This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Web of Science (102) Citing Articles via Google Scholar Google Scholar Articles by Herridge, D. F. Articles by Pate, J. S. Search for Related Content PubMed PubMed Citation Articles by Herridge, D. F. Articles by Pate, J. S. Agricola Articles by Herridge, D. F. Articles by Pate, J. S.

Articles

Utilization of Net Photosynthate for Nitrogen Fixation and Protein Production in an Annual Legume ¹

^a Department of Botany, University of Western Australia, Nedlands, Western Australia 6009

The economy of C and N in nodulated cowpea (Vigna unguiculata [L.] Walp.) was described in terms of fixation of CO₂ and N₂, respiratory losses of C, and the production of dry matter and protein.

Net daytime gain of C by the shoot (net photosynthesis) rose to a maximum at flowering and then declined sharply due to abscission of leaves. Maximum N fixation occurred 10 days prior to maximum net photosynthesis. Shedding of nodules reduced fixation to zero by midfruiting. Fifty per cent of the plant's N and 37% of its net photosynthate were assimilated before flowering; 39% of plant N was incorporated into seed dry matter.

Respiration of nodules and roots utilized 24% of the C from net photosynthate assimilated over the growth cycle; night respiration of shoots, 20%; dry matter production in seeds, 17%; and dry matter production in other plant parts, 39%. The proportion of net photosynthate translocated to the nodulated root decreased from 41 to 14% during growth. Developing fruits were major competitors for translocate. Nodules consumed 9% of the C from the plant's total net photosynthate, 43% of which was respired, 6% made into dry matter, and 51% returned to the shoot with N fixation products.

For every 1 g N fixed, net photosynthate equivalent to 6.8 g carbohydrate was consumed by nodules, 25.7 g carbohydrate by the nodulated root. Translocate was used most efficiently for N fixation in late vegetative growth when nodules were most active and their carbohydrate supply still adequate.

During vegetative growth and early flowering (0 to 78 days after sowing) cowpea consumed 17.2 g net photosynthate (as carbohydrate) for every gram of protein synthesized in its shoot. The comparable conversion in seed production was 32.5 g net photosynthate/g seed protein or 6.6 g/g seed dry matter.

This article has been cited by other articles:

				A. S. Voisin, C. Salon, C. Jeudy, and F. R. Warembourg Symbiotic N2 fixation activity in relation to C economy of Pisum sativum L. as a function of plant phenology J. Exp. Bot., December 1, 2003; 54(393): 2733 - 2744. [Abstract] [Full Text] [PDF]

				A. S. VOISIN, C. SALON, C. JEUDY, and F. R. WAREMBOURG Seasonal Patterns of 13C Partitioning Between Shoots and Nodulated Roots of N2- or Nitrate-fed Pisum sativum L. Ann. Bot., April 1, 2003; 91(5): 539 - 546. [Abstract] [Full Text] [PDF]