The interaction between nitrogen source, soil pH, and drought in the growth and physiology of three poplar clones

The objective of this study was to understand how nitrogen (N) source, soil pH, and drought interact in the growth and water-use efficiency of poplars. Rooted cuttings from two hybrid poplar clones, 24 (Walker) (Populus deltoides x Populus x petrowskyana), and 794 (Brooks 6) (Populus deltoides x Populus x petrowskyana), and one native balsam poplar clone 1004 (Populus balsamifera L.), were grown in a greenhouse for a period of 8 weeks. Trees received a combination of two N sources (ammonium sulphate [(NH4)(2)SO4] and calcium nitrate [Ca(NO3)(2)]), two soil pHs (5 and 7), and two drought levels (85% and 40% field capacity, as determined by mass). Trees had reduced growth, net photosynthesis, and stomata] conductance with NO3- fertilization, and these effects were accentuated at soil pH 7. The drought treatment only slightly reduced growth and rarely interacted with N source or soil pH. Drought also did not affect instantaneous measurements of water-use efficiency, but it increased delta C-13 by an average of 0.55 parts per thousand. The poplar clones used in this study appear to be better adapted to take up N from NH4+ than from NO3 =N sources.