Geoscience Reference
In-Depth Information
stomata at night, CAM plants keep their stomata open during the darkness of night.
Although there are other fundamental differences between C3, C4, and CAM plants,
photosynthesis is the basic process for the development of plant organs achieved
and completed by macro- and microelements accepted from the soil. In point of
fact, even photosynthesis cannot exist without the presence of the element phospho-
rus accepted from the soil.
11.2
Plants' Pantry
Soil is a pantry for all plants where the following elements are continuously stored
and waiting to be accepted by roots as ions of simple inorganic compounds dis-
solved in water. We segregate the macroelements into primary and secondary
nutrients.
The primary nutrients are nitrogen N as ions NO
3
−
and NH
4
+
, phosphorus P in
ionic forms of H
2
PO
4
−
and HPO
4
2−
, and potassium K as K
+
. The secondary nutrients
are calcium Ca as Ca
2+
, magnesium Mg as Mg
2+
, and sulfur S as SO
4
2−
. Among
microelements, the most important are the next micronutrients: boron B as H
2
BO
3
−
.
chlorine Cl as Cl
−
, cobalt Co as Co
2+
, copper Cu as Cu
2+
, iron Fe as either Fe
2+
or
Fe
3+
, manganese Mn as Mn
2+
, molybdenum Mo as MoO
4
2−
, and zinc Zn as Zn
2+
. The
division between macro and micro does designate that one nutrient element is more
important than another. Instead, they are merely required in different quantities and
concentrations. A lack of some of the abovementioned biogenic elements could
result in an abnormal evolution of the plant or some of its organs. As a result, the
harvest could decrease, and in extreme, the plant could wither and die.
However, soil is sometimes also a medium where toxic elements reside. Among
them are Al, Cd, Pb, Cr, and Hg. They initially cause a retarded growth that may
well eventually stop the growth of all the plant. They do so by disturbing the func-
tion of the stoma which is so important in photosynthesis and transpiration or by
disturbing the enzymatic activity and function of plant membranes.
One of the most eminent personalities in studies on plant nutrition was the
German chemist Justus von Liebig (1803-1873). In addition to many improvements
of chemical analysis procedures, he is famous for being the fi rst person to introduce
nitrogen-based fertilizer. Recognizing the possibility of substituting chemical fertil-
izers for natural fertilizers coming from animal dung, he proposed to supply nitro-
gen in the form of ammonia to plant roots. Indeed, he initiated the broad use of
chemical fertilizers. We recognize now that 30-50 % of crop yields are attributed to
natural and synthetic commercial fertilizers. His broad-minded approach is docu-
mented by his famous Law of Minimum stating that a plant's development is limited
by the essential mineral that is in the relatively shortest supply. Or if one crop nutri-
ent is defi cient, plant growth will be poor, even if all other essential nutrients are
abundant. It is well demonstrated on “Liebig's barrel,” Fig.
11.3
.
Fertilization will not compensate for poor soil preparation, the lack of water,
weed competition, and other non-nutrient growth-limiting factors. Fertilization will
