Abstract: Aim Soil microorganisms are essential for the functioning of terrestrial ecosystems. Although soil microbial communities and functions are linked to tree species composition and diversity, there has been no comprehensive study of the generality or context dependence of these relationships. Here, we examine tree diversity-soil microbial biomass and respiration relationships across environmental gradients using a global network of tree diversity experiments. Location Boreal, temperate, subtropical and tropical forests. Time period 2013. Major taxa studied Soil microorganisms. Methods Soil samples collected from 11 tree diversity experiments were used to measure microbial respiration, biomass and respiratory quotient using the substrate-induced respiration method. All samples were measured using the same analytical device, method and procedure to reduce measurement bias. We used linear mixed-effects models and principal components analysis (PCA) to examine the effects of tree diversity (taxonomic and phylogenetic), environmental conditions and interactions on soil microbial properties. Results Abiotic drivers, mainly soil water content, but also soil carbon and soil pH, significantly increased soil microbial biomass and respiration. High soil water content reduced the importance of other abiotic drivers. Tree diversity had no effect on the soil microbial properties, but interactions with phylogenetic diversity indicated that the effects of diversity were context dependent and stronger in drier soils. Similar results were found for soil carbon and soil pH. Main conclusions Our results indicate the importance of abiotic variables, especially soil water content, for maintaining high levels of soil microbial functions and modulating the effects of other environmental drivers. Planting tree species with diverse water-use strategies and structurally complex canopies and high leaf area might be crucial for maintaining high soil microbial biomass and respiration. Given that greater phylogenetic distance alleviated unfavourable soil water conditions, reforestation efforts that account for traits improving soil water content or select more phylogenetically distant species might assist in increasing soil microbial functions

Since 2013, United Nations Secretary-General Ban Ki-moon has been urging countries around the world to adopt ambitious climate change policies so as to avoid a global temperature increase of more than 2oC during this century. Answering this call, we formed the Sustainable Canada Dialogues, an initiative that mobilizes over 60 researchers from every province, working to identify a possible pathway to a low-carbon economy in Canada. Our position paper, Acting on Climate Change: Solutions from Canadian Scholars, launched in March 2015, identifies ten policy orientations illustrated by actions that could be immediately adopted to kick-start Canada's necessary transition to a low-carbon economy and a sustainable society. Scholars from Sustainable Canada Dialogues unanimously recommend putting a price on carbon. Besides putting a price on carbon, Acting on Climate Change: Solutions from Canadian Scholars examines how Canada can reduce its greenhouse gas emissions (GHG) by (1) producing electricity with low-carbon-emissions sources; (2) modifying energy consumption through evolving urban design and transportation advancements; and (3) linking the transition to a low-carbon economy with a broader sustainability agenda, through the creation of participatory, well-coordinated, and open governance institutions that engage the Canadian public. Our proposals take into account Canada's assets and are based on the well-accepted “polluter pays” principle.