To prevent rooting into an irrigation mat, five water porous materials, perforated black plastic, perforated ground cover, polyester, woven polypropylene and porous plastic, were evaluated as mat covers. Only polyester, woven polypropylene and porous plastic prevented penetration of roots of marigold seedlings into the mat. Under high moisture stress, root tips were killed at the cell drainage hole; however, under low moisture stress the roots formed a mat on top of these mat covers. To prevent root penetration out the drainage hole, polyester and porous plastic were glued over the hole. No difference in shoot growth was observed between the control (only polyester mat cover) and seedlings produced in drainage hole covered cells. Total root growth of plug seedlings with drainage hole covered were greater than the control. Ten days after transplanting, seedlings that had been produced in plugs, with covered drainage holes, were larger.
Guogiang Hou, Jack W. Buxton, and Donna Switzer
Jack W. Buxton, Donna Switzer, and Guoqiang Hou
Marigold seedlings, 3 weeks old, were grown in natural light growth chambers at 3 day/night temperature regimes, 8°N/16°D, 13°N/20°D and 18°N/24°D, in a factorial combination with ambient and 1000-1500 ppm CO2. Seedlings were harvested at regular intervals during a 24 hr period and were analyzed for soluble sugars (reducing sugars and sucrose) and starch. Neither temperature nor CO2 concentration affected the accumulation of soluble sugars or starch during the day or night. The soluble sugar concentration ranged from 3% of dry weight at sunrise to 6% at mid-day; the concentration changed little during the night. Light intensity was different during replications of the experiment. Increased light intensity appeared to cause a slight increase in the soluble sugars maintained by the seedling during the day. Accumulated starch increased 6% to 8% from sunrise to late afternoon. Preliminary results indicate that light intensity greatly affected the concentration of starch. On the higher light intensity day, starch accumulated to a maximum of 18% of dry weight; whereas on the lower light intensity day the maximum concentration was 10%. During the night following the lower light intensity day, the starch concentration decreased to approximately 3% by the end of the night; following a brighter day the starch content was 13% at the end of the night.