Agriculture Reference
In-Depth Information
Certain elements may stimulate growth in higher plants even though they
are not essential or may only be essential for particular species. These are known as
beneficial elements and include Na‚ Si‚ Co‚ Se‚ Al and possibly I‚ Ti‚ V‚ La and Ce
(Marschner‚ 1995). For example‚ rice is known to accumulate Si which interacts with
other nutrient elements to confer resistance or tolerance to insect pests and diseases
and to such abiotic stresses as Al toxicity and salt injury (Savant
et al
.‚ 1997). Na is
essential for a number of species that use the C4 photosynthetic pathway such as
the halophyte
Atriplex vesicaria
(Chenopodiaceae) but not for others such as sugarcane
(
Saccharum
spp.).
While it is as yet unknown whether silicon and selenium are essential for higher
plants‚ certain prokaryotes require these elements‚ cobalt and vanadium (Salisbury and
Ross‚ 1991). Our knowledge of the trace element requirements of micro-organisms is
poor and it is likely that further elements will be demonstrated as essential for certain
organisms‚ but only in very minute amounts.
Certain micro-organisms may accumulate very high concentrations of essential
elements such as copper and zinc and non-essential elements such as lead‚ mercury and
cadmium (Lepp‚ 1992; Gadd‚ 1993). The human health consequences of ingesting
contaminated wild mushrooms can be severe although large inter-specific differences
in metal uptake occur. Further‚ eight to nine years after widespread contamination asso-
ciated with the Chernobyl reactor accident‚ and possibly also nuclear weapons testing
(Gadd‚ 1993)‚ wild mushrooms in affected parts of the Russian Federation were shown
to have substantially higher activity concentrations of radiocaesium than
other human foods. In these contaminated areas‚ human radiocaesium body loads were
highly correlated with mushroom intake (Skuterad
et al
.‚ 1997); other food chain effects
are also likely.
