Foliar δ13C values of nine dominant species in the Loess Plateau of China

uThe foliar stable carbon isotope compositions (delta C-13) of nine dominant species in seven sites, Yangling, Yongshou, Tongchuan, Fuxian, Ansai, Mizhi, and Shenmu, standing from the south to the north in the Loess Plateau of China were studied. The results showed that foliar delta C-13 values ranged from -22.61 to -30.73 parts per thousand with an average of -27.23 parts per thousand in 141 C-3 plant samples collected from the Loess Plateau. Foliar VC values varied significantly (p<0.001) among the nine C-3 species, which were Pinus tabulaeformis Carr., Robinia pseudoacacia L., Zizyphus jujuba Mill. var. spinosus Hu., Rubus parvifolius L., Hippophae rhamnoides L., Caragana korshinskii Kom., Lespedeza davurica (Laxm.) Schindl., Artemisia sacrorum Ledeb. var. incana Mattf., and Agropyron cristatum Gaertn. Comparatively, R. pseudoacacia, H. rhamnoides, and C. korshinskii had much higher VC values than the other six species, while A. sacrorum had the lowest delta C-13 value. There was no significant difference in foliar delta C-13 value among five species, P. tabulaeformis, Z jujuba, R. parvifolius, L. davurica, and A. cristatum. Considering the life forms categorized from nine C-3 species, trees and shrubs had significantly higher delta C-13 values than herbs (p<0.001). The deciduous tree R. pseudoacacia had much higher delta C-13 value than the evergreen tree P. tabulaeformis (p<0.01). Among the four shrubs, foliar VC values in H. rhamnoides and C. korshinskii were markedly higher (p<0.01) than those in Z. jujuba and R. parvifolius. Among the three herbs, L. davurica and A. cristatum had significantly higher delta C-13 values than A. sacrorum (p<0.01). Leguminous species such as R. pseudoacacia, C. korshinskii, and L. davurica as well as a non-leguminous species with nitrogen-fixation capacity, H. rhamnoides, had higher delta C-13 values than other non-leguminous species with same life-form. The mean delta C-13 value increased by about 7 % from Yangling in the south to Shenmu in the north as climatic drought increased, and foliar delta C-13 values differed much (p<0.001) among the seven sites. For nine species in the Loess Plateau, foliar delta C-13 values were significantly and negatively (p<0.001) correlated with the mean annual precipitation, moreover, an increase of 100 mm in annual precipitation would result in a decrease of 1.2 %o in delta C-13 value.