Cadmium (Cd) and Zinc (Zn) tolerance and phytoextraction efficiency of arum (Colocasia esculenta L.) were investigated in hydroponics. Plants were grown for 60 d in nutrient solution after addition of Cd and Zn at the levels of 0, 15, 30 and 60 mmol L−1 and 0, 100, 500 and 1,000 μmol L−1, respectively. Growth of arum was unaffected by low levels of metal concentration (15 μmol L−1 Cd and 100 μmol L−1 Zn) whereas it decreased gradually with the increase of metal concentration in solution. Concentration of metals in parts of arum increased significantly (P<0.05) with the levels of metals in growth media. In arum shoots, Cd and Zn concentrations were 713 and 10,120 mg kg−1 respectively, at their low levels in solution. These concentrations (15 μmol L−1 Cd and 100 μmol L−1 Zn) did not cause any growth retardation indicating that arum is a metal hyperaccumulator. Transfer factor (TF) greater than one confirmed the hyperaccumulating behavior of arum for Cd and Zn in solution. Cadmium and Zn uptake in arum shoots without growth retardation and TF of these metals in arum indicates that this plant is a suitable candidate for the phytoremediation of water contaminated with Cd and Zn.
Plant growth promoting rhizobacteria (PGPR) is applied as biofertilizer to expect better production potential on commercial crops while keeping sustainability, but their function is dependent on the combination of PGPR and target crops. It has been reported that the application of PGPR in the soil resulted in the increment of strawberry yield, but other reports argue that PGPR has no effect on the yield potential. In addition, it is not clear whether the application timing of PGPR affects in a forcing cultivation system which usually requires transplanting. In this study, responses of diploid wild strawberry (Fragaria vesca) and garden strawberry (F.×ananassa Duch.) varieties to PGPR application were examined. Application of PGPR, Bacillus cereus KI-2, during the flower induction increased the total yield and number of fruits in F. vesca ‘Hawaii-4’, and in garden strawberry ‘Hoko-wase’. The application resulted in earlier flowering in ‘Hoko-wase’ while no difference was observed in ‘Tochi-otome’. Sucrose content was also altered in cultivar dependent manner so that it was increased in ‘Hawaii-4’, while it was decreased in ‘Tochi-otome’. These results indicate that PGPR has a potential to improve the yield factors while keeping the quality of the fruits, but the effect is cultivar dependent.
Effects of the irradiation patterns of red and blue LED lights on the growth of leaf lettuce were investigated. Seedlings of leaf lettuce (Lactuca sativa L.“Greenwave”) were transplanted and grown under four irradiation patterns consisted of simultaneous irradiation of blue light with PPFD of 120 μmol m −2 s −1 and red light with PPFD of 120 μmol m −2 s −1 during a 12 h photoperiod (RB 12 h/dark period 12 h), 4 h shifted irradiation of blue light (R 4 h/RB 8 h/B 4 h/dark period 8 h), 8 h shifted irradiation of blue light (R 8 h/RB 4 h/B 8 h/dark period 4 h), and alternating irradiation (R 12 h/B 12 h). The results demonstrated that larger shifts in irradiation times between red and blue lights led to increasing fresh/dry weight of leaf lettuce. A similar trend was observed under the irradiation patterns that replaced the red and blue. An experiment to examine the effects of simultaneous or alternating irradiation of red and blue light under equal day length and light integral was also conducted. As a result, alternating red and blue light irradiation produced better results compared to simultaneous treatment for Greenwave in both experiments.
Sedum species, which utilize crassulacean acid metabolism (CAM) photosynthetic pathway, have been the most commonly used plants in extensive green roofs. Previous investigations on Sedum green roofs have focused on their establishment and survival under drought conditions. Several Sedum species have been described as “inducible type of CAM” plants, suggesting that their photosynthetic and transpiration rates under wet conditions might greatly affect the carbon sequestration and the cooling effect of a Sedum green roof. Therefore, we investigated the photosynthetic and transpiration rates of three Sedum species (Sedum japonicum Siebold ex Miq., Sedum lineare Thunb., and Sedum sarmentosum Bunge) under wet and dry treatments. All three Sedum species exhibited CO2 uptake only during the light period under wet conditions as well as under dry treatment for several days after irrigation. Moreover, in the wet treatment, their photosynthetic and transpiration rates were found to be similar to those of the other green roof plants, Zoysia matrella (L.) Merr. and Ophiopogon japonicus (Thunb.) Ker Gawl. Thus, we suggest that the carbon sequestration and the cooling effect of the Sedum green roofs are equivalent to those of the green roofs utilizing the other plant under wet conditions from the standpoint of physiological traits.
Fourteen medicinal plants from northern Thailand, which dominate and form large colonies, were dried, powdered, and evaluated for growth inhibitory activity using a modified sandwich method. All the plants showed inhibitory activities on the growth of lettuce seedlings: Cymbopogon nardus had the strongest activity, completely inhibiting the growth of the lettuce hypocotyls and radicles; Piper retrofractum completely inhibited the hypocotyl growth and 93.5% of the radicle growth; and the remaining plants inhibited hypocotyl and radicle growth by 30.9–57.4% and 44.1–75.3%, respectively. Inhibitory active compounds may have been released from the plants into the sandwich method medium and inhibited the growth of the lettuce seedlings. The present results suggest that C. nardus and P. retrofractum are possible candidates for developing alternative natural herbicides in sustainable agriculture because of their strong inhibitory activity.