Abstract:

Objectve: 'Fengdan'(Paeonia ostii) is a new woody oil crop. It is not clear about the carbon, nitrogen, and phosphorus stoichiometry and source-sink structure in this plant species. This study compared the seasonal variations of C, N, P, and soluble sugar concentrations and allocations, as well as the ratios of C:N, C:P and N:P in different organs of 'Fengdan' in an annual cycle at different stages of development, in order to lay a foundation for the analysis of its yield composition and provide a guidance for the cultivation and management of oil peony. Method: A destructive strategy was applied to sample roots, stems, leaves, flowers and fruits of 4-, 6-, and 8-year-old plants from Tongling peony garden in Anhui Province at the stage of bud dormancy, flowering, fruit mature, and defoliation. The dynamic changes of C, N, P and soluble sugar concentrations in those samples were measured, and then the allocation and stoichiometry dynamics were analyzed. Result: The results showed that:1) all organs had a similar seasonal dynamics of C content, and it increased with tree age. N content in roots and stems had a similar seasonal variation, and it also increased with tree age. Whereas N contents in leaves of different plant ages had a similar changing trend, and it reached the highest values at flowering stage. There were differences in P concentrations in both different organs and different plant ages. 2) The C:N ratio in all Fengdan organs increased first and then decreased in the annual cycle, which was significantly influenced by tree age. The change trend of C:P ratio over seasons in all organs was different. The C:P ratio in roots and stems was 6 a > 8 a > 4 a. The C:P ratio in leaves presented difference only at flowering stage, with 4 a < 6 a < 8 a. The C:P ratio of reproductive organs was 6 a > 8 a > 4 a. In the annual cycle, the N:P ratio of 'Fengdan' decreased gradually. The N:P ratio in all organs ranged from 2.71 to 7.62, and was 6 a > 4 a > 8 a. 3) At dormancy and defoliation stages, C, N, and P were all equally allocated to root and stem. At flowering and fruit mature stages, C was evenly portioned to each organ, whereas N and P were relatively more distributed in leaves and reproductive organs. The effects of plant age on the element allocations were different among C, N and P. 4) There was significantly difference in soluble sugar concentration among different organs. Soluble sugar concentration in source or sink structure was used to indirectly express the source or sink strength, and then to estimate the ratio of source:sink. At the beginning of annual cycle (at dormancy stage), the source structure was root and stem, and it was leaf at flowering and fruiting stages when reproductive organs (flower or fruits) were the main sink structure. At the same time the sink structure included root and stem, as well as flower and fruit. Six-year-old plants had the biggest source strength and eight-year-old plants had the biggest sink strength. Six-year-old plants had the highest source:sink ratio at flowering stage, whereas 4-year-old plants had the highest source:sink ratio at fruiting stage. Conclusion: Stoichiometry and source-sink structure of 'Fengdan' varied with plant development and growth stages, and were influenced by tree age. N was a limiting factor for plant growth in 'Fengdan', and appropriate addition of N was able to increase seed yield of oil peony.

Key words: Paeonia ostii, stoichiometric characteristics, plant age effect, source-sink