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Lu Gan, Xunzhong Zhang, Silu Liu and Shuxia Yin

Turfgrass performance under drought stress is impeded by plant water deficit and oxidative damage, which might be improved by the external application of osmoprotectants. Creeping bentgrass (Agrostis stolonifera L.) is a valuable species for low-cut golf surfaces as a result of its high density and fine texture. However, weak tolerance to drought stress is a primary shortcoming. In this study, the effect of exogenous glycinebetaine (GB) pretreatment on mitigating the damage from drought stress in creeping bentgrass cultivar ‘T-1’ was evaluated. Pieces of creeping bentgrass sod were subjected to four treatments: 1) well-watered control, 2) well watered and sprayed with 100 mm GB, 3) drought stress, and 4) drought stress and sprayed with 100 mm GB. Drought stress resulted in a remarkable decrease in turf quality (TQ), relative water content (RWC), and chlorophyll content, with significant increases in superoxide anion content (O2 ), malondialdehyde (MDA) content, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activity. In contrast, pretreatment with 100 mm GB decreased the O2 and MDA content in water-stressed plants, and increased turf quality, chlorophyll content, SOD, CAT, and POD activity. Meanwhile, the expression level of the psbA, SAMS4, CMO, and ACS1 genes in leaf samples collected during the drought-stress stage was elevated in GB pretreatment. Notably, SAMS4 gene expression in GB pretreatment was significantly greater than in the untreated GB groups subjected to water stress. These results suggested that GB could mitigate the adverse effect of water stress on creeping bentgrass. The amelioration related strongly to the maintenance of the antioxidant enzyme system, accumulated endogenous compatible metabolites, and the elevation of gene expression levels. These findings lead us to conclude that GB pretreatment could be used as an ameliorative agent for creeping bentgrass against the deleterious effects of water stress.

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Shanshan Sun, Mengying An, Liebao Han and Shuxia Yin

Perennial ryegrass (Lolium perenne L.) is a widely used turfgrass. In this study, the effect of exogenously applied 24-epibrassinolide (EBR) on salt stress tolerance of perennial ryegrass was investigated. The results indicated that pretreatment with four concentrations of EBR (0, 0.1, 10, 1000 nM) improved salt tolerance of perennial ryegrass. Exogenous EBR treatment decreased electrolyte leakage (EL), malondialdehyde (MDA), and H2O2 contents and enhanced the leaf relative water content (RWC), proline, soluble sugar, and soluble protein content under salt stress condition. Meanwhile, EBR reduced the accumulation of Na+ and increased K+, Ca2+, and Mg2+ contents in leaves after salt treatment. Moreover, EBR pretreatment also increased superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) activity, as well as ascorbic acid (AsA) and glutathione contents. These results suggested that EBR improved salt tolerance by enhancing osmotic adjustment and antioxidant defense systems in perennial ryegrass.

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Nikolaos Ntoulas, Panayiotis A. Nektarios, Thomais-Evelina Kapsali, Maria-Pinelopi Kaltsidi, Liebao Han and Shuxia Yin

Several locally available materials were tested to create an optimized growth substrate for arid and semiarid Mediterranean extensive green roofs. The study involved a four-step screening procedure. At the first step, 10 different materials were tested including pumice (Pum), crushed tiles grade 1–2 mm (T1–2), 2–4 mm (T2–4), 5–8 mm (T5–8), 5–16 mm (T5–16), and 4–22 mm (T4–22); crushed bricks of either 2–4 mm (B2–4) or 2–8 mm (B2–8); a thermally treated clay (TC); and zeolite (Zeo). All materials were tested for their particle size distribution, pH, and electrical conductivity (EC). The results were compared for compliance with existing guidelines for extensive green roof construction. From the first step, the most promising materials were shown to include Pum, Zeo, T5–8, T5–16, and TC, which were then used at the second stage to develop mixtures between them. Tests at the second stage included particle size distribution and moisture potential curves. Pumice mixed with TC provided the best compliance with existing guidelines in relation to particle size distribution, and it significantly increased moisture content compared with the mixes of Pum with T5–8 and T5–16. As a result, from the second screening step, the best performing substrate was Pum mixed with TC and Zeo. The third stage involved the selection of the most appropriate organic amendment of the growing substrate. Three composts having different composition and sphagnum peat were analyzed for their chemical and physical characteristics. The composts were a) garden waste compost (GWC), b) olive (Olea europaea L.) mill waste compost (OMWC), and c) grape (Vitis vinifera L.) marc compost (GMC). It was found that the peat-amended substrate retained increased moisture content compared with the compost-amended substrates. The fourth and final stage involved the evaluation of the environmental impact of the final mix with the four different organic amendments based on their first flush nitrate nitrogen (NO3 -N) leaching potential. It was found that GWC and OMWC exhibited increased NO3 -N leaching that initially reached 160 and 92 mg·L−1 of NO3 -N for OMWC and GWC, respectively. By contrast, peat and GMC exhibited minimal NO3 -N leaching that was slightly above the maximum contaminant level of 10 mg·L−1 of NO3 -N (17.3 and 14.6 mg·L−1 of NO3 N for peat and GMC, respectively). The latter was very brief and lasted only for the first 100 and 50 mL of effluent volume for peat and GMC, respectively.