Extra and intracellular enzymes help soil microbes to degrade soil organic matter and plant residues into smaller digestible molecules. The goal of this study was to investigate the reaction of urease, alkaline phosphatase, β-glucosidase, and aryl sulfatase to two levels of 0.5

Biochar as an organic amendment improves soil attributes, with a potentially significant effect on soil chemical fertility and quality. The main objective of this study was to quantify the effect of biochar addition on nutrients, carbon sequestration and microbial activity and understand the mechanisms of controlling biochar effects in calcareous soils. Maize residue biochars produced at 200, 400 and 600 °C were added at 5 and 10 g kg−1 rates to sandy loam and clayey texture calcareous soils. The soil properties measured were pH and electrical conductivity (EC), plant-available potassium (K) and available phosphorus (P), total nitrogen (TN), C sequestration; and the fluorescein diacetate (FDA) hydrolysis activity. Addition of raw material and biochars increased pH (0.15–0.46 units), EC (0.14–0.38 dS m−1), TN (63–120%), K (12–41%) and FDA activity (27–280%), but tended to decrease plant-available P (23–86%). Increasing pyrolysis temperature increased soil C pool index (CPI), but decreased the FDA and the changes depended largely upon the application rate and soil texture. The positive effects of biochar addition and its pyrolysis temperature on soil C sequestration potential were more pronounced at high than low application rate and in sandy loam than clayey soils. Nevertheless, the effect of biochar addition and pyrolysis temperature on the FDA activity was higher at high than low application rates, but lower in sandy loam than clayey soils. Although biochar application may successfully improve soil processes and attributes and have a high potential for C sequestration, its effects are controlled by soil texture, pyrolysis temperature and application rate.

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 , Δ H 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 , Δ H 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.

The aim of this research was to evaluate the response of soil arylsulfatase (ARS) kinetic and thermodynamic parameters to biochar application. The kinetic parameters including V-max , K-m and catalytic efficiency (V-max K-m(-1)) as well as thermodynamic ones (E-a, Delta H-a and Q(10)) were determined in two different textured clayey and sandy loam soils amended with 0.5 and 1.0% (w/w) of unpyrolyzed maize residue (UMR) or its biochars prepared at 200 and 600 degrees C (B200 and B600, respectively). The results showed that the application of amendments to sandy loam soil increased enzymatic activity (16-106%), K-m (37-113%) and the enzyme concentration (V-max) (13-39%), whereas the V-max K-m(-1) (38-86%), E-a (6-21%) and Q(10 )(8-11%) were decreased in the biocharamended soils compared to the unamended control (CK). In clayey soil, biochar addition increased ARS activity (16-150%) and decreased the V max (10-41%), V-max K-m(-1) (63-355%), E-a (20-63%) and Q(10) (10-32%) and had no significant effect on K-m. Generally, the effects of the amendments application were greater at 1% than 0.5% application rate and in clayey than sandy loam soil. Soil texture is a determinant factor in soil arylsulfatase response (activity, kinetics and thermodynamics) to biochar application.

Biochar addition to soil often increases the activity of alkaline phosphatase (ALP) involved in phosphorus (P) cycling, but the underlying mechanisms of its effect is poorly understood. This study investigated the response of kinetic parameters including maximal velocity (V-max) and Michaelis-Menten constant (K-m), and thermodynamic parameters including activation energy (E-a), enthalpy (Delta H-a) and temperature coefficient (Q(10)) of ALP to addition of two maize biochars (400 and 600 degrees C) in two calcareous (Typic Haplocalcid) soils with clayey and sandy loam texture. The biochars were added to the soils at 1% (w/w) and the mixtures were incubated for 90 days under laboratory conditions (25 +/- 1 degrees C and 70% of water holding capacity). Soils with addition of raw residue were used as positive controls and soils without biochar and raw residue were included as negative controls. The potential activity of ALP was assayed at the end of incubation period. The kinetic parameters of ALP were estimated using non-linear regression techniques and the thermodynamic characteristics were determined at different incubation temperatures (17, 27, 37, 47 and 57 degrees C) using the Arrhenius equation. Compared with the negative control, the addition of raw residue and biochars increased ALP activity (3.1- to 4.4-fold) after the 90 day incubation, depending upon the pyrolysis temperature and soil texture. The positive effect of biochar addition on soil ALP was greater with low than high temperature biochars and in sandy loam than clayey soils. Biochar addition increased the K-m and V-max values of ALP in the clayey soil but decreased these parameters in the sandy loam soil compared with the corresponding negative controls. Generally, application of maize raw residue and biochars increased the E-m Delta H-a and Q(10) values of ALP compared with the negative controls, and the increases were similar for the two pyrolysis temperatures. Soil ALP can be strongly adsorbed by biochar particles; increasing its thermal stability and decreasing its sensitivity to elevated temperatures. In conclusion, application of maize biochar to arid-soils has a high potential to improve the ALP activity, with implications for organic P mineralization and availability. Biochar would change ALP kinetic and thermodynamic characteristics differently, depending mainly on soil texture, through the surface adsorption of this enzyme on biochar particles. These changes will be useful for modeling P mineralization and biochemical processes in biochar-amended calcareous soils.

Application of pyrolysed feedstocks or biochar has the potential to affect soil enzyme activity and function. Nevertheless, our detailed understanding of the mechanisms responsible for biochar-enzyme interaction is limited in arid soils. The main aim of this study was to study how the potential activity of several extra- and intra-cellular enzymes involved in C and N cycling, and microbial metabolism would respond to addition of biochar in two calcareous soils with fine and coarse texture. Three corn stalk biochars were prepared at 200, 400 and 600°C and added to sandy and clayey soils at 0.5 and 1% (w/w). Soils with uncharred feedstocks; and without biochar and feedstock additions as the control treatment were also included in the experiment. The potential activities of soil enzymes were assayed. Compared with the control, addition of uncharred and charred feedstocks significantly stimulated the activities of catalase (1.3- to 4.3-fold), dehydrogenase (1.2- to 3.1-fold), cellulase (1.1- to 1.7-fold), invertase (1.3- to 5.8-fold) and protease (1.03- to 2.9-fold), which varied with pyrolysis temperature and addition rate as well as soil texture. The positive effects of biochar addition on soil enzymes were much greater at 1% than 0.5% application rates for all the assayed enzymes and in sandy than clayey soils for catalase, dehydrogenase and invertase. The change in enzyme activity with biochar addition primarily attributed to the change in soil microbial biomass. However, enzyme activities were lower in the soils amended with charred than uncharred biomass, and decreased as pyrolysis temperature increased. Our results showed clearly that uncharred feedstock and lower temperature biochars gave higher benefits to both contrasting textured soils than higher temperature biochars, largely connected to changes in the physiochemical properties of biochars. Nevertheless; long-term field experiments are required to verify whether the beneficial effect of uncharred vs. charred feedstocks would be maintained over long timescales under the conditions of this study. We conclude that although biochar application may improve enzyme activities of calcareous soils with low organic matter content, increasing pyrolysis temperature adversely affects soil enzymatic functions, depending mainly on soil texture and application rate. The study evidently indicates that corn biochar addition to arid-soils may have a high potential for improving the enzyme activities as important indicators of soil quality, and subsequently carbon sequestration and biogeochemical cycles.

Biochar can be used as an organic amendment to improve soil physical and chemical attributes, with a potentially significant influence on soil microbial performance. However, this effect of biochar is poorly understood for arid soils with low organic matter content. The main objective of this study was to quantify the response of microbial attributes to corn biochar in two calcareous soils with different texture. Three slow pyrolysis biochars were prepared at 200, 400 and 600 degrees C from corn feedstocks. The biochars were added to sandy and clayey soils at 0.5 and 1% (w/w) and the mixtures were incubated for 90 days under standard laboratory conditions (25 +/- 1 degrees C and 70% of soil field capacity). Soils amended with raw (uncharred) feedstock and unamended (without biochar and raw residue) as the control were also considered in the experiment. The soil properties measured included microbial respiration during 60 days, microbial biomass carbon (C), substrate-induced respiration (SIR), fungal (FR) and (BR) bacterial respiration at the end of the incubation. Compared with the unamended control, the addition of corn raw feedstock or its biochar significantly increased cumulative microbial respiration (62-462%), MBC (66-169%), SIR (50-216%), BR (129-308%) and FR (42-200%), but tended to decrease FR/BR ratio (5-90%), depending largely upon its production temperature and application rate as well as soil texture. The positive effects of biochar addition on increasing microbial properties were more pronounced at 1% than 0.5% application rates for all the attributes and in sandy than clayey soils for MBC, SIR and FR attributes. Overall, the measured microbial attributes were all greater in uncharred than charred feedstock treatments and tended to decline with increasing pyrolysis temperature. The relative abundance of soil bacteria increased with biochar addition and pyrolysis temperature, while that of soil fungi decreased. Biochar addition increased microbial performance potentially due to an increase in soil C content while increasing pyrolysis temperature altered biochar chemistry and properties which may have contributed to the decreased microbial performance. It is concluded that although biochar application may improve microbial processes and attributes in calcareous soils with low organic matter content, its effects on microbiological properties are mainly meditated by soil texture, pyrolysis temperature for biochar production and application rate. The greatest response by the microbial indicators can occur when corn biochars produced at low temperatures were added to less fertile sandy soils at 1% addition rate. The study provided clear evidence that application of low temperature corn biochars at 45-50 t ha(-1) to calcareous soils may have a great potential for improvements in the microbial indicators of soil quality. (C) 2017 Elsevier B.V. All rights reserved.