Stella Woeltjen's PhD thesis defense

Описание: Evaluating crop physiological and stand age-related controls over soil carbon and nitrogen dynamics in perennial and annual grains

Wednesday, March 22, 2023
Stella Woeltjen's doctoral thesis defense seminar
LAAS PhD candidate advised by Profs. Jess Gutknecht and Jake Jungers
https://laas.umn.edu/events/woeltjen-...

Intermediate wheatgrass (IWG, Thinopyrum intermedium (Host) Barkworth and Dewey), a cool-season grass domesticated for grain and forage production, is currently gaining attention as a perennial alternative to annual grain crops. The extensive root systems, high carbon (C) uptake and belowground C partitioning, and well-developed nitrogen (N) conservation strategies make perennial crops like IWG well-suited to improve soil C storage and minimize N inputs and losses. However, little is known about how these attributes are expressed in IWG systems, and whether these processes change within a growing season and across IWG stand age. As IWG stands often remain in production for 3 - 5 years, this gap in knowledge significantly challenges the understanding of how IWG can be profitably managed and how it will contribute to soil C storage and crop-soil N retention as stands age. To evaluate these ideas, we established three studies to address stand age-related effects on IWG 1) root growth and decomposition, 2) C uptake and partitioning to crop-soil-microbial pools, and 3) N sources and N conservation.

Together, these studies illuminated important changes in resource use and nutrient availability that develop over the 1 – 3 years following IWG establishment. Within just two years of establishment, we saw clear evidence that IWG shifts from a system dominated by root growth and belowground C allocation, to one characterized by root decomposition and exportation of new C inputs via soil respiration. While the enhanced decomposition in the second-year IWG suggests a greater capacity to transform root-derived C into more stable soil C compounds and recycle root-derived N into soil pools, the increase in decomposition may also signal changes in the nutrient status of IWG that could be detrimental to the ability of it to contribute to soil C accrual. We found an increased reliance on N derived from fertilizer and N derived from internal translocation in older stands, and coupled with the evidence of limited N availability in crop tissues and soil pools in older IWG stands, we conclude that N limitation of IWG in ageing stands should be a concern for producers. As such, optimizing IWG N management recommendations to more adequately meet the N demands of IWG will be critical to maximizing IWG contributions to soil C storage, reducing reliance on external fertilizer inputs and ensuring IWG remains a profitable and sustainable alternative to annual grains in agricultural landscapes.

In partial fulfillment of the requirements for the doctoral degree in the Graduate Program in Land and Atmospheric Science at the University of Minnesota.