Cyanobacterial Symbiosis and Nutrient Dynamics in Cycad Ecosystems

Cycads represent one of the most ancient lineages of seed plants and possess specialised coralloid roots that harbour nitrogen-fixing cyanobacteria, predominantly from the genera Nostoc and Calothrix. These endophytic symbionts convert atmospheric dinitrogen into ammonium, supplying the host plant with essential nitrogen in nutrient-poor soils. In exchange, the cycad provides photosynthate and a protective niche. Beyond nitrogen provisioning, cyanobionts may synthesise phytohormones and siderophores, influencing phosphorus mobilisation and metal ion availability. The symbiosis also alters rhizosphere chemistry, enhancing soil heterogeneity and driving localised shifts in carbon : nitrogen : phosphorus stoichiometry. Community assembly within coralloid roots reflects both host control and environmental filters, with next-generation sequencing revealing a core microbiome of bacterial taxa that contribute to nutrient acquisition, pathogen resistance and ecological resilience. Understanding these interactions has profound implications for cycad conservation, sustainable agriculture through bio-inoculants and ecosystem restoration in degraded habitats.

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Cyanobacterial Symbiosis and Nutrient Dynamics in Cycad Ecosystems publication trend

The graph below shows the total number of articles in cyanobacterial symbiosis and nutrient dynamics in cycad ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Coralloid roots: specialised lateral roots of cycads that host nitrogen-fixing cyanobacteria and appear as coral-like clusters.

Cyanobacteria: photosynthetic prokaryotes capable of converting atmospheric nitrogen to bioavailable ammonia in symbiosis with plants.

Nitrogen fixation: biochemical reduction of atmospheric dinitrogen to ammonia, mediated by the nitrogenase enzyme complex.

Endophyte: microorganism that colonises internal plant tissues without causing disease, often conferring nutritional or protective benefits.

Heterocyst: specialised cyanobacterial cell with a thickened envelope and suppressed oxygen evolution, dedicated to nitrogen fixation.

References

1. Symbiosis between cyanobacteria and plants: from molecular studies to agronomic applications. Journal of Experimental Botany (2023).
2. Core Endophytic Bacteria and Their Roles in the Coralloid Roots of Cultivated Cycas revoluta (Cycadaceae). Microorganisms (2023).
3. Exploring the Influence of Ecological Niches and Hologenome Dynamics on the Growth of Encephalartos villosus in Scarp Forests. Soil Systems (2024).
4. The identification of the coralloid root endophytes of the southern African cycads and the ability of the isolates to fix dinitrogen. South African Journal of Botany (1987).