KR bluestem (Bothriochloa ischaemum var. songarica) has some direct allelopathic effects on germination but not on seedling growth in a native/non-native mixed community of warm season grasses in Texas

Purpose Allelopathy is a plant interaction in which a donor species releases chemicals that suppress the development of receptor species. Allelopathy has been suggested as one explanation for catastrophic loss of native biodiversity in some invaded biomes; however, experimental tests of this hypothesis have had inconsistent results. Here, we examine if a previous finding of strong allelopathic effects of the warm-season, invasive C4 grass Bothriochloa ischaemum on North American prairie grasses can be reproduced in a different geographic setting. Methods We examined the effects of sterilized (autoclaved or microfiltered) and unsterilized leachate on germination and the effect of sterilized leachate on seedling growth, including five native species and two exotic warm season grass species. For nine weeks, seedlings were irrigated with water or autoclaved leachate from B. ischaemum or Schizachyrium scoparium , a native species. Results Germination rates were significantly suppressed only in the two invasive species and only when treated with sterilized leachates. Seedling biomass at harvest was largely insensitive to leachate application. Conclusions The present study did not replicate earlier results, though many details of the experimental designs were similar. However, we used sterilized leachates and soils, whereas the previous study did not, which could indicate mediation by indirect microbial effects in the previous study. In addition, historic differences in the introduction of B. ischaemum in Oklahoma and Texas, along with climatic differences, may have affected the evolution of allelopathy post-invasion. Future studies would benefit from comparisons of allelopathic effects across invasive species’ ecotypes, using sterilized and unsterilized extracts.