Assessment of the salinity tolerance, response mechanisms and nutritional imbalance to heterogeneous salt supply in Populus alba

Salinity responses of Populus alba L. clone 'Marte' were evaluated using a split-root system to simulate the heterogeneous soil conditions in the field and to assess the salinity tolerance of clone 'Marte'. During the 26 days of experiment, we measured morpho-physiological parameters as well as the mineral content in substrate and plant organs in split-root plants watered with no salt on both sides of the system (0/0 mM - S1), salt on one side (0/100 mM - S2) and salt on both sides (100/100 mM - S3). Shoot elongation, stem diameter increase, and number of new leaves were not significantly different among and within each salt treatment. Leaf relative chlorophyll content and chlorophyll a fluorescence did not show any difference, while there was a decrease of 85% in terms of net photosynthesis (Pn) and 88% in stomatal conductance (g(s)) in S3 plants compared to S1. Na, absorbed by one side of the 0/100 mM plants, was equally distributed in all aerial organs and reached a concentration in-between the other two groups, as a confirmation of the physiological results obtained. An increase in Mn concentrations in woody cutting, stems and leaves of S2 and S3 system compared to S1 group was observed. Moreover, S3 plants showed an increase of K concentration in leaves. In 'Marte' poplar, Na increment was only translated in a reduction of photosyntetic performances, and the increase of some key mineral elements at leaf level such as K and Mn suggested an attempt to overcome the stress.