Variation of foliar silicon concentrations in temperate forbs: effects of soil silicon, phylogeny and habitat

Silicon (Si) accumulation is known to alleviate various biotic and abiotic stressors in
plants with potential ecological consequences. However, for dicotyledonous plants our
understanding of Si variation remains limited. We conducted a comparative
experimental study to investigate (1) interspecific variation of foliar Si concentrations
across 37 dicotyledonous forbs of temperate grasslands, (2) intraspecific variation in
foliar Si concentration in response to soil Si availability, the influence of (3)
phylogenetic relatedness, and (4) habitat association to moisture. Foliar Si differed
markedly (approx. 70-fold) across the investigated forbs, with some species exhibiting
Si accumulation similar to grasses. Foliar Si increased with soil Si availability, but the
response varied across species: species with higher Si accumulation capacity showed
a stronger response, indicating that they did not actively upregulate Si uptake under
low soil Si availability. Foliar Si showed a pronounced phylogenetic signal, i.e. closely
related species exhibited more similar foliar Si concentrations than distantly related
species. Significant differences in foliar Si concentration within closely related species
pairs nevertheless support that active Si uptake and associated high Si concentrations
has evolved multiple times in forbs. Foliar Si was not higher in species associated with
drier habitats, implying that in dicotyledonous forbs of temperate grasslands high foliar
inter- and intraspecific variation in foliar Si concentration in temperate forbs. This
variation should have pervasive, but so far understudied, ecological consequences for
community composition and functioning of temperate grasslands under land-use and
climate change.