Chapter 24, Problem 8TYU

SCIENTIFIC INQUIRY

INTERPRET THE DATA The nitrogen-fixing bacterium Rhizobium infects the roots of some plant species, forming a mutualism in which the bacterium provides nitrogen and the plant provides carbohydrates. Scientists measured the 12-week growth of one such plant species (Acacia irrorata) when infected by six different Rhizobium strains. (a) Graph the data. (b) Interpret your graph.

Rhizobium strain	1	2	3	4	5	6
Plant mass (g)	0.91	0.06	1.56	1.72	0.14	1.03
Data from J. J. Burdon et al~ Variation In the effectiveness of symbiotic associations between native rhizobia and temperate Australian Acacia: Within-species interactions, Journal of Applied Ecology 36:398-408 (1999).
Note: Without Rhizobium, after 12 Weeks, Acacia plants have a mass of about 0.1 g.