Abstract: Understanding carbon and nitrogen stable isotopic abundance (δ¹³C and δ¹⁵N) and carbon-to-nitrogen ratio (C/N) in different organs of Caragana liouana across ages and elucidating the patterns along the age sequence can provide scientific insights into the ecophysiological mechanisms of its degradation and sustainable utilization. With four C. liouana plantations with different ages (11 a, 28 a, 38 a and 57 a) in a desert steppe located at the southern edge of Mu Us Desert in Ningxia, we investigated the variation in δ¹³C, δ¹⁵N and C/N of different organs (leaf, branch, pod, and seed) and the driving factors. Results showed that plant δ¹³C, δ¹⁵N, and C/N of C. liouana ranged from -27.54‰ to -21.16‰, from -2.39‰ to 3.02‰ and from 7.02 to 45.16, respectively. There were significant differences in δ¹³C, δ¹⁵N, and C/N among plant organs, with seed δ¹³C > branch δ¹³C > pod δ¹³C > leaf δ¹³C, leaf δ¹⁵N > seed δ¹⁵N > branch δ¹⁵N > pod δ¹⁵N, and pod C/N > branch C/N > leaf C/N> seed C/N. With increasing planting years, the δ¹³C of all organs showed significant decreasing trends, the δ¹⁵N showed a bell-shaped pattern, and the trends of C/N were opposite to those of δ¹⁵N. Both planting years and organs significantly affected δ¹³C, δ¹⁵N and C/N. Redundancy analysis further indicated that plant δ¹³C was primarily influenced by ages. Plant δ¹⁵N was mainly affected by leaf nitrogen per unit area (LN_area) and soil pH. Plant C/N was influenced by LN_area and ages. C. liouana can adapt to resource limited environments by altering the relationships between plant traits and resource use efficiencies.

Key words: carbon and nitrogen isotopes, carbon to nitrogen ratio, stand age, plant organ, Caragana liouana