Are plants locally adapted to both biotic and abiotic environmental conditions?

Background/Question/Methods

Local adaptation is when a population of organisms evolves to be better suited to its local environment than other members of the same species. While studies have shown that plants have higher fitness when grown with sympatric microbes than with allopatric microbes, few studies have looked at how environmental conditions and microbial communities interact to influence plant fitness. In this study we investigate local adaptation of plants to soil microbes and moisture conditions. We focus on Geum rossii (R. Br.) Ser. (Rosaceae), an abundant alpine plant found along a soil moisture gradient. To test for effects of soil moisture and microbes on plant fitness, we conducted a fully factorial greenhouse experiment using seeds from different populations (dry meadow and moist meadow). We treated them with a moisture regime (high or low) and an inoculum (sterile, dry origin, or moist origin). We hypothesize that (1) plants will have higher fitness when grown with live inoculum versus sterile, (2) plants will show local adaptation to moisture regardless of inoculum, and (3) plants will show local adaptation to microbes regardless of moisture.

Results/Conclusions

An ANOVA of a generalized linear model with inoculum treated as sterile or alive (representing both dry and moist origin) showed that only moisture significantly increases plant biomass; inoculum, population origin, and interaction terms do not influence plant biomass. These results do not support our hypothesis that plants would have higher fitness in the presence of live microbes. However, when we analyzed the data for moist and dry inoculum separately, we found that when plants are grown with dry inoculum, dry meadow plants have higher biomass than moist meadow plants at low soil moisture, while moist meadow plants have higher biomass than dry meadow plants at high soil moisture, a pattern suggesting local adaptation to moisture. However, when plants are grown with moist inoculum the opposite pattern is seen, a pattern suggesting maladaptation. In a similar way, when the data was analyzed separately for high and low moisture, we saw evidence of local adaptation to microbial communities at low moisture but not at high. These results suggest that climate change, and the resulting mismatch between plants, microbial communities, and local conditions, will have different consequences depending on the abiotic conditions and biota involved.