Data from: Anatomical trait variation across root orders shapes the distinct root economics space of herbaceous monocots and dicots

The trait-based root economics space provides a useful framework for
understanding the nutrient acquisition strategies across species. However,
it remains poorly understood how differences in anatomical features across
root branching orders shape the root economics space. We measured
order-based resource economics and anatomical traits of absorptive roots
of 32 perennial herbaceous monocots and dicots in a temperate steppe and
examined the trait coordination across root orders to gain insights into
the nutrient acquisition strategies of herbaceous grassland plants. We
found that differences in proportion of cortex in root cross-section and
secondary growth drive variation in the root economics space across root
orders of herbaceous species. In monocots, the absence of secondary growth
resulted in comparably consistent trait coordination across root orders.
Specifically, the gradient of root collaboration with arbuscular
mycorrhizal (AM) fungal constituted the main dimension of root trait
variation, mediated by the proportion of cortex in the root cross-section.
In contrast, we found substantial variation in the trait distribution of
dicots across root orders due to secondary growth. In lower-order roots of
dicots, mycorrhizal colonization rates varied independently of specific
root length, but were negatively associated with root nitrogen (N) content
along a principal component axis. These relations seemed to be due to the
alternative root symbiosis with nitrogen-fixing bacteria weakening the
classic collaboration gradient within the root economics space.
Importantly, our results demonstrate that the mycorrhizal colonization
rates were more strongly correlated with the proportion of cortex than
with root diameter in dicots. Consequently, secondary growth in
higher-order roots of dicots turned the widely recognized trade-off
between specific root length and mycorrhizal colonization rates into a
positive correlation. Our study reveals the contrasting resource
acquisition strategies of monocots and dicots across root orders,
highlighting the fundamental role of root anatomical traits in shaping the
root economics space. These findings provide valuable insights into how
root anatomical traits predict plant strategies and set the foundation for
exploring the potential influence of root anatomy on plant and ecosystem
functions.