Recent studies on fine root functional traits proposed a root economics hypothesis where adaptations associated with mycorrhizal dependency strongly influence the organization of root traits, forming a dominant axis of trait covariation unique to roots. This conclusion, however, is based on tradeoffs of a few widely studied root traits. It is unknown how other functional traits fit into this mycorrhizal‐collaboration gradient. Here, we provide a significant extension to the field of root ecology by examining how fine root secondary compounds coordinate with other root traits. We analyzed a dataset integrating compound‐specific chemistry, morphology and anatomy of fine roots and leaves from 34 temperate tree species spanning major angiosperm lineages. Our data uncovered previously undocumented coordination where root chemistry, morphology and anatomy covary with each other. This coordination, aligned with mycorrhizal colonization, reflects tradeoffs between chemical protection and mycorrhizal dependency, and provides mechanistic support for the mycorrhizal‐collaboration gradient. We also found remarkable phylogenetic structuring in root chemistry. These patterns were not mirrored by leaves. Furthermore, chemical protection was largely decoupled from the leaf economics spectrum. Our results unveil broad organization of root chemistry, demonstrate unique belowground adaptions, and suggest that root strategies and phylogeny could impact biogeochemical cycles through their links with root chemistry.
Changes in fine‐root morphology are typically associated with transitions from the ancestral arbuscular mycorrhizal (AM) to the alternative ectomycorrhizal (ECM) or nonmycorrhizal (NM) associations. However, the modifications in root morphology may also coincide with new modifications in leaf hydraulics and growth habit during angiosperm diversification. These hypotheses have not been evaluated concurrently, and this limits our understanding of the causes of fine‐root evolution. To explore the evolution of fine‐root systems, we assembled a 600+ species database to reconstruct historical changes in seed plants over time. We utilise ancestral reconstruction approaches together with phylogenetically informed comparative analyses to test whether changes in fine‐root traits were most strongly associated with mycorrhizal affiliation, leaf hydraulics or growth form. Our findings showed significant shifts in root diameter, specific root length and root tissue density as angiosperms diversified, largely independent from leaf changes or mycorrhizal affiliation. Growth form was the only factor associated with fine‐root traits in statistical models including mycorrhizal association and leaf venation, suggesting substantial modifications in fine‐root morphology during transitions from woody to nonwoody habits. Divergences in fine‐root systems were crucial in the evolution of seed plant lineages, with important implications for ecological processes in terrestrial ecosystems.
- NSF-PAR ID:
- 10449074
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 228
- Issue:
- 2
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- p. 541-553
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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