Gordillo F J, Niell F X, Figueroa F L
Departamento de Ecología, Facultad de Ciencias, Universidad de Málaga, Spain.
Planta. 2001 May;213(1):64-70. doi: 10.1007/s004250000468.
The effects of increased CO2 levels (10,000 microl l(-1)) in cultures of the green nitrophilic macroalga Ulva rigida C. Agardh were tested under conditions of N saturation and N limitation, using nitrate as the only N source. Enrichment with CO2 enhanced growth, while net photosynthesis, gross photosynthesis, dark respiration rates and soluble protein content decreased. The internal C pool remained constant at high CO2, while the assimilated C that was released to the external medium was less than half the values obtained under ambient CO2 levels. This higher retention of C provided the source for extra biomass production under N saturation. In N-sufficient thalli, nitrate-uptake rate and the activity of nitrate reductase (EC 1.6.6.1) increased under high CO2 levels. This did not affect the N content or the internal C:N balance, implying that the extra N-assimilation capacity led to the production of new biomass in proportion to C. Growth enhancement by increased level of CO2 was entirely dependent on the enhancement effect of CO2 on N-assimilation rates. The increase in nitrate reductase activity at high CO2 was not related to soluble carbohydrates or internal C. This indicates that the regulation of N assimilation by CO2 in U. rigida might involve a different pathway from that proposed for higher plants. The role of organic C release as an effective regulatory mechanism maintaining the internal C:N balance in response to different CO2 levels is discussed.
以硝酸盐作为唯一氮源，在氮饱和及氮限制条件下，测试了高二氧化碳水平（10,000微升/升）对嗜氮绿大型海藻硬石莼（Ulva rigida C. Agardh）培养物的影响。二氧化碳富集促进了生长，而净光合作用、总光合作用、暗呼吸速率及可溶性蛋白含量均下降。在高二氧化碳条件下，内部碳库保持恒定，而释放到外部培养基中的同化碳不到在环境二氧化碳水平下所获值的一半。这种更高的碳保留为氮饱和条件下额外的生物量生产提供了来源。在氮充足的藻体中，高二氧化碳水平下硝酸盐吸收速率及硝酸还原酶（EC 1.6.6.1）活性增加。这并未影响氮含量或内部碳氮平衡，这意味着额外的氮同化能力导致了与碳成比例的新生物量的产生。二氧化碳水平升高对生长的促进完全依赖于二氧化碳对氮同化速率的增强作用。高二氧化碳条件下硝酸还原酶活性的增加与可溶性碳水化合物或内部碳无关。这表明硬石莼中二氧化碳对氮同化的调节可能涉及一条与高等植物不同的途径。讨论了有机碳释放作为一种有效调节机制在响应不同二氧化碳水平时维持内部碳氮平衡的作用。
