Belowground Processes to Enhance Durable Soil Carbon Storage: Evidence from a Long-Term Poplar Genetic Diversity Trial

There is great interest in breeding or engineering plants for increased carbon uptake, and increased carbon storage in live tissues and soils. Various plant bio-design approaches have been proposed for enhancing soil carbon storage, including selecting for more recalcitrant root tissues, and modulating root exudation to inhibit or stimulate soil microbial activity to better accumulate particulate organic matter (POM) or mineral-associated organic matter (MAOM). However, datasets and modeling tools to support such approaches are still very limited. Here we report on data collected from a long-term poplar genetic diversity trial established by the Center for Bioenergy Innovation (CBI) in northwestern Oregon in 2009, which includes over 1000 different poplar genotypes replicated across three spatial blocks. The wide plant genetic diversity, relative environmental homogeneity, and long duration of this trial make it an ideal system for quantifying the potential of plant bio-design for increased soil carbon storage, and probing the underlying mechanisms. Soil cores were collected to a depth of 30 cm for a subset of 24 poplar genotypes, fractionated, and analyzed for texture, carbon, nitrogen, and other chemistry. These data show significant genotype-level differences in total soil carbon and MAOM in particular, with minimal correlation to tree size or root chemistry (lignin content and C:N ratio). In addition, root exudates were collected in situ for a subset of 6 of those genotypes, and chemically profiled using liquid chromatography-mass spectrometry (LC-MS). Preliminary results suggest the presence of multiple phenolic compounds known to modulate soil microbial activity. Follow-up laboratory soil incubation experiments are being planned to test the effects of these phenolic compounds on the decomposition of isotope-labeled substrates, and associated effects on POM and MAOM levels.