Spatial patterns of foliar stable carbon isotope compositions of C3 plant species in the Loess Plateau of China

The spatial pattern of foliar stable carbon isotope compositions (delta C-13) of dominant species and their relationships with environmental factors in seven sites, Yangling, Yongshou, Tongchuan, Fuxian, Ansai, Mizhi and Shenmu, standing from south to north in the Loess Plateau of China, was studied. The results showed that in the 121 C-3 plant samples collected from the Loess Plateau, the foliar delta C-13 value ranged from -22.66 parts per thousand to -30.70 parts per thousand, averaging -27.04 parts per thousand. The foliar delta(13)upercript stopC value varied significantly (P < 0.01) among the seven sites, and the average delta C-13 value increased by about 1.69 parts per thousand from Yangling in the south to Shenmu in the north as climatic drought increased. There was a significant difference in foliar delta C-13 value among three life-forms categorized from all the plant samples in the Loess Plateau (P < 0.001). The trees (-26.74 parts per thousand) and shrubs (-26.68 degrees) had similar mean delta C-13 values, both significantly (P < 0.05) higher than the mean delta C-13 value of herbages (-27.69 degrees). It was shown that the trees and shrubs had higher WUEs and employed more conservative water-use patterns to survive drier habitats in the Loess Plateau. Of all the C-3 species in the Loess Plateau, the foliar delta C-13 values were significantly and negatively correlated with the mean annual rainfall (P < 0.001) and mean annual temperature (P < 0.05), while being significantly and positively correlated with the latitude (P < 0.001) and the annual solar radiation (P < 0.01). In general, the foliar delta C-13 values increased as the latitude and solar radiation increased and the rainfall and temperature decreased. The annual rainfall as the main influencing factor could explain 13.3% of the spatial variations in foliar delta C-13 value. A 100 mm increment in annual rainfall would result in a decrease by 0.88 parts per thousand in foliar delta C-13 values.