Nectar peroxide: Assessing variation among plant species, microbial tolerance and effects on microbial community assembly

Nectar contains antimicrobial constituents including hydrogen peroxide,
yet it is unclear how widespread nectar hydrogen peroxide might be among
plant species or how effective against common nectar
microbes. Here, we surveyed 45 flowering plant species across 23
families and reviewed the literature to assess the field-realistic range
of nectar hydrogen peroxide (Aim 1). We experimentally explored whether
plant defense hormones increase nectar hydrogen peroxide (Aim 2). Further,
we tested the hypotheses that variation in microbial tolerance to peroxide
is predicted by microbe isolation environment (Aim 3); increasing hydrogen
peroxide in flowers alters microbial abundance and community assembly (Aim
4), and that microbial community context affects microbial tolerance to
peroxide (Aim 5). Peroxide in sampled plants ranged from
undetectable to ~3000 µM, with 50% of species containing less than 100 µM.
Plant defensive hormones did not affect hydrogen peroxide in floral
nectar, but enzymatically upregulated hydrogen peroxide significantly
reduced microbial growth. Together, our results suggest that
nectar peroxide is a common but not pervasive antimicrobial defense among
nectar-producing plants. Microbes vary in tolerance and detoxification
ability, and co-growth can facilitate the survival and growth of less
tolerant species, suggesting a key role for community dynamics in
microbial colonization of nectar.