Root and Rhizosphere Traits as affected by Phosphorus Availability in Field Grown Maize Hybrids

Soil phosphorus (P) availability is a frequent limiting factor for plant growth. Hence, plants have evolved root and rhizosphere traits to enhance the acquisition of sparingly available P. To identify traits favoring P acquisition efficiency (PAE) we tested maize hybrids at low and high soil P availability in a long-term, experimental trial near Toulouse (France). Previous study indicated steep gradient of calcium-carbonate, which impacted plant performance. Hence, the trial was divided into alkaline and neutral soil plots. Eight hybrids were tested in the alkaline soil and four in the neutral soil. Representative plants were harvested for determining traits at the 6-8-leaf and flowering stages. Rhizosphere and bulk soil were assayed for various chemical and microbial parameters. Similar hybrids were grown in pots filled with low-P soil from the same plots to determine aerenchyma development.

At both stages and across hybrids, Olsen-P was significantly correlated to P uptake, indicating that soil variability had large effect on plant performance, and should therefore be taken into account when evaluating hybrids in field conditions. However, in the low-P soil, P uptake was significantly higher in the alkaline soil in spite of comparable Olsen-P levels. For the high P level, P uptake was significantly higher in the neutral soil. The superior P acquisition in the low-P alkaline soil can be related to higher microbial activities. Microbial biomass and phosphatase activity were identical in the bulk soil for both soil types. In the rhizosphere, these microbial activities were higher in the alkaline than the neutral soil. The development of root aerenchyma was consistently higher in the alkaline soil in pot-grown plants. Furthermore, P uptake at low-P level was significantly correlated to aerenchyma development. The results indicate that root aerenchyma and rhizosphere microbial activities are key traits for high PAE in maize grown in low-P soils.