Cotyledons as the primary source of carbon and mineral nutrients during early growth of a savanna tree

Seed reserves are a significant source of essential elements and carbon for seedlings. Trees in the Cerrado vegetation (known as ‘Brazilian savanna’) of Central Brazil are subjected to seasonal drought and grow on dystrophic soils, suggesting that seedlings are dependent on seed reserves for rapid development in the growing season to thrive  during the subsequent dry season. However, little is known about the role of cotyledon reserves as a source of carbon and mineral nutrients for recently germinated tree seedlings in the Cerrado. We tested the effects of removing one cotyledon 11 days after germination on growth, biomass distribution, carbon and mineral nutrient stocks of seedlings of Magonia pubescens (Sapindaceae), a large-seeded, anemochorous tree. Seedlings were grown in nutrient-deficient and nutrient-enriched sand for 120 days. For most mineral nutrients (N, P, K, Mg, S, B, Cu and Zn), the stocks in the seeds would be sufficient for seedling development. However, the amounts of Ca, Fe and Mn in the seeds would not be sufficient to meet the needs for plant growth  at early stages and must be absorbed from the soil. Fatty acids and soluble sugars were the main carbon reserves in the seeds. The fatty acids were rapidly consumed in the early stages of seedling development. On the other hand, seedlings stored carbon as soluble sugars and starch. Removing one of the cotyledons led to a significant decline in growth, biomass accumulation and mineral nutrient stocks. Fertilization did not reverse the effects of removing one of the cotyledons or increased growth.