Emerging tools for measuring and modeling the in situ activity of soil extracellular enzymes

Biogeochemistry, 2014

Acid forest soils in the Bohemian Forest in Central Europe are biogeochemically imbalanced in organic C, N and P processing. We hypothesized that these imbalances can be due to different temperature sensitivities of soil enzyme activities and their affinities to substrate in litter and organic soil horizons. We measured potential activities of five main soil enzymes (b-glucosidase, cellobiohydrolase, Leu-aminopeptidase, Ala-aminopeptidase, and phosphatase) responsible for organic carbon, nitrogen and phosphorus acquisition. We also modeled potential in situ enzyme activities and nutrient release based on continuous in situ temperature measurements. We determined basic kinetic parameters (K m , V max ), enzyme efficiencies (k cat ) and temperature sensitivities (E a and Q 10 ) according to Michaelis-Menten kinetic and modified Arrhenius models. Our results showed significant differences in substrate affinities between the litter and organic soil horizons. Higher aminopeptidase affinity (lower K m ) in the litter soil horizon can lead to leaching of peptidic compounds to lower soil horizons. b-Glucosidase and phosphatase showed high temperature response following the Arrhenius model. However, both aminopeptidases showed no or even decreased activity with increasing temperature. The aminopeptidase temperature insensitivity means that peptidic compounds are degraded at the same or even lower rate in warmer and colder periods of the year in acid forest soils. This imbalance results in different release of available nutrients from plant litter and soil organic matter which may affect bacterial and fungal community composition and nutrient leaching from these ecosystems.

Ecology, 2012

Resource stoichiometry (C:N:P) is an important determinant of litter decomposition. However, the effect of elemental stoichiometry on the gross rates of microbial N and P cycling processes during litter decomposition is unknown. In a mesocosm experiment, beech (Fagus sylvatica L.) litter with natural differences in elemental stoichiometry (C:N:P) was incubated under constant environmental conditions. After three and six months, we measured various aspects of nitrogen and phosphorus cycling. We found that gross protein depolymerization, N mineralization (ammonification), and nitrification rates were negatively related to litter C:N. Rates of P mineralization were negatively correlated with litter C:P. The negative correlations with litter C:N were stronger for inorganic N cycling processes than for gross protein depolymerization, indicating that the effect of resource stoichiometry on intracellular processes was stronger than on processes catalyzed by extracellular enzymes. Consistent with this, extracellular protein depolymerization was mainly limited by substrate availability and less so by the amount of protease. Strong positive correlations between the interconnected N and P pools and the respective production and consumption processes pointed to feed-forward control of microbial litter N and P cycling. A negative relationship between litter C:N and phosphatase activity (and between litter C:P and protease activity) demonstrated that microbes tended to allocate carbon and nutrients in ample supply into the production of extracellular enzymes to mine for the nutrient that is more limiting. Overall, the study demonstrated a strong effect of litter stoichiometry (C:N:P) on gross processes of microbial N and P cycling in decomposing litter; mineralization of N and P were tightly coupled to assist in maintaining cellular homeostasis of litter microbial communities.

2012

Accurate prediction of future atmospheric CO 2 concentrations is essential for evaluating climate change impacts on ecosystems and human societies. One major source of uncertainty in model predictions is the extent to which global warming will increase atmospheric CO 2 concentrations through enhanced microbial decomposition of soil organic carbon. Recent advances in microbial ecology could help reduce this uncertainty, but current global models do not represent direct microbial control over decomposition. Instead, all of the coupled climate models reviewed in the most recent Intergovernmental Panel on Climate Change (IPCC) report assume that decomposition is a first-order decay process, proportional to the size of the soil carbon pool. Here we argue for the development of a new generation of models that link decomposition directly to the size and activity of microbial communities in coupled global models. This process begins with the formulation and validation of fine-scale models that capture

PLoS ONE, 2013

Journal of Environmental Science and Health, Part B, 2014

Canadian Journal of Soil Science, 2011

Journal of Geophysical Research: Biogeosciences, 2012

1] Humified soil organic matter storage in boreal forests is large, and its responses to warming over relatively long timescales is critical for predicting soil feedbacks to climate change. To derive information relevant across decades to centuries from manipulative short-term experiments, we conducted incubations of soils from two forested sites along the Newfoundland-Labrador Boreal Ecosystem Latitude Transect in eastern Canada and assessed linkages between incubation data and these sites' profile characteristics. The sites differ in mean annual temperature by 3.4 C, but vegetation and soil types are similar. Organic soils (Oe + Oa) were incubated for 120 days at 15 C and 20 C, with and without a replaced Oi subhorizon possessing a distinct d 13 C signature. Laboratory warming induced significantly greater mineralization and leaching of humified SOM relative to replaced Oi, congruent with greater warming-induced increases in phenol oxidase activity relative to enzymes associated with labile C acquisition (percent increases of 101% versus 50%, respectively). These data suggest that warming can influence microbial communities and their enzymatic dynamics such that relative losses of humified SOM are disproportionately enhanced. This is consistent with stable isotopic, C:N, and radiocarbon profile differences between the two sites, which suggest a greater degree of microbial processing and greater relative losses of older SOC over the preceding decades at the warmer site, given our knowledge of organic inputs in these soils. This study is a first step toward linking the divergent timescales represented by soil profiles and laboratory manipulations, an important goal for biogeochemists assessing climate change impacts on SOM dynamics.

FEMS microbiology ecology, 2018

The structure and function of soil microbiomes often change in response to experimental climate manipulations, suggesting an important role in ecosystem feedbacks. However, it is difficult to know if microbes are responding directly to environmental changes or are more strongly impacted by plant responses. We investigated soil microbial responses to precipitation and temperature manipulations at the Boston-Area Climate Experiment in Massachusetts, USA, in both vegetated and bare plots to parse direct vs. plant-mediated responses to multi-factor climate change. We assessed the bacterial community in vegetated soils in 2009, two years after the experiment was initiated, and bacterial and fungal community in vegetated and bare soils in 2011. The bacterial community structure was significantly changed by the treatments in vegetated soils. However, such changes in the bacterial community across the treatments were absent in the 2011 bare soils. These results suggest that the bacterial co...

Soil Systems

Processes controlling microbial access to soil organic matter are critical for soil nutrient cycling and C stabilization. The bioavailability of soil organic matter partly depends on the rate that substrates become water-soluble, which is determined by some combination of biological, biochemical, and purely abiotic processes. Our goal was to unravel these biotic and abiotic processes to better understand mechanisms controlling the dynamics of bioavailable soil organic carbon (SOC). We sampled soils in a California annual grassland from manipulated plots with and without plants to help distinguish bioavailable SOC generated from mineral-associated organic matter versus from plant detritus (i.e., the "light fraction"). In the laboratory, soils were incubated for 8 months under all possible combinations of three levels of moisture and two levels of microbial biomass using continuous chloroform sterilization. We measured cumulative carbon dioxide (CO 2) production and the net change in soil water-extractable organic C (WEOC) to quantify C that was accessed biologically or biochemically. Under the driest conditions, microbes appeared to primarily access WEOC from recent plant C, with the other half of CO 2 production explained by extracellular processes. These results suggest that dry, uncolonized conditions promote the adsorption of WEOC onto mineral surfaces. Under wetter conditions, microbial access increased by two orders of magnitude, with a large concomitant decrease in WEOC, particularly in soils without plant inputs from the previous growing season. The largest increase in WEOC occurred in wet sterilized soil, perhaps because exoenzymes and desorption continued solubilizing C but without microbial consumption. A similar amount of WEOC accumulated in wet sterilized soil whether plants were present or not, suggesting that desorption of mineral-associated C was the abiotic WEOC source. Based on these results, we hypothesize that dry-live and wet-uncolonized soil microsites are sources of bioavailable SOC, whereas wet-live and dry-uncolonized microsites are sinks.

Soil Systems

Knowledge of how interactions of clay minerals and extracellular enzymes (EEs) influence organic matter turnover in soils are still under discussion. We studied the effect of different montmorillonite contents on EE activities, using two experiments—(1) an adsorption experiment with a commercially available enzyme (α-glucosidase) and (2) an incubation experiment (10 days) where microorganisms were stimulated to produce enzymes through organic carbon (OC) addition (starch and cellulose). Soil mixtures with different montmorillonite contents were created in four levels to a sandy soil: +0% (control), +0.1%, +1%, and +10%. The potential enzyme activity (pEA) of four enzymes, α-glucosidase, β-glucosidase, cellobiohydrolase, and aminopeptidase, involved in the soil carbon and nitrogen cycle were analysed. The adsorption experiment revealed a reduction in the catalytic activity of α-glucosidase by up to 76% with increasing montmorillonite contents. However, the incubation experiment showe...

Journal of Taibah University for Science, 2014

Soil enzyme activities provide a unique biochemical means for assessing soil function as an indicator of soil fertility, which can be altered by a profusion of fluoride in the soil and seasonal changes. Seven sites were chosen in the fluoride-affected area of Nasipur, Birbhum District, West Bengal, India, to compare seasonal changes in enzymes (urease, amylase, cellulase and invertase), fluoride content, physicochemical characteristics and the availability of microbes in the soil with a control. The activity of all the enzymes varied with season. Urease had greater activity in the summer, followed by winter; it showed marginal differences from the control area during the winter (p < 0.002) and summer (p < 0.110) but a significant (p < 0.000) difference during the rainy season. Soil pH had a negative impact on urease activity during both winter and summer. Cellulase activity was accelerated by the organic matter and organic carbon content of the soil. Fluoride therefore had the greatest activity against urease activity during the rainy, summer and winter seasons. The microbial population of the soil also showed a negative impact of fluoride, which may in turn affect the soil enzymes and characteristics.

Elementa: Science of the Anthropocene

Microbial processes, including extracellular enzyme (exoenzyme) production, are a major driver of decomposition and a current topic of interest in Arctic soils due to the effects of climate warming. While enzyme activity levels are often assessed, we lack information on the specific location of these exoenzymes within the soil matrix. Identifying the locations of different soil enzymes is needed to improve our understanding of microbial and overall ecosystem function. Using soil obtained from Utqiaġvik, Alaska, our objectives in the study are (1) to measure the activity of enzymes in soil pore water, (2) to examine the distribution of activity among soil particle size fractions using filtration, and (3) to cross these particle size fraction analyses with disruption techniques (blending to shred and sonication to further separate clumped/aggregated soil materials) to assess how tightly bound the enzymes are to the particles. The results of the soil pore water assays showed little to ...

Biochar

Soil β-glucosidase (BG), the rate-limiting enzyme in the final step of cellulose hydrolysis, plays a key role in microbial metabolism, carbon (C) cycling and sequestration in terrestrial ecosystems. Biochar application is known to affect soil BG activity; however, most of the biochar studies have focused on the potential activity of BG, and it is not clear how biochar influences the kinetic and thermodynamic behavior of BG in the soil. The objective of this study was to investigate the effect of maize residue biochar on soil BG kinetic and thermodynamic parameters. Soil BG kinetic (V max and K m) and thermodynamic (E a , ΔH a and Q 10) parameters were determined within soils (clayey and sandy loam soils) amended with either maize residue (as positive control) or its biochar (600 °C) at 0.5 and 1.0% ratios (w/w), and the mixtures were incubated for 90 days. BG showed an increase in potential enzymatic activity (81%), enzyme concentration (higher V max value) (25%) and substrate affinity (lower K m value) (32%) in the biochar-amended sandy loam soil only at high addition rates compared with the control, and an increase by about 86% of the catalytic efficiency (V max /K m). In the clayey soil, biochar addition decreased potential BG activity (by 10-29%), increased the V max value (by 20-25%) and had no impact on enzyme-substrate binding affinity, but still increased the catalytic efficiency by 47-72%. Adsorption of soil BG by biochar particles did not affect the catalytic efficiency in the soil. Generally, application of maize residue biochar to the soil decreased the E a , ΔH a and Q 10 values of BG compared with the negative controls at both biochar rates in the light-textured soil and only at low biochar rate in heavy-textured soil. The direction and magnitude of BG responses (activity, kinetics, and thermodynamics) to biochar were more related to the soil characteristics. Biochar would increase soil BG thermal stability and decrease its sensitivity to increasing temperature and global warming.

Minerals, 2020

This study was conducted to evaluate the strength and volume change characteristics of a sedimentary residual soil mixed with bentonite (S1) when treated with three different enzymes. In addition, three reference clays including bentonite, illite, and kaolinite were also treated with enzymes to study the effect on their strength characteristics. Soil samples prepared at the optimum moisture content (OMC) were sealed and cured for four months. After curing, reference clays were tested for unconfined compressive strength (UCS). For swell tests, the S1 soil samples were placed on porous stones, which were immersed in water to allow capillary soaking of the samples. S1 samples were allowed to dry at ambient temperature for shrinkage test until the rate of reduction in volume became negligible. On completion of swell tests, the samples were tested for UCS to determine the decrease in strength due to saturation. No increase in strength and decrease in volume change were observed for any o...

Plant-Plant Allelopathic Interactions II, 2014

This chapter provides an abridged version of the known effects, physicochemical and biotic factors that modify effects, and the modes of action of allelopathic compounds using phenolic acids as the model compounds.

Biogeosciences, 2021

PLoS ONE, 2013

Enzyme dynamics are being incorporated into soil carbon cycling models and accurate representation of enzyme kinetics is an important step in predicting belowground nutrient dynamics. A scarce number of studies have measured activation energy (E a) in soils and fewer studies have measured E a in arctic and tropical soils, or in subsurface soils. We determined the E a for four typical lignocellulose degrading enzymes in the A and B horizons of seven soils covering six different soil orders. We also elucidated which soil properties predicted any measurable differences in E a. b-glucosidase, cellobiohydrolase, phenol oxidase and peroxidase activities were measured at five temperatures, 4, 21, 30, 40, and 60uC. E a was calculated using the Arrhenius equation. b-glucosidase and cellobiohydrolase E a values for both A and B horizons in this study were similar to previously reported values, however we could not make a direct comparison for B horizon soils because of the lack of data. There was no consistent relationship between hydrolase enzyme E a and the environmental variables we measured. Phenol oxidase was the only enzyme that had a consistent positive relationship between E a and pH in both horizons. The E a in the arctic and subarctic zones for peroxidase was lower than the hydrolases and phenol oxidase values, indicating peroxidase may be a rate limited enzyme in environments under warming conditions. By including these six soil types we have increased the number of soil oxidative enzyme E a values reported in the literature by 50%. This study is a step towards better quantifying enzyme kinetics in different climate zones.

The ISME Journal, 2016

Terrestrial systems support a variety of free-living soil diazotrophs, which can fix nitrogen (N) outside of plant associations. However, owing to the metabolic costs associated with N fixation, free-living soil diazotrophs likely rely on soil N to satisfy the majority of cellular N demand and only fix atmospheric N under certain conditions. Culture-based studies and genomic data show that many free-living soil diazotrophs can access high-molecular weight organic soil N by releasing N-acquiring enzymes such as proteases and chitinases into the extracellular environment. Here, we formally propose a N acquisition strategy used by free-living diazotrophs that accounts for high-molecular weight N acquisition through exoenzyme release by these organisms. We call this the 'LAH N-acquisition strategy' for the preferred order of N pools used once inorganic soil N is limiting: (1) low-molecular weight organic N, (2) atmospheric N and (3) high-molecular weight organic N. In this framework, free-living diazotrophs primarily use biological N fixation (BNF) as a short-term N acquisition strategy to offset the cellular N lost in exoenzyme excretion as low-molecular weight N becomes limiting. By accounting for exoenzyme release by free-living diazotrophs within a costbenefit framework, investigation of the LAH N acquisition strategy will contribute to a process-level understanding of BNF in soil environments.

Plant and Soil, 2014

Background and Aims Alien success has frequently been associated with changes in the concentrations of soil nutrients. We aim to investigate the effects of plant invasion on soil nutrients, potential enzyme activity and litter elemental composition and stoichiometry. Methods We compared stands of secondary forest invaded by Ligustrum lucidum and those dominated by natives, and performed litter and soil chemical analyses on 3 native and 2 exotic tree species. Results Soils of invaded sites had 20% and 30% increase in β-glucosidase and alkaline phosphatase activity, higher Olsen-phosphorus (P) and potassium (K) concentrations and lower nitrogen (N) concentration and N:P, N:K and ammonium:Olsen-P ratios. Invaded and non-invaded sites differed in their overall nutrient composition and enzyme activity. Natives and exotics differed in nine of the 16 litter elemental composition and stoichiometry variables analyzed. Conclusions The low N:P ratio in litter, the decrease in soil N in invaded stands and the low N concentration of exotics suggest that N is the limiting nutrient and that exotic success is related to higher N uptake and use efficiency. The higher investment in the acquisition of soil resources, higher nutrient uptake and use efficiency of limiting nutrients contribute to the success of exotics in this subtropical forest.

Biogeochemistry, 2013

Extracellular enzymes produced by heterotrophic microbial communities are major drivers of carbon and nutrient cycling in terrestrial, freshwater, and marine environments. Although carbon and nutrient cycles are coupled on global scales, studies of extracellular enzymes associated with terrestrial, freshwater, and marine microbial communities are not often compared across ecosystems. In part, this disconnect arises because the environmental parameters that control enzyme activities in terrestrial and freshwater systems, such as temperature, pH, and moisture content, have little explanatory power for patterns of enzyme activities in marine systems. Instead, factors such as the functional diversity of microbial communities may explain varying patterns of enzyme activities observed in the ocean to date. In any case, many studies across systems focus on similar issues that highlight the commonalities of microbial community organization. Examples include the effective lifetime of enzymes released into the environment; the extent to which microbial communities coordinate enzyme expression to decompose complex organic substrates; and the influence of microbial community composition on enzyme activities and kinetics. Here we review the often-disparate research foci in terrestrial, freshwater, and marine environments. We consider the extent to which environmental factors may regulate extracellular enzyme activities within each ecosystem, and highlight commonalities and current methodological challenges to identify

Environmental microbiology, 2017

Soil carbon (C) stabilization is known to depend in part on its distribution in structural aggregates, and upon soil microbial activity within the aggregates. However, the mechanisms and relative contributions of different microbial groups to C turnover in different aggregates under various management practices remain unclear. The aim of this study was to determine the role of soil aggregation and their associated microbial communities in driving the responses of soil organic matter (SOM) to multiple management practices. Our results demonstrate that higher amounts of C inputs coupled with greater soil aggregation in residue retention management practices has positive effects on soil C content. Our results provide evidence that different aggregate size classes support distinct microbial habitats which supports the colonization of different microbial communities. Most importantly our results indicate that the effects of management practices on soil C is modulated by soil aggregate si...

Microorganisms, 2021

Soil is one of the key elements for supporting life on Earth. It delivers multiple ecosystem services, which are provided by soil processes and functions performed by soil biodiversity. In particular, soil microbiome is one of the fundamental components in the sustainment of plant biomass production and plant health. Both targeted and untargeted management of soil microbial communities appear to be promising in the sustainable improvement of food crop yield, its nutritional quality and safety. –Omics approaches, which allow the assessment of microbial phylogenetic diversity and functional information, have increasingly been used in recent years to study changes in soil microbial diversity caused by agronomic practices and environmental factors. The application of these high-throughput technologies to the study of soil microbial diversity, plant health and the quality of derived raw materials will help strengthen the link between soil well-being, food quality, food safety and human h...

Soil Biology and Biochemistry, 2020

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Journal of Ecology, 2020

1. In high-latitude ecosystems bryophytes are important drivers of ecosystem functions. Alterations in abundance of mosses due to global change may thus strongly influence carbon (C) and nitrogen (N) cycling and hence cause feedback on climate. The effects of mosses on soil microbial activity are, however, still poorly understood. Our study aims at elucidating how and by which mechanisms bryophytes influence microbial decomposition processes of soil organic matter and thus soil nutrient availability. 2. We present results from a field experiment in a subarctic birch forest in northern Sweden, where we partly removed the moss cover and replaced it with an artificial soil cover for simulating moss effects on soil temperature and moisture. We combined this with a fertilization experiment with 15 N-labelled N for analysing the effects of moss N sequestration on soil processes. 3. Our results demonstrate the capacity of mosses to reduce soil N availability and retard N cycling. The comparison with artificial soil cover plots suggests that the effect of mosses on N cycling is linked to the thermal insulation capacity of mosses causing low average soil temperature in summer and strongly reduced soil temperature fluctuations, the latter also leading to a decreased frequency of freezethaw events in autumn and spring. Our results also showed, however, that the negative temperature effect of mosses on soil microbial activity was in part compensated by stimulatory effects of the moss layer, possibly linked to leaching of labile substrates from the moss. Furthermore, our results revealed that bryophytes efficiently sequester added N from wet deposition and thus prevent effects of increased atmospheric N deposition on soil N availability and soil processes. 4. Synthesis. Our study emphasizes the important role of mosses in carbon and nutrient cycling in high-latitude ecosystems and the potential strong impacts of reductions in moss abundance on microbial decomposition processes and nutrient availability in subarctic and boreal forests. K E Y W O R D S bryophytes, extracellular enzyme activities, microbial communities, microbial processes, moss, nitrogen availability, nitrogen cycling, soil temperature This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Plant and Soil, 2019

The aim of this study was to identify how land-use intensity shapes the kinetic properties of extracellular hydrolytic enzymes (EHEs) in rhizosphere soil among and within plant species representing different i) resource acquisition strategies (exploitative (ex) vs. conservative (co) plant species) and ii) response types to land-use intensification (winner (Wi) vs. loser (Lo), i.e. species that increase in abundance due to land-use intensification vs. species that decrease in abundance). The potential enzyme activities (Vmax) and the apparent substrate affinities (Km) of βcellobiohydrolase (CBH), β-glucosidase (BG), xylanase (XYL), N-acetylglucosaminidase (NAG), and phosphomonoesterase (PH) were determined in rhizosphere samples of Agrimonia eupatoria (co, Lo), Dactylis glomerata (ex, Wi), Lotus corniculatus (co, Lo), Taraxacum sect. Ruderalia (ex, Wi) and Trifolium repens (ex, Wi). Samples (n=37) were taken on six permanent grasslands along a gradient in land-use intensity in central Germany. Plant species identity and performance of species to land-use intensity are less important for explaining enzyme kinetics than are land-use intensity and associated changes in soil properties (especially organic carbon, pH and C:N ratio) and composition of the surrounding plant community, i.e. the abundance of herbs and plant diversity. However, the rhizosphere of winner species of intensive land-use was characterized by higher Km of CBH and two out of the three winners were associated with lower Km of PH. Higher Vmax of XYL in the rhizosphere of winner species suggest higher production of hemicellulose-degrading enzymes in rhizospheres of higher land-use intensity. This study demonstrates that both land-use intensity and to a lower degree the type of plants' resource acquisition strategy affect EHEs of C-, N-, and P-cycles in the rhizosphere. Rhizospheres of common grassland species are hotspots of hemicellulose, chitin, and organic P degradation but not of cellulose degradation. Further studies should consider variations in the kinetics of EHEs as a function of root orders and soil depths.

Ecology and Evolution, 2020

Microorganisms govern soil carbon cycling with critical effects at local and global scales. The activity of microbial extracellular enzymes is generally the limiting step for soil organic matter mineralization. Nevertheless, the influence of soil characteristics and climate parameters on microbial extracellular enzyme activity (EEA) performance at different water availabilities and temperatures remains to be detailed.

Ecology and Evolution, 2020

Microbial extracellular enzyme activity (EEA) is critical for the decomposition of organic matter in soils. Generally, EEA represents the limiting step governing soil organic matter mineralization. The high complexity of soil microbial communities and the heterogeneity of soils suggest potentially complex interactions between microorganisms (and their extracellular enzymes), organic matter, and physicochemical factors. Previous studies have reported the existence of maximum soil EEA at high temperatures although microorganisms thriving at high temperature represent a minority of soil microbial communities. To solve this paradox, we attempt to evaluate if soil extracellular enzymes from thermophiles could accumulate in soils. Methodology at this respect is scarce and an adapted protocol is proposed. Herein, the approach is to analyze the persistence of soil microbial extracellular enzymes at different temperatures and under a broad range of water availability. Results suggest that so...

PeerJ

Soils are highly heterogeneous and support highly diverse microbial communities. Microbial extracellular enzymes breakdown complex polymers into small assimilable molecules representing the limiting step of soil organic matter mineralization. This process occurs on to soil particles although currently it is typically estimated in laboratory aqueous solutions. Herein, estimates of microbial extracellular enzyme activity were obtained over a broad range of temperatures and water availabilities frequently observed at soil upper layers. A Pseudomonas strain presented optimum extracellular enzyme activities at high water activity whereas a desiccation resistant bacterium (Deinococcus) and a soil thermophilic isolate (Parageobacillus) showed optimum extracellular enzyme activity under dried (i.e., water activities ranging 0.5–0.8) rather that wet conditions. Different unamended soils presented a distinctive response of extracellular enzyme activity as a function of temperature and water a...