Date of Award
Master of Science (MS)
Plant and Environmental Science
McCarty, Lambert B
Golf courses continue to explore all options for relief of summer stress on bentgrass [Agrostis stolonifera L. var palustris (Huds.)] putting greens. The use of colorants and other pigment-containing products has recently been suggested as a means of relieving this stress by reducing temperatures and respiration, and increasing photosynthesis. Research supporting these claims is limited, especially on bentgrass putting greens located in stressful environments. The objective of this experiment was therefore to investigate the impacts of pigment-containing products on turfgrass physiology during hot and humid summer months in the Southeastern USA.
Four pigment-containing products were selected for the two 2012 summer field studies: Turf Screen (a combination of zinc oxide and titanium dioxide), PAR and Foursome (copper-based pigments), and a paint designed for dormant turfgrass throughout the winter months. Products were applied weekly for ten weeks. Two of the products, Turf Screen and PAR, were also used in two 10 day growth chamber studies to evaluate their effects on bentgrass plugs under stressful high temperatures.
In field studies, lower carbon dioxide exchange rates (CER) were measured in untreated turf compared to Turf Screen, PAR, Foursome and the paint, indicating that these products reduced photosynthesis. In both studies, the paint had the highest CER of any treatment. Turf Screen and PAR performed similarly in both studies (0.182 and 0.118 µmol CO2 cm-2 s-1 in study one, 0.090 and 0.091 in study two). In study two, evaporation rates of untreated plots averaged 1.00 µmol H2O cm-2 s-1, which was significantly higher than Turf Screen at -9.10 µmol H2O cm-2 s-1. None of the tested products lowered canopy temperature, and treated turf plots often exhibited significantly higher temperatures (~1.5¡F or 1.0¡C) than the untreated controls. In study one, the untreated control had higher normalized difference vegetation index (NDVI) values than PAR, Turf Screen, and the paint throughout the summer. Differences in NDVI were not observed between Turf Screen, PAR, and Foursome in either study. Visual quality of turf treated with Turf Screen, PAR, and Foursome was similar to the untreated control in both studies. Images analyzed with the WinRHIZO program to calculate percent cover provided data consistent with the visual turfgrass quality ratings. Products had no significant effects on root mass. Tissue analysis showed Turf Screen treated foliage had higher zinc concentrations in both studies, averaging 911 ppm compared to 88 ppm for the untreated control. Soil zinc levels in Turf Screen treated plots were twice those of the other treatments in both studies. The paint treated turf had significantly higher tissue copper concentrations in both studies, averaging 155 ppm compared to the other treatments, which averaged 61 ppm.
In growth chamber studies, CER was significantly lower in the unstressed control (35/24¼C) at -1.15 compared to Turf Screen at 1.53, PAR at 0.67, and the stressed control (28/22¼C) at 1.12 µmol CO2 cm-2 s-1 in study one. Positive CER values indicate that respiration rates exceeded photosynthetic rates in these pots. The unstressed control had significantly higher evaporation rates compared to Turf Screen, PAR, and the stressed control in study one. The stressed control, Turf Screen, and PAR had significantly lower Fv/Fm values compared to the unstressed control in both studies.
A significant reduction in the transmission of photosynthetically active radiation (400-700 nm) occurred when products were applied to transparent acrylic sheets. PAR and Foursome had least impact on the transmission of (PAR) wavelengths by only reducing ~20%. Turf Screen (39%) and the paint (46%) had the largest reductions.
Microscopy images visualized the specific interactions between products and leaf blades. While Turf Screen (higher viscosity) remained on the leaf surface and covered the stomata, pigments such as PAR (lower viscosity) entered the leaf via stomata.
Higher CER for treated turf in field study two indicates net photosynthesis is reduced when these products are applied. Higher evaporation rates for the untreated in field study two indicate that transpiration is also being affected by these products. Spectroradiometer data show a significant reduction in the transmission of photosynthetically active radiation when products are applied. In summary, these products failed to significantly enhance any plant processes normally associated with improved turf health and quality. On the contrary, products appeared to disrupt the plant's ability to cool itself through transpiration. The significant increases in heavy metal concentrations such as zinc and copper should also be considered, especially with long-term use.
Gann, James, "EVALUATION OF PIGMENT-CONTAINING PRODUCTS ON CREEPING BENTGRASS [Agrostis stolonifera L. var palustris (Huds.)] PERFORMANCE" (2013). All Theses. 1576.