Structure of transpiration ecoboundary layer of organs of poplar seedlings Effects of Municipal Sewage Sludge on Photosynthetic Characteristics in Poplar Seedlings Effect of NaCl Stress on Growth, Cell Ultrastructure and Ion Homeostasis in Poplar Seedlings Secretion Dynamics of Phenolic Acids from Poplar (Populus×euramericana ‘Neva’) Seedling Roots under N,P Deficiency Conditions