Phosphorus Efficiency of Buckwheat (Fagopyrum esculentum)

The ability of buckwheat (Fagopyrum esculentum) roots to acquire phosphorus (P) was characterized by investigating P uptake, morphological features, and chemical changes in the rhizosphere. Over a range of nutrient solution P concentrations (5–500 μmol · L−1), maximum shoot growth was achieved with a P supply between 5 and 100 μmol · L−1. Root weight and root length, as well as length and frequency of root hairs, were higher at low P levels. Root surface and the root surface/shoot dry weight ratio reached high values. Though P uptake rates were only moderate (0.15 pmol · cm−1 root · sec−1), shoot P concentrations were high (1.8% of dry weight with 100 μM P) predominantly being inorganic (80%). Phosphorus efficiency was characterized by a high specific absorption rate (810 mmol P · kg−1 root dry wt · d−1) rather than by an efficient utilization for dry weight production. Root exudates of low‐P plants had lower pH values than exudates of high‐P plants and increased the solubility of FePO4 and MnO2 to a greater extent. Amounts of exuded organic acids and phenolics were low and could not account for the observed solubilization of FePO4 and MnO2. Enhanced hydrolysis of glucose‐6‐phosphate by exudates from low‐P plants was due to an increased “soluble” acid phosphatase activity, and root surface phosphatase activity was also slightly enhanced with P deficiency. In the rhizosphere soil of buckwheat, some depletion of organic P forms was observed, and in pot trials with quartz sand, buckwheat utilized glucose‐ 6‐phosphate as a P source at the same rate as inorganic P.