Chapters authored
The Excretion of Di- and Tricarboxylic Acids by Roots of Higher Plants Can Strongly Improve the Acquisition of Phosphate (P) by Plants in P-Fixing Soils
The excretion of di- and tricarboxylates by roots of higher plants represents a very efficient way to acquire phosphate (P) from soils, which are low in available P. Despite the extensive experimental work in evaluating the effect of carboxylates on the acquisition of soil phosphate in the fields of plant physiology, plant nutrition and soil chemistry in the last three decades, the effect of root excreted carboxylates on soil P acquisition by higher plants is still a matter of debate. This still ongoing debate has its origin in methodological deficits in experiments and misconceptions considering the role of carboxylates in P-fixing soils on P acquisition. The main, often found misconception is to assume that the parameter carboxylates in the rhizosphere soil solution is the most important parameter driving the P mobilization by carboxylates. Carboxylates in the soil solution are an easily degradable source of rhizosphere microorganisms, and carboxylates will induce P mobilization if the carboxylate is adsorbed onto the soil solid phase, a step which also will reduce microbial carboxylate degradation. Thus, often realistic concepts to quantify the effect of carboxylates on P mobilization are still missing. Second, the very important parameter of carboxylate accumulation at the rhizosphere soil solid is often ignored or is measured by weak extractants, which do not allow the quantitative determination of carboxylates bound to the soil solid phase. Both shortcomings are critically discussed in this chapter, and a experimental and mathematical procedure is presented to evaluate the effect of carboxylate excretion on P acquisition by higher plants.
Part of the book: Carboxylic Acid