Green roofs are considered effective in the reduction of atmospheric CO 2 because of their ability to reduce energy consumption of buildings and sequester carbon in plants and substrates. However, green roof system components (substrate, water proofing membrane, etc.) may cause CO 2 emissions during their life cycle. Therefore, to assess the CO 2-payoff for extensive green roofs, we calculated CO 2 payback time it takes their CO 2 sequestration and reduction to offset the CO 2 emitted during its production process and maintenance practices. The amount of CO 2 emitted during the production of a modular green roof system was found to be 25.2 kg-CO 2 •m −2. The annual CO 2 emission from the maintenance of green roofs was 0.33 kg-CO 2 •m −2 •yr −1. Annual CO 2 sequestration by three grass species with irrigation treatment was about 2.5 kg-CO 2 •m −2 •yr −1 , which was higher than that of Sedum aizoon. In the hypothetical green roofs, annual CO 2 reduction due to saved energy was between 1.703 and 1.889 kg-CO 2 •m −2 •yr −1. From these results, we concluded that the CO 2 payback time of the extensive green roofs was between 5.8 and 15.9 years, which indicates that extensive green roofs contribute to CO 2 reduction within their lifespan.

Tipburn (calcium (Ca) deficiency disorder) is a major problem in the production of lisianthus cultivars. However, few studies have investigated the influence of different Ca concentrations in nutrient solution on tipburn incidence and Ca acquisition and distribution. Thus, it remains unclear why some cultivars exhibit tipburn under high Ca concentrations. To address this, we used three lisianthus cultivars ‘Azuma-no-Kaori’ (AK), ‘Celeb Wine’ (CW), and ‘Voyage Yellow’ (VY) and compared tipburn incidence and Ca acquisition and distribution under different Ca concentrations in a nutrient solution (low (40 ppm), moderate (80 ppm), and high (120 ppm) Ca). Tipburn severity and incidence in AK and VY significantly decreased with increasing nutritional Ca concentrations; the Ca concentrations in each organ and Ca acquisition competence (RGRCa) increased at higher nutritional Ca concentrations. In contrast, tipburn incidence in CW was 100% for all treatments. In CW, Ca acquisition competence and Ca concentrations in most organs increased with increasing nutritional Ca concentrations, but the Ca concentrations in the tips of the upper leaves did not differ significantly between treatments. Thus, our results suggest that the cause of tipburn under sufficient Ca conditions is an inability of the plant to distribute Ca to the tips of its upper leaves.

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Tipburn is a major problem for the production of lisianthus (Eustoma grandiflorum (Raf.) Shinn.) cultivars. Relative air humidity is regarded as a key environmental factor affecting tipburn severity in commercial crops. However, there are limited studies comparing the occurrence of tipburn and calcium (Ca) distribution in lisianthus cultivars under different relative air humidity conditions. Accordingly, we investigated the effect of relative air humidity on tipburn severity, transpiration rate, and Ca content in seven lisianthus cultivars. Under a high humidity treatment (70%), only two cultivars (“Voyage pink” (VP) and “Azuma-no-kaori” (AK)) showed significantly higher tipburn severity than those under a low humidity treatment (50%), which suggests that high humidity conditions do not always increase tipburn severity in lisianthus. Transpiration rates of all cultivars, except for AK, were either significantly lower under the high humidity treatment than under the low humidity treatment, or did not vary significantly between the treatments. In contrast, total Ca concentrations in all cultivars, except for “Piccolosa snow” (PS), were significantly higher under the high humidity treatment than under the low humidity treatment. These results suggest that Ca acquisition and distribution in lisianthus cultivars are strongly influenced by Ca uptake from root pressure.