Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.07.21.213900v1?rss=1 Authors: Lu, J.-Z., Scheu, S. Abstract: Coniferous and deciduous trees growing in pure and mixed forests are likely to supply different resources to soil microorganisms thereby shaping microbial communities. However, effects of forest type on microorganisms and their variations with site conditions remain poorly studied. We investigated microbial basal respiration, microbial biomass (substrate-induced respiration method) and phospholipid-derived fatty acids (PLFAs) in the litter and soil at four nutrient-rich and four nutrient-poor sites in Lower Saxony, Germany. At each site, pure stands of European beech (Fagus sylvatica), Norway spruce (Picea abies) and Douglas-fir (Pseudotsuga menziesii), as well as mixed species stands of beech and spruce, and beech and Douglas-fir were investigated, i.e. a total of 40 forest stands. Forest type only affected soil microorganisms at nutrient-poor sites, but not at nutrient-rich sites. In coniferous and mixed forests at nutrient-poor sites, basal respiration and microbial biomass was lower and stress indicators were higher than in beech forests. Compared to beech, microbial biomass (-59%) and stress indicators (+46 - +87%) in Douglas-fir forests were particularly affected both in litter and in soil at nutrient-poor sites. The results suggest that higher resources in beech forests beneficially affect microorganisms in litter and soil at nutrient-poor sites, whereas Douglas-fir forests are characterized by low resources as indicated by low microbial specific respiration and fungal PLFA. The results indicate that in particular at nutrient-poor sites long-term effects of planting non-native tree species such as Douglas-fir on ecosystem functioning need further attention before planting pure or mixed forests of Douglas-fir with beech at large spatial scale. By contrast, from the perspective of microbial communities and their functioning planting Douglas-fir at nutrient-rich sites appear of little concern. Overall, the results highlight the importance of resources in determining microbial community structure and functioning, and document the sensitivity of soil microorganisms to planting non-native tree species differing in the provisioning of these resources from native species. Copy rights belong to original authors. Visit the link for more info