Leaf Pigments in Relation to UV-B Tolerance of Cool-season Turfgrasses.

Ultra-violet B (280-315 nm) radiation is a major factor causing quality decline of newly transplanted sod. Significant differences in UV-B tolerance among cool-season turfgrass species and varieties have been observed in our previous studies.  Mechanisms of tolerance to UV-B are not well documented.  The objective of this study was to investigate the role of leaf pigments in UV-B tolerance of cool-season turfgrasses. Eight-week old seedlings of two to three varieties from each of four cool-season species Chewings fescue (Festuca rubra L.), Kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.), and tall fescue (Festuca arundinacea Schreb.) were subjected to artificial UV-B treatment for 10 days, followed by 15 days of recovery in the university greenhouse. The concentrations of chlorophyll a, b, total chlorophyll, and carotenoids were measured at days 0, 5, 10 and 25 after UV-B initiation. Total chlorophyll concentration remained stable or increased slightly in all species after 5 d UV-B treatment, except for perennial ryegrass which showed a 17% reduction. When measured at 10 days of UV-B stress, carotenoids in all species were increased by 24% to 41% relative to initial levels. Both chlorophyll and carotenoid concentrations in the four species decreased after 10 d UV-B stress and increased after 15 d recovery. As a UV-B sensitive species, Kentucky bluegrass showed greater fluctuation in leaf pigments than other species. Difference in pigments between Kentucky bluegrass varieties was observed after 5 d UV-B stress.  ‘Midnight’ Kentucky bluegrass retained greater pigment concentrations than ‘BlueTastic’. The data indicate that leaf pigments, especially carotenoids, play a role in UV-B protection.