[Effects of different nitrogen application rate on allocation of photosynthetic electron flux in Rumex K-1 leaves].

The total photosynthetic electron flux through PSII [J(e) (PSII)], the electron flux used for carbon assimilation [J(e) (PCR)], the electron flux used for photorespiration [J(e) (PCO)], the electron flux used for Mehler reaction [J(a) (O(2)-depend)] and the electron flux used for nitrogen metabolism [J(a) (O(2)-independ)] in leaves of Rumex K-1, a fodder crop with high protein content, were measured under three levels of nitrogen application (Fig.2). The nitrate reductase (NR) activity, glutamine synthetase (GS) activity, the leaf protein content, the chlorophyll content, P(n) and Phi (PSII) and F(v)/F(m) (Table 1) were also measured. The results showed that with the increase of nitrogen application, the NR and GS activities increased remarkably (Fig.3) and more electron flux was allocated to nitrogen metabolism as well as photorespiration (Fig.2). Nitrogen metabolism and carbon metabolism competed for energy, and the proportion of energy used in nitrogen metabolism to that used in carbon metabolism changed with nitrogen application rate. The electron flux used for nitrogen metabolism is about 15%-21% of the total electron flux under the three levels of nitrogen application (NO(3)(-) 0-30 mmol/L). Under lower nitrogen application, though energy used for carbon and nitrogen assimilation remarkably decreased, no significant increase of electron flux allocated to Mehler reaction was observed. The excess excitation energy in the leaves under the lower nitrogen application was efficiently dissipated via other energy dissipation mechanisms to protect the leaves against photo-damage.