Ontogenetic changes in root traits and root‐associated fungal community composition in a heteroblastic epiphytic bromeliad

Abstract

Heteroblastic variations among leaf traits is a well‐known process, especially in bromeliad species that show abrupt changes, but little effort was directed to test whether comparable ontogenetic variation occurs among root traits and their fungal partners. Usually considered for their mechanical role, roots of bromeliads may also play a role in resource use that we expect to differ between ontogenetic stages, namely nutrient pulse‐supplied atmospherics (young stage) and continuously‐supplied tanks (later stage). On a selection of adventitious roots of the heteroblastic epiphyte Lutheria splendens, we explored 1) ontogenetic variations in morphological and anatomical root traits, namely the number of adventitious roots and tips, total root length, average root diameter, root tissue density, specific root length and root tissue areas, and 2) ontogenetic changes in the composition of the root‐associated fungal communities using ITS1 region‐based high‐throughput sequencing. Plant size, taken as an indicator of gradual ontogenetic variations, and plant stage had significant effects on root traits, unless for root tissue density. The number of adventitious roots and tips, the total root length, average root diameter and all root tissue areas (i.e. velamen, outer cortex, inner cortex, vascular cylinder) increased gradually with ontogeny while the specific root length decreased abruptly. The root‐associated fungal communities varied with plant stage. The tank stage showed higher proportion of mycorrhizal fungi and a lower abundance of dark septate endophyte as compared to atmospheric stage. Overall, we demonstrated significant ontogenetic variations of root traits and fungal partners in bromeliad species that suggest important changes in the strategy for resource use as plants mature. We invite future root trait studies to better account for ontogenetic variations.

Special Issue: Root traits and functioning: from individual plants to ecosystems

“…In contrast, Merino‐Martín and collaborators (2023) only observed differences in fungal, but not bacterial communities, between rhizosphere and bulk soil along an elevation gradient. This rhizosphere effect is also partly related to variation in inter‐ (Mafa‐Attoye et al 2023, Merino‐Martín et al 2023) and intraspecific (Gagliardi et al 2023, Leroy et al 2023) variation in root morphological traits that are found here to predict the community composition of the root‐associated microbiome.…”

“…1) may appear to shift along the collaboration axis but this may not reflect a shift in the species' dependency on mycorrhizal fungi. Similarly, root traits may change with plant ontogeny, changing from thin to thick roots as plants grow bigger (Leroy et al 2023) (Species 2; Fig. 1).…”

“…representing the ‘outsourcing' strategy) at the interspecific level, but Gagliardi and co‐workers (2023) found the opposite pattern intra‐specifically. Additional variables, such as plant ontogeny (Leroy et al 2023); the spatial scale at which plant–microbe interactions are studied (Merino‐Martín et al 2023); and the necessity to invest in plant root pathogen defense (Dai et al 2023) may provide valuable insights in unraveling the extent to which soil properties, root traits and microbial communities (and associated functioning) interact (in)directly, and ultimately, shape plant community diversity and ecosystem functioning.…”

“…Reference in this Special Issue Temperate Alonso-Crespo et al 2023, Klimešová and Herben 2023, Mafa-Attoye et al 2023, Mao et al 2023, Schuster et al 2023, Slette et al 2023, Yang et al 2023(Sub)Tropical Dallstream et al 2023, Dai et al 2023,Gagliardi et al 2023, Guo et al 2023, Leroy et al 2023, Kotowska et al 2023 a large variety of fine-root systems coexist in hyper-diverse tropical plant communities. Besides adding information from underexplored biomes, this Special Issue further highlights the importance of incorporating additional traits covering all belowground trait categories (McCormack et al 2017) -albeit to different extents -in the context of a RES (Table 1).…”

“…Guo et al (2023) further showed that allometric relationships (and thus covariations) among root traits also changed as a function of tree size in a tropical forest community. The position of species within the RES may thus change with time (at least, along the collaboration axis), but whether these shifts indeed reflect changes in the degree of mycorrhizal dependency is still controversial (Leroy et al 2023). Temporal variation in root traits in including mycorrhizal colonization rates, both at the intra-, interspecific and community level, will warrant future research.…”