Natural abundances of ¹⁵N and ¹³C in leaves of some N₂-fixing and non-N₂-fixing trees and shrubs in Syria

Abstract

A survey study was conducted on man-made plantations located at two different areas in the arid region of Syria to determine the variations in natural abundances of the ¹⁵N and ¹³C isotopes in leaves of several woody legume and non-legume species, and to better understand the consequence of such variations on nitrogen fixation and carbon assimilation. In the first study area (non-saline soil), the δ¹⁵N values in four legume species (Acacia cyanophylla,−1.73 ‰ Acacia farnesiana,−0.55 ‰ Prosopis juliflora,−1.64 ‰; and Medicago arborea,+1.6 \textperthousand) and one actinorhizal plant (Elaeagnus angustifolia,−0.46 to−2.1 ‰) were found to be close to that of the atmospheric value pointing to a major contribution of N₂ fixing in these species; whereas, δ¹⁵N values of the non-fixing plant species were highly positive. δ¹³C ‰; in leaves of the C3 plants were found to be affected by plant species, ranging from a minimum of−28.67 ‰; to a maximum of−23 ‰. However, they were relatively similar within each plant species although they were grown at different sites. In the second study area (salt affected soil), a higher carbon discrimination value (Δ¹³C ‰) was exhibited by P. juliflora, indicating that the latter is a salt tolerant species; however, its δ¹⁵N was highly positive (+7.03 ‰) suggesting a negligible contribution of the fixed N₂. Hence, it was concluded that the enhancement of N₂ fixation might be achieved by selection of salt-tolerant Rhizobium strains.

Keywords:

• carbon-13
• isotope ecology
• natural isotope variations
• nitrogen-15
• N₂-fixation
• salinity
• shrubs
• trees

Acknowledgements

We would like to thank Professor I. Othman, General Director of AECS, for his support. The technical assistance of the staff at the AECS Department of Agriculture is greatly acknowledged.