Early cotyledon removal has stronger negative effects on root growth and storage than on shoots in Quercus variabilis seedlings, regardless of soil fertility

Oak cotyledons are hypogeal and non-photosynthetic. Animal predation on cotyledons during the seedling stage is a very common phenomenon and may hinder oak forest regeneration. However, no studies have compared the effects of cotyledon loss on shoot and root growth, as well as mineral or nonstructural carbohydrate (NSC) storage, under different soil fertility conditions, making it difficult to identify whether root or shoot traits are the most reliable indicators for assessing the effects of cotyledon predation on seedling recruitment. We subjected Quercus variabilis seedlings to fifteen cotyledon removal times and two fertilization levels to measure cotyledon resource decrease kinetics and seedling mass at early growth stages and subsequent seedling performance at the end of first year. Cotyledon resource remobilization completed at 32 days after emergence, with phosphorus and NSC remobilizing more efficiently than nitrogen and potassium. Soil nutrients had no impact on cotyledon resource remobilization and early seedling growth. Cotyledon removal imposed stronger negative effects on root growth and storage than on shoots at the end of first year, which can be alleviated by fertilization. Cotyledon removal after 14 days of emergence did not decrease seedling growth and storage. In conclusion, cotyledon resources are more important than soil nutrients for early seedling growth, and early cotyledon removal greatly hinders subsequent seedling growth and storage, with roots being more sensitive to cotyledon removal than shoots. To improve oak seedling regeneration, cotyledons should be protected from animal predation at least 14 days after emergence by setting up a fence around acorns.