| By measurement of chlorophyll fluorescence, gas exchange, allocation of photosynthetic excitation energy,the activities of nitrate reductase (NR) and glutamine synthetase(GS)and the total protein content etc., the effects of drought and different nitrogen application on allocation of photosynthetic excitation energy in leaves of Rumex K-1 (Rumex patientia×R.tianschanicus) were investigated in this paper. The main results are as follow:1,With the reduction of nitrogen(NO3-) application, the photosynthetic rate (Pn),the actual PSII photochemical efficiency (ΦPSⅡ),Stomatal conductance(Gs),Carboxylation efficiency(CE) reduced, but NPQ increased. Energy used for carbon reduction (Je(PCR)),energy used for photorespiratory (Je(PCO)),energy used for nitrogen metabolism ( Ja(O2-independ)),total photosynthetic excitation energy (Je(PSII)),alternative energy(Ja)all reduced. Less excitation energy was used in carbon assimilation, photorespiratory and nitrogen metabolism. But Ja(O2-depend) changed insignificantly, indicating that Mehler reaction changed little.2,The activities of nitrate reductase (NR) and glutamine synthetase (GS),total protein contents and chlorophyll contents increased with the increase of nitrogen (NO3-) application.The ratio of Ja(O2-independ)/Je(PSII) and Ja(O2-independ)/Je(PCR) increased too,which was caused by more energy allocated to nitrogen metabolism. The energy used in nitrogen metabolism is aroud 15%-21% of total photosynthetic excitation energy.3,Drought had different effects on the plants with different nitrogen (NO3-) application . Pn,ΦPSⅡ,Gs,CE,Je(PCR),Je(PCO),Ja(O2-independ), Je(PSII) and Ja in plants with moderate nitrogen application were the biggest among plants with the 3 different nitroge application, indicating that moderate nitrogen application improved drought resistance in the plants . Pn,ΦPSⅡ,Gs,CE,Je(PCR),Je(PCO),Ja(O2-independ),Je(PSII) and Ja in plants with higher and lower nitrogen application decreased greatly after drought stress. In drought condition, excitation energy allocated to nitrogen metabolism (Ja(O2-independ) in plants with higher nitrogen application was not an effective pathway to dissipate energy because the activities of the key enzymes involved in nitrogen metabolism were sensitive to drought stress , as an result the Ja(O2-independ)reduced greatly. Compared to the plants with lower and higher notroge application ,the plants with moderate nitrogen application had higher activities of GS and NR, and higher ratio of Ja(O2-independ)/Je(PSII)and Ja(O2-independ)/Je(PCR) and nitrogen metabolism.4,Ja(O2-depend) changed greatly in plants with different nitrogen application under drought stress. Ja(O2-depend) in plants with moderate nitrogen application was the highest so that the Mehler reation might dissipate more excitation energy. Ja(O2-depend) in plants with high nitrogen application was smaller, whereas, Ja(O2-depend) in plants with low nitrogen application was the smallest. The ratio of Ja(O2-depend) to Je(PSII) all increasd in plants with the 3 different nitorge application, which indicates that Ja(O2-depend) could dissipate excitaion energy in drought conditions. The effect of NH4+ on allocacation of photosynthetic excitation energy was different from that of NO3-. Ja(O2-independ) in plants with NH4+ application was smaller than that with NO3- application. The NR activity in plants with NH4+ application was very low but the GS activity was similar to that with NO3- application.The total protein contents and chlorophyll contents in plants with NH4+application was similar to that with NO3- application. In plants, the NO3- must be reduced to NH4+ to be synthesized to protein, so the Ja(O2-independ) in plants with NH4+ application should be smaller than that with NO3- application. The difference of Ja(O2-independ) between application of NO3- and NH4+ could be used to estimate difference in energy used for the reduction of NO3- to NH4+ .5,The allocation of photosynthetic excitation energy between the young leaves,vigorous leaves and old leaves were significantly different. Je(PCR) in young leaves was smaller than that in vigorous leaves but Ja(O2-independ) was bigger than that in vigorous leaves. Young leaves need more proteins to produce enzymes and other substances associated with growth .Correspondingly the activities of NR and GS in young leaves were higher than that in vigorous leaves. All data indicate that more energy was used in nitrogen metabolism in young leaves. Since the synthesis of protein became very low in old leaves, they did not need extra energy to support these metablism .The NR and GS activities in old leaves was very low, which was consistent with a great decrease in Ja(O2-independ) in old leaves.In conclusion, Ja(O2-independ) was a good index to reflect the magnitude of nitrogen metabolism.The carbon and nitrogen metabolism competed each other for photosynthetic excitation energy. The competition changed the ratio of excitation energy allocation .The magnitude of nitrogen metabolism could be quantified. Suitable nitrogen application improved drought resistance in the plants. .
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