Phosphorus Use Efficiency in \u3cem\u3eLotus\u3c/em\u3e spp. under Contrasting Levels of Water Availability: A Comparison of Pot and Field Measurements

The results of the phosphorus (P) use efficiency measurements in pot experiments with soil as subtratum are controversial because they may not be representative of an equivalent situation under field conditions. Under P-stress conditions, strategies for improving phosphorus-use efficiency are: (1) increase the root surface soil contact area by modifying root morphology; (2) increase the effective root area by root symbiosis with arbuscular mycorrhizal fungi; (3) increase nutrient availability through rhizosphere modification. The level of water availability and P supply are of high interest because the water stress, which limits growth more than any other environmental factor, can be minimized by improving the supply of P. P use efficiency (PUE) depends on the internal capacity of individual species to produce more DM from a given amount of P absorbed, and an external efficiency which enables the plant to yield more due to an increased ability to extract P (phosphorus absorption efficiency, PAE) from the soil (Trolove et al. 1996). Because of the deep root of Lotus species in may be difficult to evaluate L. corniculatus and L. tenuis in pots. To examine the value of pot experiments to assess the phosphorus use efficiency of L. corniculatus and L. tenuis grown in a Vertisol, we compare responses under two contrasting levels of water availability and phosphorus supply, obtained in both pot and field conditions, for their consistency or discrepancy in order to determine the actual value of the pot results