Partitioning of above and below ground costs during phosphate stress in Medicago truncatula

Phosphate (P) availability for plant uptake can limit the yield of natural and agricultural systems. Under P limited conditions, the P-requirement of symbiotic nodules of legumes may exacerbate the P stress of host plants. Adaptations to survive under P stress may vary between different functioning tissues. This study investigated the physiological adaptations to P stress in above and below ground organs of nodulated Medicago truncatula Gaertner. Seedlings were inoculated with Sinorhizobium meliloti in quartz sand and fed nutrient solution with either 0.01 mM or 0.5 mM P concentrations. P-stressed nodulated plants showed compromised photosynthetic responses. Alternative growth allocation during stressed conditions was observed between different organs. The concentration of inorganic P, carbon, and nitrogen were lower during stressed conditions. The above ground tissues scavenged P and lowered their dependence on adenosine-triphosphate required for metabolism. Whereas the below ground tissues recycled phosphate from phosphate monoesters in the cell.