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Pyro-Chemiluminescent Differentiation of Oxidized and Reduced N Forms Evolved from Plant Foliage¹

Evaluations were made to differentiate the forms of water soluble, non-elemental nitrogen lost with the trans. piration water vapors from plant foliage. Chemiluminescent detection of chemically bound N, with O₂ present as a reactant-carrier gas, and then absent and replaced with N₂ during the pyrolysis of transpiration samples, distinguished the oxidized from the reduced N forms in the transpirate. The majority of the N in several crop and weed species was in the reduced state; however, at least 5% of the N in all species tested was in an oxidized form. The percent of loss of oxidized N was fairly constant in cotton (Gossypium hirsutum L.), ‘Forrest’ beans [Glycine max (L) Merr.], and palmer amaranth [Amaranthus palmeri (S.) Wats.] over the solar day. Older soybean leaf tissue lost a higher percentage of oxidized forms than did younger tissue. Both younger and older soybean tissue evolved greater total amounts of N than foliage in the middle of the plant canopy; yet the rate of transpiration was maximal in the middle foliage. Water-stressed soybeans evolved greater quantities of oxidized N forms than did irrigated soybeans. The N loss increased in ‘Davis’ soybeans and transpiration decreased in the cultivar ‘Forrest’ as a result of water stress.

Key Words: Transpiration • Diurnal • Water stress

² Dep. of Agronomy, Altheimer Laboratory, Univ. of Arkansas, Fayetteville, AR 72701.

Received for publication February 16, 1979.