Global changes, such as climatic warming, can alter biological diversity across levels of organization, from populations to communities. Understanding the ecosystem-level consequences of changes in biological diversity has been a major thrust of ecological research for decades. Shifts in biodiversity, alongside the decline, can exert strong impacts on ecosystem processes such as litter decomposition. Using a mesocosm experiment, we manipulated genetic diversity in pairs of a dominant grass commonly found across mixed grass prairies in South Central U.S., Schizachyrium scoparium (little bluestem). Little bluestem is declining in abundance as a function of climatic warming as documented in a long-term warming experiment. Understanding the consequences of the decline in plant genotypic diversity from temperate grasslands, is imperative to predict future the changing functions of terrestrial ecosystems. Using little bluestem genotypes that vary in genetic relatedness and in above- and belowground functional traits, we investigated the consequences of varying plant genotype combinations in constructed mesocosms and tracked above and belowground functional traits, plant-soil microbiome diversity, primary productivity, and net mesocosm carbon exchange with the atmosphere. Specifically, we asked: (1) Does decreasing genetic relatedness promotes niche complementarity to shape productivity and greater ecosystem carbon uptake; (2) Does niche partitioning vs. plant microbial facilitation shape plant-genotype interactions to influence the functioning of grasslands?
We found that plant genotype pairs that were more genetically distant had greater productivity and ecosystem-level carbon uptake than plant genotype pairs that were more genetically similar. Niche complementarity via greater niche partitioning in less related plant genotype combinations likely contributed to our findings. For instance, above- and belowground traits shifted towards resource utilization rather than conservation amongst genetically distant pairs when compared to more closely related pairs, supporting the concept of greater niche complementarity (greater overall resource utilization). Both the variance and mean in above- and belowground traits (specific leaf area and specific root length) were greater between less related plant genotype pairs than in more related ones. Further, microbial communities in the rhizosphere did not differentiate as a function of genetic distance among plants in a given pair, indicating that niche partitioning, rather than plant microbial facilitation, influences plant-genotype interactions. Taken together, we show that plant genotype interactions of a dominant grass species can influence ecosystem function (productivity) and service (ecosystem carbon uptake). Future studies, should consider manipulating the soil microbiome, along with plant genotypes, to further understand the consequences of global changes on terrestrial ecosystems.