Siderophore molecules stable in dead plants, good for iron uptake, Citric Acid Fe3+
By Gregory Jackson, Founder of Groundz, firstname.lastname@example.org
(Photo: Demonstrates two strategies Poaceae Family of grassy and cereal plants do in order to help them absorb iron from calcareous soils. Citrate, or derivative of citric acid may also assist plants uptake iron from the soil, thus allowing the plant to transport and use Fe3+ as the plant metabolizes it to Fe2+ allowing the iron to be bound to sodium. The other strategy is for the plant to secrete Phytosiderophore and absorb (complexation) the Fe3+ iron. Source of image: Metal Stable Isotopes: Signals in the Environment: Fractionation of Metal Isoptopes by Higher Plants by Friedhelm von Blanckenburg, Nicolaus von Wiren, Monika Guelke, Dominik J. Weiss, and Thomas D. Bullen. Elements, December 2009, Vol.5, p.6: 375:380).
Iron is one of the most abundant minerals in the earth’s crust. Soluble iron is scare in all four ecosystems where iron is known to be a vital mineral for respiration and DNA synthesis.
Siderophore are molecules secreted by microorganisms like bacteria, fungi, and grasses that make available Fe3+ for living organisms found in the four ecosystems where they are common: Soil and Surface Water, Marine ecosystems, plant tissue (pathogens), and animal tissue (pathogens). Siderophore in oceans bind iron ligands for iron cycles and metal speciation in the carbon cycle. While siderophore in plant and animal tissue may be pathogenic: Bacteria in plants produce their own siderophores to obtain iron, in medical research, iron is tightly bound within proteins and pathogenic bacteria produce their own siderophores; medical research involves iron mobilization for iron-deficient diseases and increase potency of antibiotics.
While iron is abundant in the soil, it is not available for plants without the assistance of siderophores in the soil. All plants need iron for proper respiration and DNA synthesis.
In soils and surface water, Siderophores, which are secreted by microorganisms and grasses, are able to make Fe3+ soluble. Siderophore found in soils are cyclic hexapeptides, they are resistant to environmental degradation only associated with the pH condition of hydrolytic enzymes that cultivate best in soil humus.
Soil humus made from decaying plant material has low pH values that are between 3-4. These conditions are ideal for organisms that secrete hydroxamate siderophore molecules because the acidity is stable for these siderophores in compost processes. At Cleveland Botanical Garden’s Buckeye Farms, every year Green Corps clear out post-harvest waste: Old corn stalks, dead tomato plants, basil, grasses, and other last year season’s crop. Groundz recycles 16.5 cubic feet per week of this material as part of our Buckeye Farms’ compost mix to grow local foods and make compost.
Cover crops do have a place for increasing Fe3+ availability for plants. These plants grow in calcareous soils from the low Fe solubility. Calcareous soils make up 30 percent of all farmland.
The Poaceae Family like grasses, cereals, grains, barley, wheat, and rice secrete their own version of siderophores into the rhizosphere known as Phytosiderophores, through their roots. The difference between bacterial/fungal and plant secreted siderophores is the plant secreted version has two binding receptors with a single alpha-hydroxycaroboxlate ideal for Fe3+ absorption in iron deficient calcareous soils.
We are learning siderophore favorability in organic waste recycling, for example the use of citric acid in active compost piles (which acts like a “siderophore”) and the use of cover crops, especially in the Poaceae Family to encourage Fe3+ in soil is ideally available for plant nutrition and nourishment.
(Photo: At Cleveland Botanical Garden’s Buckeye Farm is 14 cubic feet of dead plant material that Groundz mixed with 330 pounds of Dunkin Donuts coffee grounds. The dead plant material provides excellent breakdown materials that feed microbia that produce siderophores. We recycle 5-25 cubic feet/week of Buckeye Farms own urban farm waste that adds siderophores to our compost)