Compensatory growth responses of seedlings of Pharbitis purpurea (Convulvulaceae) to tissue removal at different seeding depths of seeds

Tissue damage to seedlings can limit their later growth, and the further effects may be greater with increasing seedling age. Seedlings, however, can minimize the effect of damage through compensatory growth. Seedlings of Pharbitis purpurea grow in frequently disturbed habitats and generally tolerate damage to leaf tissues. We evaluated the compensatory responses of the cotyledon to different levels of defoliation and their effect on seedling growth and development. We also examined the relationship between seeding depth and compensatory growth. We tested seven defoliation treatments with one or both cotyledons and/or the apical meristem of seedlings removed from seeds buried at a seeding depth of either 2 or 5?cm. We then measured 12 growth traits of the seedlings to assess development and growth compensation. The area, thickness, biomass, and longevity of the remaining cotyledon were also measured to quantify increased growth as result of treatment effects at both seeding depths. The results showed that defoliation reduced seedling height, belowground length, and total biomass significantly in subsequent growth in all treatments. However, defoliation treatments had direct positive impacts on growth at 2?cm depth compared with 5?cm depth. In contrast, the compensation of cotyledon area (C _area), biomass (C _mass), and thickness (C _thickness) was greater at 5?cm depth than at 2?cm depth. The results thus indicate that P. purpurea seedlings adopted a compensatory growth strategy to resist leaf loss and minimize any adverse effects using the remaining cotyledon. Increasing seeding depth can aggravate the compensatory growth of remain cotyledon after partial defoliation.