Effect of flooding on growth, stem anatomy, and ethylene production of Pinushalepensis seedlings

Abstract

Flooding of soil for 43 days greatly altered growth and stem anatomy and increased ethylene production by stems of 10-month-old Pinushalepensis seedlings. Flooding reduced the dry weight increment of seedlings primarily as a result of decay of roots and, to a lesser extent, inhibition of growth of roots and needles. Flooding did not influence height growth of seedlings but increased stem diameter, largely because of an increase in bark thickness at all stem heights and stem hypertrophy associated with proliferation of phloem parenchyma cells and an increased amount of intercellular space in the phloem. The effects of flooding on xylem increment varied appreciably with stem height. In the submerged portion of the stem, flooding greatly reduced the number of tracheids laid down per radial file. Flooding also slightly reduced the number of tracheids produced in the portion of the stem just above the water level. In the upper stem, however, flooding had little effect on xylem increment and on tracheid production for the first 29 days but increased both thereafter. Flooding also induced formation of short, thick-walled, rounded tracheids resembling those in compression wood. However, these tracheids developed an S3 wall layer, which is absent in well-developed compression wood. Flooding also increased the number of longitudinal resin ducts as well as the number and size of the xylem rays. The basic density of stem segments was lower in flooded than in unflooded seedlings, largely because of the high proportion of parenchyma cells and more intercellular spaces in the wood and bark of flooded seedlings. Flooding greatly increased production of 1-amino-cyclopropane-1-carboxylic acid by roots and ethylene by stems. The capacity for production of ethylene increased faster in stem segments just above the water line than in submerged portions of stems. However, the capacity for ethylene production as a flooding response declined progressively with increase in stem height above the basal whorl of branches. The data indicated an important regulatory role of ethylene in altering growth and stem anatomy of woody plants.