Switchgrass (Panicum virgatumL.) is a perennial C4 grass native to the tallgrass prairies and a most promising feedstock in the U.S. for bioenergy production. Capable of abundant biomass yield with minimal fertilizer or water, SG can survive and even thrive on marginal soils, providing positive benefit on soil nutrient condition. This study aims to improve our understanding of the effects of long-term establishment of switchgrass on soil carbon storage and nutrient availability along depth (0-150cm). Specifically, we focus on how the accumulation of root biomass (i.e., the continuous input of slow-C via root litter) in deep soil layers influences soil heterotrophic respiration (based on priming incubation experiment) by mediating the structure and functionality of microbial communities, which will consequently regulate the soil carbon balance. To this end, we attempt to (1) address the differential responses (i.e., the dynamics of their decomposition/respiration along a depth profile) to plant residual carbon inputs (slow-C) between long-term selected microbial communities from deep and shallow root systems; and (2) illustrate different potential consequences of long-term cultivation of SG on carbon sequestration at different soil types.
Results/Conclusions
After priming incubation, deep root system didn’t stimulate higher heterotrophic respiration compared to native shallow root system, and similar magnitude of priming effect was found. This suggested that the addition of root biomass litter from switchgrassdidn’t significantly increase the decomposition of soil organic matter at least under the same level of slow-C input. The ratio of primed to substrate-induced respired CO2-C (PI ratio) was further examined and higher PI ratio suggests higher percentage of the substrate-induced respired CO2-C comes from the mineralization of soil-derived carbon compared to the added substrates. Our results revealed significantly higher PI ratio at deeper soils with relatively higher total N and organic matter, implying long-term cultivation of switchgrass (more C input in deep soil) may cause different dynamics of carbon sequestration at different soil types. This suggested that, at moderate nutrient condition, more induced priming effect comes from the soil-derived carbon, and the differential microbial communities may have higher activity to access the mineral-protected compounds and promote carbon loss from deeper soils. Our on-going modeling research will further provide prediction of deep soil carbon accrual after SG cultivation by considering the dynamics of different carbon pools that are potentially mediated by microbial communities.