Living on the edge: environmental and genetic influences on plant growth and mycorrhizal root colonization in dolomite glades

Background/Question/Methods

Environmental differences between edge and core habitat can alter species composition and interactions. Previous research in dolomite glades (dry rocky grassland openings in the Ozark Plateau woodlands) indicates higher mean AMF root colonization in core habitat (0.56±0.033, mean±SE) than edge habitat (0.46±0.030, mean±SE). However, implications of spatial variation in AMF for glade plant productivity are unknown. We conducted a common garden experiment exploring how the soil community affected growth of the glade species Schizachyrium scoparium. We also tested for genetic variation in growth response to soil microbes between edge and core ecotypes of S. scoparium. Eighteen S. scopariumplants collected in core and edge habitats of three glades were split into individual shoots (ramets), and the root mass was removed to allow regrowth of sterile roots.  Ramets were placed in edge soil, core soil, sterile edge soil, and sterile core soil. After three months, plants were harvested and final leaf number counted. An ANCOVA was used to characterize reaction norms of edge and core ecotypes across the range of AMF colonization captured in the soil treatments. 

Results/Conclusions

Ramets in the sterile soil treatments produced fewer leaves than ramets in either core or edge soil. Additionally, parent identity explained 32% of the variation in leaf number among ramets.  Average AMF root colonization in the habitats from which soil sources were taken was positively correlated with plant growth. Moreover, reaction norms differed with plants collected at the edge producing more leaves than plants collected from the core habitat when grown in sterile soil. These results suggest that AMF have strong effects on glade plant growth and that S. scoparium exhibits ecotypic specialization to edge and core soils.  Specifically, loss of microbial endosymbionts reduces growth more strongly in plants from core habitat than those from edge habitat. Based on this experiment, we recommend initial plantings that include seed from edge residents when restoring plant communities in edge-dominated, fragmented or highly disturbed sites.