Facultative mycorrhization in a fern (Struthiopteris spicant L. Weiss) is bound to light intensity

Abstract

Background The establishment of mycorrhizal relationships between a fungus and a plant typically enhances nutrient and water uptake for the latter while securing a carbon source for the fungus. However, under a particular set of environmental conditions, such as low availability of light and abundant nutrients in the soil, the resources invested in the maintenance of the fungi surpass the benefits obtained by the host. In those cases, facultative mycorrhizal plants are capable of surviving without symbiosis. Facultative mycorrhization in ferns has been overlooked until now. The present study measured the response of Struthiopteris spicant L. Weiss, and its root-associated fungi to different levels of light and nutrient availability in terms of growth, mycorrhizal presence, and leaf nutrient content. This fern species exhibits a great tolerance to variable light, nutrient, and pH conditions, and it has been found with and without mycorrhizae. We conducted a greenhouse experiment with 80 specimens of S. spicant and three factors (Light, Phosphorus, and Nitrogen) resulting in eight treatments. Results We found a significant influence of the factor light on fungal community composition, plant biomass, and nutrient accumulation. Departing from a lack of colonization at the initial stage, plants showed a remarkable increment of more than 80% in the arbuscular mycorrhizal fungi (AMF) richness and abundance in their roots when grown under high light conditions, compared with the ones in low light. We also observed an upward trend of C:P and C:N ratios and the above- and belowground biomass production when AMF abundance increased. Furthermore, the compositional analysis of the whole fungal communities associated with S. spicant roots revealed clear differences among low-light and high-light treatments. Conclusions This study is the first to investigate the importance of light and nutrient availability in determining fern-AMF relationships. We confirmed that Struthiopteris spicant is a facultative mycorrhizal plant. The composition and diversity of AMF found in the roots of this fern are strongly influenced by light and less by nutrient conditions. Our study shows that ferns respond very sensitively to changes in environmental factors, leading to shifts in the associated mycorrhizal communities.

Fern mycorrhizae do not respond to fertilization in a tropical montane forest

“…In our case, we trust the negative results for three reasons. First, in another fertilization study on ferns, using the same metabarcoding approach, we obtained clear differences in the fungal communities between nutrient treatments (Guillen-Otero et al, 2024), showing that the methods are suitable for detecting responses of root-associated fungi in ferns. Second, our analyses revealed clear and biologically meaningful differences between fern species and life forms, both for root-associated fungi and leaf nutrients, again confirming the suitability of the methods.…”

“…A: M. wolfii (F = 7.976, p < .001***). B: C. peladensis (F = 6.303, p < .01**), E. latifolium (F = 6.331, p < .001***), H. polyanthos (F = 0.694, p < .001***), and M. wolfii (F = 4.036, p < 0.05*).degree of mycorrhization in the temperate fern species Struthiopteris spicant was found to be strongly influenced by light availability (hence carbon limited), and not by nutrient availability (nutrient limited)(Guillen-Otero et al, 2024). Although this finding suggests that mycorrhization in ferns is not as linked to nutrient availability as it is in other vascular plant groups, there is still a need for more detailed studies to understand its nature and role in ferns.AUTHO R CO NTR I B UTI O N S M.K.…”

“…It has been suggested that the causes of this phenomenon might be the existence of a greater limitation in development by assimilate availability than by nutrient availability, compared to angiosperms (Kessler et al, 2010(Kessler et al, , 2014. However, except for a greenhouse experiment on a single fern species (Guillen-Otero et al, 2024), to date there are no experimental studies manipulating nutrient levels to assess the importance of soil nutrients in determining mycorrhization in ferns.…”

Comparative analysis of mycorrhizal communities associated with Struthiopteris spicant (L.) Weiss across Europe and North America

“…However, the percentage of AMF presence is lower in ferns, at approximately 67% ( Lehnert et al., 2017 ). It has been suggested that the relatively low percentage of mycorrhization in ferns stems from limited photosynthetic capabilities, so that their growth may be more strongly limited by carbon rather than nutrients ( Kessler et al., 2014 ; Guillen-Otero et al., 2024 ). However, the majority of AMF research has been conducted on angiosperms, leaving ancient plant lineages like ferns poorly studied ( Pressel et al., 2016 ; Lehnert et al., 2017 ; Strullu-Derrien et al., 2018 ; Field et al., 2019 ).…”

“…In consequence, there is a lack of understanding of the fungal taxonomic diversity and their functionality in ferns ( Lehnert et al., 2017 ; Strullu-Derrien et al., 2018 ; Sandoz et al., 2020 ; Guillen-Otero et al., 2023 ). Moreover, while it is well known that fern communities are impacted by precipitation, resource availability, and temperatures, among other factors ( Kessler et al., 2011 ; Weigand et al., 2020 ), there is limited data related to the influence of environmental factors on fern-fungus interactions ( Lehnert et al., 2017 ; Sandoz et al., 2020 ; Weigand et al., 2022 ; Guillen-Otero et al., 2024 ). In seed plants, the distribution, composition, and abundance of their associated AMF communities has been found to be influenced by temperature, precipitation, light availability, soil vertical structure, pH and nutrient concentration, biotic interactions, and the host and the fungus genotypes ( Hodge et al., 2000 ; Öpik et al., 2006 ; Lekberg et al., 2007 ; Dumbrell et al., 2010b ; Liu et al., 2014 ; Shi et al., 2014 ; Tedersoo et al., 2014 ; Bennett and Klironomos, 2019 ; Větrovský et al., 2019 ; Neuenkamp et al., 2021 ; Peña Venegas et al., 2021 ; Han et al., 2024 ; Lekberg et al., 2024 ).…”