Abstract
Wood ash is alkaline and contains base-cations. Application of wood ash to forests therefore counteracts soil acidification and recycle nutrients removed during harvest. Wood ash application to soil leads to strong vertical gradients in physicochemical parameters. Consequently, we designed an experimental system where small-scale vertical changes in soil properties and prokaryotic community structure could be followed after wood ash application. A mixed fly and bottom ash was applied in dosages of 3 and 9 t ha−1 to the surface of soil mesocosms, simulating a typical coniferous podzol. Soil pH, exchangeable cations and 16S prokaryotic community was subsequently assessed at small depth intervals to 5 cm depth at regular intervals for one year. Wood ash significantly changed the prokaryotic community in the top of the soil column. Also, the largest increases in pH and concentrations of exchangeable cations was found here. The relative abundance of prokaryotic groups directionally changed, suggesting that wood ash favors copiotrophic prokaryotes at the expense of oligotrophic and acidophilic taxa. The effect of wood ash were negligible both in terms of pH- and biological changes in lower soil layers. Consequently, by micro-vertical profiling we showed that wood ash causes a steep gradient of abiotic factors driving biotic changes but only in the top-most soil layers.
Highlights
Wood ash is alkaline and contains base-cations
Such investigations are presently scarce because assessment of wood ash effects on ecosystems typically relies on bulk sampling that combines soil from the upper 5–15 cm of the soil column, which may mask or average stratified effects[39,40]
Wood ash application creates strong vertical gradients in environmental parameters down the uppermost part of the soil profile. This is seen as large increases in pH and exchangeable cation concentrations just below the soil surface with less pronounced increases at deeper soil layers
Summary
Wood ash is alkaline and contains base-cations. Application of wood ash to forests counteracts soil acidification and recycle nutrients removed during harvest. Ash-induced changes in vertical gradients of environmental variables and nutrient availability can potentially affect biological processes, ecosystem structure and soil ecosystem services. It is important to investigate the interaction between wood ash induced physicochemical gradients in top soils and the derived biotic consequences at the micro-vertical scale Such investigations are presently scarce because assessment of wood ash effects on ecosystems typically relies on bulk sampling that combines soil from the upper 5–15 cm of the soil column, which may mask or average stratified effects[39,40]
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