Many plants interact with soil organisms like arbuscular mycorrhizal fungi (AMF) and plant parasitic nematodes (PPN) which are known to affect biomass production, both above- and belowground. However, little is known about how belowground interactions may influence other plant traits, such as lignin composition. Understanding bioenergy crops’ responses to belowground organisms is especially important, as both the quantity and quality of biomass can affect bioenergy economics. Our objective in this study was to evaluate the effects of AMF and PPN on lignin composition of switchgrass, a candidate perennial bioenergy feedstock crop. In 2017, we conducted a split plot experiment at the W.K. Kellogg Biological Station LTER site, manipulating soil organisms using four biocide treatment combinations (fungicide, nematicide, both and none) on mature stands of one of two switchgrass varieties (Southlow or Cave-In-Rock) crossed with two fertilizer levels (0 or 56 kg N ha-1). Plant aboveground and belowground biomass were sampled, weighed, and analyzed for lignin monomer composition at two times, mid-season and harvest.
Results/Conclusions
While total lignin did not vary among treatments, both whole-plot and split-plot treatments had significant effects on monomeric composition of lignin by the end of the growing season. By October, the fungicide treatment increased syringyl (S) compared to control plants. When both biocides were applied, gyaiacyl (G) and p-hydroxyphyenl (H) were reduced compared to control plants. Additionally, switchgrass varieties differed in their lignin monomer composition, with Cave-In-Rock with nitrogen fertilizer having more S units than other whole-plot treatments, while Southlow without nitrogen fertilizer had more H units than other whole-plot treatments. No effects of any treatments were found on aboveground biomass. The results indicate that belowground organisms and fertilizers can alter the biomass quality of bioenergy crops, even when biomass quantity is not affected, as increases in S:G is generally desirable for biomass processing. Changes in lignin composition affects feedstock processing efficiency as well as plants’ mechanical strength and resistance to biotic and abiotic stresses.