The mandate by the Energy Independence and Security Act of 2007 to increase renewable fuel production in the USA has resulted in extensive research into the sustainability of perennial bioenergy crops such as switchgrass (Panicum virgatum) and miscanthus (Miscanthus9 giganteus). Perennial grassland crops have been shown to support greater aboveground biodiversity and ecosystem function than annual crops. However, management considerations, such as what crop to plant or whether to use fertilizer, may alter belowground diversity and ecosystem functioning associated with these grasslands as well. In this study, we compared crop type (switchgrass or miscanthus) and nitrogen fertilization effects on arbuscular mycorrhizal fungal (AMF) and soil nematode abundance, activity, and diversity in a long-term experiment. We quantified AMF root colonization, AMF extra-radical hyphal length, soil glomalin concentrations, AMF richness and diversity, plant-parasitic nematode abundance, and nematode family richness and diversity in each treatment. Mycorrhizal activity and diversity were higher with switchgrass than with miscanthus, leading to higher potential soil carbon contributions via increased hyphal growth and glomalin production. Plant-parasitic nematode (PPN) abundance was 2.3 9 higher in miscanthus plots compared to switchgrass, mostly due to increases in dagger nematodes (Xiphinema). The higher PPN abundance in miscanthus may be a consequence of lower AMF in this species, as AMF can provide protection against PPN through a variety of mechanisms. Nitrogen fertilization had minor negative effects on AMF and nematode diversity associated with these crops. Overall, we found that crop type and fertilizer application associated with perennial bioenergy cropping systems can have detectable effects on the diversity and composition of soil communities, which may have important consequences for the ecosystem services provided by these systems.

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Perennial grass energy crop production is necessary for the successful and sustainable expansion of bioenergy in North America. Numerous environmental advantages are associated with perennial grass cropping systems, including their potential to promote soil carbon accrual. Despite growing research interest in the abiotic and biotic factors driving soil carbon cycling within perennial grass cropping systems, soil fauna remain a critical yet largely unexplored component of these ecosystems. By regulating microbial activity and organic matter decomposition dynamics, soil fauna influence soil carbon stability with potentially significant implications for soil carbon accrual. We begin by reviewing the diverse, predominantly indirect effects of soil fauna on soil carbon dynamics in the context of perennial grass cropping systems. Since the impacts of perennial grass energy crop production on soil fauna will mediate their potential contributions to soil carbon accrual, we then discuss how perennial grass energy crop traits, diversity, and management influence soil fauna community structure and activity. We assert that continued research into the interactions of soil fauna, microbes, and organic matter will be important for advancing our understanding of soil carbon dynamics in perennial grass cropping systems. Furthermore, explicit consideration of soil faunal effects on soil carbon can improve our ability to predict changes in soil carbon following perennial grass cropping system establishment. We conclude by addressing the major knowledge gaps that should be prioritized to better understand and model the complex connections between perennial grass bioenergy systems, soil fauna, and carbon accrual.

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Patterns of tree species distributions in bottomlands are a result of various environmental and biological factors, including flood tolerance, seed dispersal, and species interactions. We evaluated the patterns of distribution and seed dispersal of tree species in a naturally regenerating bottomland hardwood forest in northeast Louisiana. We used nearest neighbor analysis to determine distribution patterns of the following canopy-dominant tree species: Carya aquatica, Celtis laevigata, Diospyros virginiana, Fraxinus pennsylvanica, Gleditsia triacanthos, and Quercus nigra. Results indicated an aggregated distribution pattern for Q. nigra, G. triacanthos, D. virginiana, and Ce. laevigata, while Ca. aquatica and F. pennsylvanica had random distributions in the study area. Additionally, we designed and used three types of seed traps to assess the seed dispersal of tree species. Modeled patterns of seed dispersal for F. pennsylvanica, Ca. aquatica, and Crataegus viridis indicated aggregated seed dispersal for these species. Low seed captures for all other species prevented modeling of their seed dispersal patterns. These results indicate that many of the tree species characteristic of bottomlands have nonrandom distributions. These distributions could be due to a variety of biotic or abiotic factors. Seed dispersal was similarly aggregated, at least for species where seed capture totals were high enough for modeling. Characterizing patterns in plant distribution and seed dispersal is important for understanding how plant communities develop during succession. Bottomland reforestation efforts should focus on planting species to match their natural distributions in an attempt to restore these communities to a more natural state.