Simulated predation of Quercus variabilis acorns impairs nutrient remobilization and seedling performance irrespective of soil fertility

Abstract

Predators may partially or completely consume Quercus spp. acorns, but effects on nutrient remobilization and seedling performance are poorly understood. We investigated interactions between soil fertility and the removal of Quercus variabilis acorn cotyledons at different early developmental stages on seedling nutrition and development. Seedlings were grown in two soils of contrasting fertility and the kinetics of acorn nitrogen, phosphorus and potassium remobilization, and seedling survival, growth and nutrient content were analyzed. Acorn mass and macronutrients decreased remarkably <2 weeks after emergence, with nitrogen and phosphorus remobilizing faster than potassium. Acorn removal at or 1 week after emergence inhibited seedling survival, growth and fine root formation, whereas removal from 2 to 10 weeks after emergence had minor effects. Acorn macronutrient remobilization and effects of acorn removal on seedling performance were not reversed under high soil fertility. When acorns were removed ≥2 weeks after emergence, fertilization increased root surface and seedling nitrogen content. Acorn nutrients are more important than soil nutrients during very early seedling development. Cotyledon damage at emergence impairs seedling performance despite no direct damage to the remainder of the seedling. This effect cannot be reverted by high soil fertility and has potential ecological and practical implications for oak regeneration.