The 2012 ASHS Annual Conference

The plant response to phosphorus (P) deficiency is well defined: plants tend to shift growth to roots in order to explore the soil for more P, root-zone pH declines as the rhizosphere adjust to increasing availability of P, and high-affinity P transporters are up-regulated.  If P deficient for prolonged periods, P is reallocated from older to younger leading to marginal, and eventually total, leaf necrosis.  At what point a plant can recover from P deficiency is less well understood, and the physiological adjustments to P replenishment have not been characterized.  In a series of experiments, tomato plants were grown hydroponically for different periods of time in P-deficient conditions. After defined periods of time, plants were re-supplied complete nutrient solutions and allowed to recover.  We evaluated dry weight, nutrient content, and nutrient regulatory enzymes (chiefly for N and P uptake and regulation) during deficiency and recovery.  We found that after only 8 days of deficiency, both the root and shoot mass were significantly less in plants experiencing P deficiency.  Additionally, the high-affinity P transporter was up-regulated under these conditions, as was nitrate reductase. Upon recovery, plants tend to accumulate P in their tissue to concentrations greater than control plants (~30% greater), perhaps reflecting improved P uptake efficiency early in the recovery phase.  Together, these data illustrate the complex acclimations to P supply, and can provide practical guidance to plant producers to decide if it is feasible to try and recover P-starved plants or start over with healthy, unstressed plants.