Relationships between plant-soil feedbacks and functional traits

Plant-soil feedbacks (PSF) and functional traits are two active but not
well theoretically integrated areas of research. However, PSF and traits
are both affected by life history evolution, so the two should
theoretically be related. We provide a conceptual framework to link plant
functional traits to two types of PSF metrics, and hypothesize that
individual PSF (plant performance in conspecific versus heterospecific
soil) should be related to the fast-slow trait spectrum, while pairwise
PSF (the sum of the individual feedbacks for two species growing in each
other’s soils) should be related to trait dissimilarity. We performed
meta-analyses to test these hypotheses by compiling two datasets, one
dataset consisting of individual PSF values and plant trait values
(specific leaf area, SLA; leaf N concentration, LNC; specific root length,
SRL; fine root diameter, FRD; plant height; seed mass), and the second
consisting of pairwise PSF values and trait dissimilarity. Our
meta-analyses showed that individual PSF values were more negative in
faster-growing species with greater SLA, LNC and SRL, supporting the
growth-defence trade-off hypothesis. Plant height was positively
correlated with individual PSF, perhaps because large, long-lived plants
defend against pathogens better than smaller, shorter-lived plants. We
also found that larger-seeded species had more positive or less negative
PSF, likely reflecting greater tolerance of soil pathogens. The direction
of relationships between trait dissimilarity and pairwise PSF varied with
trait identity. Dissimilarities in SRL and FRD were negatively correlated
with pairwise PSF, while height dissimilarity was positively correlated
with pairwise PSF. The contrasting relationships may reflect distinct
links between trait dissimilarity and niche and fitness differences.
Synthesis. Our results demonstrate how an integration of PSF and
trait-based approaches can advance plant community ecology.