Lemna For Fish
Oxalic acid
Nutrient assimilation potential is greatly reduced by oxalic acid (oxalate). Oxalic acid may combine with several minerals (eg calcium, iron) to form oxalates. Oxalate may form crystals. Oxalate is generally insoluble, except for calcium-oxalate, which is somewhat soluble (up to only 6 mg/L at 18 C). Oxalate accumulation is influenced by:
- Glyoxylate and glycolate are major precursors of oxalate (induced by glycolate-oxidase (as in L. minor[1]) and lactate dehydrogenase).
- C2/C3 cleavage of ascorbic acid may also yield oxalate in oxalate accumulators.
- D-glucosone may yield ascorbic acid and oxalate
- nitrogen source (ammonium/nitrate; Oxalic acid was 40–50% lower in the leaves (of Purslane) grown in solutions containing ammonium compared to the leaves grown with no ammonium [2]. More crystal are formed by L. minor grown on nitrogen from ammonium than by plants grown on nitrogen from nitrate.[3] (http://pubs.acs.org/doi/abs/10.1021/jf00078a019]
- inorganic ion availability (oxalate plays a role in ion regulation and osmoregulation)
- some plants may catabolize oxalate and recycle the carbon
Oxalate primarily accumulates as:
- soluble oxalate
- insoluble calcium oxalate
The greates oxalate accumulators (>5% of dry weight) are members of Caryophillaceae, Chenopodiaceae and Polygonaceae. Crystal formation (as opposed to oxalate formation) in L. minor is not tightly coupled to nitrogen assimilation or absolute calcium concentration. Dark-grown plants form almost four times as many crystal cells (idiobblasts) as do light-grown plants.[4] Low oxalate production in Lemna plants grown in the dark and supplied with organic nutrients correlates with lower glycolate oxidase activity.[5]
Nutrient loading
Lemna minor responds indifferently to nutrient loading. Lemna minuta responds opportunistically to high nutrient availability. As a result, the L. minuta is dominant (60% in dry biomass) in high nutrient availability but loses (< 50%) to L. minor at low nutrient availability.[6]
