Effect of Concentration of Oxygen and Pressure of Water upon Growth of Rhizomes of Semi-Submerged Water Plants

Abstract

1. Semi-submerged water plants inhabit their particular habitats very largely on the basis of adaptation in respect to their oxygen requirements for respiration and growth. The oxygen requirements for growth are different for different species. 2. The percentage of oxygen found to be most conducive to the growth of young shoots in certain of the species studied was, respectively, Nuphar advenum 0 to 1, Peltandra virginica 0 to 1.5, Pontederia cordata 0 to 10, Typha latifolia 4.6, Acorus calamus 10, Scirpus validus 10. Buds of all these species were able to endure prolonged exposure to pure nitrogen, but no growth occurred in A. calamus, S. validus, and T. latifolia in nitrogen. Shoots of S. validus previously formed were killed in nitrogen. 3. The excellent growth of N. advenum in nitrogen was not affected by either the presence or absence of oxygen in the internal atmosphere of the rhizome so long as the apex was surrounded by nitrogen. When the apex was surrounded by air, no growth occurred even though the rest of the rhizome was surrounded by nitrogen. 4. Even though the shoots of most of the water plants studied grew best in a medium having a low oxygen content and rarely in one having a high content, nevertheless the roots invariably grew best when the oxygen content was high and never when it was very low. Roots previously formed in air were killed in nitrogen. 5. Pressure of water as high as 91/2 feet did not prevent growth in Nuphar advenum, but growth was usually better under pressures not exceeding 4-6 feet. A pressure of nitrogen gas equivalent to 10 feet of water did not prevent growth, but the young leaves were unable to endure this high pressure for as long as they could endure pressures equivalent to 2 and 4 feet. Growth did not occur in a reduced pressure of nitrogen gas equal to 30 inches of water less than atmospheric pressure.