A silicon (Si)-deficient top soil was used in a pot experiment to investigate the effect of Si application on the shoot and root morphology of alfalfa (Medicago sativa L.). Silicon was applied to the alfalfa plants at 6 different rates (0, 0.025, 0.05, 0.10, 0.20, 0.30 g/kg), and each treatment was replicated 6 times. This study indicated that the Si content of roots and shoots increased significantly (P<0.05) with increasing Si concentration in the soil, and that the Si content of roots was greater than that of shoots. Plants treated with Si had increased leaf area, height, forage yield and shoots per plant during the reproductive period in comparison with controls. The application of Si also increased root volume, the number of secondary roots and root biomass. The effects of Si application were greater on roots than on shoots. The ratio of shoot to root dry weight was below 1.62 when Si was applied to plants and 1.91 without Si application. Overall, overcoming available Si deficiency resulted in a significant increase in shoot and root growth.
Commercial farming of the intertidal brown alga Hizikia fusiformis (Harvey) Okamura in China and South Korea in the sea depends on three sources of seedlings: holdfast-derived regenerated seedlings, young plants from wild population and zygote-derived seedlings. Like many successfully farmed seaweed species, the sustainable development of Hizikia farming will rely on a stable supply of artificial seedlings via sexual reproduction under controlled conditions. However, the high rate of detachment of seedlings after transfer to open sea is one of the main obstacles, and has limited large-scale application of zygotederived seedlings. To seek the optimal condition for growing seedlings on substratum in land-based tanks for avoidance of detachment in this investigation, young seedlings were grown in both outdoor tanks exposed directly to sunlight and in indoor raceway tanks in reduced, filtered sunlight. Results showed that young seedlings, immediately after fertilization, could withstand a daily fluctuation of direct solar irradiance up to a level of 1800 μmol photons m −2 s −1 , and maintained a faster growth rate than seedlings grown in indoor tanks. Detailed experiments by use of chlorophyll fluorescence measurements further demonstrated that the overnight (12 h) recovery of optimal fluorescence quantum yield (F v /F m ) of seedlings after 1 h treatment at 40°C was 98%, and the 48 h recovery of F v /F m of seedlings after 1 h exposure to 1800 μmol m −2 s −1 was 92%. Forty-one-day-old seedlings showed no significant decrease of optimal fluorescence quantum yield at salinity ranging from 30 to 5 ppt for a treatment up to 17 h. Sixhour desiccation treatment did not have any influence on the optimal fluorescence quantum yield. Exposure to 18 mmol L −1 sodium hypochlorite for 10 min did not damage the PSII efficiency, and thus could be used to remove epiphytic algae. The strong tolerance of young seedlings to high temperature, high irradiance, low salinity and desiccation found in this investigation supports the view that mass production of Hizikia seedlings should be performed in ambient light and temperature instead of in shaded greenhouse tanks.
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