The effects of supplementary UV-B radiation on Allium vineale var. vineale, Ecological, Mutualistic and Reproductive Perspectives

The plant species Allium vineale commonly includes populations with disparate allocation patterns to three modes of reproduction: aerially produced bulbils, belowground asexual offsets and sexual flowers producing viable seed. Adaptive explanations for the persistence of this diversity suggest trade-offs among these alternate components of fitness. Several previous studies of the ecological characteristics between seeds and bulbils produced by A. vineale have proffered explanations on the continued prevalence of sexual reproduction over its inherent cost but although this reproductive plasticity is well documented, the role that sexual reproduction plays in A. vineale remains contentious. In this study the effects of UV -B lighting regimes, (together with nutrient availability and mycorrhysal colonisation), and the resulting pattern of phenolic secondary metabolite production was examined in order to test the concept of trade-off between growth, photodamage and allocation to sexual / asexual reproduction ratios in this species.
A glasshouse experiment was conducted to examine the effects of UV-B exposure (at a fluence rate of 3.2 μmol m-2 s-1 of biologically active UV-B, 280 320 nm) on leaf growth and secondary metabolite production in the species Allium vineale. Specimen plants were taken from a natural population and subjected to enhanced UV-B over a successive period of growing seasons. Leaves of plants exposed to enhanced UV-B radiation showed changes in secondary metabolites, (specifically flavonol production). Changes in the balance of the production of quercetin, kaempferol and isorhamnetin were identified
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using high performance liquid chromatographic (H.P.L.C.) separation methods and morphological changes were observed in epidermal tissue.
Nutrient treatments in conjunction with supplementary UV-B radiation did not induce any changes in sexual/asexual balance with all plants maintaining asexual bulbil production for the duration of the study. Leaf growth was reduced in the long-term by UV-B exposure but reproductive output as defined by inflorescence viability and dry weight was unaffected suggesting the presence of a dedicated UV-B photoreceptor present in leaf tissue and not oxidative damage per se. The plants were able to mitigate effectively any UV-B damage over the period of the study. Phenotypic plasticity was not found for sexual / asexual reproduction modes and in response to nutrient availability. Plants produced bulbils whose average size and weight was unaffected in both UV-B treated and untreated groups. This limited degree of plasticity suggests that the plants in this study lack the capacity to change their allocation patterns between different reproductive modes as nutrient levels or environmental UV-B radiation varies.
I suggest that an important role of plant phenolics in this species may be to protect leaves from photodamage and their levels in leaves may vary depending on environmental levels of UV-B radiation. There is evidence for the presence of a dedicated UV-B photoreceptor in this species underpinned by the shortening of leaves in treated samples.