Microbial Biomass Content Research Articles

Development of mathematical model and experimental Validation for batch bio-drying of municipal solid waste: Mass balances

Bio-drying of solid waste is a complex process that involves anoxic hydrolysis, aerobic oxidation, evaporation, absorption, and condensation. To understand the interaction between different variables (concentration of volatile matter, moisture, microbial biomass, and temperature) and to predict the system performance, a powerful tool is necessary for improved drying rates. Hence, a mathematical model of mass balances of the batch bio-drying of municipal solid waste (MSW), associated with rate equations of evaporation of moisture from the waste matrix and absorption of leachate on absorbents is developed which is the novelty of the present study. This model integrates 18 first-order differential equations based on process kinetics for mass balances of components in the solid, liquid, and gas phases, comprising the specific degradability of food, paper, and inert material of the MSW. The proposed model is simulated using MATLAB ode15s solver and validated with experimental data from the pilot-scale bio-drying reactor. The model predicted values are in good agreement with experimental values with a deviation of ±10%.

Imbalanced nitrogen–phosphorus input alters soil organic carbon storage and mineralisation in a salt marsh

A large imbalance in soil nitrogen (N) and phosphorus (P) inputs induced by anthropogenic activities is anticipated to profoundly influence soil carbon (C) budgets in salt marshes. In this study, we hypothesized that imbalances in the nitrogen–phosphorus (N–P) input would result in the nonlinear response of soil organic carbon (SOC) content, fractions and mineralization to the N–P input ratio. We applied three N–P input ratios (low (5:1), medium (15:1), high (45:1)) in a salt marsh of the Yellow River Delta (YRD) for four years (in which N added increased from 8.67 to 26.01 g N m−2 y−1 and P added decreased from 1.73 to 0.58 g P m−2 y−1) and quantified their impacts on SOC fractions and SOC mineralisation. The control treatment did not receive fertilization. The results showed that the N and P input led to overall increases in the availability of soil nutrients (i.e., inorganic N (IN) and available P (AP)), stimulation of plant biomass and changes of microbial community structure (i.e., γ- and δ-Proteobacteria and Acidobacteria). N and P input increased soil dissolved organic carbon (DOC) and decreased aromatic DOC components through improving N availability and stimulating plant growth. Notably, though, there may be a threshold N–P input ratio between 15:1 and 45:1 that, once crossed, triggers the loss of SOC. Appropriate increase in N availability induced by low and medium N-P input ratios would stimulate the SOC mineralization. However, excessive N-P input ratio would reduce SOC mineralization. Path analysis indicated that N–P input ratios dominantly regulate SOC mineralisation by changing soil DOC and microbial biomass (MBC)contents and microbial community structure. Thus, we speculate that the continuous increase in N input causes a growing N–P imbalance that reduces SOC stocks, despite a reduction in SOC mineralisation.

Patterns and drivers of global gross nitrogen mineralization in soils.

Soil gross nitrogen (N) mineralization (GNM), a key microbial process in the global N cycle, is mainly controlled by climate and soil properties. This study provides for the first time a comprehensive analysis of the role of soil physicochemical properties and climate and their interactions with soil microbial biomass (MB) in controlling GNM globally. Through a meta-analysis of 970 observations from 337 published papers from various ecosystems, we found that GNM was positively correlated with MB, total carbon, total N and precipitation, and negatively correlated with bulk density (BD) and soil pH. Our multivariate analysis and structural equation modeling revealed that GNM is driven by MB and dominantly influenced by BD and precipitation. The higher total N accelerates GNM via increasing MB. The decrease in BD stimulates GNM via increasing total N and MB, whereas higher precipitation stimulates GNM via increasing total N. Moreover, the GNM varies with ecosystem type, being greater in forests and grasslands with high total carbon and MB contents and low BD and pH compared to croplands. The highest GNM was observed in tropical wet soils that receive high precipitation, which increases the supply of soil substrate (total N) to microbes. Our findings suggest that anthropogenic activities that affect soil microbial population size, BD, soil substrate availability, or soil pH may interact with changes in precipitation regime and land use to influence GNM, which may ultimately affect ecosystem productivity and N loss to the environment.

Decoding the link between bacterial diversity and enzymatic activities of soil from Cymbopogon flexuosus growing dryland

The rhizospheric microbial communities and enzymes involved in nutrient mineralization play a vital role in plant and soil health particularly under abiotic stress conditions. Hence, the investigation has been made on the activities of enzymes involved in carbon, nitrogen, phosphorus, and sulfur cycles and metabolic potentials microbial communities of rhizospheric soil of drought-affected areas planted with Cymbopogon flexuosus (lemongrass). The slips of C. flexuosus were planted in the six drought-affected areas of India along with one irrigated region as control following randomized block design. The pH of soils varied from 5.7 to 9.4, whereas, microbial biomass content ranged from 80 μg g−1 (sodic soil) to 813 μg g−1 (black humus granitic soil) μg g−1. Enhanced enzymatic activities were found after two years at all the experimental sites planted with C. flexuosus. In comparison with the drought-affected site, higher microbial diversity (highest Shannon Index) was observed at the irrigated site. The results showed that soil microbiota was dominated by Proteobacteria followed by Firmicutes and Acidobacteria, whereby, Methylobacterium, Escherichia-Shigella, Sphingomonas, Microbacterium, and Brevibacillus were the dominant genera in the study zone. Acidic soils (pH: 5.7) were observed to have a relatively higher abundance of Acidobacteria, while, alkaline soils (pH: 9.4) demonstrated a higher relative abundance of Proteobacteria. The dominance of Escherichia-Shigella and Sphingomonas was observed in all drought sites and these microbes are involved in carbon metabolism. The relative abundance of Methylobacterium was higher in soils having higher microbial biomass and carbon content. Results revealed that despite the homogenizing effect of the lemongrass cover, the soil pH accounted for an important fraction of the variance of microbial composition and enzymatic activity.

Distinct storage mechanisms of soil organic carbon in coniferous forest and evergreen broadleaf forest in tropical China

The impact of human activities on soil carbon (C) storage in tropical forests has aroused wide concern during the past decades, because these ecosystems play a key role in ameliorating global climate change. However, there remain uncertainties about how land-use history alters soil organic carbon (SOC) stability and storage in different forests. In this study, we measured the C content and mass distributions of soil aggregates, density fractions, mineral-bound C and microbial biomass C in the organic horizon, 0-10 cm and 10-20 cm soil layers in coniferous forest and evergreen broadleaf forest at Dinghushan Biosphere Reserve in tropical China. The broadleaf forest had larger SOC stocks than the coniferous forest, but the proportion of SOC stored in different density fractions at 0-10 cm soils was similar between forest types, while a greater proportion of SOC was stored in microaggregates in the coniferous forest. Most of the SOC was held as light fraction C in the organic horizon in the coniferous forest, whereas the concentrations of mineral-bound C were higher in the broadleaf forest. These findings indicate clear differences in the protection of SOC between broadleaf and coniferous forests growing on the same soil type. We propose that historic conversion of broadleaf forest to coniferous forest has reduced soil C sequestration capacity by altering the diversity and quality of plant inputs to the soil, which in turn affected macroaggregate formation, soil chemical properties and microbial biomass. Our results thus demonstrate that changes in forest tree species composition could have long-lasting effects on soil structure and carbon storage, providing crucial evidence for policy decisions on forest carbon sink management.

Salinization depresses soil enzyme activity in metal-polluted soils through increases in metal mobilization and decreases in microbial biomass.

Salinity may increase metal mobilization with a potentially significant consequence for soil enzymatic activity and nutrient cycling. The goal of this study was to investigate changes in soil enzyme activity in response to salinization of a clay loam soil artificially polluted with cadmium (Cd) and lead (Pb) during a 120-day incubation experiment. Soil samples were polluted with Cd (10 mg Cd kg-1), Pb (150 mg Pb kg-1), and a combination of Cd and Pb, then preincubated for aging and eventually salinized with three levels of NaCl solution (control, low and high). NaCl salinity consistently increased the mobilization of Cd (12-22%) and Pb (5-16%) with greater increases at high (17-22% for Cd, 9-16% for Pb) than low (12% for Cd, 5-7% for Pb) salinity levels. While the increased Cd mobilization was greater in co-polluted (22%) than Cd-polluted (17%) soils, the increase of Pb mobilization was lower in co-polluted (9%) than Pb-polluted (16%) soils at high salinity level. The salinity-induced increases in metal mobilization significantly depressed soil microbial respiration (up to 43%), microbial biomass content (up to 63%), and enzymatic activities (up to 87%). The multivariate analysis further supported that the increased soil electrical conductivity, Cd mobilization, and pH after salinization were the most important factors governing microbial activity and biomass in metal-polluted soils. Results showed that changes in microbial biomass and mobile metal pool with increasing salinity had a major effect on enzyme activities, particularly under the combined metals. This study indicated that the secondary salinization of metal-polluted soils would impose an additional stress on enzymatic activities as biochemical indicators of soil quality, and therefore should be avoided for the maintenance of soil microbial and biochemical functions, especially in arid regions. In metal-polluted soils, the observed responses of extracellular and intracellular enzymes to salinity can be used to advance our knowledge of microbial processes when modeling the carbon and nutrient cycling.

Soil N2O flux and nitrification and denitrification gene responses to feed-induced differences in the composition of dairy cow faeces

Faeces from cows with different milk yield and non-lactating cows were applied to soil to investigate whether soil N2O efflux is related to feeding-induced differences in faecal microbiome and abundances of nitrification and denitrification genes. Fungal 18S-rRNA gene abundance was the highest in the faeces of the non-lactating group. The 18S-rRNA/ergosterol ratio showed a strong positive correlation with the 18S-rRNA/fungal glucosamine ratio. The milk-yield groups did not affect the gene abundances of bacterial 16S rRNA, AOB amoA, nirS and nosZ clade I, or the 16S-rRNA/muramic acid (MurN) ratio. In contrast, nirK gene abundance was generally the lowest in the high-yield group. The 16S-rRNA/MurN ratio showed a strong positive correlation with the 16S-rRNA/bacterial PLFA ratio. Cow faeces application to soil increased microbial biomass and ergosterol contents as well as the gene abundances of 18S-rRNA and nosZ clade I, compared with the non-amended control soil. Cumulative ΣCO2 efflux was roughly twice as high as the control, without differences between the faeces treatments. Cumulative ΣN2O efflux showed a 16-fold increase after applying high-yield cow faeces to soil, which was above the sevenfold increase in the non-lactating faeces treatment. The ΣN2O efflux from soil was positively related to faecal MurN and total PLFA concentration but also to soil nirK at day 14. The comparison of genome markers with cell wall (glucosamine) and cell membrane components (ergosterol) showed that the fungal cells were much larger in energy-rich faeces than in C-limited soil. A cow diet reduced in protein decreased the ΣN2O efflux from faeces amended soil.

Rates of soil respiration components in response to inorganic and organic fertilizers in an intensively-managed Moso bamboo forest

Fertilization is a common practice to increase forest productivity; however, the responses of soil respiration (RS) components to the application of inorganic and organic fertilizers and the associated mechanisms are not clear in subtropical forest ecosystems. In this field trial conducted within an intensively-managed Moso bamboo (Phyllostachys edulis) forest, we aimed to compare the effects of inorganic and organic fertilizers, and their combination on seasonal variations in RS components, i.e., heterotrophic (RH) and autotrophic (RA) respiration, and to establish the relations of RS components with soil properties. Fertilizer additions increased RH (P < 0.05), with the increase being greater with organic than with inorganic fertilizer. Fertilization also increased RA, but the effect was greater with inorganic fertilizer. Furthermore, fertilizer additions increased (P < 0.05) the concentrations of water-soluble organic C (WSOC) and microbial biomass C, invertase and β-glucosidase activities, as well as the biomass and N concentration of fine roots. Irrespective of fertilizer treatment, strong seasonal patterns were observed in both RS and RH, and an exponential relation (P < 0.01) was found between RS components (RH and RA) and soil temperature. Additionally, the Q10 for RH was higher (P < 0.05) in the inorganic than the organic fertilizer treatment. Although RS and RH showed no correlation with soil moisture content in any treatment, each of them was positively correlated with WSOC concentration and activities of invertase and β-glucosidase (P < 0.05). In the fertilized treatments, RA was positively related to β-glucosidase activities (P < 0.05) but not to the concentrations of WSOC or microbial biomass C. In conclusion, soil RA and RH in the subtropical Moso bamboo forest responded differently to the application of inorganic and organic fertilizers, indicating that separation of total RS into soil RH and RA is critically necessary to predict RS in subtropical forests under different fertilizer regimes.

Mineral weathering and lessivage affect microbial community and enzyme activity in mountain soils

The aim of the study was to assess if pedogenic processes such as mineral weathering and lessivage, other than organic matter accumulation, can affect soil microbial population and enzyme activities. This study examines six soil profiles located in a karst region of the North-Eastern Italian Alps and characterized by a vertical textural differentiation due to lessivage. For each soil, four pedological layers were recognized according to the dominant soil forming process: i) the top soil (Tp layer), formed by A and AB horizons, characterized by organic matter accumulation; ii) the subsurface eluviated layer (Elu layer), comprising AE and EB horizons; iii) the layer dominated by the in-situ mineral weathering (Wh layer), made by Bw horizons; iv) the deepest layer (Ls), subjected to clay illuviation and comprised by Bt horizons. In the upper layers (Tp and Elu), because of the low pH, weathering also occurred, as indicated by the presence of disordered smectite and by the high values of pedogenic Fe oxi-hydroxides to pseudo-total Fe ratio.The microbial biomass content and structure, and the enzyme activities significantly differed in the four pedological layers. The amount of microbial biomass was, as expected, most abundant in the Tp layer, where bacteria and actinomycetes abounded. Conversely, in Elu and Wh we observed a fungal-to-bacterial biomass ratio significantly higher than in Tp and Ls; in Elu, also the gram (+)/gram (−) ratio was the highest. In the upper layer, the interaction between enzymes and minerals like disordered smectite and pedogenic Fe-oxides appeared as responsible for the inhibition of the total enzyme activity per unit of organic C, and of the lipase activity. In Ls layer, where clay illuviation and high organo-minerals interaction occurred, the potential hydrolysis of organic matter was low, as revealed by the SEI/TOC ratio, the reduced lipase activity, and the inhibited activity of α-fucosidase and α-mannosidase. Even if the activity of most enzymes depends on the substrate availability, which decreases with soil depth, those involved in lipid degradation displayed the maximum activities in Elu and Wh layers, where a relative increase of the fungal population was observed. In conclusion, our findings showed that the soil functionality, expressed by the microbial community structure and enzymes activity, can vary according to organic matter–mineral interaction following the weathering and lessivage gradients along the soil profiles.

Glomalin and microbial activity affected by cover crops and nitrogen management in sandy soil with cotton cultivation

In most sandy soils with low organic matter content, nitrogen fertilizers are often applied to achieve desired crop yields, which may negatively affect microbial activity in the soil. We hypothesize that cover crops can mitigate the negative effects and balance the system via increased supply of carbon. The objective, therefore, was to evaluate the effect of cover crops (fallow, one grass species, two grass species, one grass species and legumes, and a mixture of three cover crops), nitrogen doses (70, 100, and 130 kg ha−1), and nitrogen sources (conventional urea and controlled-release urea) on soil microbial activity, glomalin content, and relationship of these parameters of soil quality with cotton fiber yield. Grass systems increased the soil dry matter supply. The carbon of the microbial biomass was 117% higher in the mixture and soil respiration and the metabolic quotient was 128% and 372% higher in the mixture compared to fallow. Fluorescein diacetate hydrolysis was (averaging two-year data) 60% higher in mixed cover crop systems than with fallow. Carbon from microbial biomass (grass + legume system) and glomalin content (all systems) were lower with the highest dose of N. Controlled-release urea can mitigate the negative effects of high nitrogen doses in environments with low dry matter input (as noted for enzyme β-glucosidase). Microbial biomass carbon, β-glucosidase, and qCO2 were the principal indicators of soil quality and were highly correlated with cotton yield. We recommend the use of a diversity of cover crops, moderate nitrogen doses, and controlled-release urea activate microbial and glomalin activity in sandy soil.

Diversity and functional structure of soil animal communities suggest soil animal food webs to be buffered against changes in forest land use

Forest soil and litter is inhabited by a diverse community of animals, which directly and indirectly rely on dead organic matter as habitat and food resource. However, community composition may be driven by biotic or abiotic forces, and these vary with changes in habitat structure and resource supply associated with forest land use. To evaluate these changes, we compiled comprehensive data on the species composition of soil animal communities and environmental factors in forest types varying in land-use intensity in each of three regions in Germany, i.e., coniferous, young managed, old managed, and unmanaged beech forests. Coniferous forests featured high amounts of leaf litter and low microbial biomass concentrations contrasting in particular unmanaged beech forests. However, soil animal diversity and functional community composition differed little between forest types, indicating resilience against disturbance and forest land use. Structural equation modelling suggested that despite a significant influence of forest management on resource abundance and quality, the biomass of most soil fauna functional groups was not directly affected by forest management or resource abundance/quality, potentially because microorganisms hamper the propagation of nutrients to higher trophic levels. Instead, detritivore biomass depended heavily on soil pH. Macrofauna decomposers thrived at high pH, whereas mesofauna decomposers benefitted from low soil pH, but also from low biomass of macrofauna decomposers, potentially due to habitat modification by macrofauna decomposers. The strong influence of soil pH shows that decomposer communities are structured predominantly by regional abiotic factors exceeding the role of local biotic factors such as forest type.

Microbial activity in alpine soils under climate change

Soil enzymatic activity was assessed in the Stelvio Pass area (Italian Central Alps) aiming to define the possible effects of climate change on microbial functioning. Two sites at two different elevations were chosen, a subalpine (2239 m) and an alpine belt (2604–2624 m), with mean annual air temperature differing by almost 3 °C, coherent with the worst future warming scenario (RCP 8.5) by 2100. The lower altitude site may represent a proxy of the potential future situation at higher altitude after the upward shift of subalpine vegetation due to climate change. Additionally, hexagonal open top chambers (OTCs) were installed at the upper site, to passively increase by about 2 °C the summer inner temperature to simulate short term effects of warming before the vegetation shift takes place. Soil physicochemical properties and the bacterial and fungal abundances of the above samples were also considered. The subalpine soils showed a higher microbial activity, especially for hydrolytic enzymes, higher carbon, ammonium and hydrogen (p < 0.001) contents, and a slightly higher PO4 content (p < 0.05) than alpine soils. Bacterial abundance was higher than fungal abundance, both for alpine and subalpine soils. On the other hand, the short term effect, which increased the mean soil temperature during the peak of the growing season in the OTC, showed to induce scarcely significant differences for edaphic parameters and microbial biomass content among the warmed and control plots. Using the manipulative warming experiments, we demonstrated that warming is able to change the enzyme activity starting from colder and higher altitude sites, known to be more vulnerable to the rising temperatures associated with climate change. Although five-years of experimental warming does not allow us to make bold conclusions, it appeared that warming-induced upwards vegetation shift might induce more substantial changes in enzymatic activities than the short-term effects, in the present vegetation context.

Biochar and Cow Manure on Chemical and Microbial Community in Regosol with Bean

The effects of coffee biochar residue combined with cow manure fertilizer on soil chemical attributes, microbial biomass, and structure and abundance of the soil microbial community are not fully understood. Thus, the objective of this study was to evaluate the effect of coffee biochar combined with cow manure on chemical and microbial attributes in soil cultivated with bean (Phaseolus vulgaris). We hypothesized that biochar from coffee residues drives the bacteria, fungi, and diazotrophic communities in a sandy soil and increases the abundance of these microorganism groups, raising soil basal respiration and microbial biomass. The experiment was carried out in a completely randomized design and was distributed in a factorial scheme (2 × 3 + 2) including two types of biochar (coffee ground-CG and coffee husk-CH) at three dosages (4, 8, and 16 t ha−1), and two control groups (S = native soil without treatment (−control) and E = fertilization with cow manure at dosage of 15 m3 ha−1 (+control)). The experiments were conducted with four repetitions. All treatments received the same dosage of cow manure applied in sandy soil and bean seeds were grown in pots. Soil samples were collected after 45 days to evaluate chemical attributes, total organic carbon (TOC), microbial biomass (C, N, and P), soil basal respiration, structure and abundance of total bacterial and fungal community (16S rRNA, 18S rRNA) and diazotrophs (nifH) in the soil by DGGE (denaturing gradient gel electrophoresis) and qPCR (real-time quantitative PCR), respectively. The results showed that TOC increased 9 and 11.5% with highest dosage of CG and CH biochar, respectively; thus, CG at 4 t ha−1 increased the C:N ratio in soil (4.7 times). The addition of biochar combined with cow manure increased soil basal respiration in CG at 16 t ha−1. The combined application of CH at 16 t ha−1 and cow manure increased the P content (2.37 times) and K+ (5.6 times). The highest increase in C from microbial biomass was found in CG at 16 t ha−1 and the addition of biochar and cow manure did not affect the P content in microbial biomass; nevertheless, biochar increased the nifH gene abundance by 8.23% at 16 t ha−1. Biochar addition influenced the structure of soil microbial communities, presenting distinct and well-differentiated communities in the multivariate analysis, according to the dosage and type of biochar. The group formed by different CG dosages showed a higher number of 16S genes, and greater amounts of Nmic, nifH, soil basal respiration, metabolic quotient, K, and Na. The major conclusion of this study was that coffee biochar, used in combination with cow manure, significantly improves the chemical and microbiological attributes of sandy soil cultivated with bean.

Wetland reclamation homogenizes microbial properties along soil profiles

Wetlands store approximately one-third of soil carbon (C) in terrestrial ecosystems, and the loss of C in wetlands has been accelerated by reclamation. However, how wetland reclamation affects microbial properties along soil profiles remains unclear. In this study, we sampled 100 cm soil cores from a wetland and an adjacent cropland that has been cultivated for 23 years to evaluate the impacts of land conversion on soil microbial community structure and soil element concentrations in the Sanjiang Plain, Northeastern China. The C and nitrogen (N) concentrations in microbial biomass declined exponentially with depth in both the wetland and cropland with different magnitudes. Continuous cultivation for 23 years tended to homogenized C, N, phosphorus (P), and sulfur (S) contents in soils and microbial biomass along the soil profile. Compared with the wetland, C and N in cropland soils were lower, and microbial biomass C, N, P and S were lower in surface soils (0–30 cm), while higher in both middle soils (40–70 cm) and deep soils (70–100 cm). Cultivation narrowed the C:N:P:S stoichiometry in soils and microbial biomass, with large changes in surface soils and minor changes in deep soils. The Bray-Curtis dissimilarity test confirmed the large changes in surface soils while minor changes in deep soils. After 23-years of cultivation the abundances of fungi and bacteria were significantly reduced by approximately 90% and 78% in surface soils, but the bacterial abundance was enhanced by approximately 2–3 times in middle soils, leading to a decreasing fungi:bacteria ratio along soil profile in cropland. Soil TC and pH were the predominant factors controlling the microbial composition in wetland. The homogenizing impact of wetland reclamation on microbial properties along soil profiles suggests the different responses of microbial and soil elements to human activities, indicating a critical need of differentiating microbes from soils when examining soil elements under a changing environment.

The Influence of Forest Management and Changed Hydrology on Soil Biochemical Properties in a Central-European Floodplain Forest

Anthropogenic modifications to water regimes are one of the main factors threatening the stability and existence of floodplain forests. This study presents an analysis of topsoil biogeochemistry within three floodplain forest stands with different levels of human alteration. Decreasing contents of soil organic carbon (OC) and microbial biomass were observed along the gradient from natural to plantation forest. High annual variations were observed in soil N contents and in microbial biomass, while comparable spatial variations were observed within the natural forest. High ground-water levels resulted in increased accumulation of available Na+ and SO42− in the natural forest soil, yet the concentrations of ions were at sub-saline levels. The increasing contents of available Mn, SO42− or Cl− had mostly positive effects on soil microbial activity across the sites, though the results indicate the existence of a certain ecological limit for soil microorganisms. Reintroduction of surface-water flooding should be considered in future forest and water management to promote the dilution of ions accumulated in soils and natural deposition of sediments rich in organic matter (OM) at the sites.

Application of In-Situ and Soft-Sensors for Estimation of Recombinant P. pastoris GS115 Biomass Concentration: A Case Analysis of HBcAg (Mut+) and HBsAg (MutS) Production Processes under Varying Conditions.

Microbial biomass concentration is a key bioprocess parameter, estimated using various labor, operator and process cross-sensitive techniques, analyzed in a broad context and therefore the subject of correct interpretation. In this paper, the authors present the results of P. pastoris cell density estimation based on off-line (optical density, wet/dry cell weight concentration), in-situ (turbidity, permittivity), and soft-sensor (off-gas O2/CO2, alkali consumption) techniques. Cultivations were performed in a 5 L oxygen-enriched stirred tank bioreactor. The experimental plan determined varying aeration rates/levels, glycerol or methanol substrates, residual methanol levels, and temperature. In total, results from 13 up to 150 g (dry cell weight)/L cultivation runs were analyzed. Linear and exponential correlation models were identified for the turbidity sensor signal and dry cell weight concentration (DCW). Evaluated linear correlation between permittivity and DCW in the glycerol consumption phase (<60 g/L) and medium (for Mut+ strain) to significant (for MutS strain) linearity decline for methanol consumption phase. DCW and permittivity-based biomass estimates used for soft-sensor parameters identification. Dataset consisting from 4 Mut+ strain cultivation experiments used for estimation quality (expressed in NRMSE) comparison for turbidity-based (8%), permittivity-based (11%), O2 uptake-based (10%), CO2 production-based (13%), and alkali consumption-based (8%) biomass estimates. Additionally, the authors present a novel solution (algorithm) for uncommon in-situ turbidity and permittivity sensor signal shift (caused by the intensive stirrer rate change and antifoam agent addition) on-line identification and minimization. The sensor signal filtering method leads to about 5-fold and 2-fold minimized biomass estimate drifts for turbidity- and permittivity-based biomass estimates, respectively.

三峡库区马尾松人工林土壤酶活性和微生物生物量对氮添加的季节性响应

以三峡库区马尾松人工林为对象，分析土壤微生物生物量、酶活性和养分含量对氮添加的初期响应规律，为预测该地区在大气氮沉降持续增加的背景下森林土壤的季节动态提供参考。结果表明：氮添加初期，中氮水平（60 kg hm^-2 a^-1）的氮添加处理使得各季节土壤β-1-4葡萄糖苷酶、N-乙酰氨基葡萄糖苷酶、酸性磷酸酶、多酚氧化酶、过氧化物酶活性均增加，高氮（90 kg hm^-2 a^-1）水平的添加处理增加了土壤有机碳、全氮和微生物生物量碳、氮、磷的含量和酸性磷酸酶及多酚氧化酶活性，降低了土壤pH值、全磷含量和β-1-4葡萄糖苷酶及N-乙酰氨基葡萄糖苷酶活性。土壤酶活性和微生物生物量存在明显的季节变化，秋季水解酶活性和微生物生物量碳、磷含量显著高于春夏两季，而氧化酶活性和微生物生物量氮含量则是春夏季较高。土壤酶活性与季节、土壤含水量、养分含量及微生物生物量碳氮磷含量存在显著的相关性，酶活性变化是多因子综合作用的结果，冗余分析表明土壤含水量、微生物生物量碳、氮、磷和全氮是驱动土壤酶活性的主要环境因子。氮沉降的持续增加会加速当地马尾松人工林土壤腐殖质的形成，增加有机碳的积累，导致土壤酸化，并产生磷限制。;Anthropogenic nitrogen (N) enrichment is a concern worldwide, as it affects almost every aspect of ecosystem function and composition. Many nitrogen (N) addition experiments have been well documented to decrease plant biodiversity across various terrestrial ecosystems. However, such generalizations about the impacts of nitrogen addition on soil enzyme activities and microbial biomass are lacking, especially in the Three Gorges Reservoir area, as a key sensitive ecological barrier of the middle and lower reaches of the Yangtze River. Therefore, we conducted nitrogen addition experiments in February 2019 in Pinus massoniana plantation in the Three Gorges Reservoir area of subtropical China. Soil samples were collected from three control plots (N_CK), three low-nitrogen addition plots (N_low), three middle-nitrogen addition plots (N_middle), three high-nitrogen addition plots (N_high) in May, August and November, 2019. We studied the soil enzyme activities, microbial biomass and nutrient content in response to nitrogen addition, which provided a theoretical basis for predicting soil seasonal dynamics in an increasing atmospheric nitrogen deposition background in the Three Gorges Reservoir area. The results show that, in the early stage of nitrogen addition, the medium nitrogen (60 kg hm^-2 a^-1) treatment increased the activities of β-1-4 glucosidase (BG), N-acetylglucosaminosidase (NAG), acid phosphatase (AP), polyphenol oxidase (PPO) and peroxidase (POD); the high nitrogen (90 kg hm^-2 a^-1) treatment increased the contents of soil organic carbon, total nitrogen, microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP), and the activities of AP, PPO, while decreased the soil pH, total phosphorus content and the activities of BG and NAG. There were significantly seasonal differences between soil enzyme activities and microbial biomass. Hydrolase activities, MBC and MBP contents in autumn were significantly higher than those in spring and summer, while oxidase activities and MBN contents were higher in spring and summer. Soil enzyme activities were significantly correlated with season, soil moisture content, soil nutrient, MBC, MBN, MBP. The change of soil enzyme activities is due to the comprehensive action of multiple factors. Redundancy analysis (RDA) showed that soil moisture content, MBC, MBN, MBP and total N greatly accounted for the variation in soil enzyme activities. The increasing nitrogen deposition will accelerate the formation of soil humus, increase organic carbon accumulation, lead to soil acidification, and produce phosphorus limitation in the local Pinus massoniana plantation.

川西亚高山不同林龄粗枝云杉人工林土壤微生物生物量及酶活性

林分结构随林龄增加发生变化，致使土壤微环境变化，进而对土壤微生物生物量和酶活性产生直接或间接影响。以川西亚高山米亚罗林区25、40、50、60年生粗枝云杉（Picea asperata）人工林表层（0-20 cm）土壤为研究对象，分析不同林龄表层土壤微生物生物量碳（MBC）、氮（MBN）和酶活性的变化以及驱动土壤酶活性变化的主要环境因子，为人工林生态系统恢复效果评价及经营管理提供科学依据。结果表明：随着林龄的增加，MBC和MBN先上升后下降，在40年生达到最大；β-葡萄糖苷酶（βG）、β-N-乙酰氨基葡萄糖苷酶（NAG）和多酚氧化酶（PHO）活性与微生物生物量碳氮变化趋势相似，其中βG、NAG活性在50年生人工林达到最大，PHO活性于40年生人工林达到最大；50年生人工林过氧化物酶（PEO）活性显著低于其他林龄人工林；纤维素水解酶（CBH）活性随林龄增加而显著增加。冗余分析显示，碱解氮（AN）、pH和可溶性有机碳（DOC）是影响土壤酶活性变化的主导因子，分别解释了土壤酶活性变异的65.4%、9.7%和7.6%。综上可知，林龄对粗枝云杉人工林表层土壤微生物生物量和酶活性变化产生了显著影响，60年粗枝云杉林地力呈现衰退态势。为此，可对近60年的粗枝云杉人工林增加碳氮元素（尤其是氮素）的输入，以提升土壤质量和酶活性。;Stand structure changes with forest age caused the variation of soil microenvironment, which can directly or indirectly affect soil microbial biomass carbon and nitrogen, and soil enzyme activities. To better understand the change characteristics of soil microbial biomass contents and enzyme activities along an age sequence of spruce plantations, this study was conducted to evaluate the theoretical basis for restoration and effective management of subalpine plantations. In this study, Picea asperata plantations of various ages (25, 40, 50, and 60 years old) were selected in Miyaluo forest area of western Sichuan, China. The soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), available nitrogen (AN) and pH, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and light fraction organic carbon (LFOC), soil enzyme activity index(β-glucosidase, βG; Cellulose hydrolysis, CBH; β-N-acetylglucosaminidase, NAG; Phenol oxidase, PHO and Peroxidase, PEO) in 0-20 cm soil was measured,respectively. The results showed that the MBC and MBN increased up to 40 years, and then decreased with the increase of age. There was a similar trend in changes of the activities of βG, NAG and PHO, while βG and NAG were highest at 50 years, and PHO was highest at 40 years. PEO activity of 50 years was significantly lower than other plantations. The activity of CBH increased with the increasing age of Picea asperata plantation stands. Redundancy analysis (RDA) indicated that AN, pH and DOC were main influence factors of soil enzyme activities in the top-layer soil, accounted for 65.4%, 9.7% and 7.6% of total variation of soil enzyme activities, respectively. Overall, our results suggested that the growth of Picea asperata had a significant effect on soil microbial biomass and enzyme activities. The soil fertility in 60 years of Picea asperata plantation was the lowest in all Picea asperata plantations. Therefore, we can increase carbon and nitrogen elements (especially nitrogen) devotion to improve soil quality and enzyme activities in Picea asperata plantations nearly 60 years.

川西亚高山天然次生林不同演替阶段土壤-微生物生物量及其化学计量特征

开展不同恢复演替阶段天然次生林土壤-微生物生物量及其化学计量特征关系的研究，可为有效和持续管理川西亚高山次生林提供科学依据。以川西亚高山米亚罗林区20世纪60、70、80年代3种采伐迹地经自然恢复演替形成的次生林（SF60、SF70和SF80）和岷江冷杉（Abies faxoniana）原始林（PF）为研究对象，探讨了表层（0-20 cm）土壤有机碳（C_soil）、全氮（N_soil）、全磷（P_soil）含量及微生物生物量碳（C_mic）、氮（N_mic）、磷（P_mic）含量随自然恢复演替的变化特征，分析了它们的化学计量比与微生物熵（qMB）之间的相互关系。结果表明：（1）随着恢复演替年限的增加，C_soil和N_mic含量显著降低，N_soil和P_soil及C_mic和P_mic含量呈现先升后降的显著变化趋势，且3种次生林的表层土壤碳、氮、磷及其微生物生物量的含量均低于PF。（2）次生林恢复年限对土壤微生物熵C（qMBC）和P（qMBP）没有显著影响，但对土壤微生物熵N（qMBN）存在显著影响。（3）土壤-微生物化学计量不平衡性C_imb：N_imb随自然恢复演替进程呈先降后升的显著变化趋势，C_imb：P_imb呈不显著的降低趋势，N_imb：P_imb呈现显著降低趋势。冗余分析显示，N_imb：P_imb和C_mic：N_mic是影响qMB变化的主导因子，其中N_imb：P_imb解释了qMB变化的62.6%，说明土壤氮磷及其活性组分（N_mic和P_mic）含量变化可能会影响到qMB变化。综上可知，次生林近60 年的自然恢复演替引起了土壤碳氮磷含量的显著变化；天然次生林土壤-微生物生物量碳氮磷化学计量比主要受到氮磷的协同影响，且SF60土壤质量状况较差，为此，对SF60林分可适当增加氮素供给以促进其林木生长，进而提升土壤质量。;The change characteristics of soil and soil microbial biomass contents of the natural secondary forests could significantly affect the soil organic carbon (C_soil), total nitrogen (N_soil), total phosphorus (P_soil), soil microbial biomass carbon (C_mic), microbial biomass nitrogen (N_mic), microbial biomass phosphorus (P_mic) contents, and their stoichiometry. To gain insights into the change characteristics of soil and soil microbial biomass contents and their stoichiometry along different successional stages of natural secondary forest, four forest types were selected in Miyaluo forest area of western Sichuan, China, which compose of three natural secondary forests (SF60, SF70 and SF80 from clear-logging area during the 1960s, 1970s and 1980s, respectively) and one Abies faxoniana primary forest (PF, 160 years old). C_soil, N_soil and P_soil, C_mic, N_mic and P_mic in 0-20 cm soil were measured. The results showed that contents of C_soil and N_mic marginally significantly decreased, whereas the contents of N_soil and P_soil, C_mic and P_mic increased initially but decreased over time late in the course of restorative succession of natural secondary forests. The contents of C_soil, N_soil, P_soil, C_mic, N_mic, and P_mic in the three natural secondary forests were lower than those in the PF, while the contents of C_soil, N_soil and soil microbial biomass had no significant changes between SF80 and SF70. The content of P_soil was significantly higher in SF70 than that in SF80. The soil C:N:P stoichiometry ratio was dominated by the synergy effect interaction of N_soil and P_soil contents. There was no obvious difference among forests of different successional stages for soil microbial nitrogen carbon quotient (qMBC) and phosphorus quotient (qMBP), but did exist for soil microbial nitrogen quotient (qMBN). qMBN was significantly greater in SF60 than that in the other two successional stages and PF. C_imb:N_imb ratio of the stoichiometric imbalances showed first decreased and then increased; C_imb:P_imb and N_imb:P_imb ratio of the stoichiometric imbalances showed a slightly and significantly gradual reduction, respectively. Redundancy analysis showed that soil microbial quotient (qMB) was significantly correlated with N_imb:P_imb and C_mic:N_mic ratio. N_imb:P_imb ratio revealed 62.6% of the variations in qMB, which implied that changes of qMB values were effected by the contents of N_soil, P_soil and their active components (N_mic and P_mic). Furthermore, our results revealed that nitrogen and phosphorus contribution could be an optimal strategy to meet the microbial stoichiometric demands and enhance nutrient availability for natural secondary forest at the early-successional stages (<60 a) in high-altitude sub-alpine forest ecosystems.

Assessing microbial residues in soil as a potential carbon sink and moderator of carbon use efficiency

A longstanding assumption of glucose tracing experiments is that all glucose is microbially utilized during short incubations of ≤2 days to become microbial biomass or carbon dioxide. Carbon use efficiency (CUE) estimates have consequently ignored the formation of residues (non-living microbial products) although such materials could represent an important sink of glucose that is prone to stabilization as soil organic matter. We examined the dynamics of microbial residue formation from a short tracer experiment with frequent samplings over 72 h, and conducted a meta-analysis of previously published glucose tracing studies to assess the generality of these experimental results. Both our experiment and meta-analysis indicated 30–34% of amended glucose-C (13C or 14C) was in the form of residues within the first 6 h of substrate addition. We expand the conventional efficiency calculation to include residues in both the numerator and denominator of efficiency, thereby deriving a novel metric of the potential persistence of glucose-C in soil as living microbial biomass plus residues (‘carbon stabilization efficiency’). This new metric indicates nearly 40% of amended glucose-C persists in soil 180 days after amendment, the majority as non-biomass residues. Starting microbial biomass and clay content emerge as critical factors that positively promote such long term stabilization of labile C. Rapid residue production supports the conclusion that non-growth maintenance activity can illicit high demands for C in soil, perhaps equaling that directed towards growth, and that residues may have an underestimated role in the cycling and sequestration potential of C in soil.