Microbial interactions and activities affecting sago palm growth

Abstract

Microbes are ubiquitous soil inhabitants. Both aboveground and belowground parts of plants are associated with diverse and abundant microbes. Such microbes have positive and negative impacts on the plant productivity. Biological nitrogen fixation (BNF) is such a beneficial interaction. To reveal BNF by free-living bacteria in sago palm, different parts (root, rachis, petiole, leaflet, bark, pith, and extracted starch) were collected in the Philippines, and their nitrogen-fixing ability was measured. Almost all the samples showed positive nitrogen fixation. Then, nitrogen-fixing bacteria (NFB) were isolated, belonging to different genera, such as Klebsiella sp., Pantoea sp., Burkholderia sp., Stenotrophomonas sp., and Bacillus sp. All the isolates preferred simple carbon compounds, like glucose, sucrose, and mannitol, as their substrates for nitrogen fixation, while they showed very low activity in starch, pectin, and hemicellulose media. When NFB were cocultured in such a medium with the polymer-degrading bacteria, nitrogen-fixing ability was markedly increased. Stimulatory effects were observed in Rennie medium by co-inoculation of NFB and indigenous bacterial consortia isolated from sago palm samples. These results indicate that complex microbial interactions may increase in situ nitrogen fixation and contribute to nitrogen nutrition in sago palm. This chapter also introduces characteristics of nitrogen-fixing bacteria and amounts of BNF in palm trees in recent studies.