Dynamics of Short-Term Phosphorus Uptake by Intact Mycorrhizal and Non-mycorrhizal Maize Plants Grown in a Circulatory Semi-Hydroponic Cultivation System

Abstract

A non-destructive cultivation system was developed to study the dynamics of phosphorus (Pi) uptake by mycorrhizal and non-mycorrhizal maize plantlets. The system consisted of a plant container connected via silicon tubes to a glass bottle containing a nutrient solution supplemented with Pi. The nutrient solution is pumped with a peristaltic pump to the upper part of the container via the silicon tubes and the solution percolate through the plantlet container back into the glass bottle. Pi is sampled from the glass bottle at regular intervals and concentration evaluated. Maize plantlets were colonized by the AMF Rhizophagus irregularis MUCL 41833 and Pi uptake quantified at fixed intervals (9, 21, and 42 h) from the depletion of the Pi in the nutrient solution flowing through the plantlets containers. Plants and fungus grew well in the perlite substrate. The concentration of Pi in the bottles followed an almost linear decrease over time, demonstrating a depletion of Pi in the circulating solution and a concomitant uptake/immobilization by the plantlet-AMF associates in the containers. The Pi uptake rate was significantly increased in the AMF-colonized plantlets (at 9 and 21 h) as compared to non-colonized plantlets, although no correlation was noticed with plant growth or P accumulation in shoots. The circulatory semi-hydroponic cultivation system developed was adequate for measuring Pi depletion in a nutrient solution and by corollary Pi uptake/immobilization by the plant-AMF associates. The measurements were non-destructive so that the time course of Pi uptake could be monitored without disturbing the growth of the plant and its fungal associate. The system further opens the door to study the dynamics of other micro and macro-nutrients as well as their uptake under stressed growth conditions such as salinity, pollution by hydrocarbon contaminants or potential toxic elements.

Keywords: Hoagland modified solution; Rhizophagus irregularis; circulatory semi-hydroponic cultivation system; maize (Zea mays L.); non-destructive; phosphorus uptake; short-term phosphorus depletion.

FIGURE 1

The circulatory semi-hydroponic cultivation system. (A) Schematic representation of the experimental set-up to monitor Pi depletion in Hoagland^-P solution circulating through containers with pre-mycorrhized (PM) or non-mycorrhized (NM) maize plantlets. The nutrient solution in the glass bottle (1) is pumped with a peristaltic pump (2) to the upper part of the container (3) via silicon tubes. The solution percolate through the plantlet container back into the glass bottle. Gray arrows indicate the direction of flow of the nutrient solution in the tubing. (B) Experimental set up under greenhouse conditions. One table contained randomly disposed containers. Scale bar: 10 cm.

FIGURE 2

Schematic representation of nutrient solution flushing before Pi short-term monitoring. Hoagland^-P solution was added to the plant (4 × 50 mL). Silicon tubes were unified with a plastic hose joint. The multichannel peristaltic pump was turned on. Gray arrows indicate the direction of flow of the nutrient solution in the tubing.

FIGURE 3

Short-term time course of phosphorus (Pi) depletion (mg L^-1) from a 90% P-impoverished Hoagland solution (i.e., Pi = 6.245 mg L^-1) circulating through plant containers in presence of pre-mycorrhized (PM) and non-mycorrhized (NM) maize plantlets. Pi was sampled at 0, 9, 21, and 42 h of circulating solution. Data are mean values and standard errors (SE) of 8 (NM) and 9 (PM) replicates. Different letters at 9, 21, and 42 h indicate significant differences between treatments.