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Plants 2013, 2(4), 712-725; doi:10.3390/plants2040712

Responses of African Grasses in the Genus Sporobolus to Defoliation and Sodium Stress: Tradeoffs, Cross-Tolerance, or Independent Responses?

Department of Biology, Wake Forest University, Winston-Salem, NC 27109, USA
Author to whom correspondence should be addressed.
Received: 3 October 2013 / Revised: 30 October 2013 / Accepted: 31 October 2013 / Published: 8 November 2013
(This article belongs to the Special Issue Interaction Between Abiotic and Biotic Stresses in Plants)
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In the Serengeti ecosystem of East Africa, grazing ungulates prefer areas with elevated grass Na, suggesting that some grasses tolerate both high soil Na and defoliation. We performed a factorial Na-by-defoliation greenhouse study with five abundant Sporobolus congeners to explore whether Serengeti grasses possess traits which: (i) confer tolerance to both Na and defoliation (cross-tolerance); (ii) display a tradeoff; or (iii) act independently in their tolerances. Our expectation was that related grasses would exhibit cross-tolerance when simultaneously subjected to Na and defoliation. Instead, we found that physiological tolerances and growth responses to Na and defoliation did not correlate but instead acted independently: species characterized by intense grazing in the field showed no growth or photosynthetic compensation for combined Na and defoliation. Additionally, in all but the highest Na dosage, mortality was higher when species were exposed to both Na and defoliation together. Across species, mortality rates were greater in short-statured species which occur on sodic soils in heavily grazed areas. Mortality among species was positively correlated with specific leaf area, specific root length, and relative growth rate, suggesting that rapidly growing species which invest in low cost tissues have higher rates of mortality when exposed to multiple stressors. We speculate that the prevalence of these species in areas of high Na and disturbance is explained by alternative strategies, such as high fecundity, a wide range of germination conditions, or further dispersal, to compensate for the lack of additional tolerance mechanisms. View Full-Text
Keywords: sodium; defoliation; stress; stress interactions; salinity; congener comparison sodium; defoliation; stress; stress interactions; salinity; congener comparison

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Griffith, D.M.; Anderson, T.M. Responses of African Grasses in the Genus Sporobolus to Defoliation and Sodium Stress: Tradeoffs, Cross-Tolerance, or Independent Responses? Plants 2013, 2, 712-725.

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