Canopy profiles of photosynthetic parameters under elevated CO2 and N fertilization in a poplar plantation
http://www.sciencedirect.com/science/article/pii/S0269749105001260?casa_token=J9AojDbcFUEAAAAA:IBGfaFCfBs-sr8xOM_9FqT-c9b1rGjFbG9yKF1sZeteZTH55b_YNTY9BNqarKNT3IOMIsH_zvg