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Emily B. Merewitz and Sha Liu

Naturally derived products that may enhance the functionality of fertilizers or other agricultural inputs are needed to reduce inputs associated with stress damage and increase the sustainability of turfgrass management. Damage to high-value creeping bentgrass (Agrostis stolonifera) turf areas caused by heat stress is a widespread problem. This study aimed to evaluate multiple, diverse treatments that may illicit antioxidant responses in plants, melatonin, rutin, and Si, when applied as foliar pretreatments to heat stress. Creeping bentgrass plants were grown in growth chambers at optimal (23 °C) or heat stress conditions (35 °C). Turfgrass quality, chlorophyll content, leaf electrolyte leakage, photochemical efficiency, lipid peroxidation, antioxidant enzyme activity, and fatty acid content were measured to determine the effects of foliar treatments on heat stress responses. Melatonin, Si, and rutin were all found to improve some or all of the physiological parameters measured in the study, but only melatonin and Si reduced lipid peroxidation, increased antioxidant enzyme activity, and altered fatty acid contents. Melatonin- and Si-treated plants had greater superoxide dismutase and peroxidase activity and increased the content of the unsaturated fatty acid, linoleic acid, in creeping bentgrass leaves during heat stress compared with controls. Rutin improved turf quality and reduced electrolyte leakage during heat stress, but the mechanism associated with these changes is unclear because no changes were found in antioxidant enzyme activities or fatty acids. Melatonin and Si treatment promoted antioxidant enzyme activity and linoleic acid content of leaves, which have been associated with the improved heat tolerance of creeping bentgrass plants.

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Bing Liu, Hong Zhou, Sha Cao, Yi-ping Xia and Rajeev Arora

Seasonal deacclimation was investigated during Jan. to Mar. 2014 in leaves of 10 azalea cultivars (Rhododendron section Tsutsusi) under natural conditions in eastern China. Based on the midwinter leaf freezing tolerance (LFT), these cultivars were grouped as “more-hardy” vs. “less-hardy.” Eight of the 10 cultivars first showed deacclimation when daily mean temperature over 2-week period preceding the LFT measurement was ≈9.5 °C. Deacclimation for other two cultivars was somewhat delayed and might have involved deacclimation–reacclimation cycling before eventual deacclimation. Our data indicate that the “more-hardy” group deacclimated slower than the “less-hardy” ones over the first half of the deacclimation period. This trend reversed during the second half of the deacclimation period. Accordingly, “more-hardy” and “less-hardy” cultivars depicted a “curvilinear” and “reverse curvilinear/linear” deacclimation kinetics. “More-hardy” cultivars generally had higher total soluble sugars (TSS) than “less-hardy” ones at acclimated state. TSS declined during deacclimation in all cultivars, and the loss was positively correlated with the loss in LFT. Leaf starch content generally followed opposite trend to that of TSS, i.e., it was at lowest during acclimated state and increased during deacclimation.

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Yi Kai, Yang Bin, Zhang Min, Gao Ainong, Zhang Jinger, Liu Zhi, Sha Shoufeng and Xie Chongxin