Microbial Treatments to Increase Carbon Sequestration in Biofuel Crop Systems

Authors:

Sanna Sevanto¹*, Eric Moore², Buck Hanson², Taraka Dale², Sangeeta Negi², Susannah Tringe³

Institutions:

¹Earth and Environmental Sciences Division, Los Alamos National Laboratory; ²Bioscience Division, Los Alamos National Laboratory; ³Lawrence Berkeley National Laboratory

Abstract

Improving soil carbon sequestration in agricultural systems is critical for reaching net-zero carbon goals. It is estimated that 50% of soil carbon in agricultural lands has been lost, making them a natural sink for rapid carbon restoration. In these systems, plant carbon inputs to the soil such as root exudates and liter are rapidly metabolized by microbes back to carbon dioxide (CO₂). However, recent research shows that diﬀerences in soil microbial communities can produce three-fold diﬀerence in the amount of dissolved organic carbon (DOC) leading to a proportionate decrease in CO₂ release to the atmosphere. This combined with the fact that microorganisms can beneﬁcially inﬂuence plant growth, carbon uptake, and root morphology, promoting deeper rooting, suggest that microbiome optimization either alone or combined with other plant treatments could be a solution for increasing soil carbon sequestration in agricultural systems without compromising crop yield. One of the main challenges for microbiome optimization is to develop and produce microbiomes that maintain their viability in natural environments.

To develop beneﬁcial microbiomes that could maintain their viability in natural soils, researchers tested inoculating plant seeds with growth promoting endophytic bacteria that live within the plant cells. This team hypothesized that provided successful inoculation, this habitat would protect the beneﬁcial microbes from the impacts of the complex, existing microbiome in natural soils and help them maintain their beneﬁcial eﬀects on plant growth and carbon uptake. After developing the endophytic inocula, researchers tested their impact on plant growth in the laboratory on Camelina sativa and sorghum and on greenhouse gas emissions during growth in natural soils for C. sativa utilizing a soil core-based testbed with arid agricultural soil collected from a C. sativa ﬁeld in the greenhouse. The group also compared the eﬀects of endophytes on greenhouse gas emissions to the eﬀects of inoculating the soil with nitrogen ﬁxing cyanobacteria.

The preliminary results show that, overall, inoculation with the endophytes slightly decreased CO₂ emissions from the plant-soil system for C. sativa but increased the nitrous oxide (N₂O) emissions or reduced N₂O soil sink at high water contents compared to uninoculated plants. Interestingly, the eﬀect of inoculating the topsoil with nitrogen ﬁxing cyanobacteria on CO₂ and N₂O emissions was similar to having plants with or without endophyte inoculation. In both cases, the CO₂ and N₂O emissions increased above bare soil at mid-range soil moisture contents (20 to 28%), and the natural soil N₂O sink at soil moisture contents close to saturation was removed. This suggests that plant growth promoting endophytes can positively inﬂuence carbon sequestration in soil-plant systems, but the eﬀects and their magnitude will depend complex interactions between the plant-soil-microbiome systems and environmental conditions.