127-19
Partitioning of N in Field Pea As Determined by in Situ Shoot and Atmospheric 15N Labeling.
Poster Number 1203
Monday, October 22, 2012
Duke Energy Convention Center, Exhibit Hall AB, Level 1, 1
Melissa Arcand, Soil Science, University of Saskatchewan, Saskatoon, SK, Canada
Based on results from 15N labeling experiments rhizodeposition has been touted as an important contributor to the total N balance of pulse-cropping systems. However, N rhizodepositionby maturefield pea (Pisumsativum) reportedlyvaries between 4-71% of total plant N.In greenhouse experiments with field pea, plant and soil partitioning of 15Nwas assessed at various stages in the plant's lifecycleusing two 15N-labeling methods: direct feeding of 15N-ureato the plant stem (stem-wick labeling) and continuous atmospheric labeling via symbiotic 15N2 fixation. Stem-wick labeling resulted in preferential 15N enrichment in aboveground components compared to atmospheric15N2 labeling, reflecting the different pathways of 15N assimilation presented by the two methods. Using stem-wick labeling, belowground N (roots, nodules, and rhizodeposits) comprised 47% of total plant N during the vegetative stage of pea, but diminished over time as plant N was allocated for grain development. By the time the plant reached maturity,rhizodeposits comprisedonly 8.4% of total plant N. Poor nodulation of pea plants labeled using the15N2atmospheric labeling method resulted in negligible soil 15N enrichment; nevertheless, enrichment of nodules was evident throughout plant growth. These results show that N fixation was active, particularly during podfilling, although not enough to enrich plant roots (max. 0.477 atom% 15N at maturity) to a significant degree. Despite the advantage of atmospheric labeling in providing a direct assessment of the contribution of fixed N to soil via rhizodeposition, the expense and technical difficulty negate its extensive use, particularly if N fixation is low as in this study
