Seasonal dynamics of biomass allocation of Paeonia ostii ‘Fengdan’ and the effects of tree age and shading

The study of biomass accumulation and distribution is of great significance to understand the mechanisms of crop yield formation. ‘Fengdan’ is a new woody oilseed crop originated from Paeonia ostii T.Hong et J.X.Zhang, though its production mechanism remains unclear. In the study, destructive sampling was applied to test the seasonal variations in biomass accumulation and allocation of different organs of ‘Fengdan’ plant in an annual cycle between different aged populations and under different shading treatments. Plant biomass of each age and each organ varied in different seasons and reached the highest levels during the mature fruit stage. Total biomass increased with tree age, whereas the relative growth rate displayed the reverse tendency. Biomass allocation of plant parts changed in different stages; the roots and stem exhibited the highest values during bud dormancy, whereas the highest value in the leaf occurred at the mature fruit stage. The reproductive allocation was only 3.24%-6.85% of total biomass, but this increased with age (fruit biomass was (7.74 ±0.31)g/plant for a 4-year-old fruit, but (26.81 ±0.44)g/plant for an 8-year-old fruit). Total assimilation in the annual cycle ranged from 161.21 g to 232.34 g and the seed harvest index was 2.71%-6.87%, which was positively correlated with tree age (R²=0.8178). Under shading treatments, the biomass of the root, stem, leaf, or whole plant decreased slightly, but the reproductive biomass and harvest index increased significantly to 3.66 g per plant and 389.36%, respectively, under 30% shading treatment. These findings demonstrate that the source-sink relationship in the ‘Fengdan’ plant changed dynamically over the annual cycle, tree age had a significant effect on biomass allocation and yield, and moderate shading may be more suitable for growth.