Biochar effects on soil microbial communities and resistance of enzymes to stress

2013 Fall.Includes bibliographical references.Biochar, a product of the pyrolysis of organic material, has received wide attention as a means to improve soil fertility and crop productivity, absorb pollutants in soil, and sequester carbon to mitigate climate change. Little information exists on the short- and longer-term effects of biochar on soil microbial communities and enzyme activities, relative to other organic amendments such as manure. Therefore, the objectives of this study were to determine the short and longer terms effects of biochar amendment on soil microbial communities, arbuscular mycorrhizal (AM) fungi, and enzyme activities in a semi-arid soil. Secondly, due to the porosity and surface area of biochar, enzyme stabilization on biochar was assessed to determine if biochar could prohibit the loss of extracellular enzyme activity following a denaturing stress. In a field study, a fast pyrolysis biochar (CQuest) derived from oak and hickory hardwood was applied to calcareous soil of replicate field plots in fall 2008 at a rate of 22.4 Mg ha-1 (dry wt.). Other plots received dairy manure (42 Mg ha-1 dry wt), a combination of biochar and manure at the aforementioned rates, or no amendment (control). Plots were annually cropped to corn (Zea maize L.). Surface soils (0-30 cm) were sampled directly under corn plants in late June 2009 and early August 2012, one and four years after treatment application, and assayed for microbial community fatty acid profiles and six extracellular enzyme activities involved in C, N, and P cycling in soil. In addition, AM fungal colonization was assayed in corn roots in 2012. Relative to the manure treatment, biochar had no effect on microbial community biomass, community structure, extracellular enzyme activities, or root colonization of corn by AM fungi. Manure amendment increased microbial biomass in 2009, when total FAME concentration was 2.3-fold and 2.6-fold greater in manure and biochar plus manure treatments, respectively, compared to non-amended soil. The concentration of the AM fungal FAME biomarker (16:1ω5c) was significantly reduced by the manure treatments in 2009 (P=0.014) but not in 2012. In 2009, principle components analysis (PCA) revealed shifts in the FAME structure of the soil microbial community in response to the manure treatments. However, the effects of manure on microbial biomass and community structure were short-lived, as no effects were observed in 2012. A laboratory incubation study was conducted to determine whether biochar would stabilize extracellular enzymes in soil and prohibit the loss of potential enzyme activity following a denaturing stress such as microwaving. Soil was incubated in the presence of biochar (0, 1, 2, 5, or 10% by weight) and exposed to increasing levels of microwave stress. Results showed that extracellular enzymes responded differently to biochar rate, stress level and their interactions. The main effect of stress level was highly significant (P<0.0001) on the potential activities of β-glucosidase, β-D-cellobiosidase, N-acetyl-β-glucosaminidase, and phosphatase enzymes. Potential activity of leucine aminopeptidase was significantly affected by biochar rate (P=0.016), stress level (P<0.0001), and their interaction (P=0.0008). In addition, potential activity of β-xylosidase was marginally affected by biochar's interaction with stress level (P=0.066). The potential activity of these two enzymes were reduced after a 36-day incubation in the presence of biochar. For β-xylosidase, intermediate application rates (1 and 5 %) of biochar prevented a complete loss of this enzyme's potential activity after soil was exposed to 400 (1% biochar treatment) or 1600 (5% biochar treatment) J microwave energy g-1 soil. In conclusion, this study demonstrated that land application of biochar may not affect microbial community biomass, potential activities of soil enzymes, or AM fungal biomass in soil, or alter community structure, presumably because of the type of biochar employed in this study. Both biochar and manure added carbon to soil, but microorganisms were responsive to manure rather than biochar. While biochar had no effect on potential activity of soil enzymes in the field study, the laboratory incubation study revealed that biochar has the potential to stabilize extracellular enzymes and prohibit the loss of potential enzyme activity in soil when exposed to a denaturing stress

Stabilizing effect of biochar on soil extracellular enzymes after a denaturing stress

Stabilization of extracellular enzymes may maintain enzymatic activity for ecosystem services such as carbon sequestration, nutrient cycling, and bioremediation, while protecting enzymes from proteolysis and denaturation. A laboratory incubation study was conducted to determine whether a fast pyrolysis biochar (CQuest) derived from oak and hickory hardwood would stabilize extracellular enzymes in soil and prohibit the loss of potential enzyme activity following a denaturing stress, in this case microwaving. Soil was incubated in the presence of biochar (0, 1, 2, 5, or 10% by weight) for 36 days and subsequently exposed to microwave energies of 0, 400, 800, 1600, or 3200 Joules per gram of soil. Soil enzymes (ß-glucosidase, ß-D-cellobiosidase, N-acetyl-ß-glucosaminidase, phosphatase, leucine aminopeptidase, and ß-xylosidase) were analyzed by fluorescence-based assays. Biochar amendment significantly reduced the potential activity of leucine aminopeptidase and ß-xylosidase after the incubation period and prior to stress exposure. Microwaving provided stress through heat and loss of soil water, although at the lowest stress level (400 Joules per gram of soil) soil water loss was significantly reduced in soil amended with 10% biochar. Enzyme stabilization was demonstrated for ß-xylosidase, whereby intermediate biochar application rates (1 and 5 %) prevented a complete loss of this enzyme’s potential activity after soil was exposed to 400 (1% biochar treatment) or 1600 (5% biochar treatment) Joules of microwave energy per gram of soil. Potential activities of ß-glucosidase, ß-D-cellobiosidase, N-acetyl-ß-glucosaminidase, and phosphatase enzymes were not affected by biochar, and activities of these enzymes decreased significantly with increasing levels of microwave energy. We concluded that biochar has the potential to prevent evaporative losses of soil water to some degree and stabilize certain extracellular enzymes such as ß-xylosidase so that activity is maintained after a denaturing stress. This effect was dependent, however on biochar application rate and the enzyme itself. Furthermore, while biochar may reduce the potential activity of certain extracellular enzymes in soil, this phenomenon was not universal as the majority of enzymes assayed in this study were unaffected by exposure to biochar

Contrasting effects of biochar versus manure on soil microbial communities and enzyme activities in an Aridisol

Biochar has been shown to increase microbial activity, alter microbial community structure, and increase soil fertility in arid and semi-arid soils, but at relatively high rates that may be impractical for large-scale field studies. This contrasts with organic amendments such as manure, which can be abundant and inexpensive if locally available, and thus can be applied to fields at greater rates than biochar. In a field study comparing biochar and manure, a fast pyrolysis hardwood biochar (10 tons per acre), dairy manure (19 tons per acre), a combination of biochar and manure at the aforementioned rates, or no amendment (control) was applied to an Aridisol (n=3) in fall 2008. Plots were annually cropped to corn. Surface soils (0-12 inches) were sampled directly under corn plants in late June 2009 and early August 2012, and assayed for microbial community fatty acid methyl ester profiles and six extracellular enzyme activities involved in soil carbon, nitrogen, and phosphorus cycling. Arbuscular mycorrhizal fungal colonization was assayed in corn roots in 2012. Biochar had no effect on microbial biomass, community structure, extracellular enzyme activities, or arbuscular mycorrhizal fungi root colonization of corn. In the short-term, manure amendment increased microbial biomass, altered microbial community structure, and significantly reduced the soil concentration of the arbuscular mycorrhizal fungal fatty acid methyl ester biomarker 16:1'5c. Manure also reduced the percent root colonization of corn by arbuscular mycorrhizal fungi in the longer-term. Depending on the rate applied, biochar may not cause significant shifts in the microbial community status and therefore not affect soil nutrient cycling activities and nutrient availability