2.4. Sampling
At harvest, an aerial part of each plant was removed, which, by
means of the Scholander chamber method, permitted immediate
determination of water potential. The aerial part was then cut into
separate organs, i.e., needles, the main stem and ramifications.
Afterward, the root portion was carefully removed from the pot,
separated from the adhering soil and washed with distilled water.
The lateral roots were removed from the taproot after their lengths
had been measured. Each sample was lyophilized. Also, the dry
mass of each sample was determined before being reduced to a
fine
powder using a ball mill (Retsch MM 200, Germany). Soil samples
were simultaneously collected from three levels in each pot as
follows:
(i) the sludge layer (Sl), corresponding to the upper layer of the
pot with a depth of approximately 2 cm. This layer is primarily
composed of organic matter that was previously contained in the
sludge and formed via mineralization;
Fig. 1. Schematic representation of the experimental design.
M. Bourioug et al. / Ecological Engineering 77 (2015) 216–224 217