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The study of the regulatory mechanism of exogenous plant growth regulators (PGRs) on the relevant physiological indicators is essential to maintain the normal growth of Rosa hybrida under high-temperature conditions. The photosynthetic and physiological characteristics of the ornamental cut rose Rosa hybrida ‘Carolla’ under high temperature were studied by spraying leaves with various concentrations of exogenous salicylic acid (SA; 0.5, 1.0, 1.5, or 2.0 mmol·L−1), 6-benzylaminopurine (6-BA; 10, 20, 30, or 50 μmol·L−1), abscisic acid (ABA; 10, 20, 30, or 50 mg·L−1), or distilled water (control). The results indicated that a foliar spray of either SA, 6-BA, or ABA could mitigate the impact of high temperatures. Compared to the control, the application of SA, 6-BA, or ABA increased the net CO2 assimilation rate (An), transpiration rate (E), stomatal conductance (Gs), and water use efficiency (WUE) of ‘Carolla’, while decreasing the leaf relative electrical conductivity (REC) and malondialdehyde (MDA) content. The applications of SA, 6-BA, or ABA increased the activities of the antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) and altered the proline (Pro), soluble protein, and soluble sugar contents. The results showed that foliar sprays of SA, 6-BA, or ABA could enhance the heat tolerance of ‘Carolla’ by promoting photosynthesis, cell membrane structural stability, antioxidant enzyme activity, and osmoregulation in plants under high-temperature stress. The experiment showed that 1.5 mmol·L−1 SA, 20 μmol·L−1 6-BA, or 20 mg·L−1 ABA could alleviate the damage caused by high temperatures, with 20 μmol·L−1 6-BA having the best effect.

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Root pruning during early root development can optimize the root structure of woody plants. To determine the effects of root pruning on tree peony (Paeonia suffruticosa), seedlings of the tree peony cultivar 'Fengdanbai' were subjected to varying degrees or different styles of root pruning. Various indexes were analyzed, including the anatomical structure of the root, root vitality, the activity levels of antioxidant enzymes, and the contents of endogenous hormones and their ratios. Comprehensive morphological observation showed that pruning freshly germinated roots that are 3 cm long by 1/3 (i.e., removing 1 cm) yielded the greatest rooting rate (90%), lateral root initiation (2.34 per seedling), and subsequent growth. Analysis of physiological and biochemical indicators during the critical rooting period (3-5 days after root pruning) showed that the levels of superoxide dismutase and abscisic acid (ABA) were decreased, while the oxidase activities of peroxidase, polyphenol oxidase, and indole acetate oxidase and the contents of the endogenous hormones indole acetic acid (IAA), gibberellin (GA 3 ), and zeatin (ZT) were increased. IAA plays a key role in the process of adventitious root formation and the ratios of IAA/GA3, IAA/ABA, and IAA/ZT reflect endogenous hormone homeostasis during adventitious root formation. IAA/ABA and IAA/ZT showed higher values in the pruned roots compared to the control roots, which favor adventitious root induction and elongation. These results provide a basis for the study of adventitious root formation in tree peony.

This study was designed to investigate the effects of exogenous calcium on the tolerance of Rosa hybrida ‘Carolla’ to high-temperature and the physiological mechanisms underlying this response. Leaves of ‘Carolla’ grown under stress were treated by spraying four different concentrations of calcium chloride (CaCl2; 50, 100, 150, or 200 μM). The photosynthetic responses, antioxidant enzyme activities, and osmotic substance contents were measured under high-temperature stress at the flowering stage. Temperature-stressed ‘Carolla’ with CaCl2 treatment showed significantly increased chlorophyll (Chl) content, net photosynthetic rate (An), transpiration rate (E), stomatal conductance (gs), water use efficiency (WUE), superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) activities together with proline (Pro), soluble sugar (SS), and soluble protein (SP) concentrations, while malonaldehyde (MDA) content and relative electrical conductivity (REC) were significantly reduced. The damages caused by high-temperature stress were alleviated by applying CaCl2. Among the CaCl2 treatments, 100 μM CaCl2 best minimized the damage caused by high-temperature to ‘Carolla’. This study showed that exogenous calcium could improve the tolerance of Rosa hybrida ‘Carolla’ to high-temperature stress by regulating photosynthesis, the antioxidant system, and osmotic substances.