Effects of long-term mowing on leaf- and root-associated bacterial community structures are linked to functional traits in 11 plant species from a temperate steppe

Long-term mowing can cause morphological stuntedness of plants, thus
reducing grassland productivity and exacerbating grassland degradation.
Although plant microbiomes can enhance plant resistance against
disturbance, considerable uncertainty exists regarding how mowing and
mowing-induced plant trait plasticity affect plant microbiomes in natural
grasslands. Here we examined the responses of leaf-/root-associated
bacterial (LAB/RAB) communities of 11 dominant herbaceous perennials (6
replicates per species) to a 17-year mowing treatment in a temperate
grassland. We also measured leaf/root physiological and morphological
traits and analyzed the relationships among mowing practice, bacterial
community structures, and leaf/root trait parameters.  We found
that both leaf and root functional traits showed interspecific variations
(variations across different plant species), while only the leaf traits
exhibited intraspecific variation (treatment-induced variations within
plant species) between the treatments. Similarly, the LAB community
structure was more sensitive to mowing but less influenced by host species
identity, compared to the RAB community. The RAB community structure was
primarily shaped by host species identity, while mowing was a secondary
influencing factor.  The different patterns of LAB and RAB
communities in response to mowing could be specifically explained by the
inter-/intraspecific variations of the related leaf and root traits. The
LAB community was strongly correlated with the leaf traits which exhibited
mowing-induced plasticity (intraspecific variation), with the correlations
with nitrogen resorption efficiency and aboveground dry weight being the
greatest. The root traits were important indicators of bacterial community
structure in the root compartment across the hosts, rather than between
the treatments. Root tissue density showed the strongest interspecific
variation, and was identified as an overwhelming driver of the RAB
community. The shifts in LAB/RAB communities under mowing were largely
attributed to the increased proportions of Actinobacteria. The high mowing
sensitivity of the LAB community was associated with the enrichment of
soil-derived Actinobacteria in leaves under mowing. Actinobacteria were
also the main keystone taxa in the bacterial community networks under
mowing. Our results demonstrate that the magnitude of plant-associated
microbial community response to long-term mowing is plant compartment- and
trait-variation-dependent, and advance our understanding of the leaf/root
microbiome-trait relationships in complex plant communities.