Glomalin mediation of plant functional traits unveiled in an extreme ecosystem

Edaphic filters associated with symbiotic relationships are determinants of plant phenotypes. Here we investigate whether glomalin, a by-product of mycorrhizal fungi that improves soil structure and quality, is involved in the filtering of traits that determine plant ecological strategies. This study was developed in two substrate types (ferruginous and quartzitic) of the harsh and ancient Brazilian grasslands known as campo rupestre. We carried out a vegetation functional survey along with soil sample analyses for glomalin content. We compared glomalin content (and its proportion in relation to soil iron content) between habitats and applied the fourth corner analysis to evaluate its relationship with various plant functional traits. Glomalin content in the ferruginous habitat was significantly higher than in the quartzitic habitat. In ferruginous plots, the persistent form of glomalin (total glomalin, TG) was associated with enhanced plant ruderality, increased specific leaf area and reduced leaf dry matter content. In contrast, in quartzitic plots the freshly produced and more volatile form of glomalin (easily extractable glomalin, EEG) was associated with enhanced plant competitiveness evident as larger leaf area, and reduced ruderality evident as increased leaf density and reduced specific leaf area. The pattern of trait filtering in relation to glomalin content was scale dependent, and differed markedly between the ferruginous and quartzitic habitats, underlining the idiosyncratic nature of plant-soil relationship in these two adjacent plant communities. Our study unveils the association between plant life history and a metabolite produced by a soil symbiont, showing how close interspecific interactions are to ecosystem functionality.