抄録
Changes with growth in photosynthetic ability of various organs, such as leaf blades, leaf sheaths, culms (parts without leaf sheaths) and ears of barley, wheat, oat and rye plants sown in autumn were measured during 1969-74 (table 1). Photosynthetic rates were measured under controlled conditions in assimilation chambers with artificial illumination of 0.6 ly·min-1. Respiration rates were measured in dark chambers. In both measurements, surface temperature of each organ was kept either at 14-18°C (Nov.-Mar.) or at 18-23°C (Apr.-Jun.). All samples were collected from the fields, cut off from adjacent organs, and measured. Field study of dry matter production of six-rowed barley, wheat and oat was conducted. Due to being various photosynthetic organs other than leaf blades, a new index LAI* was introduced, which was obtained from mutiplying LAI (leaf blade area index) by the ratio of total gross photosynthesis of a productive tiller to leaf blades. Net assimilation rate calculated by using LAI* was named NAR*. The main results obtained are summarized as follows; 1. Changes with growth in the ability of photosynthesis and dark respiration of leaf blade. The mean gross photosynthesis of whole leaves of a shoot was found to be high during winter in six-rowed barley, wheat and rye, but low in oat (fig. 3). After heading date, their values decreased gradually in all of the four crops. A detailed study of changes of photosynthetic rates of some leaves of wheat and rye sown in 1973, clearly showed that the life span of the leaves grown in winter was long, but the one grown in spring (at the stage of culm elongation) was half of the one in winter (fig. 4, 5). The third leaves on main stems of both crops, which developed before winter, decreased gradually their photosynthetic ability in winter. On the other hand, the fifth leaves which developed in winter showed high photosynthetic ability during long winter period. The dark respiration of leaf blades was clearly found to be of higher value during winter than spring in all four crops (fig. 3). 2. Photosynthetic ability of various organs in ripening stage (including two-rowed barley): In ripening stage, the gross photosynthesis of leaf blades per a productive tiller decreased more drastically than that of the other photosynthetic organs in all crops (fig. 7). The contribution of each organ to the total gross photosynthesis of a productive tiller was calculated on the assumption that every organ were equally illuminated. In the early ripening stage the contribution of leaf blades was high, but at the later stage decreased drastically in all crops (fig. 8). In the early ripening stage the contribution of leaf blades of two-rowed barley was low compared to the other crops, and those of ears were low in wheat and rye. In the later stage the contribution of culms of rye became higher. On the other hand, the contribution of leaf sheaths of two-rowed barley and rye were found to be higher than the other crops, through whole ripening stage (fig. 8). 3. Growth analysis of dry matter production: Both NAR and NAR* from middle to late April were more than 3.6 times of those in winter in six-rowed barley, wheat and oat. This fact did not agree with the results of the measurements of photosynthetic ability (table 3, fig. 3). It is presumably concluded that winter cereals cannot display enough their photosynthetic ability because of injurious environment of winter in field, especially low temperature. Growth pattern of dry matter of oat was characteristically different from those of six-rowed barley and wheat (table 3, fig. 12). Both six-rowed barley and wheat kept more than four of LAI* during the period from culm elongation stage to the early ripening stage (table 3). This clearly shows that the various organs other than leaf blades play in an important role for the production of photosynthates.
