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

The foliar C and N stable isotopic compositions （δ^13C and δ^15N） 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 δ^13C 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 δ^15N 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 δ^15N explained more than half of the observed variation in the δ^15N values （r2= 0.54, P 〈 0.001）; a modest positive relationship was also found between δ^15N and temperature （r2 = 0.32, P 〈 0.01）. A weakly positive relationship existed between δ^13C and temperature, and changes in δ^13C 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.

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

The foliar C and N stable isotopic compositions (δ ¹³C and δ ¹⁵N) 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 δ ¹³C 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 δ ¹⁵N 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 δ ¹⁵N explained more than half of the observed variation in the δ ¹⁵N values (r ² = 0.54, P < 0.001); a modest positive relationship was also found between δ ¹⁵N and temperature (r ² = 0.32, P < 0.01). A weakly positive relationship existed between δ ¹³C and temperature, and changes in δ ¹³C 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. Supported by the Import-Talents Program of the Cold and Arid Regions Environmental and Engineering Research Institute (Grant No. 2005104), the National Natural Science Foundation of China (Grant No. 40501076), the Chinese Science Expedition (DEEP) of the China Association for Scientific Expedition, and International Partnership Project of Chinese Academy Sciences (Grant No. CXTD-Z2005-2)