Carry‐over of enhanced ultraviolet‐B exposure effects to successive generations of a desert annual: interaction with atmospheric CO2 and nutrient supply

Abstract

The performance of fifth generation offspring of a desert annual (Dimorphotheca sinuata DC.) were compared in the absence of UV‐B, under variable atmospheric CO2 and nutrient supply, after four consecutive generations of concurrent exposure of their progenitors to UV‐B at ambient (seasonal range: 2.55–8.85 kJ m–2 d–1) and enhanced (seasonal range: 4.70–11.41 kJ m–2 d–1) levels. Offspring of progenitors grown under elevated UV‐B exhibited a diminished photosynthetic rate, a consequence of a reduced leaf density, and diminished foliar levels of carotenoids, polyphenolics and anthocyanins. Conversely, nonstructural carbohydrate and chlorophyll b levels were increased. Altered physiology was accompanied by reduced apical dominance and earlier flowering, features generally considered under photomorphogenic control, increased branching and inflorescence production and greater partitioning of biomass to reproductive structures, but diminished seed production. Many of these changes were magnified under nutrient limitation and intensified under atmospheric CO2 enriched conditions. The latter disagrees with current opinion that elevated CO2 may reduce detrimental UV‐B effects, at least over the long‐term. Observed correlations between seed production and polyphenolic, especially anthocyanin, levels in offspring, and indications of diminished lignification (thinner leaves, less robust stems and fewer lignified seeds set) all pointed to the involvement of the phenylpropanoid pathway in seed formation and plant structural development and its disruption during long‐term UV‐B exposure. Comparisons with earlier generations revealed trends with cumulative generations of enhanced UV‐B exposure of increasing chlorophyll b and nonstructural carbohydrates, decreasing polyphenolics and biomass allocation to vegetative structures, and diminishing seed production despite increasing biomass allocation to reproductive structures. Notwithstanding some physiological compensation (increased chlorophyll b), the accumulation and persistence of these ostensibly inherited changes in physiological and reproductive performance suggest a greater impact of elevated UV‐B on vegetation, primary production and regeneration over the long‐term than presently envisaged.

How substantial are ultraviolet-B supplementation inaccuracies in experimental square-wave delivery systems?

“…These UV-B supplementation deficiencies in the SQW delivery system were due to a consistent underestimation of clear-sky background UV-B irradiance by the computer-encoded semiempirical model. Published spectral data along a latitudinal gradient (Caldwell et al, 1980), and one year's spectroradiometer measurements at a separate southern-hemisphere location (Musil et al, 1999) concur with this observation.…”

Potential vulnerability of Namaqualand plant diversity to anthropogenic climate change

“…It is also interesting to note that the Namaqualand annuals Dimorphotheca pluvialis and Dimorphotheca sinuata show some resilience of both growth and reproductive output under elevated UV-b levels, and little impact on these performance measures by elevated CO 2 levels (Wand et al, 1996), although there is some evidence to suggest a gradual accumulation of genetic damage under these conditions (Midgley et al, 1998;Musil, 1996;Musil et al, 1999). Therefore, although succulent species may be susceptible to climate change impacts, it is very likely that other plant growth forms will be more resilient, and may at least persist or even thrive under changing conditions.…”

Health effects from stratospheric ozone depletion and interactions with climate change

“…25, 26 If this is a widespread phenomenon among species, an amplification of sorts might be effected. The mechanism for this is not understood.…”