Plant Diversity and Nitrogen Addition on Belowground Biodiversity and Soil Organic Carbon Storage in Biofuel Cropping Systems

Bioenergy production may reduce the emission of CO 2 which contributes to climate change, particularly when management strategies are adopted that promote soil carbon (C) sequestration in bioenergy cropping systems. Planting perennial native grasses, such as switchgrass ( Panicum virgatum L. ) and big bluestem ( Andropogon gerardii Vitman ) may be used as a strategy to enhance soil C accumulation owing to their extensive root systems. Fertilizer use may further promote soil C sequestration, because of its positive impacts on plant production and soil C input. However, the influence of fertilizer addition on soil C accumulation is variable across bioenergy cropping systems, and fertilizer can negatively impact the environment. Increasing plant diversity may be used as a strategy to enhance soil C accumulation while augmenting other ecosystem properties such as soil biodiversity. The present study evaluates how inter- and intra- specific plant community diversity and N addition influence soil C storage and soil biodiversity. Soil was collected from a long-term (9 growing seasons) field experiment located at the Fermilab National Environmental Research Park in Illinois, USA. Treatments included [1] three cultivars of big bluestem and three cultivars of switchgrass cultivars grown in monoculture, [2] plant community diversity manipulated at both the species- and cultivar level, and [3] nitrogen (N) applied annually at two levels (0 and 67 kg ha -1 ). The soil at the site was dominated by C 3 grasses for 30 years before replacement with C 4 bioenergy grasses, which enabled quantification of plant-derived C accumulation owing to the natural difference in isotopic signature between C 3 and C 4 grasses. Soil samples were analyzed for [1] soil C and its δ 13 C isotopic signature, and [2] nematode and soil bacterial diversity. Our results indicate that both plant diversity and N addition influence soil community structure but not soil C storage or soil nematode biodiversity. However, the addition of big bluestem to the plant species mixes enhanced plant-derived C storage. In summary, our findings suggest that plant species identity can control soil C accumulation in the years following land conversion, and that manipulating plant community structure in bioenergy cropping systems may have a greater positive impact on soil C accumulation than N fertilization.