DHA and total endosulfan levels
Soil function and characteristics may influence a pesticide's
availability, metabolism and, ultimately, its uptake and translocation
by plants. As a result, plant growth will also influence soil
processes. Among other parameters used to characterize the soil
system, dehydrogenase enzymes, which occur intracellularly in all
living microbial cells and are linked with microbial respiratory
processes (Bolton et al., 1985), could be used as an indicator of the
overall microbial activity of soils. Spiked soils (SS) exhibited higher
dehydrogenase activity (DHA) than non-spiked soils (NSS, Table 1).
Several studies reported either DHA inhibition or stimulatory effects
in the presence of pesticides (Singh and Singh, 2005). Some
microbial groups are capable of using applied pesticides as a source
of energy and nutrients to multiply, whereas the pesticide may be
toxic to other groups (Johnsen et al., 2001). As a result, microbial
communities with a high metabolic capacity for using organic
pollutants as carbon and energy sources might be favored. The
analysis of spiked planted soils showed that the DHA activity in BS
and NRS plants at 15 days of growth was higher than at 60 days, in
all species, except tomato NRS (Table 1). This depletion of DHA
activity was also in agreement with a reduction in the total endosulfan
levels for all species and soil fractions, except in soybean BS.
Additionally, the pH values in BS and NRS were higher at 60 days
than at 15 days of growth (except in sunflower plants). Plant
growth is known to modify these soil parameters (Yan et al., 1996),
because plant growth might lead to the decarboxylation of organic
anions present in root exudates by microorganisms. The increase in
soil pH and pesticide metabolism with plant age was previously
reported for the same species growing in DDT-polluted soils
(Mitton et al., 2014), however, it was associated with increments in
DHA activity. Thus, the dynamics in the rootesoil system seem to
depend on both soil and pesticide characteristics.