1978 Volume 47 Issue 1 Pages 118-123
Two kinds of experiments were conducted to elucidate the relationship between atmospheric CO2 concentration and nitrogen nutrition on the dry matter production of crop seedlings. One was a water culture (Table 1) of rice, and the other was a soil culture of rice, Japanese millet and maize at 5 to 6-leaf stages. In the former experiment, nitrogen was applied at 5 to 40 ppm in ammonium nitrate form, and in the latter, 30 to 160 mg nitrogen per plant was applied in ammonium sulfate form. CO2 enrichment or depletion treatments (160 to 3200 ppm) were carried out in transparent plastic growth chambers placed outdoors for 8 to 10 days in June and August. The following results were obtained:
1. In rice plant (C3-species), higher CO2 concentration promoted dry matter production, and the effect was accelerated by higher nitrogen levels due mainly to increased leaf area of tillers (Tables 2, 3, 4; Fig.2). No change was caused in the response of net assimilation rate (NAR) to CO2 concentration by nitrogen levels in the soil (Fig.1).
2. Japanese millet (C4-species) was similar to rice in its response of leaf area growth to CO2 and nitrogen, but its low response of NAR to CO2 brought the lower response of dry matter growth rate (GR) to CO2 as compared with rice (Table 4; Fig.1).
3. In maize (C4-species), leaf area growth showed fairly a high response to CO2 at both nitrogen levels, but the response of NAR to CO2 was very low, causing its low response of GR to CO2. Little response of NAR to nitrogen levels was observed both in rice and Japanese millet alike (Table 4; Fig.1).
From these results, it may be concluded that the pattern of dry matter production of crop plants in their response to CO2 concentration or nitrogen nutrition does not always reflect their CO2-photosynthesis characteristics as C3-or C4-species, due principally to their differential response in leaf area growth.
