Intra-specific variability and sex influence the allelopathic capacity of Empetrum nigrum

Allelopathic plant species play significant roles in shaping natural
ecosystems. While a high degree of inter-species variation in allelopathic
capacities is commonly reported, variation across intra-specific groups
and between dioecious sexes is limited. Here we use the ecologically
important, allelopathic dwarf shrub Empetrum nigrum L. to assess how
allelopathic capacity varies between intra-specific groups (i.e., the
diploid and dioecious “nigrum” group and the tetraploid and synoecious
“hermaphroditum” group of Empetrum) and sex (i.e., male and female plants
of the nigrum group). Specifically, we tested Icelandic Empetrum,
as its allelopathic nature may influence long-term land degradation across
Icelandic highlands. The allelopathic capacity of Empetrum leaves was
measured in a series of bioassays as the inhibition of seed germination
and seedling root elongation of the grass Festuca richardsonii. A very
strong allelopathic response of Empetrum leaves was observed.
Intra-specific and sex-related differences in allelopathic capacity were
also detected, with the hermaphroditum group possessing a greater
germination inhibitory effect compared to the nigrum group, and males of
the nigrum group inhibited germination more than females. Targeted liquid
chromatography-mass spectrometry (LC-MS) quantification of two known
Empetrum allelopathic constituents – Batatasin-III (BIII) and
3,4-dimethoxy-2´,5-dihydroxybibenzyl (DDB) – showed that BIII
concentrations were significantly higher in leaves from the hermaphroditum
group compared to the nigrum group, but no differences were observed
between males and females within the nigrum group. DDB was not detected in
the sampled Icelandic Empetrum populations. Our results indicate that
Empetrum may differentially impact plant interactions and ecosystem
processes depending on the relative abundance of Empetrum intra-specific
groups and sexes within populations, and that BIII is not solely
responsible for the allelopathic capacity of Icelandic Empetrum.