Lianas have a faster resource acquisition strategy than trees: belowground evidence from root traits, phylogeny, and the root economics space

1. The competitive advantage of lianas over trees has been widely
documented in studies of their leaf functional traits across diverse
habitats; however, the relative contribution of root functional traits to
the competitive superiority of lianas over trees has not yet been
evaluated. The aim of this study was to explore the root functional
traits, phylogenetic structure of these traits, and root trait dimensions
of lianas to clarify why lianas can outperform trees. 2. We sampled 69
liana species from tropical and temperate forests in China and measured
nine key functional traits of first-order roots of each species, including
morphological, architectural, anatomical, and chemical traits, as well as
the percentage of mycorrhizal colonization. Data on these traits were then
compared with similar data of 127 tree species from the same biome
obtained from the Global Root Traits (GRooT) database and our previous
studies. 3. Liana roots had lower construction costs and could acquire
resources more rapidly compared with tree roots. Significant differences
were observed in most tree root traits between tropical and temperate
sites. However, no significant differences were observed in any of the
liana root traits between tropical and temperate sites, apart from the
root branching ratio. 4. Lianas showed much weaker phylogenetic
conservatism in their root traits than trees when species were pooled
across sites. Phylogenetic constraint was lower for nearly all root traits
of both temperate lianas and trees compared with those of tropical lianas
and trees. 5. The root economics space of lianas and trees had two
orthogonal dimensions with “conservation” and “collaboration” axes.
However, lianas occupied the trait space with higher root nitrogen
concentration and greater specific root length, showing “fast” resource
acquisition strategy, while trees placed opposite space and exhibited
relatively “slow” strategy. 6. Synthesis. The ability of lianas to
outcompete trees in harsh environments might be explained by their faster
resource acquisition strategy and the lower phylogenetic constraint in
root traits. Generally, lianas might play an increasingly important role
in the structure and function of forest ecosystems in the future with
ongoing habitat fragmentation and climate change.