C, N, P stoichiometry traits of different flue-cured tobacco organs at different growth stages

Ecological stoichiometry studies energy balance of multiple chemical elements in the process of ecological interaction, and C, N, P stoichiometry is the core element of various ecological processes. Ecological stoichiometry has two important theories — the theories of homeostasis and growth-rate hypothesis (GRH). Ecological stoichiometry has been incorporated successfully into many levels of biology, ranging from molecular, cellular, organismal and population levels to ecosystem and global levels. At present, the principles of ecological stoichiometry are broadly applied in population dynamics, trophie dynamics, microbial nutrition, host-pathogen interactions, symbiosis, comparative ecosystem analysis and consumer-driven nutrient cycle. The research on plant C, N, P stoichiometry traits has immensely contributed to the understanding of the allocation of C, N and P contents in different plant organs and the determination of correlations between the theories of GRH and homeostasis. Flue-cured tobacco (Nicotiana tabacum L.) is one of the most important economic crops in China. The main planting areas of flue-cured tobacco cover seven provinces, including Sichuan Province, Yunnan Province and Guizhou Province. The study of stoichiometric characteristics of different flue-cured tobacco organs (leaf, stem and root) is highly significance in understanding the mechanisms of growth and nutrient utilization of flue-cured tobacco. In a field experiment in Liangshan Prefecture of Sichuan Province, three tobacco varieties (‘Yunyan 87’, ‘Chuanyan 1’ and ‘KRK26’) were used to determine C, N and P contents and stoichiometry traits of different organs of tobacco varieties at different growth stages. It was found that: 1) above-ground biomass increased gradually and reached maximum at maturity stage. The specific growth rate of tobacco decreased initially and then increased and again decreased gradually, reaching maximum value at vigorous growth stage. Also the C︰N, C︰P and N︰P ratios increased significantly at vigorous growth stage. These results were not consistent with the theory of GRH, according to which the higher growth rates of plant corresponded to lower C︰N, C︰P and N︰P ratios. 2) C content of tobacco increased initially and then decreased, reaching highest values at vigorous growth stage. Also N and P contents continuously decreased from root elongation stage to maturity stage. The ratios of C︰N and C︰P of root and leaf increased gradually during the entire growth period while C︰N ratio of stem decreased gradually throughout the growth period. The overall trend in stem increased initially before eventually decreasing. Finally, small variations were noted in C content and N︰P ratio (lower than 20%) during the growth period. This suggested strong homeostasis during the growth stages in the above parameters. However, huge variations were noted in N and P contents and in C︰N and C︰P ratios. 3) N content of leaves was positively correlated with leaf P content, suggesting relative consistency in leaf N-P content. The positive correlation between leaf N content and stem N content was driven by the structure of plant canopy.