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 latergrowth, and the further effects may be greater withincreasing seedling age. Seedlings, however, can minimizethe effect of damage through compensatorygrowth. Seedlings of Pharbitis purpurea grow in frequentlydisturbed habitats and generally tolerate damageto leaf tissues. We evaluated the compensatoryresponses of the cotyledon to different levels of defoliationand their effect on seedling growth and development.We also examined the relationship betweenseeding depth and compensatory growth. We tested sevendefoliation treatments with one or both cotyledonsand/or the apical meristem of seedlings removed fromseeds buried at a seeding depth of either 2 or 5 cm. Wethen measured 12 growth traits of the seedlings to assessdevelopment and growth compensation. The area,thickness, biomass, and longevity of the remaining cotyledonwere also measured to quantify increased growthas result of treatment effects at both seeding depths. Theresults showed that defoliation reduced seedling height,belowground length, and total biomass significantly insubsequent growth in all treatments. However, defoliationtreatments had direct positive impacts on growth at2 cm depth compared with 5 cm depth. In contrast, thecompensation of cotyledon area (Carea), biomass (Cmass),and thickness (Cthickness) was greater at 5 cm depth thanat 2 cm depth. The results thus indicate that P. purpureaseedlings adopted a compensatory growth strategy toresist leaf loss and minimize any adverse effects using theremaining cotyledon. Increasing seeding depth canaggravate the compensatory growth of remain cotyledonafter partial defoliation.