The authors construct a thorough context and support the approach
The authors construct a thorough context and support the approach by citing prior research to highlight the significance of their work. The authors compared the treatment of the rhizobial strain and the relevance of fitness and damage during the statistical analysis using Boege and Marquis (2005) and Winer (2004), taking into consideration "fruit production as a covariate to account for effects of plant reproductive" (654). To build up a solid base on the existence of potentially exploitative partners among plants, the authors also consulted earlier writers. For example, they used Pate et al. to establish a theoretical model indicating that variation "in mutualist quality can be maintained by frequency-dependent selection" due to mixed infection (652).
Hypothesis
The authors wanted to test the hypothesis that the presence of exploitative rhizobia affects plant herbivory and fitness.
Research Methods
The experimental design involves the manipulation of herbivory and rhizobial community. The experiment occurs across RBI single inoculation, RB7 single inoculation, T2 single inoculation, a mix of the three beneficial strains (RB1 + RB7 + T2), and a mixture of all three beneficial strain and exploitative strains (RB1 + RB7 + T2 + T173).
The plant-rhizobium and plant-insect qualification is a method used to estimate insect herbivore leaf damage. This is achieved by counting the proportion of leaflets with the presence of sap-sucking, leaf-chewing, and leaf-mining damage. During the third week, the researcher measure nodule density and the mean of individual nodule mass on the root sample.
The measure of plant performance involves the measure of whether rhizobial communities affect plant trait and the feeding behavior in an insect. The measure considers three strains: nitrogen per unit leaf area, trichome density, and carbon per unit leaf area in leaves. Statistical analysis uses a parametric model in SAS to evaluate numerical measurement of biomass and carbon per unit leaf area, proportional damage, and trichome density. The standard general linear model helps the researchers to estimate strain, block, and herbivory treatment.
Research Results
The herbivore treatment has no substantial overall impact on leaf carbon content (F1,103= 0.07; P=0.7854). Moreover, the mean nodules mass was higher on plant root when herbivores were excluded (F1,116= 3.63; P=0.0592). This implies that rhizobial inoculation treatment has great effects on the plant roots. When the plant were exposed to herbivores, there was no significant fitness difference in the presence of rhizobia. The average of RBI, RB7, T2 and Mix vs Mix + Exploiter is F1,136= 0.96; P=0.3298; q=0.1384; Mix vs Mix+Exploiter: F1,136= 0.96; P=0.1787; q=0.1031.
Oveall, there is a direct relationship between fitness and plant traits in Medicago Lupulina (carbon content, leaf nitrogen, nodule density, trichome density, and individual nodule mass). On the other hand, there is an indirect relationship between fitness and plant trait through insect herbivory. That is, leaf nitrogen content affects host fitness "indirectly through herbivore damage" (656). Lower damage on the plant exposed to rhizobia acts the same as nitrogen which reveals that exploitative rhizobia reduced leaf tissue quality.
Conclusion
The main conclusion is that theoretical models have made assumptions that exploiters are harmful to their host. The authors support this view by providing contradictory findings through different ecological conditions such as in the presence and absence of herbivores.
Work Cited
Simonsen, Anna K., and John R. Stinchcombe. “Herbivory eliminates fitness costs of mutualism exploiters.” New Phytologist 202.2 (2014): 651-661.
