暖地型イネ科牧草

The effect of daylength and fertilizer level on the growth responses of dallisgrass (Paspalum dilatatum) and green panic (Panicum maximum var. trichoglume) under chilling temperatures was studied. Grasses were grown in pots in the open for about four weeks from emergence. They were then transferred into the phytotron at Biotron Institute, Kyushu University. They were subjected to a spontaneous long-day (ca. 14-hours) at constant temperatures (day and night) of 15, 20 and 30℃, respectively, and a short-day (restricted 8-hours) at 15 and 20 ℃ under two levels (1-0.7-1 and 3-2. 1-3kg NP_2O_5-K_2O/a) of fertilizer. They were harvested after three weeks. The increase in plant height, stem number, leaf area or dry-matter weight was similar under different daylengths and fertilizer levels at 15℃. The growth characteristics at 20℃ tended to be great under the long-day or the high level of fertilizer but only the leaf area in green panic was greater under the short-day than under the long-day. The distribution of total dry-matter increase to plant top was high under the long-day, except under the high level of fertilizer for green panic. The ratio of stem number increase to top dry-matter increase was increased with decreasing temperature and was high under the short-day, especially for dallisgrass. Also the high level of fertilizer raised the ratio for dallisgrass. The relative growth rate at the chilling temperatures was higher under the long-day than under the short-day, especially for dallisgrass. Similarly, the net assimilation rate was high under the long-day, showing a great effect of daylength. In contrast, the relative leaf growth for green panic was high under the short-day. The high level of Fertilizer increased the relative growth rate through the net assimilation rate at 20℃ with the long-day for both grasses and through the relative leaf growth rate for green panic except at 15℃ with the long-day. Total non-structural carbohydrates (TNC) content of whole plant was low at 15℃. Green panic showed less values at 15℃ and 20℃ with the short-day than dallisgrass. The distribution of TNC for reserve to stem and root was high at 15℃ and was low at 20℃ with the short-day. In dallisgrass the distribution of TNC for reserve to stem and root under the chilling temperatures tended to be high compared with green panic and also it tended to increase under the high level of fertilizer. Although concentration of most minerals in plant top was high at 15℃ and under the short-day, average rate of absorption of mineral (calculated per mean root dry-weight per a week) tended to decrease with decreasing temperature and to be high under short-day and the high level of fertilizer at 20℃. The species difference in growth responses under the chilling temperatures indicated that dallisgrass had accumulating ability of assimilate and green panic had consuming ability of assimilate for new plant structure.