Overcoming desiccation in an African cycad genus: adaptive approaches for improving recruitment in Encephalartos

Abstract

Cycad populations in the wild are declining due to human pressures, and recovery efforts are constrained by the high mortality of seeds and seedlings, particularly as a result of desiccation. Desiccation reduces seed survival and thus seedling recruitment in the wild. This limits the viability of cycad populations in the wild. Therefore, this study involved testing different substrates designed to retain moisture and thus improve cycad seed survival and juvenile establishment in the wild. It was hypothesized that the addition of water-retaining compounds, such as Coir and Hydrogel, into the growing medium would improve moisture availability and increase seed and juvenile establishment and survival under drought conditions. To test the hypothesis, experimental treatments comprising four substrates and three watering regimes, representing no drought, moderate drought and prolonged drought, were tested in a greenhouse to evaluate their effects on cycad establishment and survival. Chapter two of this thesis investigates the effects of these treatments on growth from seeds for Encephalartos altensteinii, with an additional test to determine the effect of sowing depth on seedling emergence and survival. Chapter three tested the effectiveness of the treatments on translocated juvenile plants (8 years old) of Encephalartos altensteinii. The results proved that Coir and Hydrogel significantly enhanced substrates moisture content used for growing cycad seeds and juveniles. Seedling development and survival was also significantly influenced by substrates, watering regimes, and sowing depth, as seeds sown 3cm deep had higher seedling survival than at the surface within all the substrates except in Coir. However, for the cycad juveniles, neither substrates or watering treatments significantly influenced survival. Hydrogel and Coir proved to enhance moisture retention which subsequently improving seedling establishment and survival, thus provides key information for cycad restoration protocols. This study further impactfully contributes to the conservation of threatened cycads by providing new knowledge that could be essential to maximize moisture availability and thus improve the establishment and survival of cycad seeds and juveniles in the wild.