Wood Ash Induced pH Changes Strongly Affect Soil Bacterial Numbers and Community Composition

Abstract

Recirculation of wood ash from energy production to forest soil improves the sustainability of this energy production form as recycled wood ash contains nutrients that otherwise would be lost at harvest. In addition, wood-ash is beneficial to many soils due to its inherent acid-neutralizing capabilities. However, wood ash has several ecosystem-perturbing effects like increased soil pH and pore water electrical conductivity both known to strongly impact soil bacterial numbers and community composition. Studies investigating soil bacterial community responses to wood ash application remain sparse and the available results are ambiguous and remain at a general taxonomic level. Here we investigate the response of bacterial communities in a spruce forest soil to wood ash addition corresponding to 0, 5, 22, and 167 t wood ash ha-1. We used culture-based enumerations of general bacteria, Pseudomonas and sporeforming bacteria combined with 16S rRNA gene amplicon sequencing to valuate soil bacterial responses to wood ash application. Results showed that wood ash addition strongly increased soil pH and electrical conductivity. Soil pH increased from acidic through neutral at 22 t ha-1 to alkaline at 167 t ha-1. Bacterial numbers significantly increased up to a wood ash dose of 22 t ha-1 followed by significant decrease at 167 t ha-1 wood ash. The soil bacterial community composition changed after wood ash application with copiotrophic bacteria responding positively up to a wood ash dose of 22 t ha-1 while the adverse effect was seen for oligotrophic bacteria. Marked changes in bacterial community composition occurred at a wood ash dose of 167 t ha-1 with a single alkaliphilic genus dominating. Additionally, spore-formers became abundant at an ash dose of 167 t ha-1 whereas this was not the case at lower ash doses. Lastly, bacterial richness and diversity strongly decreased with increasing amount of wood ash applied. All of the observed bacterial responses can be directly explained by the wood ash induced changes in pH, electrical conductivity and the addition of wood ash inherent nutrients.

Total RNA-sequencing reveals multi-level microbial community changes and functional responses to wood ash application in agricultural and forest soil

“…The increase in 16S rRNA gene copy numbers after ash amendment (up to 12 t ha −1 and 90 t ha −1 for the agricultural and forest soil, respectively) is consistent with other reports of increasing bacterial numbers after wood ash application (Bååth & Arnebrant, 1994; Fritze et al , 2000; Perkiömäki & Fritze, 2002; Bang-Andreasen et al , 2017; Vestergård et al , 2018). The large increase in the forest soil is further consistent with the increased pH as most bacteria thrive better at pH around 7 (Rousk et al , 2009).…”

“…We found that ash-amendment strongly increased soil pH, which is a strong driver of microbial community composition and functioning (Fierer & Jackson, 2006; Rousk et al , 2010) also after wood ash application (Frostegård et al , 1993; Zimmermann & Frey, 2002; Högberg et al , 2007; Peltoniemi et al , 2016; Bang-Andreasen et al , 2017). DOC and phosphate concomitantly increased.…”

“…Bacteroidetes, Alphaproteobacteria and Betaproteobacteria were stimulated by wood ash application. Members of Bacteroidetes benefit from wood ash application (Noyce et al , 2016; Bang-Andreasen et al , 2017); they are initial metabolizers of labile carbon and respond positively to increased soil pH and electrical conductivity (Fierer et al , 2007; Lauber et al , 2009; Kim et al , 2016). Alpha- and Betaproteobacteria are also generally copiotrophic (Fierer et al , 2007; Cleveland et al , 2007); Betaproteobacteria thrive in soils with higher pH (Kim et al , 2016), whereas Alphaproteobacteria are favoured at high N availability (Nemergut et al , 2010; Fierer et al , 2012).…”

Unexplored potential of novel biochar-ash composites for use as organo-mineral fertilizers

“…The effects of wood ash on soil pH and nutrient status of the soil, however, are only shortlived due to the high solubility of K and Na oxides, hydroxides and carbonates which leach quickly (Ulery et al, 1993). Furthermore, the high K availability, general salinity (high electric conductivity (EC)) and high pH, change the soil chemistry rapidly which can result in toxicity in plants and soil organisms and shifts in soil microbial composition (Augusto et al, 2008;Bang-Andreasen et al, 2017;Demeyer et al, 2001;Etiegni et al, 1991b;Jagodzinski et al, 2018;Qin et al, 2017;Staples and Van Rees, 2001). Therefore, means to create an ash-M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 4 containing material which supplies nutrients in a more controlled way makes the use of ash in forestry and agriculture much more attractive and therefore, reduces the amount of ash being landfilled and closes the nutrient loops.…”

Pulp and Paper Mill Fly Ash: A Review

“…Contaminant-free PPFA has great significance as a soil liming agent and fertilizer in agriculture and forestry [6,11]; however, its direct application requires safety precautions due to its undesirable handling and spreading characteristics and associated health risks [12,13]. Further, high pH and electrical conductivity values of pore water in wood ash might have perturbing effects on the microbial community [14]. In order to withstand extreme conditions, the bacteria may enter a dormant stage, thereby decreasing the microbial population and diversity and ultimately disturbing the ecological balance.…”