Microbial community structure and resource availability drive the catalytic efficiency of soil enzymes under land-use change conditions

The turnover of nutrients bound to organic matter is largely mediated by extracellular hydrolytic enzymes (EHEs) produced by soil microorganisms. However, little is known about the environmental drivers (e.g., soil pH, C content, C:N ratio) of the catalytic properties of EHEs and their functional link to the structure of soil microbial communities. We linked catalytic properties, K_m and V_max, determined by Michaelis–Menten kinetics, to a set of environmental and microbial properties in the soils of a land-use sequence ranging from undisturbed natural forest to pastures of different ages and to secondary succession in the Andes of southern Ecuador. The sensitivity of the substrate affinity constant (K_m) and the maximum rate (V_max) of six EHEs (β-cellobiohydrolase (CBH), β-glucosidase (BG), N-acetylglucosaminidase (NAG), α-glucosidase (AG), xylanase (XYL), acid phosphomonoesterase (AP)) to changing environmental conditions was tested by fluorogenic substrates. We used the V_max-to-K_m ratio (K_a) as a proxy for the catalytic efficiency and the signature membrane phospholipid fatty acids as a proxy of microbial community structure.Microbial communities adapted to environmental changes, selected for enzymes with higher substrate affinity (K_m) and catalytic efficiency (K_a) compared with pure cultures. Along the land-use sequence, catalytic efficiency increased from natural forest to young pasture, while it decreased during long-term pasture use and secondary succession. This is consistent with three to five times faster turnover of tested substrates (estimated based on Michaelis–Menten kinetic parameters) at the young pasture compared with the long-term pasture and secondary succession. Environmental drivers of the K_m were enzyme-specific (e.g., the pH for XYL, the C:N ratio for AP, and the C availability for NAG) and differed from those for V_max. A decoupled response of V_max and K_m to land-use changes observed for AG, BG, CBH, XYL, and AP, implies divers consequences for ecosystem processes mediated by these enzymes. A high abundance of Gram(−) bacteria triggered the catalytic properties (K_m and/or K_a) of enzymes decomposing cellulose, hemicellulose, starch, and monophosphoesters. The importance of climatic factors for catalytic properties of EHEs was emphasized by the K_a values extracted from the literature and demonstrated good correspondence of K_a between soils from geographically distinct experimental plots.     

Hydrolases extracted from soil: Kinetic parameters of several enzymes catalysing the same reaction

The kinetic parameters (K_m and V_max) of ureases, phosphatases, casein and benzoylargininae-mide-hydrolysing proteases extracted from two different soils were determined. The Eadie-Scatchard plot, which is the most sensitive graphical technique for detecting deviations from Michaelis-Menten kinetics, was used. In the case of phosphatases extracted from two soils and of the benzoylarginineamide hydrolysing protease extracted from one soil the relationship between V/S and V produced two straight lines. The presence of at least two enzymes (or two forms of the same enzyme) catalysing the same reaction and characterized by markedly different K_m and V_max values, was indicated. A procedure to determine the true constants was reported. The conclusion was that the presence in soil of high and low-affinity enzymes permits an efficient reaction at either low or high substrate concentration.     

Carbon availability regulates soil respiration response to nitrogen and temperature

The response of soil CO₂ fluxes (R_soil) to interactions between carbon (C) and nitrogen (N) availability or C and temperature conditions is not well understood, but may increasingly affect future C storage under the combined anthropogenic impacts of N deposition and climate change. Here we addressed this uncertainty through a series of laboratory incubation experiments using soils from three contrasting ecosystems to investigate how changes in C, N, and temperature regulate R_soil through changes to Michaelis–Menten parameters (i.e. V_max and K_m). Results of this study demonstrate that R_soil response to N enrichment and changes in temperature are dependent on the C availability of soil substrates. N addition influenced R_soil through both the maximum rate (V_max) and the half saturation constant (K_m). The increase in K_m corresponded to a decrease in R_soil when C was limited. Alternatively, when C was abundant, N enrichment increased R_soil, which corresponded to an increase in V_max. Regulation of temperature sensitivity through V_max and K_m was also dependent on C availability. Both V_max and K_m demonstrated positive temperature responses, supporting the hypothesis of a canceling effect at low C concentrations. While temperature sensitivity was influenced by both C quantity and C complexity, our results suggested that C quantity is a stronger predictor. Despite strong differences in climate, vegetation, and management of our soils, C–N and C-temperature interactions were markedly similar between sites, highlighting the importance of C availability in the regulation of R_soil and justifying the use of Michaelis–Menten kinetics in biogeochemical modeling.     

Arylsulphatase activity in soils amended with crop residues: Kinetic and thermodynamic parameters

Laboratory experiments were performed to determine the Michaelis-constants (K_m values) and maximum reaction velocities (V_max values) of arylsulphatase in a clay-loam and a sandy clay-loam soil. When crop residues were buried in either soil, the K_m and V_max values were altered markedly; the changes depended not only on the soil properties but also on the type of crop residue incorporated in the soils. This was confirmed at various temperatures, and data obtained were used to calculate the activation energies (E_a), and changes in enthalpy (ΔH_a) and entropy (ΔS_a) of activation. Whereas these properties were also affected by incorporating crop residues, the free energies of activation (ΔG_a) values, were similar in both soils and derived soil samples.     

Kinetic parameters of dehydrogenase in the assessment of the response of soil to vermicompost and inorganic fertilisers

 Kinetic parameters (V _max and K _m) of dehydrogenase activity were determined in order to assess the metabolic response of a soil about 1 year after organic and mineral treatments. The soil was planted with maize (Zea mays) and treated with the following fertilisers: organic (vermicompost; VC), mineral (ammonium phosphate and urea), and an organo-mineral mixture. V _max, which represents a measurement of the quantity of enzyme, markedly increased in organic and organo-mineral treatments, indicating that the addition of organic matter caused an increase in dehydrogenase in the active microbial biomass. K _m, representing enzyme-substrate affinity and/or different sources of the enzymes, was similar in VC-treated soil and control soil, while it doubled in organo-mineral and mineral treatments. These results suggest that the use of VC did not alter the enzyme-substrate affinity, while mineral fertiliser reduced this affinity or changed the composition and activity of soil microbiota. A positive correlation was found between V _max, the metabolic index (dehydrogenase/water-soluble carbon ratio), and the soil organic matter content. The kinetic constants of dehydrogenase activity and the metabolic index may be considered valid parameters to monitor the evolution of microbiological activity in soil. Received: 4 February 2000     

Effect of different treatments with crop residues on soil phosphatase activity

Summary Phosphomonoesterase (both acid and alkaline) and phosphodiesterase activity was either activated or inhibited in a soil treated with different crop residues. Phosphotriesterase activity remained unaffected. The kinetic parameters (V _max and K _m) of treated soil samples were modified in the same way: Increases or decreases in the V _max values corresponded to increases or decreases in the K _m values. The V _max values, rather than the K _m values, were found to have a predominant effect on phosphatase activity, thus indicating a fundamental role for the enzyme concentration. A positive and generally significant correlation was found between the activity of each phosphatase, which suggests an unspecific source of these enzymes. The values of the determination coefficients (R ² × 100) show that a low percentage of the variability may be ascribed to interactions among phosphatase activities.     

Ermittlung kinetischer Parameter der sauren Phosphatasen intakter Zuckerrübenwurzeln bei variierter Phosphaternährung

Determination of kinetic parameters of acid phosphatases in intact sugar beet roots of variable phosphorus nutrition Organically bound phosphorus has to be hydrolysed before its P can be taken up by plants. Both microbes and plant roots possess phosphatases, which could be of importance especially in soils with low concentrations of inorganic phosphorus in the soil solution. This could be the reason why nutrient uptake models underestimate the P-uptake by plants when P-mobilization by the phosphatases of roots is not taken into consideration. Therefore the activity of acid phosphatases (P_ase) was determined to answer the following questions: 1) To which extent does the root bound acid phosphatase (P_ase) follow Michaelis-Menten kinetics? 2) By which of the four linear transformations of the Michaelis-Menten equation (Lineweaver/Burk, Hanes, Eadie/Hofstee, Eisenthal/Cornish-Bowden) can plausible values of V_max and K_m be determined? 3) Which effect has the P nutrition of the plant on these kinetic parameters? Sugar beet plants were grown in full nutrient solution containing 1 and 100 μM P respectively. The P_ase activity of the intact roots was measured at pH 5 using p-nitrophenylphosphate (25—15000 μM p-NPP). V_max values were calculated per m root length. Acid phosphatase activity principally followed Michaelis-Menten kinetics. Transformations and calculations of V_max and K_m after Eadie/Hofstee and Eisenthal/Cornish-Bowden suggested the existence of at least two enzyme systems (P_{ase 1}, P_{ase 2}). The following kinetic parameters were found: P_{ase 1}: P deficient plants: V_max: 43—45 nmol m^—1 min^—1, K_m: 31—37 μM NPP; P sufficient plants: V_max: 7 nmol m^—1 min^—1, K_m: 47—53 μM NPP. P_{ase 2}: P deficient plants: V_max: 230—293 nmol m^—1 min^—1, K_m: 1579—3845 μM NPP; P sufficient plants: V_max: 123—171 nmol m^—1 min^—1, K_m: 3027—7000 μM NPP. Thus plants with sufficient P nutrition have a lower affinity to P_org and a lower hydrolysis of P_org. For P nutrition of crops P_{ase 1} might be the most important enzyme.     

Kinetic behaviour of alkaline phosphatase desorbed from different clay minerals

The kinetic (K_m, V_max) of alkaline phosphatase (AP) desorbed from different Ca-homoionic clay minerals (montmorillonite, illite, and kaolinite) by extraction with Tris-Malate-Citrate buffer solution (pH 9.6) was studied in model experiments. After extraction (shaking for 15 min.) the K_m and V_max were measured in the extract, the remaining sediment and in the whole set-up. With kaolinite and illite, V_max of the desorbed AP was lower than that of the sediment. However, with montmorillonite, V_max of AP in the extract and whole system increased if compared to the control, but decreased in the sediment. The K_m of desorbed AP increased from 4.3 × 10^?3 (control) to 5.0 × 10^?3 M (illite), 5.4 × 10^?3M (kaolinite), and 5.5 × 10^?3M (montmorillonite). These values were lower than those obtained with the various sediments and whole experimental systems. An aberrant behaviour was recorded with the illite sorbed AP which showed an increase in affinity towards the substrate. Generally speaking, AP desorbed from clays may be reduced in its affinity towards the substrate p-nitrophenylphosphate by residual inhibitor and/or conformational change of the enzyme.     

Decomposition of atmospheric hydrogen by soil microorganisms and soil enzymes

The decomposition of atmospheric hydrogen in different types of soil was measured. The decomposition of H₂ was apparently a first-order reaction. H₂ decomposition activity was proportional to the amount of soil with maximum activities at soil water contents of approx. 6–11% (w/w). The activity was lower under anaerobic conditions, but was constant between 1–20% O₂. It was destroyed by autoclaving and was partially inactivated by fumigation with NH₃, CHC1₃ or acetone, by u.v. irradiation and by treatment with NaCN or NaN₃, indicating that biological processes in the soil were responsible for the observed H₂ decomposition. Treatment of soil with toluene or CHCl₃ caused only a partial inactivation. Incubation of soil in the presence of streptomycin or actidione reduced H₂ decomposition by less than 50%, whereas CO consumption was abolished. The H₂ decomposition rates showed H₂ saturation curves with apparent Michaelis-Menten kinetics. Cooperative effects were not observed. V_max was reached at approx. 200 μl1^?1. The K_m values for H₂ were in the range of 30μl 1^?1, but increased to higher values, when the soil had been pretreated with high H₂ mixing ratios. Apparently, the observed H₂ decomposition by soil is not only due to the activity of viable microorganisms, but soil enzymes as well.     

Extraction,purification and properties of soil hydrolases

Invertase, cellulase, phosphatases, protease and β-glucosidase were extracted from permanent pasture soil with 0.2 M phosphate buffer (pH 8) in the presence of 0.2 M EDTA. This extract was further treated with ammonium and salmine sulphates. Attempts were made to fractionate these enzyme activities by gel and anion-exchange chromatography. Specific activities were estimated in all fractions and some characteristics of the purified enzymes (optimum pH, temperature and substrate concentration, and K_m and V_max) were investigated. The results indicated that extracted enzyme activities occurred partly in soil as a carbohydrate-enzyme complex and partly as a humo-carbohydrate complex.     

Influence of natural and synthetic humic substances on the activity of urease

The activity of a purified urease, obtained from Bacillus pasteurii, was inhibited by humic and fulvic acids obtained from an agricultural soil. Enzyme kinetic studies showed that the humic substances affected the affinity of the enzyme for its substrate (K_m) and the maximum velocity of the reaction (V_max). The V_max was inhibited to the same extent by both humic (HA) and fulvic (FA) acids, the precise effect depending on the pH and concentration of humic substance. At pH 4.0, HA concentrations of 25 pg cm^?3 and 10 μg cm^?3 inhibited the V_max by 38.5% and 20% respectively. HA and FA had similar effects on the K_m but in this case the lowering of the affinity of the enzyme for its substrate was not concentration dependent in the range 0–25 μg cm^?3 of humic substance. Typically, the affinity was decreased from a K_M of 50 mM in the control to 67 mM in the presence of HA and FA. The effects were not due primarily to the ash or N contents of the humic substances because de-ashed humic acid and synthetic model humic (made from catechol, guaiacol, pyrogallol, resorcinol and protocatechuic acid) and fulvic acid (made from polymaleic acid), containing virtually no ash or N, were equally as effective. The effect was not related to the phenolic monomers which, before polymerization, had no effect on urease activity.     

Characterization of extracellular phosphatase activities in periphytic biofilm from paddy field

Periphytic biofilms exist widely in paddy fields, but their influences on the hydrolysis of organic phosphorus(P) have rarely been investigated. In this study,a periphytic biofilm was incubated in a paddy soil solution, and hydrolysis kinetic parameters(half-saturation constant(Km) and maximum catalytic reaction rate(Vmax)), optimal environmental conditions, substrate specificity, and response to different P regimes of the phosphatase activities in the periphytic biofilm were determined, in order to characterize extracellular phosphatase activities in periphytic biofilms from paddy fields. The results indicated that the periphytic biofilm could produce an acid phosphomonoesterase(PMEase), an alkaline PMEases, and a phosphodiesterase(PDEase). These three phosphatases displayed high substrate affinity, with Km values ranging from 141.03 to 212.96 μmol L^-1. The Vmax/Km ratios for the phosphatases followed the order of alkaline PMEase > acid PMEase > PDEase, which suggested that the PMEases, especially the alkaline PMEase, had higher catalytic efficiency. The optimal pH was 6.0 for the acid PMEase activity and 8.0 for the PDEase activity, and the alkaline PMEase activity increased with a pH increase from 7.0 to 12.0. The optimal temperature was 50℃ for the PMEases and 60℃ for the PDEase. The phosphatases showed high catalytic efficiency for condensed P over a wide pH range and for orthophosphate monoesters at pH 11.0, except for inositol hexakisphosphate at pH 6.0. The inorganic P supply was the main factor in the regulation of phosphatase activities. These findings demonstrated that the periphytic biofilm tested had high hydrolysis capacity for organic and condensed P,especially under P-limited conditions.     

Nitrogen requirement of fodder and sugar beet (Beta vulgaris L.) cultivars under high-yielding conditions of northwestern Europe

This study provides current data on plant nitrogen (N) uptake required for maximum sugar yield (PNUp_max) and the corresponding fertilizer N dose (ND) (optimum N dose [ND_opt]) for high-yielding beet crops (sugar yield up to 20 Mg ha^?1). In 2010 and 2011, field experiments were conducted with four cultivars from Beta genus differing in dry matter composition, and six mineral NDs (0–200 kg N ha^?1) at three sites (The Netherlands, Germany, Denmark). Differences between cultivars in PNUp_max and ND_opt were small; however, environments (defined as combination of site and year) substantially differed from each other: highest PNUp_max and lowest ND_opt occurred at environments supplying high amounts of N from soil resources, and vice versa. The level of maximum sugar yield (SY_max) was related neither to PNUp_max (200–270 kg N ha^?1) nor to ND_opt. However, N dose and plant N uptake required for 95% of maximum sugar yield was 50–80 kg N ha^?1 lower than for maximum sugar yield. To conclude, accepting a slight reduction in sugar yield might allow for a substantial decrease in the ND. Cultivar choice and yield level need not to be taken into account at present.     

Immobilization of Carbonic Anhydrase on Chitosan Stabilized Iron Nanoparticles for the Carbonation Reaction

Carbonic anhydrase (CA) has been immobilized on chitosan stabilized iron nanoparticles (CSIN) for the biomimetic carbonation reaction. CSIN was characterized using scanning electron microscope, energy dispersive X-ray, X-ray diffraction spectroscopy, and Fourier transform infrared analysis. The effect of various parameters such as pH, temperature and storage stability, on immobilized CA was investigated using a p-NPA assay. Kinetic parameters of immobilized and free CA (K _m and V _max values) were also evaluated. The K _m and V _max for immobilized CA was 1.727?mM and 1.189???mol?min^?1?ml^?1, respectively, whereas for free enzyme the K _m and V _max was 1.594?mM and 1.307???mol?min^?1?ml^?1, respectively. It was observed that the immobilized enzyme had longer storage stability and retained 50?% of its initial activity upto 30?days at room temperature. CA immobilized on CSIN has been used for hydration of CO₂, and the results were validated by using a gas chromatographic method. Proof of concept has been established for the biomimetic carbonation reaction. Immobilized CA show reasonably good CO₂ sequestration capacity of 21.55?mg of CaCO₃/mg of CA as compared to CO₂ sequestration capacity of 34.92?mg of CaCO₃/mg of CA for free CA respectively, under a limiting concentration of CO₂ (14.5?mg of CO₂/10?ml).     

Soil urease activity and kinetics

The activity and kinetic properties of urease in several Malaysian soils were examined. The values for K_m and V_max of the soils computed according to the Hanes equation were in general agreement with other reports as far as magnitudes were concerned. A significant correlation between K_m and V_max was also obtained. The urease activity of the soils was variable, and it was noted that expression of the activity as the time required to hydrolyze half of the applied urea has limited use in soils of low activity. In all soils studied, inhibition of urease activity was effectively achieved using Ag⁺, while Cu²⁺ was only effective in two soils, and marginally effective in the other two soils. Urease inhibitors have potential applications in reducing volatilization losses of ammonia derived from urea applied to soils.     

Correlations between Kinetic Parameters of Phosphate Uptake and Internal Phosphorus Concentrations in Maize Plants: Making it Possible to Estimate the Status of Phosphate Uptake according to Shoot Phosphorus Concentrations

Abstract

The relationship between internal phosphorus (P) concentration [P] and kinetics of phosphate (Pi) uptake was investigated in maize seedlings grown hydroponically at different Pi concentrations (0.1–1,000 µM) and in the phase of Pi deprivation (0–10 d). The results indicated when the internal [P] was higher than 85 µmol g^?1 dw, apparent K_m, C_min, and V_max were significantly (P<0.01) related to [P]s in shoots and roots; when the internal [P] was lower than 85 µmol g^?1 dw, K_m and C_min were small and only V_max was significantly related (P<0.01) to internal [P]s. Three equations were deduced from the linear regressions of the kinetic parameters and [P]s in shoots. Using these equations, the values of apparent K_m, C_min, and V_max of Pi uptake of seedlings grown in different circumstances were calculated according to [P]s in shoots. In all the circumstances involved, for K_m and C_min, there was a parallel relationship between the values estimated by [P]s in shoots and by the Pi‐depletion technique; for V_max, the values estimated by [P]s in shoots were consistent with those obtained from Pi‐depletion experiments except the period of supplying Pi to the Pi‐starved seedlings over several days. These results indicated it is possible to estimate the Pi‐uptake status according to shoot P concentrations in maize plants under experimental conditions, which might be helpful to estimate in‐season status of Pi uptake of maize plants in the field.     

Kinetics of glucose uptake by soil microorganisms

The kinetics of glucose uptake by soil microorganisms was investigated. Soil amended with an inorganic nutrient solution containing C glucose at concentrations of 2.5, 5.0, 10.0 or 20.0 mmol 1⁻¹ was maintained at 4, 12 or 25°C for varying times. The soil was analyzed for glucose, soluble ^14C, total organic ¹⁴C and evolved ¹⁴CO₂ to develop a carbon balance for the system and to define Michaelis-Menten kinetic parameters (K_m and V_max) for glucose uptake at each temperature.Glucose uptake rates, as measured by the depletion of glucose or soluble ¹⁴C from solution, were similar in soils maintained at 12 or 25°C. Based on the depletion of soluble ¹⁴C, values for K_m were 2.25 and 2.43 mmol I⁻¹ at 12 and 25°C, respectively, while V_max values were 0.25 and 1.61 h¹⁴', respectively. Glucose depletion at 4°C was faster than at 12C, while soluble ¹⁴C was removed at a significantly slower rate, suggesting soluble-C intermediates were produced in the 4°C system. Based on Chromatographie techniques and GC-MS, a soluble ¹⁴C-compound accumulating in the 4°C system was identified as maltose. The conversion of glucose to maltose resulted in K_m and V_max values of 17.29 mmol I⁻¹ and 0.12h⁻¹, respectively, for soluble ¹⁴C depletion and 4.96mmol1⁻¹ and 0.43 h⁻, respectively, for glucose depletion at 4δC. These results demonstrate the need to differentiate uptake rates for the parent compound as well as for transitory intermediates excreted into the growth medium. Evolution of CO₂ was shown to be a poor indicator of the rapid disappearance of glucose in soils.     

旱地长期培肥土壤脲酶和碱性磷酸酶动力学及热力学特征研究

研究了连续25年长期培肥试验条件下土壤脲酶和碱性磷酸酶酶促反应的动力学和热力学特征,从酶学角度揭示长期培肥的效应。结果表明,长期培肥增加了脲酶和碱性磷酸酶酶促反应的Vmax、Vmax/Km和k值;降低了Ea、△G、△H和△S值,说明培肥能提高酶促反应速度、减小活化自由能、加快土壤中物质的生物循环过程。酶促反应动力学参数和热力学参数与土壤性质相关分析表明,酶促反应动力学参数大多依赖于土壤化学性状,基于动力学参数的土壤肥力指标体系可评价土壤肥力水平,且U-Vmax、P-Km、P-Vmax可作为土壤肥力的重要指标。     

Effect of Metals on Decolorization of Reactive Blue HERD by <Emphasis Type="Italic">Comamonas</Emphasis> sp. UVS

Comamonas sp. UVS was able to decolorize Reactive Blue HERD (RBHERD) dye (50 mg L^?1) within 6 h under static condition. The maximum dye concentration degraded was 1,200 mg L^?1 within 210 h. A numerical simulation with the model gives an optimal value of 35.71?±?0.696 mg dye g^?1 cell h^?1 for maximum rate (V_max) and 112.35?±?0.34 mg L^?1 for the Michaelis constant (K_m). Comamonas sp. UVS has capability of decolorization of RBHERD in the presence of Mg²⁺, Ca²⁺, Cd²⁺, and Zn²⁺, whereas decolorization was completely inhibited by Cu²⁺. Metal ions also affected the levels of biotransformation enzymes during decolorization of RBHERD. Comamonas sp. UVS was also able to decolorize textile effluent with significant reduction in COD. The biodegradation of RBHERD dye was monitored by UV–vis spectroscopy, FTIR spectroscopy, and HPLC.     

Differentiating microbial and stabilized β-glucosidase activity relative to soil quality

Previous research has shown that β-glucosidase activity can detect soil management effects and has potential as a soil quality indicator, but mechanisms for this response are not well understood. A significant amount of hydrolytic enzyme activity comes from extracellular (abiontic) activity that is bound and protected by soil colloids. This study was conducted to determine how management affects the kinetics of this enzyme (K_m, substrate affinity, and V_max, maximum reaction velocity) and its degree of stabilization on soil colloids. Soils were sampled from three sites in Oregon, with a paired comparison within each site of a native, unmanaged soil, and a matching soil under agricultural production (>50 years). Microwave radiation (MW) stress was used to denature the β-glucosidase fraction associated with viable microorganisms in these soils as an estimate of abiontic activity. Total activity and V_max were decreased by both management and MW. The results showed that β-glucosidase activity is sensitive to soil management on a variety of soils and environments (135 vs. 190, 80 vs. 111 and 80 vs. 134 μg PNP g⁻¹ h⁻¹ for managed and unmanaged treatments, respectively, at the three study sites in Oregon). The evidence suggests that this sensitivity to management is not (or minimally) due to differences in isoenzymes (K_m generally was unaffected) but rather due to an overall reduction in the amount of enzyme present (V_max decreased) and that this reduction in activity is reflected more from the activity of enzymes in the stabilized fraction than that associated with viable microbial population. Although β-glucosidase activity after MW irradiation appears to be limited as a soil quality indicator, it maybe useful as research tool to separate abiontic from microbial activity ‘biomass’ β-glucosidase activity correlated with microbial biomass C (r=0.42, P<0.05) but MW irradiated, abiontic, activity did not (r=−0.20^NS).