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Effects of common European tree species on interactions between C and N processes in soil and soil biota

Periodic Reporting for period 1 - AFOREST (Effects of common European tree species on interactions between C and N processes in soil and soil biota)

Periodo di rendicontazione: 2018-09-01 al 2020-08-31

• What was the problem/issue being addressed?¨
Challenges in manipulating plant-soil interactions for enhanced C sequestration and N retention arise from the huge species and life strategy diversity of both soil biota and plants, which have precluded their comprehensive characterization and limited our understanding of their ecological functions. The present research was carried out within a unique common garden experiment with monoculture stands of six common European tree species; the broadleaves beech (Fagus sylvatica L.), pedunculate oak (Quercus robur L.), lime (Tilia cordata L.), sycamore maple (Acer pseudoplatanus L.) and ash (Fraxinus excelsior L.) and the conifer Norway spruce (Picea abies (L.) Karst.). The research project focused on effects of common European trees on processes underlying soil C and N fluxes as well as on diversity and abundance of soil biota and their potential role in C and N cycling. The project adapted novel techniques such as next generation sequencing methods with modern analytical methods such as PLFA or enzyme activity to explain complex processes and mechanisms associated with C and N fluxes in soil. Results obtained from this research will contribute to bridge gaps in ecological theory in term of ecosystem functions and services.
• Why is it important for society?
One of the greatest challenges of the 21st century is to mitigate global climate changes caused by increasing emissions of greenhouse gases. Since soils constitute a larger carbon (C) pool than the vegetation and atmosphere together an important strategy could be to sequester more C in soils. Plant-soil interactions play an important role for ecosystem services such as C sequestration and N retention in soil and such interactions receive increasing attention among scientists and policymakers. Novel techniques such as next generation sequencing methods in combination with analysis of C stock patterns under different tree species present an opportunity to highlight complex processes and mechanisms which underlie C and N fluxes in soil. Novel research has highlighted the role of soil microbial diversity for C and N fluxes. However, a specific role of various members of the soil community remains unknown. In my project, I focused on diversity and structure of various soil biota (bacteria, fungi and fauna) and the role for processes involved in C and N cycling.
• What were the overall objectives?
The AFOREST project aimed to (1) explore litter mediated effects of common European tree species on soil physico-chemical properties as proxy of C and N turnover in soil; (2) characterize effects of tree species on community structure and composition of soil biota; (3) evaluate the impact of common European tree species on metabolic diversity and structure and composition of functional genes related to C and N turnover and (4) synthesize the role of soil biota for C and N turnover in soils.
• What are the conclusions?
Our results revealed higher diversity of soil bacteria and fungi in soil planted by ash, maple and lime. I also found higher bacterial growth in soils planted by ash, maple and lime while soils planted by beech, oak and spruce showed higher fungal growth. In addition, I discovered higher metabolic activity in soils planted with ash, maple lime and oak, while beech and spruce showed lower metabolic activity. There were also differences in abundance and density of soil fauna. For example, I found higher relative abundance of phylum Annelida in soils planted with beech, oak and spruce while soil planted with ash, maple and lime showed higher relative abundance of phylum Arthropoda. Finally, I found a link between litter chemistry, soil physico-chemical soil properties and relative abundance and biomass of soil biota.
I finished soil sampling on various sites planted with common European tree species across Denmark to measure soil physico-chemical soil properties, eDNA extraction, PLFA extraction as well as extraction of soil fauna. I finished DNA extraction from soil samples. The DNA was amplified using the metabarcode PCR amplification method. The PCR amplicons were sequenced to reveal community structure and composition of soil bacteria, fungi and microeukaryotes. I finished analyses of functional groups of soil bacteria and fungi using computational methods. In cooperation with PhD student Haifeng Zheng, I performed extraction and identification of PLFA to measure relative biomass of soil bacterial and fungal community as well as activity of extracellular enzymes. Together with PhD student Yan Peng, I identified and quantified the composition and structure of soil fauna. I also designed and performed a food preference test to reveal the functional role of soil fauna in litter decomposition. Finally, I did a feeding experiment to test the composition and structure of gut microbiota involved in decomposition of soil organic matter. I used statistical methods such as structural equation modelling, partial least squares modelling, neural network analysis and regression trees using R software. So far I published one paper in Soil Biology and Biochemistry as main author and one paper in Forest Ecology and Management as co-author. Two additional manuscripts are in preparation and other manuscripts are planned.
Results obtained from AFOREST project indicated effects of tree species on soil physico-chemical properties and C and N contents in soil. I identified differences in composition and structure of soil biota among various tree species. I discovered link between composition and structure of soil biota and physico-chemical soil properties. The results are useful for forest management in terms of suitable selection of tree species to increase diversity of soil organisms which in turn affect C and N fluxes in soils. In contrast to the general hypothesis that trees with high C:N ratio play a positive role in stabilizing soil organic carbon, results obtained from AFOREST project show that trees with low C:N ratio support high diversity of soil organisms which in turn may promote microbial processing and stabilization of SOC.