Sorption to Biochar Impacts β-Glucosidase and Phosphatase Enzyme Activities

Abstract

Extracellular enzymes catalyze biogeochemical reactions in soil, cycling carbon and nutrients in agricultural systems. Enzymes respond quickly to soil management, including organic amendment inputs, such as biochar, a charcoal-like solid byproduct of bioenergy production. In a previous agricultural field trial, a pine biochar amendment caused an approximately 40% decrease in the enzyme activities of β-glucosidase (BG) and phosphatase (PHOS). The large surface area of the pine biochar has the potential to sorb nutrients and other organic molecules. To test if sorption caused decreased enzyme activity, we used a laboratory assay to quantify the activity of two sorbed enzymes: BG and acid PHOS, involved in the cycling of carbon and phosphorous. The enzymes were incubated with three solid phases: (1) the high surface area pine biochar, (2) the agricultural soil, and (3) a low surface area grass biochar, for an additional comparison. We quantified the sorbed enzymes at pH 6, 7, and 8, using a Bradford protein assay, and measured the immobilized enzyme activities via high-throughput fluorometric analysis. After sorption onto pine biochar, detectable BG and PHOS activity levels dropped by over 95% relative to the soil, supporting direct sorption as one mechanism that reduces enzyme activity in biochar amended soil. This laboratory assay demonstrated that sorption could account for the lack of priming of native soil organic matter and changes in soil phosphorous cycling after pine biochar addition.

Using Phosphorus-Rich Biochars to Remediate Lead-Contaminated Soil: Influence on Soil Enzymes and Extractable P

“…This is consistent with previous results [15]. Interestingly, biochars prepared at 400 • C led to a larger decrease in β-glucosidase compared to those prepared at 300 • C and 500 • C. Inherent differences in the biochars, for example, hydrophobicity, surface area and pore size, could also be involved in this effect [20,21], although these mechanisms are poorly understood.…”

Effect of Biochar and Irrigation on the Interrelationships among Soybean Growth, Root Nodulation, Plant P Uptake, and Soil Nutrients in a Sandy Field

“…However, in a number of experiments, the mechanisms behind the biochar effect on phosphatases has not been clarified, even though biochar can increase the soil pH. Li et al (2017) observed that biochar addition enhanced alkaline phosphatase activity [29][30][31]. Masto et al (2013) reported that biochar increased acid phosphatase activity by 32% and alkaline phosphatase activity by 22.8% [12].…”

Nitrogen Dynamics in an Established Alfalfa Field under Low Biochar Application Rates

“…Additionally, the high surface area and porous nature of biochar allows for chemi-and physi-sorption of N compounds, respectively [3,12]. Further, biochar may also limit mineralization of organic matter through suppression of enzymatic activity via direct sorption of enzymes to the biochar surface [15], which could also contribute to lower mineral N availability through reduced breakdown of nitrogenous compounds. Notably, biochar-induced SIN reductions have been shown to be associated with reduced crop yield [16], and thus biochar-induced increases in N fixation during the alfalfa phase of a crop rotation may provide an alternative N source to support overall productivity.…”

“…Ecological tools can be used to directly quantify nutrient fluxes or to gain broader characterizations of the biological system. The difference in 15 N natural abundance between a non-fixing reference plant and an N-fixing legume can indicate relative differences in N fixation between treatments and over time, as well as transfer of fixed N from the N-fixing plant to the reference plant [35,36]. Since it is challenging to measure N fixation directly, it is important to employ multiple lines of evidence to measure changes in N fixation [37].…”

“…To better understand how low application rates of engineered biochar products can affect N cycling in alfalfa, we examined the effect of two different biochars on N cycling over the growing season in an established alfalfa field on a sandy soil. We used natural abundance 15 N of alfalfa and dandelions, our reference plant, in combination with N gene abundance, enzymatic activity, and SIN availability, to assess N fixation, soil-plant N dynamics, and potential N loss. We hypothesized that biochar would increase N fixation and soil nifH abundance and reduce soil microbial gene abundance associated with N loss through decreased SIN availability.…”