| In order to identify the effects of topdressing amount of nitrogen on photosynthetic characteristics of flag leaf and assimilates transportation in different organs under limited irrigation, the field experiment was carried out in Xunxian institute of agricultural sciences, Henan, China, using the cultivar "Zhoumai 18" which had high yield. Six nitrogen treatments (N0, N1, N2, N3, N4, N5) were set, and the amount of basal and topdressing nitrogen were 0+0, 120+0, 120+60, 120+120, 120+180 and 120+240 kg N·hm-2, respectively. Net photosynthesis rate (Pn), stomatal conductance (Gn), intercellular CO2 concentration (Ci) and chlorophyll content of flag leaves were measured using Li 6400 portable photosynthesis system with an open flow gas exchange system. The results showed that photosynthetic characteristics of flag leaf and assimilates transportation in different organs were regulated significantly under the top dress nitrogen application. The highest yield was 8 749 kg·hm-2 in the 120+60 kg·hm-2treatment. With topdressing amount of nitrogen from 0 to 120 kg·hm-2, the flag leaf net photosynthetic rate and chlorophyll content increased,flag leaf senescence was delayed, period of flag leaf photosynthetic function was extended, and accumulation of photosynthetic products increased. But flag leaf net photosynthetic rate and chlorophyll content were not further increased by excessive topdressing amount of nitrogen from 180 to 240 kg·hm-2. The translocation amount of pre anthesis dry matter and nitrogen were significantly increased by nitrogen applied with 120+60 kg·hm-2, and the translocation efficiency of pre anthesis dry matter and nitrogen were high by lower nitrogen applied with 120+0 kg·hm-2, the contribution of pre anthesis dry matter to grain was the highest by nitrogen applied with 120+60 kg·hm-2, but the contribution of pre anthesis nitrogen to grain was the highest by nitrogen applied with 120+0 kg·hm-2. The translocation amount, translocation efficiency and contribution of pre anthesis dry matter and nitrogen to grains were significantly lower with excessive topdressing amount of nitrogen from 120 to 240 kg·hm-2. Without topdressing nitrogen applied, basal application of nitrogen significantly increased Pn and chlorophyll content of flag leaves, and promoted the translocation of pre anthesis dry matter and nitrogen. |
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