Abstract Detail


Johnson, Loretta [1], Reichelt, Rory [1], Nagel, Anna [2], Galliart, Matt [1].

Niche divergence in big bluestem grass ecotypes in response to experimental drought: Mechanisms of local adaptation.

Interspecific variation in plant communities is known to affect ecosystem productivity, stability, and resilience. Yet, recent work has shown that intraspecific variation can have an even greater effect than interspecific variation. Intraspecific variation is often due to local selective pressures, leading to local adaptation. From reciprocal gardens, we showed that Andropogon gerardii, the dominant grass species in tallgrass prairie, exhibits local adaptation to precipitation and occurs as wet and dry ecotypes in their home sites of southern Illinois (SIL ecotype) and central Kansas (CKS ecotype), respectively. Here, we characterize mechanisms of intraspecific competition between ecotypes of A. gerardii in watered and drought treatments in a greenhouse experiment. We hypothesize that: 1) because ecotypes are under strong heterogenous selection pressure to rainfall, we expect functional traits differences in wet and dry ecotypes in response to precipitation differences, 2) wet and dry ecotypes should respond differentially to drought, with dry ecotypes better able to tolerate drought, and 3) if differences between ecotypes are strong, then plants of the same ecotype should compete more with each other than with plants of a different ecotype. To test these, CKS and SIL ecotypes were grown in pots (4 plants/pot, 4 replicates, total 80 pots, 320 plants in total) in mixed ecotype and single ecotype combinations for 16 weeks, under drought conditions (watered at 1/3 frequency compared to controls). Metrics of plant performance included height, number of tillers, blade width, flower timing, SPAD, and photosynthesis. Flower timing and height showed significant ecotype and drought effects. CKS flowered significantly earlier compared to SIL. Drought slowed flowering regardless of ecotype.  Drought reduced height, disproportionately in SIL, suggesting the wet ecotype is more sensitive to drought. Several trait responses (blade width, flowering stalk diameter, and number of tillers) showed a significant ecotype effect, but no drought effect. SIL had wider leaves, greater stalk diameter and fewer tillers compared to CKS. CKS showed enhanced photosynthesis and SPAD under drought compared to SIL.  For the ecotype neighbor effect, for most response variables, no effect of identity of neighboring ecotype (same or different ecotype) was evident, at least after 4 months, although longer timescales may be needed to elucidate responses. Combined, these results suggest that ecotypes of Andropogon gerardii have functionally different growth strategy tradeoffs. This work provides additional evidence that local selection pressures have resulted in local adaptation and ecotypic differences in big bluestem.

1 - Kansas State University, Biology, Ackert Hall Rm 232, Manhattan , KS, 66506-4901, United States
2 - University of Minnesota, Ecology, Minneapolis-St Paul, MN, US

none specified

Presentation Type: Oral Paper
Abstract ID:756
Candidate for Awards:None

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