Morphometric analysis of Pinus banksiana Lamb. root anatomy during a 3-month field study

Tree roots are variable in their growth rates, alternating between periods of elongation and dormancy. This variability may have a strong influence on root anatomy. In the present study, field-grown Pinus banksiana Lamb. root s were divided into four distinct anatomical regions (i.e. white without my corrhizae, white with mycorrhizae, condensed tannin, and cork). Changes in root growth, the proportions of the root system occupied by the various reg ions, and cortical plasmalemma surface area (CPSA) were determined for 6- t o 9-month-old ectomycorrhizal P. banksiana seedlings during a 3-month perio d (August through October) in northern Ontario. The region in which the gre atest change in length occurred was the condensed tannin zone, which was al so the dominant contributor to root length (up to 74% of total). The roots of seedlings grown under artificial conditions had the same zones but in di fferent proportions compared to roots in the field. A correlation was noted between increased root growth, low metacutization, and high soil water ava ilability. The CPSA data were assumed to be a factor influencing ion uptake capacity in a positive manner. Interestingly, increases in CPSA were not d irectly correlated with changes in root length for field-grown seedlings. T he primary contributor to CPSA in the field-grown roots was the ectomycorrh izal zone (approximately 80%). In comparison, the bulk (85%) of the CPSA in the chamber-grown roots was found in the white root region. The conditions under which the seedlings were grown strongly influenced the anatomy of th eir roots.