Climate change models predict that future precipitation patterns will entail lower-frequency but larger rainfall events, increasing the duration of dry soil conditions. Resulting shifts in microbial C cycling activity could affect soil C storage. Further, microbial response to rainfall events may be constrained by the physiological or nutrient limitation stress of extended drought periods; thus seasonal or multiannual precipitation regimes may influence microbial activity following soil wet-up. We quantified rainfall-driven dynamics of microbial processes that affect soil C loss and retention, and microbial community composition, in soils from a long-term (14-year) field experiment contrasting "Ambient" and "Altered" (extended intervals between rainfalls) precipitation regimes. We collected soil before, the day following, and five days following 2.5-cm rainfall events during both moist and dry periods (June and September 2011; soil water potential = -0.01 and -0.83 MPa, respectively), and measured microbial respiration, microbial biomass, organic matter decomposition potential (extracellular enzyme activities), and microbial community composition (phospholipid fatty acids). The equivalent rainfall events caused equivalent microbial respiration responses in both treatments. In contrast, microbial biomass was higher and increased after rainfall in the Altered treatment soils only, thus microbial C use efficiency (CUE) was higher in Altered than Ambient treatments (0.70 +/- 0.03 > 0.46 +/- 0.10). CUE was also higher in dry (September) soils. C-acquiring enzyme activities (beta-glucosidase, cellobiohydrolase, and phenol oxidase) increased after rainfall in moist (June), but not dry (September) soils. Both microbial biomass C:N ratios and fungal:bacterial ratios were higher at lower soil water contents, suggesting a functional and/or population-level shift in the microbiota at low soil water contents, and microbial community composition also differed following wet-up and between seasons and treatments. Overall, microbial activity may directly (C respiration) and indirectly (enzyme potential) reduce soil organic matter pools less in drier soils, and soil C sequestration potential (CUE) may be higher in soils with a history of extended dry periods between rainfall events. The implications include that soil C loss may be reduced or compensated for via different mechanisms at varying time scales, and that microbial taxa with better stress tolerance or growth efficiency may be associated with these functional shifts.

Beta-glucosidase is among the suite of enzymes produced by white rot fungi (WRF) to biodegrade plant biomass. This study investigated the enzymatic activities and kinetic properties of β-glucosidase from seventeen WRF comprised of the following species from various geographical locations: Pleurotus ostreatus, Auricularia auricular, Polyporus squamosus, Trametes versicolor, Lentinula edodes, and Grifola frondosa. All the WRF studied showed β-glucosidase activities. Significant variations in protein and carbohydrate contents were also recorded. Beta-glucosidase activities after 30 min of incubation ranged from 6.4 µg (T. versicolor) to 225 µg (G. frondosa). The calculated kinetic constant (K m ) ranged from 0.47 µM (A. auricular-1120) to 719 µM (L. edodes-7). The V max depending on the kinetic transformation model ranged from 0.21 µg·min −1 (T. versicolor) to 9.70 µg·min −1 (G. frondosa-28). Beta-glucosidase activities also exhibited pH optima between 3.5 and 5.0 while temperature optima were between 60˚C and 70˚C with some media exhibiting a secondary temperature peak at 90˚C attributable to the presence of thermostable isoenzyme. WRF if appropriately screened and purified can be harnessed to potentially improve the bioconversion of cellulose to glucose and also facilitate efficient plant biomass biodegradation and production of useful plant bio-products.

The enzyme maltase (glucoinvertase; glucosidosucrase; maltase-glucoamylase; α-glucopyranosidase; glucosidoinvertase; α- d -glucosidase; α-glucoside hydrolase; α-1,4-glucosidase EC 3.2.1.20), is involved in the exo-hydrolysis of 1,4-α-glucosidic linkages and certain oligosaccharides into glucose which is an important energy source for soil microbes. This enzyme originates from different sources, which include plants, seaweeds, protozoa, fungi, bacteria, vertebrates, and invertebrates. The assay of soil maltase using maltose as substrate and the released glucose determined using a glucose oxidase–peroxidase system has not been explored or investigated to the best of our knowledge. A simple assay protocol using this system is proposed to evaluate and characterize maltase activity in soils. The protocol involves the release of glucose (determined using a glucose oxidase–peroxidase colorimetric approach) when 1 g soil is treated with toluene and incubated with 5 mM maltose in 67 mM sodium acetate buffer (pH 5.0) at 37 °C for 1 h. The optimal activity using this procedure was at pH 5.0 and decreased at temperatures above 70 °C. The calculated K m values ranged from 0.8 to 6.5 mM, and are comparable to those of enzymes purified from microorganisms. The Arrhenius equation plots for the activity in the four soils were linear between 20 and 70 °C. The activation energy values ranged from 34.1 to 57.2 kJ mol −1 , the temperature coefficients ( Q 10 ) ranged from 1.5 to 1.9 (avg. = 1.7), and the coefficients of variation (CV) of the proposed assay protocol for the soils used was <6%. While we recognize the availability of established assay protocols to determine soil α-glucosidase (referred in other literature as maltase) activity based on the p -nitrophenol (artificial product) released from p -nitrophenyl-α- d -glucopyranoside (artificial substrate), our interest was to assay its activity by determining the glucose (natural product) released from maltose (natural substrate).

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Global demand for food, coupled with degrading soils in sub Saharan Africa necessitates novel approaches to soil fertility management. Recently, amendments other than inorganic fertilizers are being promoted to improve crop yield. They vary from region to region and crop to crop. The aim of this research was to investigate the efficacy of deep litter poultry manure as a soil amendment in tomato production in Cameroon. We tested the effects of poultry manure at 60 t ha -1 and NPK 20:10:10 at 300kg ha -1 in a Randomised Complete Block Design, with the treatment sites blocked by soil type. Classical growth parameters were measured weekly. Yield attributes were measured following harvest, and data submitted to RT ANOVA and Repeated measures ANOVA in the Minitab Version 16 statistical package. Both the organic and inorganic soil amendments increased growth and yield of tomato, but this effect was more significant in plots treated with poultry manure at 60 t ha -1 two weeks before planting. Growth effects were not clear-cut across sites and were probably mitigated by sitespecific differences in rates of nutrient-leaching. We recommend poultry manure at 60 t ha -1 to small holder tomato farmers in the humid tropics.