Defining Microbial Soil Health in the Inland Pacific Northwest

Primary author: Katherine Naasko
Co-author(s): Haiying Tao
Faculty sponsor: Dr. Haiying Tao

Primary college/unit: Agricultural, Human and Natural Resource Sciences
Campus: Pullman


Phospholipid fatty acid (PLFA) biomarker identification is commonly included in microbial soil health assessments. PLFAs comprise the bilayer cellular membranes of macro and microorganisms that live within soil. Previous literature has shown that PLFA biomarkers and beta-glucosidase enzyme activity are strongly correlated to SOM stocks and associated biochemical nutrient cycling, focused primarily on the surface 20 cm of soil. Many researchers have reported a significant decrease in PLFAs with increasing soil depth, correlated with less SOM to house microbial activity. In dryland cropping systems of the Palouse, winter wheat (WW) roots grow several feet deep, along with microbial communities naturally drawn to the root also, to take advantage of water and nutrients. The objectives of this study include (i) assess how winter wheat-associated microbial communities identified through PLFA and b-glucosidase activity correlate with soil organic matter stocks to 1 meter deep; and (ii) examine relationships across different dynamic soil factors (i.e. tillage intensity) and inherent properties (i.e., precipitation and temperature) of Palouse silt loam. Agricultural sites had lower PLFA biomass compared to the grass site, however the relationships between carbon stocks and enzyme activities are not as straightforward. All sites had lower indicators deeper in the soil, which positively correlates to relative availability of carbon sources for food and energy. When comparing soils from ag sites along the precipitation and temperature gradient, significant linear correlations were found.

This is supported in part through the ARCS Fellowship and the PNNL-WSU Distinguished Graduate Researcher Program.