Wood ash application in a managed Norway spruce plantation did not affect ectomycorrhizal diversity or N retention capacity

Production of Fungal Mycelia in a Temperate Coniferous Forest Shows Distinct Seasonal Patterns

In temperate forests, climate seasonality restricts the photosynthetic activity of primary producers to the warm season from spring to autumn, while the cold season with temperatures below the freezing point represents a period of strongly reduced plant activity. Although soil microorganisms are active all-year-round, their expressions show seasonal patterns. This is especially visible on the ectomycorrhizal fungi, the most abundant guild of fungi in coniferous forests. We quantified the production of fungal mycelia using ingrowth sandbags in the organic layer of soil in temperate coniferous forest and analysed the composition of fungal communities in four consecutive seasons. We show that fungal biomass production is as low as 0.029 µg g-1 of sand in December-March, while it reaches 0.122 µg g-1 in June-September. The majority of fungi show distinct patterns of seasonal mycelial production, with most ectomycorrhizal fungi colonising ingrowth bags in the spring or summer, while the autumn and winter colonisation was mostly due to moulds. Our results indicate that fungal taxa differ in their seasonal patterns of mycelial production. Although fungal biomass turnover appears all-year-round, its rates are much faster in the period of plant activity than in the cold season.

Effect of ash application on the decomposer food web and N mineralization in a Norway spruce plantation

In the face of global climate change there is an increasing demand for biofuel, which exerts pressure on production and thus management of biofuel plantations. The intensification of whole-tree harvest from biofuel plantations increases export of nutrients. Returning ash from biofuel combustion to the forest plantations can amend the soil nutrient status and thus facilitate sustainable forest management. However, ash affects the forest floor decomposer food web, potentially changing organic matter turnover, carbon sequestration and nitrogen availability. Our aim was to examine the response of decomposer organisms, food web structure and nitrogen mineralization function after ash application. In a coniferous forest plantation amended with 0, 3, 4.5 or 6 t ash ha^-1, we sampled in several depths of the forest floor for key organisms of the decomposer food web (fungal biomass, 0-12 cm; bacteria, protozoa, nematodes and enchytraeids, 0-3 cm and 3-6 cm; microarthropods and earthworms, 0-5 cm), 2, 14 and 26 months after ash application. We used structural equation modelling (SEM) to detangle the direct and indirect effects of ash application on organisms in the decomposer food web and on nitrogen availability. We found that ash increased the abundance of bacteria and protozoa, as well as the inorganic nitrogen pool at 0-3 cm depth, whereas the effect of ash was negligible at 3-6 cm depth. Earthworm abundance increased, whereas enchytraeid abundance decreased 2 years after ash application. The structural equation modelling showed that ash application stimulated the bacterial feeding pathway and increased nitrogen mineralization. Contrary, ash had a negative effect on fungal biomass at the first sampling, however, this effect subdued over time. Our results suggest that as the soil decomposer food web is resilient to ash application, this is a viable option for sustainable management of biofuel plantations.