Species-specific competition and N fertilization regulate non-structural carbohydrate contents in two Larix species

Non-structural carbohydrates (NSC) are critical to plant signaling, gene transcription, physiological processes, survival and growth. Previous studies have demonstrated that species differing in NSC contents have various responses to stressful environments. However, effects of intra- and interspecific competition or N fertilization on NSC have not been previously studied. We employed two coniferous tree species, Larix kaempferi and Larix olgensis, to investigate the effects of intra- and interspecific competition on NSC under two N supply levels, with and without N fertilization. N fertilization significantly promoted the growth rates, biomass accumulation, carbon isotope composition and N concentration of leaves of the two species. Competition patterns significantly affected the average root diameter. Interspecific competition tended to increase the specific root length and specific root tip density. Also, interspecific competition significantly increased the N concentration of leaves but declined their C:N ratio under no N fertilization (N−) treatments. L. kaempferi greatly benefited from the presence of L. olgensis, particularly under N fertilization (N+) treatments. Competition patterns, N fertilization and their interactions promoted N and carbohydrate storage. Our results demonstrated that N was a crucial factor to drive and regulate carbon balance. Differences between species in carbohydrate metabolism may contribute to their coexistence or niche differentiation.