³ saturation coefficient for growth of process microbes on acetate - K _d h^–1 death/lysis rate constant for process microbes - K _i kg/m³ inhibition constant for growth of process microbes on acetate - K _L h^–1 lysis rate constant for whole yeast cells - K _h h^–1 hydrolysis rate constant for particulate biomass     

马铃薯全生育期内根际微生物组变化规律

[目的]陆生植物根际环境与土壤中的微生物菌群关系密切,其根际微生物群落动态极可能直接影响着植物健康及养分高效利用。虽然根际益生菌已被证实可用于提高作物生产力,但由于缺乏对这些菌群组成动态变化规律的认识了解,它们的开发受到限制。研究马铃薯全生育期根际菌群的动态变化规律,探讨根际菌群变化与马铃薯发育时期的相关性,为针对马铃薯不同生长时期开发专用生物益生菌肥奠定理论基础。[方法]本研究着眼于马铃薯田间全生命周期微生物组动态变化,通过Illumina MiSeq高通量测序技术对不同时间点马铃薯根际细菌16S rRNA基因V3-V4区和真菌ITS区测序并对操作分类单位(OTU)进行聚类,分析样品间微生物群落的多样性特征,并通过机器学习的方法建立模型,将根际菌群与田间马铃薯发育时间相关联。[结果]根际菌群在马铃薯各个发育阶段随时间变化明显,营养生长阶段的微生物群落结构发生了显著变化,随着结薯期的开始逐渐稳定,直到块茎成熟后期根际菌群再次出现较大变化,且在不同施肥处理间呈现较大差异。进一步基于模型挖掘了与马铃薯发育时间相关联的22个特征细菌类群和16个特征真菌类群,其中苗期和结薯末期的特征类群分别为梭菌(Clostridium)和放线菌(Actinobacteria)。[结论]马铃薯的生长发育时期是影响根际微生物群落组成的主要因素,益生菌肥的添加主要影响马铃薯结薯末期的细菌微生物菌群结构。     

ATP Modulates the Growth of Specific Microbial Strains

The regulatory function of extracellular ATP (exATP) in bacteria is unknown, but recent studies have demonstrated exATP induced enhanced secondary metabolite production and morphological differentiation in Streptomyces coelicolor. The growth of Streptomyces coelicolor, however, was unaffected by exATP, although changes in growth are common phenotypes. To identify bacteria whose growth is altered by exATP, we measured exATP-induced population changes in fast-growing microbes and actinomycetes in compost. Compared with the water-treated control, the addition of 10 ml 100 μM ATP to 10 g of compost enhanced the actinomycetes population by 30% and decreased fast-growing microbial numbers by 20%. Eight microbes from each group were selected from the most populated colony, based on appearance. Of the eight isolated fast-growing microbes, the 16S rRNA sequences of three isolates were similar to the plant pathogens Serratia proteamaculans and Sphingomonas melonis, and one was close to a human pathogen, Elizabethkingia meningoseptica. The growth of all fast-growing microbes was inhibited by ATP, which was confirmed in Pseudomonas syringae DC3000, a pathogenic plant bacterium. The growth of six of eight isolated actinomycetes strains, all of which were identified as close to Streptomyces neyagawaensis, was enhanced by ATP treatment. This study suggests that exATP regulates bacterial physiology and that the exATP response system is a target for the control of bacterial ecology.     

土壤灭菌处理对入侵植物南美蟛蜞菊及其伴生种生长的影响

该研究以温室盆栽法对南美蟛蜞菊重度入侵土壤进行高温高压湿热灭菌、添加杀真菌剂灭菌和添加杀细菌剂灭菌的处理后,将三种植株定植96 d后测定各生理指标参数,研究重度入侵土壤中各微生物类群对南美蟛蜞菊及其伴生种金腰箭和狗肝菜生长的影响。结果表明:在杀真菌、杀细菌以及高温高压湿热灭菌和未处理的南美蟛蜞菊重度入侵土壤中,三种植物生长情况均存在较大差异。在高温高压湿热灭菌土壤中南美蟛蜞菊的生长受到显著抑制,与未处理土壤中的生长情况相比,株高降低了17.59%,叶片数降低了38.10%,生物量降低了56.00%,电子传递速率变化不明显。在杀真菌土壤和杀细菌土壤中金腰箭的生长也受到显著抑制,与未处理土壤中的生长情况相比较,杀真菌土壤中的金腰箭株高降低最多(为42.28%),叶片数降低了38.89%,生物量降低了16.99%,电子传递速率变化不明显;在杀细菌土壤中金腰箭株高降低了36.64%,叶片数降低最多(为38.89%),生物量降低了33.67%,电子传递速率升高了11.11%。由此可见,不含微生物的土壤对南美蟛蜞菊生长有较强的抑制作用,不含真菌和细菌的土壤对金腰箭的生长有明显抑制作用。南美蟛蜞菊重度入侵土壤不仅适合南美蟛蜞菊的生长,也适合金腰箭的生长,对狗肝菜影响不大。     

控雨对荒漠草原植物、微生物和土壤C、N、P化学计量特征的影响

以宁夏荒漠草原为研究对象,于2014—2015年设置了降雨量变化(减雨50%、减雨30%、自然降雨、增雨30%和增雨50%)的野外模拟试验,测定了植物、微生物和土壤C、N、P含量,同时调查了植物群落组成和土壤含水量等指标,研究了各组分C、N、P化学计量特征对连续两年降雨量变化的响应,分析了土壤C∶N∶P和含水量分别与植物生长、养分利用以及微生物量积累的相关性。结果表明,控雨改变了植物叶片C∶N∶P,且其影响程度随物种不同而异:减雨50%提高了牛枝子(Lespedeza potanimill)绿叶N和P以及猪毛蒿(Artemisia scoparia)绿叶P摄取能力,增雨(30%和50%)降低了猪毛蒿绿叶N摄取能力。增雨提高了猪毛蒿绿叶C∶N,增雨30%提高了苦豆子(Sophora alopecuroides)绿叶C∶N。增雨降低了猪毛蒿绿叶N∶P,增雨30%降低了白草(Pennisetum centrasiaticum)绿叶N∶P。相比之下,控雨条件下枯叶C∶N∶P的变化幅度较小;随降雨量增加微生物量C、N以及C∶N逐渐增加,但增雨50%使微生物量C和C∶N降低;控雨对土壤C∶N∶P的影响较小,但增雨提高了土壤水分有效性,因此促进了植物和微生物生长;试验期内,相对稳定的土壤C∶N∶P不能很好地指示植物和微生物生长发育的养分受限状况;干旱时提高叶片养分摄取、湿润时增强叶片养分回收,可能解释了牛枝子对降雨量变化的弹性适应能力。     

Interaction of soil microbes with mycorrhizal fungi in tomato

In this study, the interaction of soil microbes with mycorrhizal fungi (MF) was performed to understand the effect on tomato. A pot and a field experiment were employed to investigate the impact of soil microbes i.e. Fusarium oxysporum f. sp. lycopersici, Trichoderma harzianum, Aspergillus niger and Rhizobium leguminosarum, on AM fungi in pots and field studies. The soils without microbes which treated controls with or without mycorrhizal inoculation were also included. Plant growth and root colonisation were measured 36, 75 and 120?days post inoculation (dpi) in the both pot experiment and field study. Soil microbes’ effects on the growth behaviour of the tomato plant were determined via the shoot and root weight. R. leguminosarum and A. niger did not affect the colonisation ability much, but F. oxysporum f. sp. lycopersici and T. harzianum resulted in the inhibition of AM fungal colonisation in both pot and field studies. Our study provides evidence for the effects of soil microbes on the diversity of AM fungi and their effect on the tomato plants. The higher concentrations of phosphorus and of proteins in the root tissues, previously colonised with AM fungi, point out their effect as biofertilizers, according to the concept of sustainable agriculture.     

Modeling of Pathogen Indicator Organisms in a Small-Scale Agricultural Catchment Using SWAT

Degradation of water quality from microbial contaminants associated with agricultural activities has significant implications for source protection of potable water. Novel environmental approaches must be adopted to assess risks from waterborne pathogenic microbes. The objective of this study was to evaluate applicability of the Soil and Water Assessment Tool (SWAT) to predict daily concentrations of E. coli in a small-scale agricultural catchment in Ireland. The study area is based on the Kilshanvey catchment located in the west of Ireland. E. coli data (n = 25) from June 2006 to June 2007 were utilized for comparison with the model's predictions. Statistical analysis indicates an unsatisfactory to fair level of correlation for the model's predictions (R² = 0.03–0.35, NSE = –0.42–0.29). A sensitivity analysis identified direct stream deposition and die-off rates for E. coli as having a significant impact on the model's predictions. Our results suggest that the model is adequate to assess the magnitude of various microbial sources within catchments but capability to replicate daily observations is uncertain. However, model outputs could provide adequate data to develop a human exposure assessment to pathogen indicator organisms in surface water and assist policy-makers in developing appropriate risk management strategies.     

Evidence for species‐specific plant responses to soil microbial communities from remnant and degraded land provides promise for restoration

Below‐ground interactions between soil microbial communities and plants play important roles in shaping plant community structure, but are currently poorly understood. Understanding these processes has important practical implications, including for restoration. In this study, we investigated whether soil microbes from remnant areas can aid the restoration of old‐fields, and whether soil microbes from an old‐field encourages further invasive establishment. In a glasshouse experiment, we measured growth and survival of two native grasses (Austrostipa nodosa and Rytidosperma auriculatum) and an invasive grass (Lolium rigidum) grown in sterile soil inoculated with whole soil from three locations: an old‐field, a remnant grassland, and a seed orchard planted with native grasses 7 years ago. Plants grown in sterile, non‐inoculated soil acted as controls. The orchard inoculant was included to test whether soil microbes from an area cultivated with native grasses induced plant responses similar to remnant areas. The remnant treatment resulted in the highest biomass and no mortality for R. auriculatum. All inoculant types increased the biomass of the invasive species equally. The native grass, A. nodosa, was the most sensitive to the addition of inoculum, whereas the invasive L. rigidum suffered very low mortality across all treatments. Overall, mortality was highest in the old‐field treatment at 42.9%. These results give insights into how soil microbes can affect community structure and dynamics, e.g. the high mortality of natives with old‐field inoculant may be one mechanism that allows invasive species to dominate. Poorer performance of native species with the orchard inoculant suggests it would not make a suitable replacement for remnant soil; therefore, more work is needed to understand the requirements of target species and their interactions before this technique can be exploited to maximum benefit.     

Characterisation of antagonistic soil microbes against Rhizoctonia spp. and Sclerotium hydrophilum

Rhizoctonia solani, R. oryzae-sativae and Sclerotium hydrophilum are responsible for sheath diseases of rice. Soil treatment measures with antagonist microbes have produced good results against various soil-borne fungi. The objective of this study included to find out the potential antagonist microbes from the paddy field soil. Ten different soil samples were collected from the disease-prone area of paddy field soil. Antagonist microbes were identified by 16S rRNA sequence analysis. Subsequent screening of antagonist microbes yield B. subtilis B37 and P. aeruginosa B258 as the potential antagonist microbes to control sheath diseases of rice in Myanmar. Bacillus subtilis strains induced the competition between antagonist and the tested fungi at the margin of the bacterial growth itself. However, P. aeruginosa induced the competition at a long range formed by the antibiotic of antagonist microbe. Bacillus subtilis B37 and P. aeruginosa B258 could be applicable in the control strategy of causal agents of rice sheath diseases in Myanmar.     

Dynamic flux balance modeling of S. cerevisiae and E. coli co-cultures for efficient consumption of glucose/xylose mixtures

Current researches into the production of biochemicals from lignocellulosic feedstocks are focused on the identification and engineering of individual microbes that utilize complex sugar mixtures. Microbial consortia represent an alternative approach that has the potential to better exploit individual species capabilities for substrate uptake and biochemical production. In this work, we construct and experimentally validate a dynamic flux balance model of a Saccharomyces cerevisiae and Escherichia coli co-culture designed for efficient aerobic consumption of glucose/xylose mixtures. Each microbe is a substrate specialist, with wild-type S. cerevisiae consuming only glucose and engineered E. coli strain ZSC113 consuming only xylose, to avoid diauxic growth commonly observed in individual microbes. Following experimental identification of a common pH and temperature for optimal co-culture batch growth, we demonstrate that pure culture models developed for optimal growth conditions can be adapted to the suboptimal, common growth condition by adjustment of the non-growth associated ATP maintenance of each microbe. By comparing pure culture model predictions to co-culture experimental data, the inhibitory effect of ethanol produced by S. cerevisiae on E. coli growth was found to be the only interaction necessary to include in the co-culture model to generate accurate batch profile predictions. Co-culture model utility was demonstrated by predicting initial cell concentrations that yield simultaneous glucose and xylose exhaustion for different sugar mixtures. Successful experimental validation of the model predictions demonstrated that steady-state metabolic reconstructions developed for individual microbes can be adapted to develop dynamic flux balance models of microbial consortia for the production of renewable chemicals.     

Microbes drive global soil nitrogen mineralization and availability

Soil net nitrogen mineralization rate (N_min), which is critical for soil nitrogen availability and plant growth, is thought to be primarily controlled by climate and soil physical and/or chemical properties. However, the role of microbes on regulating soil N_min has not been evaluated on the global scale. By compiling 1565 observational data points of potential net N_min from 198 published studies across terrestrial ecosystems, we found that N_min significantly increased with soil microbial biomass, total nitrogen, and mean annual precipitation, but decreased with soil pH. The variation of N_min was ascribed predominantly to soil microbial biomass on global and biome scales. Mean annual precipitation, soil pH, and total soil nitrogen significantly influenced N_min through soil microbes. The structural equation models (SEM) showed that soil substrates were the main factors controlling N_min when microbial biomass was excluded. Microbe became the primary driver when it was included in SEM analysis. SEM with soil microbial biomass improved the N_min prediction by 19% in comparison with that devoid of soil microbial biomass. The changes in N_min contributed the most to global soil NH₄⁺‐N variations in contrast to climate and soil properties. This study reveals the complex interactions of climate, soil properties, and microbes on N_min and highlights the importance of soil microbial biomass in determining N_min and nitrogen availability across the globe. The findings necessitate accurate representation of microbes in Earth system models to better predict nitrogen cycle under global change.     

Root microbiome assembly of As-hyperaccumulator Pteris vittata and its efficacy in arsenic requisition

The assemblage of root-associated microorganisms plays important roles in improving their capability to adapt to environmental stress. Metal(loid) hyperaccumulators exhibit disparate adaptive capability compared to that of non-hyperaccumulators when faced with elevated contents of metal(loid)s. However, knowledge of the assemblage of root microbes of hyperaccumulators and their ecological roles in plant growth is still scarce. The present study used Pteris vittata as a model plant to study the microbial assemblage and its beneficial role in plant growth. We demonstrated that the assemblage of microbes from the associated bulk soil to the root compartment was based on their lifestyles. We used metagenomic analysis and identified that the assembled microbes were primarily involved in root–microbe interactions in P. vittata root. Notably, we identified that the assembled root microbiome played an important role in As requisition, which promoted the fitness and growth of P. vittata. This study provides new insights into the root microbiome and potential valuable knowledge to understand how the root microbiome contributes to the fitness of its host.     

Comparative analysis of the flea fauna and its epizootic importance in the deserts of Southern Kazakhstan

Common features and interregional differences in the structure of the flea fauna from Moiynkum (Chu-Talas watershed), Eastern Kyzyl Kum and Betpak Dala are described. The main role of the fleas Xenopsylla gerbilli minax (Moiynkum and Betpak Dala) and X. gerbilli caspica (Eastern Kyzyl Kum) in the transmission of plague microbes is demonstrated. The long-term dynamics of these species population in different desert regions were studied. The main factors responsible for this dynamics are demonstrated.     

A consortium of non‐rhizobial endophytic microbes from Typha angustifolia functions as probiotic in rice and improves nitrogen metabolism

• Endophytic microbes isolated from plants growing in nutrient‐deficient environments often possess properties that improve nutrition of agriculturally important plants. A consortium of non‐rhizobial endophytic microbes isolated from a macrophyte Typha angustifolia growing in the marginal wetlands associated with a Uranium mine was characterized for their beneficial effect on rice and the mechanisms of growth promotion were investigated.
• The microbes were identified and characterized for their potential plant growth promoting (PGP) properties. Effect of these microbes on nitrogen (N)‐metabolism of rice was tested as Typha endophytes were predominantly (N)‐fixing. Relative N‐use efficiency and expression of genes involved in N‐uptake and assimilation were investigated in treated plants.
• Evidence of horizontal gene transfer (HGT) of dinitrogen reductase gene was observed within the consortium from a Pseudomonas stutzeri strain. The consortium behaved as plant probiotic and showed substantial growth benefits to Typha, their natural host as well as to rice. Typha endophytes colonized rice endosphere significantly increasing biomass, shoot length and chlorophyll content in rice plants both under N‐sufficient and N‐deficient conditions. N‐uptake and assimilation genes were upregulated in plants treated with the endophytes even after three weeks post infection.
• Our results suggested, HGT of nitrogen‐fixation trait to be highly prevalent among endophytes isolated from nutrient‐poor habitats of the uranium mine. A long‐term nitrogen deficiency response in the treated plants was elicited by the consortium improving N‐uptake, assimilation and relative N‐use efficiency of rice plants. This appeared to be at least one of the main strategies of plant growth promotion.

     

Phoxim and manure enhanced the population rebound and preservation of Metarhizium anisopliae applied in soil

We investigated the population dynamics of Metarhizium anisopliae during peanut growth and the effect of phoxim and manure on population dynamics. The applied population of M. anisopliae initially decreased rapidly, then slowly, and finally stabilised or revived. The 50% decline in the original three rates of treatment appeared at 41.8–57.6 days; however, the populations decreased towards similar levels at harvest time. Phoxim clearly inhibited the fungal growth and conidiation on the medium. Germination was reduced by half or was completely absent when conidia were inoculated on media containing 25 or 100 ppm phoxim. The colony number decreased by 20–65%, and the colonies grew more slowly, conidiated less and faded in colour on media containing 25–200 ppm phoxim. However, normal growth and enhanced conidiation were restored when they were subsequently subcultured on normal media. Adding phoxim or manure to the fungal treatment in potting soil caused the population to decrease faster within the first 16 days but rebound and level off after 30 days. In the field, the M. anisopliae populations at peanut harvest dropped to approximately 10% of their initial levels, regardless of whether the fungus was applied alone or with phoxim or manure. We speculated that low concentrations of phoxim might stimulate M. anisopliae sporulation and proliferation, and that manure might increase space and nutrient competition between soil microbes and increase M. anisopliae proliferation.     

Diversity and functional responses of nitrogen-fixing microbes to three wetland invasions

Impacts of invasive species on microbial components of wetland ecosystems can reveal insights regarding functional consequences of biological invasions. Nitrogen fixation (acetylene reduction) rates and diversity of nitrogen fixers, determined by genetic fingerprinting (T-RFLP) of the nifH gene, were compared between native and invaded sediments in three systems. Variable responses of nitrogen fixing microbes to invasion by a non-native mussel, Musculista senhousia, and mangrove, Avicennia marina, in Kendall Frost-Northern Wildlife Preserve (Mission Bay) and salt cedar, Tamarisk (Tamarix spp.) in Tijuana Estuary suggest microbes respond to both species- and site-specific influences. Structurally similar invaders (the mangrove and salt cedar) produced different effects on activity and diversity of nitrogen fixers, reflecting distinct environmental contexts. Despite relative robustness of microbial community composition, subtle differences in total diversity or activity of nitrogen fixers reveal that microbes are not immune to impacts of biological invasions, and that functional redundancy of microbial diversity is limited, with significant consequences for functional dynamics of wetlands.     

Bacterial diversity in the rhizosphere of maize and the surrounding carbonate‐rich bulk soil

Maize represents one of the main cultivar for food and energy and crop yields are influenced by soil physicochemical and climatic conditions. To study how maize plants influence soil microbes we have examined microbial communities that colonize maize plants grown in carbonate‐rich soil (pH 8.5) using culture‐independent, PCR‐based methods. We observed a low proportion of unclassified bacteria in this soil whether it was planted or unplanted. Our results indicate that a higher complexity of the bacterial community is present in bulk soil with microbes from nine phyla, while in the rhizosphere microbes from only six phyla were found. The predominant microbes in bulk soil were bacteria of the phyla Acidobacteria, Bacteroidetes and Proteobacteria, while Gammaproteobacteria of the genera Pseudomonas and Lysobacter were the predominant in the rhizosphere. As Gammaproteobacteria respond chemotactically to exudates and are efficient in the utilization of plants exudate products, microbial communities associated to the rhizosphere seem to be plant‐driven. It should be noted that Gammaproteobacteria made available inorganic nutrients to the plants favouring plant growth and then the benefit of the interaction is common.     

NON-STEADY STATE DYNAMICS OF ALGAL POPULATION GROWTH: EXPERIMENTS WITH TWO CHLOROPHYTES1

The relations among dissolved phosphorus, cell quota of phosphorus, and population growth rate were determined for two Chlorophytes, Chlorella sp. and Scenedesmus quadricauda var. longispina (Chod.) G. M. Smith, in two types of non-steady state continuous culture. One of these types had relatively smooth transitions between growth under different degrees of phosphorus limitation. Under these conditions, two equations often applied to growth kinetics in steady state cultures were found to apply to non-steady state growth. Monad's equation described the relation between dissolved phosphorus concentration and population growth rate, and Droop's equation described the relation between cell quota and population growth rate. The second type of culture received phosphorus only as periodic pulses, leading to sharp changes in dissolved phosphorus, cell quota, and growth rate. A simulation model based on Droop's equation described much of the observed dynamics of cell numbers and quotas in these cultures. Droop's equation could not be convincingly fitted directly to the data, however, due to its incorrect prediction of an immediate growth response to phosphorus pulses. A third relation, predicting that saturated rates of phosphorus uptake would depend on the recent nutrient history of the cells as reflected by the cell quota, was not supported.     

Species-specific effects of live roots and shoot litter on soil decomposer abundances do not forecast plant litter-nitrogen uptake

Plant species produce litter of varying quality and differ in the quality and quantity of compounds they release from live roots, which both can induce different decomposer growth in the soil. To test whether differences in decomposer growth can forecast the amount of N species acquire from plant litter, as suggested by theory, we grew individuals of three grassland plants—Holcus lanatus, Plantago lanceolata and Lotus corniculatus—in soils into which ¹⁵N-labelled litter of either Holcus, Plantago or Lotus was added. We measured the effects of live roots and litter of each species on soil microbes and their protozoan and nematode feeders, and to link decomposer growth and plant nutrient uptake, we measured the amount of N taken up by plants from the added litter. We hypothesised that those species that induce the highest growth of microbes, and especially that of microbial feeders, will also take up the highest amount of N from the litter. We found, however, that although numbers of bacterial-feeding Protozoa and nematodes were on average lower after addition of Holcus than Plantago or Lotus litter, N uptake was higher from Holcus litter. Further, although the effects on Protozoa and bacterial- and fungal-feeding nematodes did not differ between the live plants, litter-N uptake differed, with Holcus being the most efficient compared to Plantago and Lotus. Hence, although microbes and their feeders unquestionably control N mineralization in the soil, and their growth differs among plant species, these differences cannot predict differences in litter-N uptake among plant species. A likely reason is that for nutrient uptake, other species-specific plant traits, such as litter chemistry, root proliferation ability and competitiveness for soil N, override in significance the species-specific ability of plants to induce decomposer growth.