Root traits and soil micro-organisms as drivers of plant-soil feedbacks within the sub-arctic tundra meadow

Plant-soil feedback (PSF) results from the influence of plants on the composition and abundance of various taxa and functional groups of soil micro-organisms, and their reciprocal effects on the plants. However, little is understood about the importance of fine root traits and root economic strategies in moderating microbial-driven PSF. We examined the relationships between PSF and 11 chemical and morphological root traits from 18 sub-arctic meadow plant species, as well as the soil microbial community composition which we characterized using phospholipid fatty acids (PLFAs) and high-throughput sequencing. We also investigated the importance of the root economics spectrum in influencing PSF, because it indicates plant below-ground economic strategies via trade-offs between resource acquisition and conservation. When we considered the entire root economics spectrum, we found that PSFs were more negative when root trait values were more acquisitive across the 18 species. In addition, PSF was more negative when values of root nitrogen content and root forks per root length were higher, and more positive when root dry matter content was higher. We additionally identified two fungal orders that were negatively related to PSF. However, we found no evidence that root traits influenced PSF through its relationship with these fungal orders. Synthesis. Our results provide evidence that for some fine root traits, the root economics spectrum and some fungal orders have an important role in influencing PSF. By investigating the roles of soil micro-organisms and fine root traits in driving PSF, this study enables us to better understand root trait-microbial linkages across species and therefore offers new insights about the mechanisms that underpin PSFs and ultimately plant community assembly