Methodological interference of biochar in the determination of extracellular enzyme activities in composting samples

Abstract

Abstract. Biochar application has received increasing attention as a means to trap recalcitrant carbon and enhance soil fertility. Hydrolytic enzymatic assays, such as β-glucosidase and phosphatase activities, are used for the assessment of soil quality and composting process, which are based on use of p-nitrophenol (PNP) derivatives as substrate. However, sorption capacity of biochar can interfere with colorimetric determination of the hydrolysed PNP, either by the sorption of the substrate or the reaction product of hydrolysis into biochar surface. The aim of the present work is to study the biochar sorption capacity for PNP in biochar-blended composting mixtures in order to assess its impact on the estimation of the colorimetric-based enzymatic assays. A retention test was conducted by adding a solution of known amounts of PNP in universal buffer solution (pH = 5, 6.5 and 11, corresponding to the β-glucosidase, acid and alkaline phosphatase activity assays, respectively), in samples taken at the initial stage and after maturation stage from four different composting piles (two manure composting piles; PM: poultry manure, CM: cow manure and two other similar piles containing 10 % of additional biochar (PM + B, CM + B)). The results show that biochar-blended composts (PM + B, CM + B) generally exhibited low enzymatic activities, compared to manure compost without biochar (PM, CM). In terms of the difference between the initial and maturation stage of composting process, the PNP retention in biochar was shown higher at maturation stage, caused most probably by an enlarged proportion of biochar inside compost mixture after the selective degradation of easily decomposable organic matter. TThe retention of PNP on biochar was influenced by pH dependency of sorption capacity of biochar and/or PNP solubility, since PNP was more efficiently retained by biochar at low pH values (5 and 6.5) than at high pH values (11).

Role of biochar in promoting circular economy in the agriculture sector. Part 1: A review of the biochar roles in soil N, P and K cycles

“…Similarly, several other studies showed shifts in enzyme activities induced by biochar addition [65,85]; for instance, alkaline phosphomonoesterase activities were increased, whilst acidic phosphomonoesterase activities were inhibited by addition of biochar regardless of soil types [86,87]. However, this effect could have been partly due to the absorption of the substrate or enzymes, which occurs more strongly at lower pH rather than at a higher one [88,89]. In fact, the study performed by Masto et al [90] showed that both alkaline and acid phosphomonoesterase activities increased in red soils with addition of the biochar produced from Eichornia.…”

Impacts of Biochar on Physical Properties and Erosion Potential of a Mudstone Slopeland Soil

“…Biochar is composed of recalcitrant carbon from microbial degradation and of a charged surface with organic functional groups; therefore, it can increase soil organic carbon (SOC) levels and C stocks [ 20 – 23 ]. Biochar application could produce agronomic benefits, particularly fertility maintenance, SOC sequestration, and crop production [ 5 , 8 , 24 – 26 ]. However, few studies have examined the benefits of biochar application on the hydraulic properties and erosion recalcitrant of soil.…”

Corn and hardwood biochars affected soil microbial community and enzyme activities

“…β-glucosidase activity was determined based on p-nitrophenol (PNP) quantification at 415 nm (Eivazi & Tabatabai 1988). To correct for biochar interference (Jindo, Matsumoto, Izquierdo, Sonoki, & Sanchez-Monedero, 2014a) on the release of PNP, an additional set of samples was analyzed. Instead of the substrate (p-Nitrophenyl-β-D-glucopyranoside [PNG]), the reaction product (PNP) was added at the beginning of the incubation at concentrations of 100, 200, 300, and 500 nmol ml −1 (equivalent to 5 × 10 5 nmol PNP kg soil −1 ).…”