Foliar δ 13C and δ 15N values of C3 plants in the Ethiopia Rift Valley and their environmental controls

Abstract

The foliar C and N stable isotopic compositions (δ13C and δ15N) and the relationships between these compositions and environmental factors of C3 plants in the Ethiopia Rift Valley were investigated. There were three distribution patterns for foliar δ13C with mean values of −26.7‰±0.4‰, −29.7‰ ± 0.6‰, and −26.9‰ ± 1.2‰ in cold-moist, temperate-moist, and arid-hot environments, respectively. The δ15N values ranged from −1.4‰ ± 1.7‰ to 14.3‰ ± 0.1‰, with higher values under arid-hot conditions and the lowest values in plants growing at higher altitudes under cold-moist conditions. A strong negative relationship between mean annual precipitation and δ15N explained more than half of the observed variation in the δ15N values (r2 = 0.54, P < 0.001); a modest positive relationship was also found between δ15N and temperature (r2 = 0.32, P < 0.01). A weakly positive relationship existed between δ13C and temperature, and changes in δ13C values with precipitation and altitude followed quadratic curves. This suggests a shift in the effects of water and heat conditions caused by altitude on carbon isotopic discrimination.