Agriculture Reference
In-Depth Information
Li et al.
2011
). Additionally, the necessary shift from a fossil fuel to a biofuel based
economy and from petrochemicals to biochemicals increases the pressure on crop
productivity and will demand development of crop cultivars with a wider range of
agronomic features. The biofuel and biochemical industries require regenerative
plant commodities with high vegetative biomass or high seed content of specific
compounds such as particular modified starches, while food and feed production
rely mostly upon annual crops bred for high seed yield and complex quality traits.
For food and feed production, annual, hapaxanthic crop plants dominate agri-
culture, top among them the cereals wheat, rice and maize (Dyson
1999
). As they
complete their life cycle from seed to seed in one vegetative period, crop produc-
tivity and quality is tightly coupled to senescence. During the growth season, plants
follow a genetically controlled developmental programme leading to organ and
plant senescence, including regulated allocation of nutrients from vegetative tissues
to the seeds, and finally to plant death (Himelblau and Amasino
2001
; Lim
et al.
2007
; Wu et al.
2012
; Watanabe et al.
2013
). Importantly, developmental
senescence programmes are responsive to environmental conditions such as light,
temperature, water and nutrient availability (Watanabe et al.
2012
). Adverse envi-
ronmental conditions outside of the plant
s ecologically optimal niche usually result
in stress for the plant and trigger developmental acceleration, premature senes-
cence, and eventually result in reduced yields. This chapter discusses plant
responses to mineral nutrient deficiencies and whether the ability of crop plants
to utilise such nutrients can be improved to meet the global need for more nutrient
use efficient cultivars.
Agroecosystems are open systems where nutrient ions are mobilised from the
soil into crop biomass and removed with the harvest. Crop productivity depends on
mineral nutrient ions in the root environment, the availability of which is deter-
mined by soil parameters such as water content and pH as well as microbial
degradation of biomass such as straw, humus or manure, generally termed
mineralisation (von Liebig
1840
; Marschner
2012
; Buchanan et al.
2007
; Haensch
and Mendel
2009
; Amtmann and Blatt
2009
; Amtmann and Armengaud
2009
).
Mineral fertilisers are applied to compensate for nutrient losses in conventional
agriculture. Usually the provision of macronutrients (N, P, S, Mg, K, Ca) is
sufficient, while micronutrients or trace elements (Fe, Cu, Mn, Ni, Zn, Cl, B, Mo)
are supplemented depending upon the needs of specific soil types or crops
(Watanabe et al.
2012
). Nitrogen and phosphate have the largest effect on produc-
tion costs due to the quantities applied and their cost. Optimal crop production
requires a balanced supply of nutrients, as a deficiency of one nutrient cannot be
compensated for by others according to Liebig
'
s law of the minimum (von Liebig
1840
). Furthermore, both deficiency and over-accumulation can lead to negative
effects on plants due to the interaction and competition between minerals at the
level of uptake and assimilation (Hoefgen and Hesse
2008
). For example iron
uptake in barley and tomato has been shown to be dependent on sulfate availability.
Under sulfate depletion iron transporters and iron reductase are downregulated,
preventing uptake even in the presence of iron. Further, phytosiderphore biosyn-
thesis and internal iron transport are impaired as nicotianamine synthase is essen-
tially switched off (Astolfi et al.
2010
; Zuchi et al.
2009
; Cassin et al.
2009
; Klatte
'
