Additional carbohydrate supply resulting from enhanced photosynthesis under predicted future elevated CO2 is likely to increase symbiotic nitrogen fixation in legumes.
Butterly et al. use free-air CO2 enrichment (FACE) to study field pea, Pisum sativum, growing under different levels of CO2 and N supply in a semi-arid cropping system and find that increasing N reduces nodulation at ambient CO2 but this inhibitory effect is less under elevated CO2. The results indicate that field pea may perform well in semi-arid agricultural systems under future CO2 concentrations irrespective of soil N status and subsequent gains in N input via enhanced N2 fixation will be important for maintaining the N fertility of cropping systems.
Butterly, C. R., Armstrong, R., Chen, D., & Tang, C. (2015). Free-air CO2enrichment (FACE) reduces the inhibitory effect of soil nitrate on N2fixation ofPisum sativum. Annals of Botany, 117(1), 177–185. http://dx.doi.org/10.1093/aob/mcv140