Aranjuelo I, Irigoyen JJ, Nogués S, Sánchez-Díaz M. Elevated CO2 and water-availability effect on gas exchange and nodule development in N2-fixing alfalfa plants. Environ Exp Bot 2009 1;65(1):18-26.
N2-fixing alfalfa plants were grown in controlled conditions at different CO2 levels (350 μmol mol−1versus 700 μmol mol−1) and water-availability conditions (WW, watered at maximum pot water capacity versus WD, watered at 50% of control treatments) in order to determine the CO2 effect (and applied at two water regimes) on plant growth and nodule activity in alfalfa plants. The CO2 stimulatory effect (26% enhancement) on plant growth was limited to WW plants, whereas no CO2 effect was observed in WD plants. Exposure to elevated CO2 decreased Rubisco carboxylation capacity of plants, caused by a specific reduction in Rubisco (EC 184.108.40.206) concentration (11% in WW and 43% in WD) probably explained by an increase in the leaf carbohydrate levels. Plants grown at 700 μmol mol−1 CO2 maintained control photosynthetic rates (at growth conditions) by diminishing Rubisco content and by increasing nitrogen use efficiency. Interestingly, our data also suggest that reduction in shoot N demand (reflected by the TSP and especially Rubisco depletion) affected negatively nodule activity (malate dehydrogenase, EC 220.127.116.11, and glutamate-oxaloacetate transaminase, EC 18.104.22.168, activities) particularly in water-limited conditions. Furthermore, nodule DM and TSS data revealed that those nodules were not capable to overcome C sink strength limitations.