Response to root competitors and R:FR in soybean.
Murphy, Guillermo*,1, Dudley, Susan1, 1 McMaster University, Hamilton, ON, Canada
ABSTRACT- Recent studies in crop legumes have shown that plants in root competition increase allocation to roots. However, leguminous plants have been shown to respond to lowered R:FR (red to far-red ratio), the cue of aboveground competition, with increased stem elongation and increased allocation to shoots over roots, which allows the plant to better forage for light and shade their neighbours. Studies to date have concentrated on these responses individually, though in nature both cues are likely to be present. Here we ask how soybean (Glycine max) will respond to both competition cues applied simultaneously, and whether nutrient levels and the presence or absence of Rhizobium bacteria affect the response to competition. In a fully factorial study, we manipulated light quality (high R:FR or low R:FR), root competition (present or absent), nutrient availability (either the recommend level or one-tenth of recommended), and Rhizobium inoculation (present or absent). In the presence of Rhizobium, we found the same contradictory responses in root allocation that others have found in single factor studies, such that plants allocated more to roots in the presence of root competition, but less to roots in low R:FR, the cue of aboveground competition. However, in the absence of Rhizobium, plants responded to low R:FR with higher allocation to roots. As expected, plants elongated under low R:FR light. However, the degree of elongation was affected by Rhizobium and nutrients. We conclude that soybean responds to both competition cues independently, but that belowground resources such as the presence of Rhizobium and availability of nutrients may regulate the relative allocation to above and belowground competition.
Key words: phenotypic plasticity, allocation, elongation
All materials copyright The Ecological Society of America (ESA), and may not be used without written permission.