Stress to microscale of Vallisneria americana by enrichment of nutrients with stoichiometry N:P

Abstract

To distinguish between the stress of Vallisneria americana caused by increases either in the molar N:P relation (N-NO3 and P-H2PO4) or in the concentration of nutrients (CN), the nutritional regimen (NR) was examined by means of two randomized factorial experiments on plants cultured in vitro in modified MS medium. The first (RN1) crossed N:P relation of 16, 20, and 24 and CN (%) of 25, 50, and 100; while the second (RN2) evaluated N:P relations of 48, 60, 72, and CN percentages of 3.125, 6.25, 12.5, 25, and 50. The mechanism of resistance to the stress by factor was examined with the decrease in the regeneration and viability of leaves and roots; both measured by unit or percentage for 45 to 75 days, since the plants in vitro did not produce ramets. In NR1 experiments, all plants died in 100% CN and leaves registered greater resistance with 24N:P, and 25% CN (p<0.05). The algae grew in 52% of the cultures, without covariance effect (p>0.05). In RN2 experiments, leaves and roots resisted at 72N:P, within the percent ranging from 6.25 to 25 CN (p<0.05). Additional useful information was the significant relationship (p<0.01) found between regenerated leaves and roots (r=0.9), and between regeneration and viability of leaves (r=0.5). The mechanism of stress by the N: P was deciphered by metabolic stoichiometry (protein: RNA). In contrast, the mechanism for the CN was osmotic and fast. At in vitro microscale, resistance to the stress of V. americana, in high N:P and with the supply of N-oxidized, was linked to low nutrient loads.