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.
Highlights
The increasing use of wood for energy production leads to increased production of wood ash (Karltun et al, 2008; Huotari et al, 2015)
We aim to investigate bacterial community responses to wood ash addition in a spruce forest soil using 16S amplicon sequencing of bacterial rDNA and three colony forming units (CFU) approaches
Wood ash application was positively correlated to soil pH (r = 0.95, p < 0.001) and electrical conductivity (r = 0.92, p < 0.001) (Figure 1)
Summary
The increasing use of wood for energy production leads to increased production of wood ash (Karltun et al, 2008; Huotari et al, 2015). Wood ash is often treated as a waste product due to its content of toxic elements (e.g., Cd, As, Cr, and Ni) and a large proportion of the produced wood ash is deposited in landfills (Vance, 1996; Demeyer et al, 2001) This leads to considerable loss of valuable plant nutrients and potential acidification of forest plantation ecosystems (Olsson et al, 1996; Augusto et al, 2008). Addition of wood ash leads to an increase in soil pH and pore water electrical conductivity and increased concentrations of elements such as the nutrients K, S, B, Na, Ca, Mg, Si, Fe, and P (Ohno and Susan Erich, 1990; Demeyer et al, 2001; Pitman, 2006; Augusto et al, 2008). Marked changes to soil systems are known to induce sporulation of soil bacteria as a survival mechanism to unfavorable conditions (Lowe et al, 1989; Nicholson et al, 2000)
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