Impact of deadwood on functional diversity and biogeochemical traits in underlying forest soils
Forestry
Final Report Abstract
In this project, we analysed the impact of decomposing logs on fungal communities, chemical and microbial traits of underlying soils in 30 plots of the BELongDead experiment. This experiment includes logs from thirteen tree species placed in forests of different tree composition and management intensity, distinct soils and climatic conditions. Logs increased microbial biomass, C mineralization and concentrations of some nutrients in underlying soils at 0-7 cm depth. An effect of log species on soils was not observed although nutrient concentrations and wood decay rates differed among the 13 log species. The effect of logs on biogeochemical soil properties was stronger in nutrient-poor, acidic soils than in nutrient-rich soils. Likewise, soil fungal communities were affected by the presence of logs, but generally not by log species. The increase in soil fungal richness and diversity beneath logs was associated with different influences on fungal phyla and their ecological functions. Abundance of saprotrophic fungi (OTUs) increased while that of symbiotic fungi (OTUs) decreased beneath logs. The increase in saprotrophic fungi coincided with the increase in microbial biomass, in particular of the fungal biomarker ergosterol, and the C mineralization rate. Input of light available C from logs via leaching, incorporation of wood fragments or direct C translocation by fungal hyphae could have enhanced the abundance of saprotrophic fungi in underlying soils. Among saprotrophic basidiomycetes, typical wood decaying fungi such as Coprinellus micaceus, Resinicium bicolor and Hypholoma fasciculare were common in the soils. Further key drivers for fungal communities in the controls and treatments were local and regional factors. Fine root biomass at 0-10 cm depth decreased by about 20% beneath logs, indicating that the decrease in symbiotic-ectomycorrhizal fungi was linked to the decrease in fine root biomass. Decreasing fine root biomass and abundance of symbiotic fungi suggest greater competiveness of saprotrophic fungi. Higher nutrient concentrations in fine roots under Fagus logs agreed with the elevated nutrient availability in the soils whereas this effect was not observed for Picea logs. Increases in specific root length and smaller live:dead ratios of fine roots, although statistically not significant, could be related to decreasing in fine root longevity. The lab study revealed that C translocation from Fagus and Picea deadwood to spruce litter via fungal hyphae induces an increase in microbial biomass and CO2 production in spruce litter. This C translocation combined with the extension of the fungal network is a mechanism to acquire nutrients from spruce litter by its enhanced mineralization. In turn, enhanced C mineralization of spruce litter using external C sources can be classified as positive priming. Deadwood as C-rich but nutrient-poor resource can thus accelerate the decomposition of recalcitrant coniferous litter and reduce the C sequestration in organic layers of forest ecosystems. In conclusion, deadwood is an important factor in forest ecosystems functioning, regarding fungal diversity, nutrient and carbon cycling in soils.
Publications
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(2021) Changes in chemical and microbial soil parameters following 8 years of deadwood decay: an experiment with logs of 13 tree species in 30 forests. Ecosystems 24: 955-967
Minnich C., D. Persoh, C. Poll, and W. Borken
