Quantifying N-loss by root abscission: consequences for wheat N budgets and δ

Area of Science:

• Plant Physiology
• Stable Isotope Geochemistry
• Soil Science

Background:

• Lower plant nitrogen-15 (δ15N) values compared to source δ15N are often attributed to nitrogen (N) efflux.
• The contribution of root abscission to plant N loss and its effect on plant δ15N requires further investigation.

Purpose of the Study:

• To quantify the role of root abscission in plant N loss.
• To determine the consequences of root abscission for plant δ15N values.
• To compare N loss and δ15N in wheat grown under varying root growth stability.

Main Methods:

• Wheat (Triticum aestivum L.) was cultivated in hydroponic systems with three distinct aeration/stability levels.
• Nitrogen isotope ratios (δ15N) of nutrient solutions, root fragments, roots, and shoots were periodically measured.
• Biomass and N loss through root fragments were quantified relative to plant N uptake.

Main Results:

• Plants in solution exhibited significantly more negative δ15N values (-8.9 to -9.2‰) compared to those in sand (-6.9‰).
• Root fragments represented a major pathway for N loss, exceeding plant net N uptake, particularly in solution treatments.
• Estimated decrease in plant δ15N due to root fragment loss ranged from -1.0 to -3.7‰ across treatments.

Conclusions:

• Root abscission and turnover are significant N loss pathways in plants, influencing plant δ15N.
• Plant δ15N values are likely modulated by a combined effect of root abscission and N efflux.
• Hydroponic systems with less stable root environments promote greater root turnover and N loss.