Mycorrhizae on dipterocarps in rubber agroforests (RAF) in Sumatra

Abstract

In tropical lowland forests, which dominated by trees of Dipterocarpaceae family, trees and fungi are strongly linked, through ectomycorrhiza (EcM) formation. However, as part of rapid deforestation and forest transformation, mixed dipterocarp forests have been replaced by other vegetation and land use types. Considerable areas of the lowland tropical forest in Sumatra have been turned into Rubber Agroforests (RAF). RAF is a land use type in which rubber trees are planted, while allowing spontaneous establishment of forest tree species. The method presented in this thesis includes four main elements. Firstly, vegetation analysis in seven types of land use. Secondly, study in a nursery using dipterocarps species as bait plant to assess the effect of land use change on EcM inoculum and to analyze the effect of soil heating and drying on EcM propagules. Thirdly, an in-situ experiment in RAF with different history was done to assess whether fungal inoculant increased the survival, growth, nutrient uptake and EcM formation on Shorea selanica and Shorea lamellata. Finally, molecular techniques of PCR and sequencing have been applied to identify EcM fungal symbionts on dipterocarps. The study has been conducted in Jambi province, Sumatra, Indonesia. The ex-situ experiment has been conducted in the nursery of the Forest Research and Development Agency, Bogor, Indonesia. Identification of EcM fungi was done in the Fungal Biodiversity Centre (CBS), Utrecht, the Netherlands. The result of vegetation analysis showed that human activity in RAF management has strong effects on species richness. Very few trees dependent on EcM fungi were encountered in RAF. Our study in the nursery shows small differences in EcM colonization between soils derived from a wide range of land use types. It may indicate that survival of spores and colonization potential are not sensitive to the history of the site. Rapid recolonization of the heated soil in the experiment may imply sufficient availability of EcM fungi for dipterocarps under field conditions, where fire as a tool for land clearing is commonly used in Sumatra. The in-situ experiment in the RAF showed that lack of trees that are dependent on EcM fungi in RAF and in non-forested land does not necessarily imply the absence of EcM inoculum belowground in the ecosystem. EcM inoculum persists in the soil after forest was changed to RAF. Molecular identification of EcM fungi showed that Tomentella was the prevalent genus of EcM fungi colonizing dipterocarp seedlings in nursery stage and in the in-situ test 1 year after the seedlings have been planted in the field. None of the fungi was identified as Scleroderma columnare, which was inoculated to S. lamellata and S. selanica seedlings in the nursery stage. This indicated that indigenous EcM fungi dominated on the dipterocarp seedlings planted in the field, regardless of nursery inoculation. The implementation of this study is potentially of great value for reforestation efforts with dipterocarps in RAF in collaboration with rubber farmers. This reforestation approach will ensure the successfulness of the reforestation managed sustainably by the farmer, from which they may benefit in the future.