Soil and plant sampling
To study the influence of life stage on pesticide uptake and LPO,
a destructive harvestwas performed at 15 (first period) and 60 days
(second period) after germination (appearance of the first true
leaves). Two or three plants were harvested per pot and period.
Roots, stems and leaves obtained from each pot were pooled and
analyzed as a single sample. Plant subsamples were immediately
frozen and maintained at 80 C until analysis.
Within each pot, three separated soil fractions were defined
according to White (2001) in relation to the influence exerted by
the plant root. Bulk soil (BS) that had no contact with plant roots
was taken from the top of individual planted pots. The near-root
soil (NRS) was operationally defined as the soil that was under
root influence. The NRS settled within the volume occupied by the
roots. The rhizosphere soil (Ri) was defined as the soil that
remained attached to the roots and required mechanical removal.
The Ri was obtained bywashing the roots with distilled water and a
centrifugation of water-Ri solution at 840 g for 10 min at room
temperature (this procedure was selected to preserve fine roots
during rhizosphere extraction). Additionally, soil samples from Un
soils were obtained at 15 and 60 days. Soil samples were maintained
frozen (80 C) until analysis.