Effects of plant species diversity and genetic diversity on belowground community structure and function

Background/Question/Methods

In response to global declines in biodiversity, a major goal in ecology is to understand the consequences of biodiversity for communities and ecosystems.  Past research has shown that declines in plant species richness can lead to declines in primary productivity, soil properties, and the diversity of above- and below-ground communities.  However, before a species is lost from a community, it likely suffers losses in genetic diversity due to shrinking population sizes.  Therefore, it is imperative to examine how multiple levels of biodiversity (both species and genetic diversity) may influence critical ecosystem processes.  Here, we test how genetic diversity within a dominant plant species and plant species diversity interactively influence a relatively understudied aspect of ecosystem function, belowground community structure and function.  In a long-term common garden in the Great Lakes sand dunes where both levels of diversity were simultaneously manipulated, we measured how plant diversity influenced 1) abiotic soil properties, 2) soil microbial community structure and 3) soil microbial community function.

Results/Conclusions

Genetic diversity within a dominant plant species and plant species diversity interactively influenced soil nutrients.  Specifically, soil Mg, Ca, and K increased with plant species diversity when the plant community also contained high levels of genetic diversity within the dominant plant species.  The abundance of arbuscular mycorrhizal spores present in the plant communities also tended to follow this pattern.  Soil bacterial community composition did not respond to our plant diversity treatments.  However, enzymes responsible for the breakdown of soil carbon did positively respond to diversity.  Together, these results suggest that while the structure of belowground communities may not strongly respond to differences in plant diversity, the function of those communities does.  Furthermore, this work highlights the need to incorporate both plant species diversity and genetic diversity within plant species into our understanding of how biodiversity influences ecosystem function.