3.5. SPAD value, Fv/Fm and pigments
The plants were slightly greener in aquaponics compared with
hydroponics. In the control treatments, the chlorophyll index
in young leaves, determined as SPAD readings, was higher in
aquaponics as compared to hydroponics (Table 4). Foliar spraying
of Mg or Fe increased the SPAD value of young leaves in hydroponics
grown plants, while SPAD value of young leaves in aquaponics
grown plants was not affected by foliar application of any elements
(Table 4). There was no difference in maximal quantum yield of PSII
photochemistry (Fv/Fm) of young and old leaves of plants among
different treatments (Table 4). The content of chlorophyll a was
higher in aquaponics than in hydroponics grown control plants,
and foliar spraying of elements did not affect it in aquaponic grown
plants (Table 4). Greener color and higher chlorophyll content of
leaves in aquaponics grown plants could be partly due to higher
but non-toxic level of ammonium absorption by tomato plants
in aquaponics (Roosta and Schjoerring, 2007; Roosta et al., 2009).
Ammonia is the main end product of the breaking down of proteins
in fish. Fish digest the protein in their feed and excrete ammonia
through their gills and in their feces (Durborow et al., 1997a).
Although, most of this ammonia is then converted to nitrite (NO2−)
which is also quickly converted to non-toxic nitrate (NO3−) by naturally
occurring bacteria under normal conditions, plants uptake
some ammonia before its conversion toNO2− andNO3− (Durborowet al., 1997b).Except Mn,