Responses to supplementary UV radiation of some temperate meadow species
The growth and development of various meadow species was monitored while growing under enhanced UV-radiation in the natural light environment. Growth responses to supplementary ultraviolet-B (UV-B+A) were mostly inhibitory when compared to the ambient daylight treatment for Bellis perennis, Cardamine pratensis, Cynosurus critatus and Ranunculus ficaria. When the response of ultraviolet-A (UVA) treated plants were compared with those of the UV-B+A, differences were found which varied according to the species and parameter investigated. No correlation in B. perennis growth responses could be made with reallocation of carbohydrates or with photosynthesis. The stomata of B. perennis grown under enhanced UV-B+A were less capable of closing than those of the ambient plants. Increases in the concentration of UV-absorbing compounds were found in the UV radiation treatment when dry weight accumulation was inhibited in C. pratensis. To further understand the growth responses of the UV-A treatment and their relationship to the UV-B responses, polychromatic action spectra in the natural environment were employed. B. perennis had an action maximum in the UV-B (280-315 nm), while C. cristatus demonstrates no action in the UV-B but action in the UV-A region (315-400 nm). Dry weight accumulation was found to respond differently to UV treatments when investigating Arabidopsis thaliana ecotypes. UV-B+A treatment was found to inhibit dry weight accumulation in most ecotypes. When UV-B+A induced inhibition was expressed in terms of ambient growth rate for each ecotype, a linear relationship could be derived. The higher the growth rate the more susceptible the ecotype was to UV-B+A inhibition. The pertinence of the UV-A treatment and UV protocol is discussed. It is suggested that UV responses could alter the diversity of the meadow equilibrium and these effects could be exacerbated by water loss.