Arbuscular mycorrhizal fungi persist in dying Euphorbia ingens trees

Abstract

Forest declines have been reported with increasing regularity during the last decade and are expected to increase due to the ongoing environmental changes. During adverse environmental conditions, plant symbioses with mycorrhizas can help to reduce plant stress. Mycorrhizas are symbiotic associations between fungi and roots of living plants. Plants offer carbohydrates to the fungus and the fungus improves the acquisition of nutrients and water to the plant. Specifically, arbuscular mycorrhizal (AM) fungi are the most abundant mycorrhizas. In South Africa, there are increasing reports describing the decline of native Euphorbia ingens trees. This study analysed the presence and abundance of AM fungal colonisation in the roots of E. ingens trees, and the number of AM fungal spores in the surrounding soil, with the aim to improve the understanding of the rapid decline of these trees. AM fungal colonisation and spores in relation to the soil properties were also analysed. Soil and root samples were collected from different rates of declining E. ingens trees at three sites in South Africa. AM fungal colonisation of the roots was assessed and fungal spores in the surrounding soil were enumerated. Soil phosphorus, mineral nitrogen and pH were analysed from the soil samples. The results showed that AM fungi are associated with E. ingens trees. AM abundance was influenced by site specific properties and not by E. ingens health. Moreover, the level of soil NO3− and soil texture significantly influenced AM colonisation in roots and the number of spores enumerated. These preliminary findings provide background information for further research into the large-scale decline of E. ingens populations in South Africa.