Assessing the consequences of ozone depletion on ecosystem function: Effects of ultraviolet-B radiation on plant biomass, tissue quality and litter decomposition.

I investigated if variable levels of UV-B exposure during growth altered plant litter production and quality in ways that indirectly modified decomposition of litter material from ten species including three angiosperm trees, three forbs, three grasses, and one gymnosperm tree. For UV-B effects on litter production, I found that ambient UV-B levels (versus no UV-B) did not affect the aboveground biomass (litter production) of any of three grasses, one of three forbs, and the one angiosperm tree examined. However, it did alter the biomass of the two other forbs by stimulating production in one and reducing it in the other. For effects on plant tissue quality, I observed that ambient UV-B (versus no UV-B) altered different aspects of tissue chemistry (total C, C:N, lignin, lignin:N, holocellulose, tannins) in all three forb species, one of three grass species, and one of three angiosperm tree species examined and also altered leaf morphology (thickness) in another of the angiosperm tree species tested. Furthermore, in the gymnosperm tree examined, elevated UV-B (versus ambient UV-B) modified aspects of needle chemistry (lignin:N, holocellulose). Finally, for indirect UV-B effects on plant decomposition, I found that although litter quality was altered in some angiosperm species, UV-B treatment neither indirectly modified laboratory and terrestrial litter decay for any of the angiosperm trees, forbs, and grasses examined nor did it modify macro-invertebrate litter utilization and aquatic litter decomposition for the angiosperm trees tested. In contrast to those results, for the gymnosperm tree species tested, needles decay rates were significantly higher for material grown under elevated UV-B (versus ambient conditions). Overall, my results suggest that while UV-B alterations of litter production might affect the amount of litter processing and nutrient cycling, it does not appear that UV-B effects on litter quality will indirectly alter decomposition rates to a substantial degree in either terrestrial or aquatic systems receiving angiosperm litter inputs. However, UV-B effects observed on the tissue quality and decomposition of one gymnosperm species suggests that more experiments should be performed to determine if decay processes in ecosystems where gymnosperms predominate will be affected by variations in UV-B