Seasonal Changes in Moisture Contents of Gymnosperm Cones

Abstract

MOISTURE contents of growing plant tissues, which are usually expressed as a percentage of the oven dry weight, are influenced by variations in rates of water uptake or loss, dry weight, or both1. The relative rates of change in actual water content and dry weight often vary in different kinds of tissues and at different stages of development of a given tissue. For example, seasonal increases in the percentage moisture of buds of several species of angiosperms and gymnosperms were traceable to the rapid translocation of moisture into the buds. During the same period the buds also increased in dry weight but at a lower rate than that at which water moved into them. In contrast to the pattern in buds, the percentage moisture of angiosperm leaves decreased rapidly in the early part of the growing season and slowly after mid-summer. These decreases were traceable to the relatively greater increase in dry weight rather than to any decrease in actual water content. The seasonal trend in moisture content of gymnosperm foliage varied with age. The moisture content of needles which had grown in the current year declined seasonally, while in one-year-old needles it increased first and then showed little change. These differences in patterns of different aged needles were largely caused by changes in dry weight resulting from rapid carbohydrate translocation into the new, rapidly growing needles as well as translocation out of the older needles2.